The article reports that mouth breathing, whether constant or
intermittent, may reduce the benefits of NO, leading to “unobstructed viral
replication.” It concluded that “mouth breathing during sleep may therefore
worsen the symptoms of COVID-19.”39
COVID-19 presents a serious challenge. Apart from the fact that
humans have no immunity to this virus, it behaves very differently from flu,
has a high viral load, and is poorly understood. What is know n is that it
attacks a specific type of cell known as a type 2 pneumocyt e.42 Type 2
pneumocyte cells are responsible for the production and secretion of
surfactant. (If you recall, NO plays an important role in production of
surfactant.) This is one reason why the virus can be deadly , even in young,
healthy patients.It is important to remember that nasal nitric oxide cannot do its job (or
protect you from disease) unless you breathe through your nose. Nasal
breathing alone will increase the amount of NO in the airways, but research
has found that humming can produce even higher levels of nitric oxide.43
One 2015 study reports that humming produces seven times more NO than
normal exhalation.44 It is believed that oscillations in the air accelerate the
exchange of gases between the nasal cavity and sinuses.45 Another paper
discovered that “strong” humming was effective in treating chronic
rhinosinusitis, a fungal conditio n that causes inflammation and infection in
the nasal passages. Again, NO was identified, this time as an antifungal
agent.46 Other research  has found that the concentration of nasal nitric
oxide also increases during breath holding. One study comparing scuba
divers to breath-holding divers reported higher levels of circulating NO in
the breath-holding group.47
BREA THING WITH A F ACE MASK
During the 2020 coronavirus outbreak, debate has raged over the wearing of
protective face masks—whether masks lessen viral spread, protect the
wearer , or prevent the wearer from passing the virus to others. Many people
argue that the measure is ineffective. Others complain that they find it
difficult to breathe when wearing a mask. Whatever the arguments, studies
have definitively proven that masks prevent infected people from making
others sick.48
A 2020 article in the Harvar d Business Review  suggests that better
masks are needed to fully protect against virus-containing particles.49 A
study from 2003 explores the use of nasal plugs instead of face masks but
points out that it is necessary to “only breathe through the nostrils, as
breathing throug h the mouth will nullify the protection offered by the nasal
plug.”50 Unfortu nately , despite research clearly demonstrating that mouth
breathing contributes to high viral load, poor immune defense, and more
severe forms of the novel coronavirus,39 nobody  is talking about the fact
that many people are mouth breathing inside their protective face masks. In July 2020, as the UK government enforced mask-wearing in shops, I
received an email from my friend, a medical doctor . He wondered howmany people were aware of the way they breathe when wearing a mask. He
shared the follow ing example: “I went to the barber on Sunday . The barber
had a mask on. All I could hear was fast breathing through the mouth while
he wore the mask.” My friend explained his concerns:
Since April, I have tried to conv ince everyone I meet to breathe only
through the nose, with or without a mask. Many older people are
surprised when I stop them and ask how they breathe when they
have a mask on. Some said they didn’ t know or didn’ t pay attention. And more than 90% said they had to breathe through their mouth
because they couldn’ t breathe nasally with the mask on! My friend is adamant that nasal breathing will help prevent the spread
of viruses and the subsequent fatalities. He says, “When we mouth breathe,
any virus has a direct route to our lungs. Masks plus nasal breathing will
help keep the virus from entering the patient’ s respiratory system.”
An article in the Independent , “Learn ing how to breathe again in the
new normal ,” looks at breathing with and without a face mask in a post-
COVID environment51. The author describes the prevalence of unhealthy
breathing habits and calls on experts to define the problems of breathing
with a face mask. The article quotes breathing expert Paul DiTuro, who
suggests that respiratory training will help. DiTuro describe s a simple
exercise to make mask-wearing more comfortable:
Just before putting on your mask, take five “quality” breaths. With
each breath, inhale through the nose for four seconds, exhale
through the mouth for six second s, then rest for two seconds. Repeat
these five breaths as soon as you put on the mask, and again after
you remove it.51
The concepts here are good. Inhaling for four seconds and exha ling for six
equates to a breathing rate of six breaths per minute, which  maximizes
many important physiological functions, as well as activating the relaxation
centers of the nervous system. Unfortunately , as we discussed earlier , breathing in through the nose
and out through the mouth is not a good idea. It causes nasal congestion andinhibits gas exchange in the lungs. The importance of breathing only
through the nose, awake or asleep, with or without a face mask, cannot be
underlined too strongly . BEATING NASAL CONGESTION
Mask or no mask, if you suffer from a constantly blocked nose, nasal
breathing may seem impossible or even frightening. However , breath
holding and physical exercise can actually help open the nasal airways.52 In
a few pages, you’ll find a breath-holding exercise for decongesting the
nose. Exactly how this works remains a matter of debate, but holding the
breath increases CO2 in the blood, pools nitric oxide within the nose, and
activates the body’ s sympathetic stress response. While long-term
sympathetic activation is dama ging to health, the stress response plays a
necessary and beneficial role53 in the immune system54 and in regulating
inflammation.55
As far back as 1923, an article in the American Journal of Physiology
reported that holding the breath could ease nasal stuffiness.56 If this
information had been made public at the time, millions of children and
adults suffering from rhinitis could have found relief simply by holding
their breath whenever their nose was bunged up. Decades later, in 1977,
researchers showed that rebreathing exhaled air decreased nasal congestion. Even holding the breath for just 30 seconds made breathing easier for most
of the subjects tested.57 The main stimulus for this result? Carbon dioxide.58
According to Dr. James Bartley , an ear, nose, and throat surgeon, nasal
resistance is inversely related to end-tidal CO2.59 End-tidal CO2 is the
concentration of CO2 in the air at the end of an exhaled breath. It is a direct
measure of how much CO2 there is in the lungs, and under normal
circumstances, an indirect measure of the pressure of CO2 in the blood. Bartley’ s finding  means that as levels of CO2 reduce in the lungs and blood,
the nose become s more congested. Studies have shown that a reduction of
CO2 in the lungs (from normal pressure of 40 mmHg to 35 mmHg)
corresponds with a 10% increase in nasal congestion.52 Anxiety also
typically corresponds with lower end-tidal CO 2 levels.60This is also relevant in a complaint known as empty nose syndrome
(ENS)—where a patient with clear nasal airways experiences a variety of
symptoms, including sensations of nasal obstruction, dryness and crusting,
and feelings of breathlessness61 and drowning. ENS can result from major
or minor  surgical procedures including turbinate surgery, laser therapy , and
submucosal resection, even when sur gery and medical support is successful. At prese nt, its existence, diagnosis, and management are all controversial,
with discussion raging as to whether neurological or psychosomatic factors
may contribute.61
ENS can be caused by the removal of the turbinates. The turbinates are
small structures inside the nose that filter and humidify the air as it passes
through the nostrils into the airways and lungs. They are made up of a bony
structure surrounded by vascular tissue and a mucus membrane. They can
become inflamed and swollen when allergy, infection, or irritation is
present, produci ng an excessive amount of mucus, which causes  the nose to
block. ENT Jim Bartley also explored the feeling of nasal stuffiness in
hyperventilation.62 In 2005, Bartley examined 14 patients who complained
of nasal congestion after surgery and of feeling unable to breathe nasally ,
despite having an apparently adequate nasal airway with no collapsed tissue
inside the nose,  and a surgical success rate between 63% and 85%. Some
had tried nasal steroids and oral antihistamines without relief. Bartley noted
that some were breathing rapidl y, predominantly into their upper chest. He
assessed each for hyperventilation syndrome and discovered that all
displayed a heightened respirat ory rate of around 18 breaths per minute
with an upper chest breathing pattern. On a subjective breathing
questionnaire, 12 of the 14 participants had scores indicative of
hyperventilation. Three patients had an end-tidal CO2 reading of 35 mmHg,
which indicates low blood CO 2. Five had breath retraining; this successfully
relieved nasal congestion for two of them.62
Bartley concluded that patients who suffer from constant feelings of
nasal congestion, particularly after failed nasal surgery, should be assessed
for hyperventila tion syndrome. The primary issue in those patients may
actually be poor breathing patterns. Even slightly fast and/or hard breathing
causes a feeling of air hunger that patients often interpret as nasal stuf finess.While the functi oning of the physical airway is a relevant conce rn, air flow
must also be considered. If someone with chronic hyperventilation complains of nasal
obstruction, with no identifiable anatomical reason, surgery may not be the
answer .62 Breath ing reeducation may be. If you have under gone nasal
surgery and still feel as if your nose is constantly blocked, your breathing
pattern is likely to be at the root of the problem. If you do have nasal
congestion, rhinitis or asthma, try the exercises in this book first. Decongest
your nose using the following breath-holding exercise, switch to nasal
breathing, and improve your BOLT score. I have used these techniques with
thousands of people who have attended my workshops over the years and
found that many destined for nasal sur gery did not require it. Because the nose is designed to regulate air intake,63 switching to nasal
breathing signifi cantly improves  the symptoms of nasal stuffiness and will
dramatically reduce your symptoms in the long term. EXERCISE T O UNBLOCK THE NOSE
Before you read any further , try this exercise to see just how effective it is
for clear ing your nose. The exercise is the same for adults and children. This exer cise is not suitable for women who ar e pregnant. • Sit upright on a straight-backed chair . • Normalize your breathing and breathe calmly . Take a small, light breath in through
your nose if you can and a small breath out through your nose. If you are unable to
inhale through your nose, take a tiny breath in through the corner of your mouth. • After exhaling, pinch your nose and hold your breath. Keep your lips sealed. • Gently nod your head or rock your body until you feel that you cannot hold your
breath any longer . You should feel a relatively strong need for air . • At this point, let go of your nose, and breathe in gently through the nose. Breathe
gently in and out with your mouth closed. When you first breathe in, avoid taking a
deep breath. Instead, keep your breathing calm and focus on relaxation. Use the
mantra “relax and breathe less” if it helps. • Repeat the exercise until you can breathe easily through your nose. If your nose
does not become fully unblocked, wait around one minute, and practice the same
steps again. Y ou may need to do the exercise several times. After you have completed the exercise, your nose will be unblocked. However , until you have improved your BOL T score to over 25 seconds,the exercise will decongest your nose onlny temporarily . Once your BOL T
score is 25 or more, your nose will stay unblocked for much longer periods. I always explain to my students, especially the teenagers, that you have two
options. You can improve your BOL T score to 25 seconds, or you can
experience nasal congestion for the rest of your life. When you consider all
of the negative consequences of mouth breathing for sleep, stress, and other
health concerns, the choice is obvious. Remember , until you have changed the underlying breathing patterns
that contribute to nasal stuffiness, it is quite normal for the nose to block
again. With regular practice of the exercises in this book, your body will
adapt, and your nose will start to remain clear . Practice this exercise
whenever your nose feels congested. Even if you have a heavy cold, this
exercise can help you maintain nasal breathing. MAKING THE SWITCH
The first step in addressing poor breathing patterns and increasing your
BOL T score is to switch from mouth to nose breathing. Even though its
primary function  is respiratory , the nose is often underused for the essential
task of breathing . While total mouth breathing is rare, as most people tend
to switch from mouth to nose breathing and vice versa, it is incredibly
common for children and adults  to mouth breathe some of the time, either
out of habit or due to nasal obstruction. When you first switch from mouth to nasal breathing, the volume of air
you inhale with each breath may immediately reduce. This is likely to feel a
little strange to begin with. You will probably experience a slight air
shortage since the volume of air inhaled through the nose is less than you
are used to inhaling through the mouth. Don’ t worry . Air hunger is a good
sign of progress. Any discomfort will diminish in a few days. Your body
may try to trick you into breathing more by yawning, sighing, or sneaking
in the odd mouth breath. Try not to increase your breathing in those ways. When you feel the need to breat he big—for example, if you experience the
impulse to sigh—hold your breath for 5 to 10 seconds following the sigh. One thing to be aware of that may seem odd, even unfair , as you make
the switch from mouth to nasal breathing, is that the size of the nose isactually an important factor in breathing habits. People with a small nasal
airway are much more likely to breathe through an open mouth than those
with an adequat e nasal size. Mouth breathing is a very normal reaction to a
small nasal airway . The smaller the nose, the greater the resistance to
breathing, and the more air hunger is experienced in breathing through the
nose. HOW T O BREA THE DURING EXERCISE
A spacious nasal cavity and large nostrils are definitely useful for breathing
through the nose during physical exercise. If your nasal airway is small, the
resistance to breathing and the resulting air hunger may be too much during
exercise. To help open the nasal passages, you can use the exercise-specific
NasalDilator , which I have designed specifically for this purpose. Earlier , we talked about how CO2 creates the primary stimulus to
breathe and is instrumental in oxygenation. Nose breathing during physical
exercise slows the breath and reduces breathing volume, which influences
the levels of CO2 in the blood. However , most of us will not spontaneously
choose to breathe through the nose during heavy exercise.64 Without proper
training for at least six to eight weeks, the air hunger caused by nose
breathing can become quite pronounced as exercise intensifies. Breathing throu gh the nose is usually only comfortable during gentle
exercise, when the total volume of air entering the lungs every minute
(called minute ventilation ) is less than 35 liters. Once minute ventilation has
increased to between 35 and 41 liters,65 the tendency is to start mouth
breathing. The exact switching point from nose to mouth breathing is highly
personal, influen ced by individual sensitivity to CO2, metabolism, and the
size of the nose. Mouth breathing is faster than nose breathing. It feels preferable under
certain conditions because the shallow , fast breaths result in a greater
volume of air entering the lungs. This causes blood CO2 to drop, which
reduces the feeling of air hunger .66 How ever, breathing through the nose is
actually more efficient because it allows the lungs to extract more oxygen
from the air. The percentage of oxygen in expired air decreases when nasal
breathing during exercise, indicating that more of the oxygen is beingused.67 Continuing nasal breathing practice over a period of six to eight
weeks will encourage your body to adapt, delaying the onset of
breathlessness. Whether or not you currently include physical  exercise in
your weekly routine, this applies to you. We all have a threshold at which
mouth breathing feels necessary . Whatever your starting point, whether you
start to wheeze during your workout or when you just try to get up off the
couch, you can begin to improve your fitness by restoring nasal breathing. The importance of breathing through the nose rather than the mouth
should not be underestimated. It encourages functional breathin g and larger
oscillations of the diaphragm, supporting functional movement, and
preventing injur y. It is an important element of getting “in the zone”—that
state of peak focus when everything flows and you can perform at your
best. (Chapter Five looks more deeply at the connection between breathing
and movement.) It is also import ant to remember that nasal breathing helps retain heat
and moisture in the body . During  exercise, this can make a big difference as
to wheth er you experience a dry mouth. It can protect your airways from
trauma, including exercise-induced asthma and cyclist’ s cough. Nasally restricted breathing can be used during exercise to improve
performance.68 This has implic ations for nonathletes too. In a 2018 paper ,
professor of exercise science and Olympic triathlon coach, Dr. Geor ge
Dallam looked in detail at the breathing of athletes.66 Five male and five
female recreational runners trained and raced using only nasal breathing for
six months. Dallam recorded comparative results when the participants
breathed only through the nose and only through the mouth, wearing a
swimming nose clip to close the nostrils. The trial used a graded exercise
test to examine performance, breathing rate, oxygen uptake, and breathing
efficiency at VO 2 max. VO 2 max is maximum oxygen consumption during
intense exercise. It is used to measure cardiovascular fitness and aerobic
endurance in athletes. Dallam’ s study produced the following results:
• Respiratory rate was much slower in nasal breathing than in oral breathing (39.2
bpm vs 49.4 bpm). • End-tidal CO 2 was significantly higher in nose breathing than mouth breathing (44.7
mmHg vs 40.2 mmHg). • Ventilation (volume of breathing) was reduced by 22% in nasal breathing.• Nose breathing resulted in lower end-tidal oxygen pressure and a lower percentage
of oxygen in expired air , indicating that more oxygen was removed from the air by
the lungs during nasal breathing. A key finding from Dallam’ s study was that after six months’ training
with only nasal breathing, the athletes achieved the same peak performance
and oxygen consumption when  nasal breathing as they did during oral
breathing. They were pushing themselves to their limits yet still managed to
breathe in an effective way. Breathing was also more economical. The 22%
reduction in ventilation meant that breathing required less effort and the
muscles of the respiratory syste m didn’ t have to work as hard. Achieving
the same  intensity with 22% less breathing represents a significantly greater
economy . Dallam concluded that it is possible to maintain VO 2 max and
peak performanc e after a period of training using only nasal breathing. The
body naturally adapts to nasal  breathing by increasing its tolerance to
changes in CO 2, so air hunger decreases. These findings are relevant for everyone, whatever your level of fitness. If a walk  to the corner shop leaves you gasping for breath, nasal breathing
will help you. To limit air hunge r during physical exercise, work to achieve
a higher BOL T score and breathe light, slow , and deep (LSD):
• Light:  Only breathe the volume of air that you need (don’t overbreathe). • Slow:  Reduce your respiratory rate. • Deep:  Breathe with greater amplitudes of diaphragm movement. If you are healthy and exercising at the appropriate level to improve
your aerobic fitness, you should be able to breathe only through the nose
without needing any specific adaptations66. If the air hunger is so strong
that you need to open your mouth, simply slow down and allow your
breathing to calm. By breathing  nasally throughout, you should finish your
workout feeling relaxed and full of energy instead of exhausted and
dehydrated. Recreational Athletes
Healthy people exercising at the lower levels necessary to improve aerobic
fitness can breat he entirely through the nose,66 without needing any specific
adaptations. Recreational athletes should maintain nasal breathing at alltimes. If the air hunger is so strong that you need to open your mouth to
breathe, simply slow down and allow your breathing to calm. Competitive Athletes
It is best for competitive athletes to alternate nasal breathing with mouth
breathing. High- intensity trainin g helps prevent muscle deconditioning and
will require an athlete to periodi cally breathe through their mouth. For less-
than-maximum intensity training, and at all other times, nasal breathing
should be used. A competitive athlete may spend 50% of training with their
mouth closed. Research has shown that healthy adults are able to maintain nasal
breathing to 85% of VO 2 max,69 indicating that it is possible to breathe
nasally at much higher intensities of exercise than we might choose. • Use mouth breathing to maintain muscle condition when working at an all-out pace. • During competition, there is no need to intentionally take bigger breaths. Instead,
achieve a higher BOL T score and apply the OA precompetition preparation. (Y ou
can find this in Chapter T wo.) • Nasal breathing combined with breath-holding during your warm-up can be very
advantageous. As can practicing light, slow and deep breathing during the warm-
down. (Y ou will find instructions for warm-up in Chapter T wo.) SNIFFING OUT SUCCESS
One function of the nose we haven’ t yet discussed is the sense of smell via
the olfac tory nerve. In ancient yogic texts, while breath control is associated
with a “pristine” state of mind, the condition of the olfactory nerve is seen
as indicating the general state of health. Is this relevant to nasal breathing? Scientists say it could be. In 2019, researchers at the Weizmann Institute in Israel suggested that
nasal inhalation could be linked to cognition as part of an evolutionary
survival mechanism.70,71 A sense  of smell is, after all, equated with sniffing
out dang er. For our distant ancestors, this meant accurately assessing their
surroundings to make life-or -death decisions. The Weizmann team
theorized that this ancient sensory system might benefit from nasal
inhalation and that, in modern life and competitive sports, nasal inhalation
might automatically trigger conditions in the brain that optimizevisuospatial focus. They demonstrated that nasal breathing synchronized
electrical activity in the brain on a wavelength that helped maximize
visuospatial (VS) awareness. Visuospatial awareness is the way we relate visual information to the
space around us. It helps us perform everyday tasks like walking through a
door rather than bumping into the door frame, picking up a glass of water ,
catching a ball, reading a map, driving a car, and even parallel parking. Visuospatial skills can be defined as
the ability to observe the visual world, to form mental
representations of the visual objects, to mentally manipulate these
representations, and to in turn reconstruct aspects of the visual
experience.72–74
VS ability is made up of several cognitive processes, includ ing the
perception and understanding of spatial orientation, reproducing actions
through fine motor movements,  and integrating parts into a whole.72,75–77
These elements all place different demands on working memory .73
Visuospatial tasks are “complex and engage various spatial processes”, and
involve numerous areas of the brain.72
The fact that nasal breathing helps synchronize the complex mental
processes required for VS awareness has applications for sports, such as
tennis, where a keen awareness of the external environment and its
dimensions is key. In team ball games like football, soccer , basketball, and
ice hockey , the player must be able to catch, carry , kick, or hit a ball at the
same time as scanning the pitch for teammates to pass to—all this while
running at full pelt.78 During any sort of sporting activity (and during
activities like music performan ce), it’s necessary to absorb and process a
great deal of information in a very short time. Athletes have to become
highly proficient at perceiving changes in play caused by their opponents
and team members.78
Athletes and musicians display  better performance in VS tasks than
people who are physically inactive.79–81 Older people can improve their VS
skills by improving their physic al fitness.82 Several studies have examined
the influence of more general physical exercise on VS ability .83–85The influence of breathing on VS ability also has implications for
children’ s intellectual development. A 2015 study demonstrated that
visuospatial perception is instrumental when a child learns to read, and that
assessment of VS abilities could help with the early detection of
“difficulties in neurodevelopmen tal disorders associated with low academic
achievement.”86 Another paper from 2016 sugg ests that VS skills are even
important in learning mathematics, especially for things like problem
solving.72
OceanofPDF .comTCHAPTER FOUR
THE VAGUS NERVE AND THE HEART-
BREATH-BRAIN CONNECTION
o really understand the powerful interconnections between the
breath, heart, and brain, we must take a journey along the wandering
vagus nerve  and through the autonomic nervous system (ANS). This
chapter will cover a lot of ground. If we seem to be heading away from the
central issue of breathing, you will soon see how the vagus nerve connects
with the breath in powerful, life-transforming ways. The vagus nerve (the tenth cranial nerve or CN X) has multiple
branches that diver ge from two thick stems rooted in the cerebellum or
“little brain” (the area at the lower back of the brain) and the brain stem.1–3
It can be found behind the artery in your neck where you feel for your
pulse. Vagus, to wander  in Latin, comes from the same root as our words
vagabond , vagrant , and vague . The name gives some clue to just how
extensively this nerve travels. During its journey through the body , the
vagus nerve supplies nerves to the heart, respiratory system, and
gastrointestinal tract, reaching the lowest viscera of the abdomen. It is the
most wide-ranging cranial nerve  in the human body and is responsible for,
among other things, many functions of the mouth, including speech,
appetite control, and even vomiting. Ultimately , it conducts nerve impulses
to every major or gan in the body .4
The vagus nerve is made up of 80% to 90% afferent (body to brain)
nerve fibers.2 This means that most of the information it conveys travels
from the body to the brain. Instead of orders flowing from the brain,
affecting the various physiological systems and organs, the afferent fibers
take information back from the body to the brain.5 The heart, however , isinnervated with efferent (brain to body) vagus fibers—a top-down line of
communication.6 The resulting two-way flow of data provides the building
blocks for feedback loops in which information from the brain impacts the
physical systems of the body and vice versa. Many studies have shown the vagus nerve’ s positive potential to
influence physic al health, mental health, and cognition. This nerve can be
stimulated to reduce anxiety , alleviate depression, and even inhibit
inflammation to fight disease in the body by combating the cortisol-
producing stress response we know as fight or flight. To understand the vagus nerve’ s importance to the heart-breath-brain
connection, we need to start our journey by looking at the two sides of the
ANS, beginning with the fight-or -flight response. THE V AGUS NER VE AND AUT ONOMIC BALANCE
The fight-or -flight response is the body’ s instinctive survival mechanism. From a simple evolutionary perspective, it allows mammals, including
humans, to react to situations that may be life threatening. When humans
lived in constantly unsafe environments, it was useful for fighting off
enemies and hunting for food. While it still has a valuable role to play in
keeping us safe in the modern world, problems arise when we have the
same response to things that are probably not fatal. We migh t be fearful
about giving a presentation, turning up for an interview , receiving an
unexpected bill, or even being blocked on social media. When fight or
flight is constan tly in overdrive, the result is chronic stress, that all too
common modern-day malady . Fight or flight is controlled by the sympathetic nervous system  (SNS),
which is one-hal f of the overall ANS. The vagus nerve is the main driver of
the other branch of the ANS, the parasympathetic nervous system  (PNS)1. While the sympathetic nervous system triggers fight or flight, the vagus-led
PNS is responsible for rest and digestion, the state in which the body
perceives no threat, the mind is relaxed, and digestion is active. Crucially ,
as we will discover , it is throug h the ANS that the respiratory system, lung
ventilation, and blood-gas excha nge connects with the working of the heart
rate and blood vessels. Ideally , the two responses of the ANS, fight/flightand rest/digest, work in balance.7 The primary purpose of the ANS is to
regulate the body’ s main functions. The SNS (sympathetic nervous system) prepares the body for external
challenges. It increases metabolic output, stimulates and prepares the
muscles, and mobilizes existing energy reserves. It also constricts the blood
vessels, increas ing heart rate and blood pressure. In contrast, the PNS
(parasympathetic nervous system) focuses inward, supporting growth,
restoration, reproduction, relaxation, and conservation of energy. It
maintains the balance of heart frequencies; notably , it reacts much faster to
external and internal changes than the SNS, responding within just one
second, in contrast to the five or more seconds it takes the SNS to kick in.8
These two oppo sing forces within the ANS are never static. The system
continually fluctuates to maintain a stable internal environment that
operates within healthy paramet ers. This constant balancing act to maintain
homeostasis  is key to keep ing organs working properly . For example, if
your body temperature is too high, the ANS adjusts to bring it back to the
optimal tempera ture of 37° Celsius (98.6° Fahrenheit). This is not just a
reactive system  that waits passively to meet the next external crisis; it
works incessantly to promote stability within the body . While the two branches of the ANS may seem to function in opposition,
they often operate in syner gy to meet metabolic demands. For example,
during exercise,  PNS tone decreases while SNS activity increases. There
are even unique situations when both PNS and SNS are either inhibited or
activated.9 For example, sexual arousal in adult humans is characterized by
the excitement of both. Homeostasis (balance or equilibrium) is a fundamental goal of all
biological systems.10 In humans, it operates at the level of the whole body ,
within tissues, and even in individual cells. Where homeostasis can be
described as a healthy , dynamic feedback and regulation system, stress can
be defined simply as any autonomic state that reflects a disturbance of that
balance. Stress is a state where a psychological, environmental, or physical
situation, whether a single event or a long-term issue, disrupts the body’ s
ability to self-re gulate. Modern life presents us with a world where it can be
difficult to maintain that balanc e. Think about some of the terms used todescribe an emotional upset: you are “out of whack,” you feel “all over the
place,” or you are literally “of f balance.”
Stress can manifest itself in each of the three dimensions of
dysfunctional breathing. It can show up biomechanically as imbalances in
the respiratory muscles. This can lead to neck and back pain, upper chest
breathing, and poor diaphragm control. Biochemically , chronic
hyperventilation can impact the body’ s delicate pH balance. Psychologically , anxiety , depression, and anger can destroy your
equilibrium. Living in a constant state of fight or flight poses the danger of cortisol
overload. Cortisol is the primary stress hormone.11 When released into the
bloodstream, it enhances the brain’ s use of glucose (blood sugar ) and makes
substances that repair tissues more available. In essence, it prepares the
body to escape from the saber -toothed beast and not bleed too much if that
doesn’ t work out. Aligned with that purpose, cortisol also curbs bodily
functions that aren’ t immediately essential to the fight-or -flight situation. It
alters immune system responses and suppresses digestive, reproductive, and
growth processe s. As you migh t expect, it communicates with the parts of
the brain that control mood, motivation, and fear . Ideally , the body’ s stress response is self-limiting. Hormones go back to
normal levels after the perceived threat has passed, and the body returns to
homeostasis. However , when stressors are constantly present or stress is
chronic (which  is like signing up for a long-term fight-or -flight
subscription), a cortisol imbalance occurs. Considering how many of the
body’ s processes cortisol can suppress, it is hardly surprising that people
who suffer from  high levels of stress display a plethora of physical and
mental conditions, including anxiety , heart disease, weight gain, digestive
problems, depression, headaches, sleep disorders, poor memory , and
decreased ability to concentrate. On the other (balancing) side of the ANS, we find the well-studied
connection between the vagus nerve and the parasympathetic nervous
system (PNS), the rest and digest side of the ANS. The vagus nerve, which
sends impulses to all the major organs and is particularly conn ected to the
heart and respir atory system, secretes a brilliantly useful substance called
acetylcholine  or ACh.Acetylcholine (ACh), the first neurotransmitter ever to be identified,12
was discovered in 1913 by English chemist Arthur Ewins.12 Later, in 1921,
the Nobel Prize winning physio logist Otto Loewi determined its functional
significance. Loewi found that activating the vagus nerve reduced heart
rate.1 He did this by isolating the heart of a frog and stimulating the vagus
nerve to release something he called “Vagusstuf f.” This substance, later
identified as acetylcholine, caused the frog’ s heart to slow, replicating
relaxation, the reaction to a nonthreatening environment—or the rest-and-
digest state. The implications of this are huge. It means that stimulating the
vagus nerve can activate the PNS, subduing or balancing out the fight-or -
flight reaction of the SNS. This “Vagusstuf f” (ACh) released by the vagus nerve is a
neurotransmitter—a chemical messenger released by nerve cells to send
messages to other cells. This neurotransmitter is found in all motor neurons,
where it stimulates smooth muscles to contract, slows the heart rate, and
dilates the blood vessels. It is also present in many brain neuro ns where it
has a role in vital mental processes such as cognition and mem ory. Severe
depletion of acetylcholine has been associated with conditions such as
Alzheimer ’s.12
STRESS, INFLAMMA TION, AND ILLNESS
From a health perspective, if we define stress as a disruption of
homeostasis, inflammation often begins as the body’ s natural response to
stress. What’s more, chronic, low-grade inflammation has been proven to
indicate an overactive fight-or -flight response.10 It makes sense, therefore,
to deduce that inhibiting the fight-or-flight reaction (as the ACh released by
the vagus nerve does) could reduce inflammation. Inflammation is a defense mechanism triggered by injury or infection. It
is at the extreme  end of the spectrum that ranges from homeosta sis to stress
response to inflammatory response.10 It combines different immune
mechanisms that work to neutr alize invading pathogens such as bacteria
and viruses, repair injured tissues, and heal wounds. However , when out of
balance, inflamm ation plays a key role in the development and persistence
of many diseases. It can be triggered by extreme internal imbalances or byexternal challen ges that disturb homeostasis. After a stressor occurs, the
inflammatory response kicks in. While modern life has its benefits, including a much longer life span,13
advanced technology , and home  grocery deliveries, the nature of stress has
changed dramat ically . When stress is severe and prolonged, it causes the
body to compensate, physiologically and behaviorally , to maintain
homeostasis. Long term, this can put an unsustainable load on the body’ s
systems. There is increasing evidence that chronic stress increases the risk of
both physical and mental health disorders. It can play a critical role in the
onset and progress of stress-rela ted illness, including diseases of the heart,
digestive system , brain, and many forms of cancer . Chronic stressors are
known to suppress immune function. In fact, while not yet fully understood,
studies show that stress is a common risk factor in 75% to 90% of human
diseases.13 That’ s nearly all of them. Scientists at Carnegie Mellon University discovered a direct
relationship betw een chronic mental stress, the body’ s inability to regulate
inflammation, and the progression of disease.14 Their study , which used the
common cold as a model, found that prolonged stress decrease s the body’ s
sensitivity to the stress hormon e cortisol in such a way that the immune
cells become insensitive to it. This negatively affects the ability of cortisol
to regulate inflammation. Inflam mation gets out of control, and disease sets
in. The research demonstrated that the symptoms of a cold are not actually
caused by the virus. They are a side effect of the body’ s inflammatory
response, which is designed to fight infection. People who suf fer most when
they have a cold don’t have “Man Flu”—they are actually experiencing a
more extreme inflammatory reaction. The study also confirmed that stress led to the immune cells being less
able to respond to signals that normally regulate inflammation. Participants
who were stressed were much more likely to develop colds when exposed
to the virus than those who weren’ t stressed, and those people also
produced more cytokines —the chemical messengers that trigger
inflammation. Because inflamm ation is pivotal in so many illnesses, this
offers a valuable  window into the impact that psychological stress can have
on health.VAGAL STIMULA TION AND THE IMMUNE SYSTEM
A clear connection between the nervous system and the immune system
was discovered by neurosur geon Kevin Tracey in 1998. In an experiment
on a rat, he investigated the idea that stimulating the vagus nerve could
alleviate harmful inflammation.4 He found that the nervous system could be
used almost like a computer to trigger commands that stop a problem in its
tracks. The results of his expe riment were so unexpected that Tracey’ s
colleagues were apparently in the corridor outside his lab, running bets
against his theor y even as he was in the middle of testing it!4 Further trials
confirmed Tracey’ s findings. Using electronic implants to stimulate the
vagus nerve in humans, he produced a dramatic reduction and even
remission in rheumatoid arthriti s, a condition with no known cure.15 This
helped illuminate the vagal system’ s close interrelationship with the
inflammatory system. The first steps of an inflammatory reaction involve the release of those
pro-inflammatory chemicals called cytokines.8 When the body produces too
many cytokines,  they can cause more damage than the invading  pathogens. For exam ple, in sepsis, the body’s own immune reaction can cause tissue
injury , dangerously low blood pressure, and even death. Chronic
inflammation can also feature in many diseases where no infection or injury
is present. In obesity , for examp le, an overload of storage in fat cells leads
to a stress response that causes the release of inflammatory cytokines.10
The conversatio n between the immune system and the brain that
moderates this inflammatory response relies, in part, on the vagus nerve,
which, in turn, is important due to the anti-inflammatory role of
Vagusstuf f/ACh. Crucially , ACh, the neurotransmitter secreted by the vagus
nerve, blocks the release of many of the pro-inflammatory cytokines. In
studies of diseases characterized by an excessive immune reaction,
including sepsis and pancreatiti s, vagus nerve stimulation was found to be
sufficient to block cytokine activity . When the vagus nerve is stimulated
electronically , the body’ s level of inflammatory cytokines decreases.16
As it turns out, the breath also provides a (natural) gateway to influence
the vagu s nerve and the ANS— through the role of carbon dioxide (CO 2)
levels in mainta ining the body’ s acid-base balance.17 One of the functionsof breath ing is to regulate the level of blood CO2 to maintain the blood’ s
acid balance (or pH). When levels of CO2 in the blood are too high, over
time, CO2 diffuses  into the red blood cells as carbonic acid, making the
blood too acidic , a condition called acidosis . When CO2 levels are too low,
respiratory alkalosis  occurs. Both acidosis and alkalosis are serious,
potentially life-t hreatening in their acute forms and damaging to health if
they persist long term. Therefore, the proper management of CO2 through
the breath is crucial. When blood pH changes even subtly , respiration will automatically
decrease or increase to compensate. One example of this is ketoacidosis, a
serious complication which can occur in diabetes. Ketoacidosis increases
acidity in the blood, stimulating corrective overbreathing. This fast, upper
chest breathing  is also commonly seen after the acidosis following
prolonged diarrhea and as a response to increased progesterone levels in
women. Conversely , alkalosis can be induced by vomiting or the use of
steroids or diuretics. The respiratory drive is then suppressed as the body
works to restore homeostasis.17 Information about blood CO2 is sent to the
respiratory center so that breathing can adjust via pathways involving the
vagus nerve. Therefore, breathing exercises to increase CO2 have a “vagotropic
effect.”18 CO 2 directly influences the sensitivit y of the vagus nerve’ s nuclei. This slows the pulse and improves the blood-filling of the heart.19 Increased
blood CO2 is the most likely mechanism  to enhance the vagus nerve’ s
slowing effect on the heart during exhalation. Increased CO2 (hypercapnia)
and exhalation are both vital in stimulating the vagus nerve.18
What’ s particularly exciting is that the effects of vagu s nerve
stimulation don’t stop when treatment is finished. They are ongoing. Over
time, the vagus system develops and maintains much greater resilience to
stressors. This long-term condit ioning of the vagus nerve, its functionality ,
and ability to react to maintain homeostasis is known as vagal tone. This
vagal tone is key not just to reducing inflammatory responses but also to a
healthy and resilient functioning of the heart. VAGAL T ONE AND HEART RA TE V ARIABILITYWhile we often associate heartbeats with rhythm and may believe an
absolutely regul ar heartbeat is a healthy one, heartbeats are not all the
same.9 In fact, they change constantly , and the more coherent the
fluctuations are in speed and intensity , the healthier you are likely to be,
both mentally and physically .16 The heart is not a metronome. Its
oscillations are complex and constantly changing. The cardiovascular
system needs to adjust to external and internal stimuli to maintain
homeostasis. Heart rate variability  (HRV) measures the difference between
consecutive heartbeats. In clinical settings, readings are taken to the
millisecond with the help of an ECG signal. With modern technology , you
can now measu re your own HRV using a smart watch or other wearable
fitness tracker . Results are presented as time series data, a way of recording
information collected over a period of time to show variations  within that
period. Daily high and low tide data is a familiar use of a data time series. Using HRV as an objective indicater of fitness and resilience has been
gaining traction among fitness enthusiasts. While many people enjoy using
gadgets and apps to measure their own HRV, remember that technology
doesn’ t change HRV; it simply provides the information that allows you to
assess it. HRV is predominantly controlled by the ANS. Growing evidence
associates an ANS imbalance with a higher prevalence of disease and death,
which makes HRV a useful tool in predicting and assessing illness. When
you are in a fight-or -flight state, HRV changes. As the system restores
homeostasis, those changes settle down. However , if the body is under
constant stress, the heart rate becomes less resilient and less flexible. The
variation between oscillations decreases, and the body can’t shift gears as
easily . The potential impact is massive. Because lower HRV can be caused
by stress, emoti onal distress and chronic stress directly impact wellness. Studies indicate,  for example, that stress increases the risk of heart attack in
people who have no prior heart disease and that emotions like anger ,
hostility , and aggressiveness can contribute to coronary artery disease.10
HRV declines significantly with poor health.20,21 People who are
emotionally sick, older , or less physically fit often have a lower HRV.16
High concentrations of cortisol are associated with low HRV,8 and HRV isan estab lished tool in diagnosing diabetic neuropathy , the nerve damage,
often to the legs and feet, suffered by diabetics. Correlations have also been
found between changes to HRV and many high-mortality conditions,
including heart disease, cancer , stroke, Alzheimer ’s, diabetes, chronic lower
respiratory diseases, and intentional self-harm. Low HRV is related to a wide range of physical and mental illnesses
and a lower life expectancy .8 Even the stress caused by a single significant
life event can have an impact. Scientists looking at the health of divorced
people discovered that particip ants who had gone through a marriage
breakdown had a lower resting HRV than those who were married.22 The
upset caused by divorce actually made those people less healthy . While low HRV is associated with disease, people with high HRV are
likely to be healthier , both physically and mentally . All of this explains why
some people seem to be more resilient to stress, better able to field
challenging situations and take difficulties in their stride, while others get
thrown off balance. Scientists have so far failed to find satisfying answers
about the genetics of the stress response,23 but inherited conditions can
certainly contri bute to aspects of health that result in low HRV. For
example, studies  have shown that vagal tone is passed on from mother to
child.24 Mothers who are depressed,  anxious, and angry during their
pregnancy have lower vagal activity . Once the baby is born, he or she also
displays a low vagal tone. The good news is that it is possible to build better vagal tone. Just one
note of caution: it is not always better to increase vagal tone.25 For instance,
parasympathetic hyperactivity can occur in athletes who overtrain. Several
studies indicate that symptoms  of overreaching may be relate d to down-
regulation of the SNS and/or changes in the balance between  vagal and
sympathetic tone. This can cause fatigue and adversely affect performance
during periods of regular competition.26 The key is to optimize  HRV, not
just blindly augment it. Slow breathing at 4.5 to 6.5 breaths per minute has
been found to optimize sympathovagal balance, creating an ideal balance
between the two branches of the autonomic nervous system.27
Because it is closely connected with the working of the ANS, especially
the parasympathetic branch (PNS), HRV is considered a reliable measure of
how well the vagus nerve is working, that is, of vagal tone. Scientistsbelieve that vagal tone in the heart forms one of the connectio ns between
breathing and emotion.28 It is influenced by the breath and is essential to the
stimulation of the vagus nerve, which is closely tied to aspects of human
connection such as emotional regulation, reactivity , expression, empathy ,
and attachment. At the other end of the emotional spectrum, dysfunction of
the ANS is common to people suffering from anxiety , depression, PTSD,
panic disorder , and other stress-related mental and physical conditions. Parallels have even been found between vagal tone and cognitive functions
such as visual recognition memory and alertness. HRV, used as a measure
of vagal tone, provides doctors with a way to physically quantify stress and
vulnerability to stress. That means that stress can be defined by its effect on
the function of systems like the heart, rather than just on the way a
challenging life event makes you feel. RSA: THE HEAR T-BREA TH CONNECTION
The activity of the vagus nerve can be accurately measured using HRV and
the way the heart interacts with the breath. When vagal tone is healthy ,
there are small differences in heart rate during the in-breath (when it speeds
up) and out-brea th (when it slow s down). Inhaling, an increase in heart rate
is caused by a rhythmic partial withdrawal of vagal tone. Exhaling, a
release of acetylcholine causes the heart to slow, just as it did in Loewi’ s
frog. This phenomenon is called respiratory sinus arrhythmia  (RSA). It’s a
good indicator of how well the nervous system is functioning. In simple
terms, HRV measures rhythmic changes between heartbeats, whereas RSA
is HR V in synchronicity with the breath. For most of us, breathing frequency is around 9 to 24 breaths per
minute.16 Corresponding oscillations in heart rate that produce respiratory
sinus arrhythmia can be regarded as the effects of breathing on the region of
the heart that initiates the electrical impulses for it to contract. The
oscillations of RSA can be affected by stress, alterations in breathing
patterns, or sudden bouts of exercise. RSA controls the rate of gas exchange
inside the alveo li, the tiny air sacs in the lungs.16 The heart beats faster
when the air in the lungs is richest with oxygen, whereas the impulse to
exhale is triggered when CO2 in the lungs is highest. Gas exchange is mostefficient when the heart rate is synchronized with the breath such that the
heartbeat begins  to increase at the start of an inhalation and begins to
decrease at the start of an exhalation. RSA is controlle d entirely by the vagus nerve. Mirroring the function of
the ANS,16 it reveals how well the parasympathetic (or rest and digest)
branch is working.29 Because the vagus nerve activates during the
exhalation, many studies have explored whether longer exhalations and
slower breathing  would produce greater differences in RSA and HRV. HRV
is linked to breathing frequency , and greater changes occur when the breath
is controlled and slower . Reducing the rate of respiration, increasing the
amount of air delivered to the lungs with each breath, and breathing from
the diaphragm have all been shown to increase RSA significantly . The best
results for HRV, RSA, barore flex sensitivity (more on this later), and
optimal gas exchange are achiev ed with a breathing rate of 5.5 or 6 breaths
per minute.27 It has also been  suggested that RSA has a central role in the
resting state of the cardiorespira tory system. RSA maximizes during sleep,
relaxation, and slow, deep breathing but is reduced in states of anxiety .27
Energy expenditure is naturally minimized with improved pulmonary gas
exchange. HRV BIOFEEDBACK
In the 1990s, clinician and research psychologist Paul Lehrer and his
colleagues began to experiment with heart rate variability biofeedback
(HRVB). The central focus of the technique is on slowing the breath to
obtain beat-by-beat heart rate data so the participant can maximize RSA and
match it to heart rate patterns. The participant uses feedback or a breath-
pacing device to produce a heartbeat more rhythmically “in tune” with the
breath. This synchronization provides the best conditions for gas exchange
in the lungs. Significant evidence supports the benefits of HRVB for a variety of
common disorders,16 as well as for enhancing athletic performance. While
controlled studies are still needed for many specific conditions, scientists
believe that training to optimiz e the rhythms of the breath and heart has
potential applications for illnesses as varied as asthma, irritable bowelsyndrome, COPD, cyclic vomiti ng, recurrent abdominal pain, fibromyalgia,
cardiac rehabilitation, hypertension, chronic muscle pain, pregnancy-
induced hyperte nsion, depress ion, anxiety , PTSD, and insomnia. The
improved gas exchange achievable with HRVB training may help people
with respiratory diseases and stress-induced hyperventilation.16 HRVB has
been proven to restore the balance of the nervous system to combat
inflammation.30 It may also have advantages as a diagnostic tool for
cardiovascular system dysfunction and its resulting illnesses.31
While most research in the field focuses on helping people who are sick,
HRVB can also be used to reduc e stress in otherwise healthy individuals. A
study of young athletes who were taking their university exams found that
the breath training resulted in long-term improved resistance to stressful
situations (i.e., better vagal tone).32 Another small study of women
suffering from fibromyalgia concluded that actively participating in HRVB
treatment restored a level of control to the patient, improving self-esteem
and feelings of empowerment.33
RSA, THE BAROREFLEX, AND BLOOD PRESSURE
Respiratory sinus arrhythmia (RSA) is also significantly connected to blood
pressure. Remember , RSA describes changes in the heart rate during the
respiratory cycle. Its functionin g is highly dependent on the flexibility of
the vagus nerve, or the heart’ s vagal tone, as measured using HR V.
One of the most important mechanisms of RSA is the baroreflex , a
homeostatic function that helps maintain blood pressure at healthy , near-
constant levels. The baroreflex is a reflex mediated by blood pressure
sensors in the aorta (the largest artery in the body) and carotid arteries (the
ones that supply  blood to the brain, neck, and face).34 Even during rest,
blood pressure constantly fluctu ates as breathing causes the pressure in the
chest cavity to change. Scientist s consider the strengthening of homeostasis
in the baroreceptors to be the most obvious mechanism at play during
HRVB training.16
All major blood vessels contain pressure receptors. These detect the
stretching of the arteries as blood pressure increases. When blood pressure
rises, the barore flex immediatel y causes the blood vessels to dilate and theheart rate to drop. Conversely , when blood pressure falls, the baroreflex
ensures that the blood vessels constrict and heart rate increas es.16 Under
stress, the baroreflex reduces sympathetic outflow and increases vagal tone
to protect the heart against unhealthy arrhythmias.34
The baroreflex is optimized when the relationship between breathing
and heart rate is at its most efficient with regard to blood gas exchange. This means that breathing is a natural way to provide the external
stimulation to increase HRV. At the same time, each breath stimulates the
baroreflex. Hear t rate and blood  pressure are linked to the amount of air we
breathe and to the exchange of oxygen between the lungs and the blood. During HRV biofeedback, the baroreflex works more effectively . This is
associated with better mental and physical health, because as with higher
oscillations in RSA and HR V, the body is more adaptable. The sensitivity of the baroreceptors is also a good indicator of the
body’ s response to a buildup of CO2.35 The respiratory system reacts to
CO2 buildup  with involuntary contractions of the breathing muscles after an
exhalation, triggering an inhalat ion. The stronger the reaction to blood CO2,
the harder it is to hold your breath after exhaling and the sooner you need to
breathe in. The baroreceptors are most functional when the body is less
sensitive to CO2. Imagine being able to wait much longer before needing to
breathe in. A high BOL T score, indicating comfort with slower breathing,
signifies a reduced sensitivity to CO2 in the blood. A healthy baroreflex
with less sensitivity to CO2 results in more frequent reflex es, slower heart
rate, and increased vagal tone. The cardiovascular and respira tory systems are tightly interconnected
by the ANS which controls major functions of the body without conscious
direction.8,36 Blood pressure receptors are triggered by the workings of
RSA, which can be measured through HRV, providing strong indicators of
mental and physical health. The fight-or -flight reaction (SNS) causes blood
vessels to constrict, increasing heart rate and blood pressure, while ACh,
the neurotransmitter released by the PNS-controlled vagus nerve, slows
heart rate, dilates blood vessels, and suppresses the inflammatory response. The baroreflex system is more than just a control mechanism involving
heart rate and blood pressure. The activity of the baroreflex affects vascular
tone—the sensitivity with which blood vessels expand and contract.31 HRValso changes when there is inflammation. There is a clear relationship
between various pro-inflammatory cytokines and lower HRV. The impact of
the immune system on HRV, and the implications of that for health and
disease, is probably underestimated.8
The common denominator in all these systems is the breath, especially
slow breathing. Reducing the number of breaths per minute improves vagal
tone, reduces stress, and suppo rts health and cognition. The practices of
slow breathing and relaxation benefit the heart and respiratory system in
many ways. The baroreceptors become more responsive to changes in blood
pressure, the heart rate becomes more lively and elastic, the vagus nerve
more reactive, and the ANS shifts away from fight and flight toward less
stress—which supports social interaction and enables the body to thrive. BETTER BRAIN FUNCTION: SLOW V AGAL
BREA THING
It may seem obvious that it is easier to think when we are less stressed, and
that when we concentrate on a breathing exercise, there is less room for the
brain to worry . However , there is also evidence that slow breathing
exercises have a direct impact on the way the brain works. In one Belgian study , scientists discovered that vagus nerve stimulation
(VNS) in rats clearly produced a memory-enhancing effect.37 The rats
performed a gambling task in which they could learn to use reasoning to
maximize their food reward. Those that were treated with VNS developed
better decision-making. Further trials, from another Belgian lab, found that
vagal breathing could be used as a possible intervention agains t stress and
its negative effects on decision-making in humans.38 Other experiments
have shown a connection between the vagus nerve and enhanced working
memory .39 Patients given inhalant anesthetics experience an increase in
vagal tone as they regain consciousness9. Diaphragmatic  breathing can
directly lower cortisol levels,28 reducing the negative physiological
responses to stress and improving cognitive function. Research into the connection between the breath and the brain in nasal
breathing found that the breath directly affects neural activity in the brain.40
Breath actively promotes oscillatory synchronicity , which produces theconditions for optimal gas exchange and information processing in areas of
the brain that mediate goal-directed behaviors. Nasal breathing offers an
entry point to areas of the limbic brain that modulate cognitive function,
which has interesting implica tions for mental agility given that the
structures in the limbic syste m are involved in motivation, emotion,
learning, and memory .41 For example, experiments demonstrated that
breathing influenced a participant’ s ability to identify fearful emotions in
other people and their memory of visual objects. Passive inhalation of air
through the nose enhanced reaction time to scary stimuli. While there is a need for more research into the applications of VNS,
slow breathing, and activation of the PNS on cognition, these correlations
have been studied to some  extent in other fields. For example,
investigations into the impact of yogic breathing exercises have produced
interesting insig hts into the connection between breath and brain. A study
looking at Nadi Shodhana , yogic alternate nostril breathing, used EEG
measurements (from scalp electrodes) to assess the balance between the two
halves of the brain. It found that the practice generated more beta and alpha
brain waves.42 Beta waves are characteristic of a strongly engaged mind. A
person who is in active conver sation or focused on their work is in beta. Alpha represents nonarousal. It is associated with down time and relaxation. This suggests that the breathing practice allows participants to become
more mentally active while remaining calm and clear headed. Another
study looked at the way a combined practice of breathing and meditation
improved memory and influenced academic performance.43
We will look in more detail at the correlation between these
contemplative practices and the science of slow breathing, but it’s worth
noting that even meditation that doesn’ t focus on the breath can have the
effect of reducing the respira tory rate. Scientists have concluded that
regular yogic practices might improve cognitive functions, largely because
they tilt the autonomic balance in favor of the PNS. Further experiments
reported that EEG readings showed increased beta brainwave s under all
conditions in advanced meditators, that long-term meditati on practice
improves gray matter atrophy , that attention and working memory improve,
and that these techniques improve brain function in multiple pathways and
may even of fset age-related cognitive decline.43Perhaps even more important, severe depletion of ACh, the
neurotransmitter secreted by the vagus nerve when it is stimulated, has been
associated with Alzheimer ’s. Parallels have been found between the
working of the PNS and visual recognition memory and alertness. It has
also been observed that both stress and inflammation can factor in the
development of Alzheimer ’s13 and Parkinson’ s disease. Breathing
dysfunction can be related to impairments of attention or vigilance in
patients with dementia.28
VAGUS NER VE STIMULA TION: THE SECRET T O
BETTER HEAL TH
Many clinical applications of vagus stimulation, including those approved
to treat mental conditions like depression, bipolar disorder , and anxiety ,
involve a small surgical implant that electronically activates the nerve.44
However , there are less-invas ive, readily accessible option s available. Countless studie s, including those into HRVB, have shown that the power
of the vagus nerve can be accessed indir ectly  to relieve imba lances in the
nervous system.25 This is particularly helpful with stress. When the vagus
nerve is activated, the messages received by the brain become calmer . This
begins a top-dow n feedback loop where the brain reports back to the body
that it is safe, perpetuating a feeling of relaxation. Techniques to stimulate
the vagus nerve include humm ing, laughing, and any sort of conscious
breathing practice, including holding the breath, diaphragm breathing, nose
breathing, and slow , relaxed exhalations.45
To recap quickly , fibers from the vagus nerve innervate systems that
include the heart and lungs. When you breathe in, the sympathetic nervous
system (SNS) facilitates a brief acceleration in heart rate.46 On the out
breath, the vagus nerve secretes Vagusstuf f/ACh. ACh slows down the heart
rate via the PNS.
_OceanofPDF.com_The_Breathing_Cure_-_Patrick_McKeown.txt
Summarize the following text section accurately and concisely. Maintain specific details and numerical information, and use anti-repetition mechanisms:

        The article reports that mouth breathing, whether constant or
intermittent, may reduce the benefits of NO, leading to “unobstructed viral
replication. ” It concluded that “mouth breathing during sleep may therefore
worsen the symptoms of COVID-19. ”39
COVID-19 presents a serious challenge. Apart from the fact that
humans have no immunity to this virus, it behaves very differently from flu,
has a high viral load, and is poorly understood. What is know n is that it
attacks a specific type of cell known as a type 2 pneumocyt e. 42 Type 2
pneumocyte cells are responsible for the production and secretion of
surfactant. (If you recall, NO plays an important role in production of
surfactant. ) This is one reason why the virus can be deadly, even in young,
healthy patients. It is important to remember that nasal nitric oxide cannot do its job (or
protect you from disease) unless you breathe through your nose. Nasal
breathing alone will increase the amount of NO in the airways, but research
has found that humming can produce even higher levels of nitric oxide. 43
One 2015 study reports that humming produces seven times more NO than
normal exhalation. 44 It is believed that oscillations in the air accelerate the
exchange of gases between the nasal cavity and sinuses. 45 Another paper
discovered that “strong” humming was effective in treating chronic
rhinosinusitis, a fungal conditio n that causes inflammation and infection in
the nasal passages. Again, NO was identified, this time as an antifungal
agent. 46 Other research  has found that the concentration of nasal nitric
oxide also increases during breath holding. One study comparing scuba
divers to breath-holding divers reported higher levels of circulating NO in
the breath-holding group. 47
BREA THING WITH A F ACE MASK
During the 2020 coronavirus outbreak, debate has raged over the wearing of
protective face masks—whether masks lessen viral spread, protect the
wearer, or prevent the wearer from passing the virus to others. Many people
argue that the measure is ineffective. Others complain that they find it
difficult to breathe when wearing a mask. Whatever the arguments, studies
have definitively proven that masks prevent infected people from making
others sick. 48
A 2020 article in the Harvar d Business Review  suggests that better
masks are needed to fully protect against virus-containing particles. 49 A
study from 2003 explores the use of nasal plugs instead of face masks but
points out that it is necessary to “only breathe through the nostrils, as
breathing throug h the mouth will nullify the protection offered by the nasal
plug. ”50 Unfortu nately, despite research clearly demonstrating that mouth
breathing contributes to high viral load, poor immune defense, and more
severe forms of the novel coronavirus,39 nobody  is talking about the fact
that many people are mouth breathing inside their protective face masks. In July 2020, as the UK government enforced mask-wearing in shops, I
received an email from my friend, a medical doctor. He wondered howmany people were aware of the way they breathe when wearing a mask. He
shared the follow ing example: “I went to the barber on Sunday. The barber
had a mask on. All I could hear was fast breathing through the mouth while
he wore the mask. ” My friend explained his concerns:
Since April, I have tried to conv ince everyone I meet to breathe only
through the nose, with or without a mask. Many older people are
surprised when I stop them and ask how they breathe when they
have a mask on. Some said they didn’ t know or didn’ t pay attention. And more than 90% said they had to breathe through their mouth
because they couldn’ t breathe nasally with the mask on. My friend is adamant that nasal breathing will help prevent the spread
of viruses and the subsequent fatalities. He says, “When we mouth breathe,
any virus has a direct route to our lungs. Masks plus nasal breathing will
help keep the virus from entering the patient’ s respiratory system. ”
An article in the Independent, “Learn ing how to breathe again in the
new normal,” looks at breathing with and without a face mask in a post-
COVID environment51. The author describes the prevalence of unhealthy
breathing habits and calls on experts to define the problems of breathing
with a face mask. The article quotes breathing expert Paul DiTuro, who
suggests that respiratory training will help. DiTuro describe s a simple
exercise to make mask-wearing more comfortable:
Just before putting on your mask, take five “quality” breaths. With
each breath, inhale through the nose for four seconds, exhale
through the mouth for six second s, then rest for two seconds. Repeat
these five breaths as soon as you put on the mask, and again after
you remove it. 51
The concepts here are good. Inhaling for four seconds and exha ling for six
equates to a breathing rate of six breaths per minute, which  maximizes
many important physiological functions, as well as activating the relaxation
centers of the nervous system. Unfortunately, as we discussed earlier, breathing in through the nose
and out through the mouth is not a good idea. It causes nasal congestion andinhibits gas exchange in the lungs. The importance of breathing only
through the nose, awake or asleep, with or without a face mask, cannot be
underlined too strongly. BEATING NASAL CONGESTION
Mask or no mask, if you suffer from a constantly blocked nose, nasal
breathing may seem impossible or even frightening. However, breath
holding and physical exercise can actually help open the nasal airways. 52 In
a few pages, you’ll find a breath-holding exercise for decongesting the
nose. Exactly how this works remains a matter of debate, but holding the
breath increases CO2 in the blood, pools nitric oxide within the nose, and
activates the body’ s sympathetic stress response. While long-term
sympathetic activation is dama ging to health, the stress response plays a
necessary and beneficial role53 in the immune system54 and in regulating
inflammation. 55
As far back as 1923, an article in the American Journal of Physiology
reported that holding the breath could ease nasal stuffiness. 56 If this
information had been made public at the time, millions of children and
adults suffering from rhinitis could have found relief simply by holding
their breath whenever their nose was bunged up. Decades later, in 1977,
researchers showed that rebreathing exhaled air decreased nasal congestion. Even holding the breath for just 30 seconds made breathing easier for most
of the subjects tested. 57 The main stimulus for this result. Carbon dioxide. 58
According to Dr. James Bartley, an ear, nose, and throat surgeon, nasal
resistance is inversely related to end-tidal CO2. 59 End-tidal CO2 is the
concentration of CO2 in the air at the end of an exhaled breath. It is a direct
measure of how much CO2 there is in the lungs, and under normal
circumstances, an indirect measure of the pressure of CO2 in the blood. Bartley’ s finding  means that as levels of CO2 reduce in the lungs and blood,
the nose become s more congested. Studies have shown that a reduction of
CO2 in the lungs (from normal pressure of 40 mmHg to 35 mmHg)
corresponds with a 10% increase in nasal congestion. 52 Anxiety also
typically corresponds with lower end-tidal CO 2 levels. 60This is also relevant in a complaint known as empty nose syndrome
(ENS)—where a patient with clear nasal airways experiences a variety of
symptoms, including sensations of nasal obstruction, dryness and crusting,
and feelings of breathlessness61 and drowning. ENS can result from major
or minor  surgical procedures including turbinate surgery, laser therapy, and
submucosal resection, even when sur gery and medical support is successful. At prese nt, its existence, diagnosis, and management are all controversial,
with discussion raging as to whether neurological or psychosomatic factors
may contribute. 61
ENS can be caused by the removal of the turbinates. The turbinates are
small structures inside the nose that filter and humidify the air as it passes
through the nostrils into the airways and lungs. They are made up of a bony
structure surrounded by vascular tissue and a mucus membrane. They can
become inflamed and swollen when allergy, infection, or irritation is
present, produci ng an excessive amount of mucus, which causes  the nose to
block. ENT Jim Bartley also explored the feeling of nasal stuffiness in
hyperventilation. 62 In 2005, Bartley examined 14 patients who complained
of nasal congestion after surgery and of feeling unable to breathe nasally,
despite having an apparently adequate nasal airway with no collapsed tissue
inside the nose,  and a surgical success rate between 63% and 85%. Some
had tried nasal steroids and oral antihistamines without relief. Bartley noted
that some were breathing rapidl y, predominantly into their upper chest. He
assessed each for hyperventilation syndrome and discovered that all
displayed a heightened respirat ory rate of around 18 breaths per minute
with an upper chest breathing pattern. On a subjective breathing
questionnaire, 12 of the 14 participants had scores indicative of
hyperventilation. Three patients had an end-tidal CO2 reading of 35 mmHg,
which indicates low blood CO 2. Five had breath retraining; this successfully
relieved nasal congestion for two of them. 62
Bartley concluded that patients who suffer from constant feelings of
nasal congestion, particularly after failed nasal surgery, should be assessed
for hyperventila tion syndrome. The primary issue in those patients may
actually be poor breathing patterns. Even slightly fast and/or hard breathing
causes a feeling of air hunger that patients often interpret as nasal stuf finess. While the functi oning of the physical airway is a relevant conce rn, air flow
must also be considered. If someone with chronic hyperventilation complains of nasal
obstruction, with no identifiable anatomical reason, surgery may not be the
answer. 62 Breath ing reeducation may be. If you have under gone nasal
surgery and still feel as if your nose is constantly blocked, your breathing
pattern is likely to be at the root of the problem. If you do have nasal
congestion, rhinitis or asthma, try the exercises in this book first. Decongest
your nose using the following breath-holding exercise, switch to nasal
breathing, and improve your BOLT score. I have used these techniques with
thousands of people who have attended my workshops over the years and
found that many destined for nasal sur gery did not require it. Because the nose is designed to regulate air intake,63 switching to nasal
breathing signifi cantly improves  the symptoms of nasal stuffiness and will
dramatically reduce your symptoms in the long term. EXERCISE T O UNBLOCK THE NOSE
Before you read any further, try this exercise to see just how effective it is
for clear ing your nose. The exercise is the same for adults and children. This exer cise is not suitable for women who ar e pregnant. • Sit upright on a straight-backed chair. • Normalize your breathing and breathe calmly. Take a small, light breath in through
your nose if you can and a small breath out through your nose. If you are unable to
inhale through your nose, take a tiny breath in through the corner of your mouth. • After exhaling, pinch your nose and hold your breath. Keep your lips sealed. • Gently nod your head or rock your body until you feel that you cannot hold your
breath any longer. You should feel a relatively strong need for air. • At this point, let go of your nose, and breathe in gently through the nose. Breathe
gently in and out with your mouth closed. When you first breathe in, avoid taking a
deep breath. Instead, keep your breathing calm and focus on relaxation. Use the
mantra “relax and breathe less” if it helps. • Repeat the exercise until you can breathe easily through your nose. If your nose
does not become fully unblocked, wait around one minute, and practice the same
steps again. Y ou may need to do the exercise several times. After you have completed the exercise, your nose will be unblocked. However, until you have improved your BOL T score to over 25 seconds,the exercise will decongest your nose onlny temporarily. Once your BOL T
score is 25 or more, your nose will stay unblocked for much longer periods. I always explain to my students, especially the teenagers, that you have two
options. You can improve your BOL T score to 25 seconds, or you can
experience nasal congestion for the rest of your life. When you consider all
of the negative consequences of mouth breathing for sleep, stress, and other
health concerns, the choice is obvious. Remember, until you have changed the underlying breathing patterns
that contribute to nasal stuffiness, it is quite normal for the nose to block
again. With regular practice of the exercises in this book, your body will
adapt, and your nose will start to remain clear. Practice this exercise
whenever your nose feels congested. Even if you have a heavy cold, this
exercise can help you maintain nasal breathing. MAKING THE SWITCH
The first step in addressing poor breathing patterns and increasing your
BOL T score is to switch from mouth to nose breathing. Even though its
primary function  is respiratory, the nose is often underused for the essential
task of breathing. While total mouth breathing is rare, as most people tend
to switch from mouth to nose breathing and vice versa, it is incredibly
common for children and adults  to mouth breathe some of the time, either
out of habit or due to nasal obstruction. When you first switch from mouth to nasal breathing, the volume of air
you inhale with each breath may immediately reduce. This is likely to feel a
little strange to begin with. You will probably experience a slight air
shortage since the volume of air inhaled through the nose is less than you
are used to inhaling through the mouth. Don’ t worry. Air hunger is a good
sign of progress. Any discomfort will diminish in a few days. Your body
may try to trick you into breathing more by yawning, sighing, or sneaking
in the odd mouth breath. Try not to increase your breathing in those ways. When you feel the need to breat he big—for example, if you experience the
impulse to sigh—hold your breath for 5 to 10 seconds following the sigh. One thing to be aware of that may seem odd, even unfair, as you make
the switch from mouth to nasal breathing, is that the size of the nose isactually an important factor in breathing habits. People with a small nasal
airway are much more likely to breathe through an open mouth than those
with an adequat e nasal size. Mouth breathing is a very normal reaction to a
small nasal airway. The smaller the nose, the greater the resistance to
breathing, and the more air hunger is experienced in breathing through the
nose. HOW T O BREA THE DURING EXERCISE
A spacious nasal cavity and large nostrils are definitely useful for breathing
through the nose during physical exercise. If your nasal airway is small, the
resistance to breathing and the resulting air hunger may be too much during
exercise. To help open the nasal passages, you can use the exercise-specific
NasalDilator, which I have designed specifically for this purpose. Earlier, we talked about how CO2 creates the primary stimulus to
breathe and is instrumental in oxygenation. Nose breathing during physical
exercise slows the breath and reduces breathing volume, which influences
the levels of CO2 in the blood. However, most of us will not spontaneously
choose to breathe through the nose during heavy exercise. 64 Without proper
training for at least six to eight weeks, the air hunger caused by nose
breathing can become quite pronounced as exercise intensifies. Breathing throu gh the nose is usually only comfortable during gentle
exercise, when the total volume of air entering the lungs every minute
(called minute ventilation ) is less than 35 liters. Once minute ventilation has
increased to between 35 and 41 liters,65 the tendency is to start mouth
breathing. The exact switching point from nose to mouth breathing is highly
personal, influen ced by individual sensitivity to CO2, metabolism, and the
size of the nose. Mouth breathing is faster than nose breathing. It feels preferable under
certain conditions because the shallow, fast breaths result in a greater
volume of air entering the lungs. This causes blood CO2 to drop, which
reduces the feeling of air hunger. 66 How ever, breathing through the nose is
actually more efficient because it allows the lungs to extract more oxygen
from the air. The percentage of oxygen in expired air decreases when nasal
breathing during exercise, indicating that more of the oxygen is beingused. 67 Continuing nasal breathing practice over a period of six to eight
weeks will encourage your body to adapt, delaying the onset of
breathlessness. Whether or not you currently include physical  exercise in
your weekly routine, this applies to you. We all have a threshold at which
mouth breathing feels necessary. Whatever your starting point, whether you
start to wheeze during your workout or when you just try to get up off the
couch, you can begin to improve your fitness by restoring nasal breathing. The importance of breathing through the nose rather than the mouth
should not be underestimated. It encourages functional breathin g and larger
oscillations of the diaphragm, supporting functional movement, and
preventing injur y. It is an important element of getting “in the zone”—that
state of peak focus when everything flows and you can perform at your
best. (Chapter Five looks more deeply at the connection between breathing
and movement. ) It is also import ant to remember that nasal breathing helps retain heat
and moisture in the body. During  exercise, this can make a big difference as
to wheth er you experience a dry mouth. It can protect your airways from
trauma, including exercise-induced asthma and cyclist’ s cough. Nasally restricted breathing can be used during exercise to improve
performance. 68 This has implic ations for nonathletes too. In a 2018 paper,
professor of exercise science and Olympic triathlon coach, Dr. Geor ge
Dallam looked in detail at the breathing of athletes. 66 Five male and five
female recreational runners trained and raced using only nasal breathing for
six months. Dallam recorded comparative results when the participants
breathed only through the nose and only through the mouth, wearing a
swimming nose clip to close the nostrils. The trial used a graded exercise
test to examine performance, breathing rate, oxygen uptake, and breathing
efficiency at VO 2 max. VO 2 max is maximum oxygen consumption during
intense exercise. It is used to measure cardiovascular fitness and aerobic
endurance in athletes. Dallam’ s study produced the following results:
• Respiratory rate was much slower in nasal breathing than in oral breathing (39. 2
bpm vs 49. 4 bpm). • End-tidal CO 2 was significantly higher in nose breathing than mouth breathing (44. 7
mmHg vs 40. 2 mmHg). • Ventilation (volume of breathing) was reduced by 22% in nasal breathing. • Nose breathing resulted in lower end-tidal oxygen pressure and a lower percentage
of oxygen in expired air, indicating that more oxygen was removed from the air by
the lungs during nasal breathing. A key finding from Dallam’ s study was that after six months’ training
with only nasal breathing, the athletes achieved the same peak performance
and oxygen consumption when  nasal breathing as they did during oral
breathing. They were pushing themselves to their limits yet still managed to
breathe in an effective way. Breathing was also more economical. The 22%
reduction in ventilation meant that breathing required less effort and the
muscles of the respiratory syste m didn’ t have to work as hard. Achieving
the same  intensity with 22% less breathing represents a significantly greater
economy. Dallam concluded that it is possible to maintain VO 2 max and
peak performanc e after a period of training using only nasal breathing. The
body naturally adapts to nasal  breathing by increasing its tolerance to
changes in CO 2, so air hunger decreases. These findings are relevant for everyone, whatever your level of fitness. If a walk  to the corner shop leaves you gasping for breath, nasal breathing
will help you. To limit air hunge r during physical exercise, work to achieve
a higher BOL T score and breathe light, slow, and deep (LSD):
• Light:  Only breathe the volume of air that you need (don’t overbreathe). • Slow:  Reduce your respiratory rate. • Deep:  Breathe with greater amplitudes of diaphragm movement. If you are healthy and exercising at the appropriate level to improve
your aerobic fitness, you should be able to breathe only through the nose
without needing any specific adaptations66. If the air hunger is so strong
that you need to open your mouth, simply slow down and allow your
breathing to calm. By breathing  nasally throughout, you should finish your
workout feeling relaxed and full of energy instead of exhausted and
dehydrated. Recreational Athletes
Healthy people exercising at the lower levels necessary to improve aerobic
fitness can breat he entirely through the nose,66 without needing any specific
adaptations. Recreational athletes should maintain nasal breathing at alltimes. If the air hunger is so strong that you need to open your mouth to
breathe, simply slow down and allow your breathing to calm. Competitive Athletes
It is best for competitive athletes to alternate nasal breathing with mouth
breathing. High- intensity trainin g helps prevent muscle deconditioning and
will require an athlete to periodi cally breathe through their mouth. For less-
than-maximum intensity training, and at all other times, nasal breathing
should be used. A competitive athlete may spend 50% of training with their
mouth closed. Research has shown that healthy adults are able to maintain nasal
breathing to 85% of VO 2 max,69 indicating that it is possible to breathe
nasally at much higher intensities of exercise than we might choose. • Use mouth breathing to maintain muscle condition when working at an all-out pace. • During competition, there is no need to intentionally take bigger breaths. Instead,
achieve a higher BOL T score and apply the OA precompetition preparation. (Y ou
can find this in Chapter T wo. ) • Nasal breathing combined with breath-holding during your warm-up can be very
advantageous. As can practicing light, slow and deep breathing during the warm-
down. (Y ou will find instructions for warm-up in Chapter T wo. ) SNIFFING OUT SUCCESS
One function of the nose we haven’ t yet discussed is the sense of smell via
the olfac tory nerve. In ancient yogic texts, while breath control is associated
with a “pristine” state of mind, the condition of the olfactory nerve is seen
as indicating the general state of health. Is this relevant to nasal breathing. Scientists say it could be. In 2019, researchers at the Weizmann Institute in Israel suggested that
nasal inhalation could be linked to cognition as part of an evolutionary
survival mechanism. 70,71 A sense  of smell is, after all, equated with sniffing
out dang er. For our distant ancestors, this meant accurately assessing their
surroundings to make life-or -death decisions. The Weizmann team
theorized that this ancient sensory system might benefit from nasal
inhalation and that, in modern life and competitive sports, nasal inhalation
might automatically trigger conditions in the brain that optimizevisuospatial focus. They demonstrated that nasal breathing synchronized
electrical activity in the brain on a wavelength that helped maximize
visuospatial (VS) awareness. Visuospatial awareness is the way we relate visual information to the
space around us. It helps us perform everyday tasks like walking through a
door rather than bumping into the door frame, picking up a glass of water,
catching a ball, reading a map, driving a car, and even parallel parking. Visuospatial skills can be defined as
the ability to observe the visual world, to form mental
representations of the visual objects, to mentally manipulate these
representations, and to in turn reconstruct aspects of the visual
experience. 72–74
VS ability is made up of several cognitive processes, includ ing the
perception and understanding of spatial orientation, reproducing actions
through fine motor movements,  and integrating parts into a whole. 72,75–77
These elements all place different demands on working memory. 73
Visuospatial tasks are “complex and engage various spatial processes”, and
involve numerous areas of the brain. 72
The fact that nasal breathing helps synchronize the complex mental
processes required for VS awareness has applications for sports, such as
tennis, where a keen awareness of the external environment and its
dimensions is key. In team ball games like football, soccer, basketball, and
ice hockey, the player must be able to catch, carry, kick, or hit a ball at the
same time as scanning the pitch for teammates to pass to—all this while
running at full pelt. 78 During any sort of sporting activity (and during
activities like music performan ce), it’s necessary to absorb and process a
great deal of information in a very short time. Athletes have to become
highly proficient at perceiving changes in play caused by their opponents
and team members. 78
Athletes and musicians display  better performance in VS tasks than
people who are physically inactive. 79–81 Older people can improve their VS
skills by improving their physic al fitness. 82 Several studies have examined
the influence of more general physical exercise on VS ability. 83–85The influence of breathing on VS ability also has implications for
children’ s intellectual development. A 2015 study demonstrated that
visuospatial perception is instrumental when a child learns to read, and that
assessment of VS abilities could help with the early detection of
“difficulties in neurodevelopmen tal disorders associated with low academic
achievement. ”86 Another paper from 2016 sugg ests that VS skills are even
important in learning mathematics, especially for things like problem
solving. 72
OceanofPDF. comTCHAPTER FOUR
THE VAGUS NERVE AND THE HEART-
BREATH-BRAIN CONNECTION
o really understand the powerful interconnections between the
breath, heart, and brain, we must take a journey along the wandering
vagus nerve  and through the autonomic nervous system (ANS). This
chapter will cover a lot of ground. If we seem to be heading away from the
central issue of breathing, you will soon see how the vagus nerve connects
with the breath in powerful, life-transforming ways. The vagus nerve (the tenth cranial nerve or CN X) has multiple
branches that diver ge from two thick stems rooted in the cerebellum or
“little brain” (the area at the lower back of the brain) and the brain stem. 1–3
It can be found behind the artery in your neck where you feel for your
pulse. Vagus, to wander  in Latin, comes from the same root as our words
vagabond, vagrant, and vague. The name gives some clue to just how
extensively this nerve travels. During its journey through the body, the
vagus nerve supplies nerves to the heart, respiratory system, and
gastrointestinal tract, reaching the lowest viscera of the abdomen. It is the
most wide-ranging cranial nerve  in the human body and is responsible for,
among other things, many functions of the mouth, including speech,
appetite control, and even vomiting. Ultimately, it conducts nerve impulses
to every major or gan in the body. 4
The vagus nerve is made up of 80% to 90% afferent (body to brain)
nerve fibers. 2 This means that most of the information it conveys travels
from the body to the brain. Instead of orders flowing from the brain,
affecting the various physiological systems and organs, the afferent fibers
take information back from the body to the brain. 5 The heart, however, isinnervated with efferent (brain to body) vagus fibers—a top-down line of
communication. 6 The resulting two-way flow of data provides the building
blocks for feedback loops in which information from the brain impacts the
physical systems of the body and vice versa. Many studies have shown the vagus nerve’ s positive potential to
influence physic al health, mental health, and cognition. This nerve can be
stimulated to reduce anxiety, alleviate depression, and even inhibit
inflammation to fight disease in the body by combating the cortisol-
producing stress response we know as fight or flight. To understand the vagus nerve’ s importance to the heart-breath-brain
connection, we need to start our journey by looking at the two sides of the
ANS, beginning with the fight-or -flight response. THE V AGUS NER VE AND AUT ONOMIC BALANCE
The fight-or -flight response is the body’ s instinctive survival mechanism. From a simple evolutionary perspective, it allows mammals, including
humans, to react to situations that may be life threatening. When humans
lived in constantly unsafe environments, it was useful for fighting off
enemies and hunting for food. While it still has a valuable role to play in
keeping us safe in the modern world, problems arise when we have the
same response to things that are probably not fatal. We migh t be fearful
about giving a presentation, turning up for an interview, receiving an
unexpected bill, or even being blocked on social media. When fight or
flight is constan tly in overdrive, the result is chronic stress, that all too
common modern-day malady. Fight or flight is controlled by the sympathetic nervous system  (SNS),
which is one-hal f of the overall ANS. The vagus nerve is the main driver of
the other branch of the ANS, the parasympathetic nervous system  (PNS)1. While the sympathetic nervous system triggers fight or flight, the vagus-led
PNS is responsible for rest and digestion, the state in which the body
perceives no threat, the mind is relaxed, and digestion is active. Crucially,
as we will discover, it is throug h the ANS that the respiratory system, lung
ventilation, and blood-gas excha nge connects with the working of the heart
rate and blood vessels. Ideally, the two responses of the ANS, fight/flightand rest/digest, work in balance. 7 The primary purpose of the ANS is to
regulate the body’ s main functions. The SNS (sympathetic nervous system) prepares the body for external
challenges. It increases metabolic output, stimulates and prepares the
muscles, and mobilizes existing energy reserves. It also constricts the blood
vessels, increas ing heart rate and blood pressure. In contrast, the PNS
(parasympathetic nervous system) focuses inward, supporting growth,
restoration, reproduction, relaxation, and conservation of energy. It
maintains the balance of heart frequencies; notably, it reacts much faster to
external and internal changes than the SNS, responding within just one
second, in contrast to the five or more seconds it takes the SNS to kick in. 8
These two oppo sing forces within the ANS are never static. The system
continually fluctuates to maintain a stable internal environment that
operates within healthy paramet ers. This constant balancing act to maintain
homeostasis  is key to keep ing organs working properly. For example, if
your body temperature is too high, the ANS adjusts to bring it back to the
optimal tempera ture of 37° Celsius (98. 6° Fahrenheit). This is not just a
reactive system  that waits passively to meet the next external crisis; it
works incessantly to promote stability within the body. While the two branches of the ANS may seem to function in opposition,
they often operate in syner gy to meet metabolic demands. For example,
during exercise,  PNS tone decreases while SNS activity increases. There
are even unique situations when both PNS and SNS are either inhibited or
activated. 9 For example, sexual arousal in adult humans is characterized by
the excitement of both. Homeostasis (balance or equilibrium) is a fundamental goal of all
biological systems. 10 In humans, it operates at the level of the whole body,
within tissues, and even in individual cells. Where homeostasis can be
described as a healthy, dynamic feedback and regulation system, stress can
be defined simply as any autonomic state that reflects a disturbance of that
balance. Stress is a state where a psychological, environmental, or physical
situation, whether a single event or a long-term issue, disrupts the body’ s
ability to self-re gulate. Modern life presents us with a world where it can be
difficult to maintain that balanc e. Think about some of the terms used todescribe an emotional upset: you are “out of whack,” you feel “all over the
place,” or you are literally “of f balance. ”
Stress can manifest itself in each of the three dimensions of
dysfunctional breathing. It can show up biomechanically as imbalances in
the respiratory muscles. This can lead to neck and back pain, upper chest
breathing, and poor diaphragm control. Biochemically, chronic
hyperventilation can impact the body’ s delicate pH balance. Psychologically, anxiety, depression, and anger can destroy your
equilibrium. Living in a constant state of fight or flight poses the danger of cortisol
overload. Cortisol is the primary stress hormone. 11 When released into the
bloodstream, it enhances the brain’ s use of glucose (blood sugar ) and makes
substances that repair tissues more available. In essence, it prepares the
body to escape from the saber -toothed beast and not bleed too much if that
doesn’ t work out. Aligned with that purpose, cortisol also curbs bodily
functions that aren’ t immediately essential to the fight-or -flight situation. It
alters immune system responses and suppresses digestive, reproductive, and
growth processe s. As you migh t expect, it communicates with the parts of
the brain that control mood, motivation, and fear. Ideally, the body’ s stress response is self-limiting. Hormones go back to
normal levels after the perceived threat has passed, and the body returns to
homeostasis. However, when stressors are constantly present or stress is
chronic (which  is like signing up for a long-term fight-or -flight
subscription), a cortisol imbalance occurs. Considering how many of the
body’ s processes cortisol can suppress, it is hardly surprising that people
who suffer from  high levels of stress display a plethora of physical and
mental conditions, including anxiety, heart disease, weight gain, digestive
problems, depression, headaches, sleep disorders, poor memory, and
decreased ability to concentrate. On the other (balancing) side of the ANS, we find the well-studied
connection between the vagus nerve and the parasympathetic nervous
system (PNS), the rest and digest side of the ANS. The vagus nerve, which
sends impulses to all the major organs and is particularly conn ected to the
heart and respir atory system, secretes a brilliantly useful substance called
acetylcholine  or ACh. Acetylcholine (ACh), the first neurotransmitter ever to be identified,12
was discovered in 1913 by English chemist Arthur Ewins. 12 Later, in 1921,
the Nobel Prize winning physio logist Otto Loewi determined its functional
significance. Loewi found that activating the vagus nerve reduced heart
rate. 1 He did this by isolating the heart of a frog and stimulating the vagus
nerve to release something he called “Vagusstuf f. ” This substance, later
identified as acetylcholine, caused the frog’ s heart to slow, replicating
relaxation, the reaction to a nonthreatening environment—or the rest-and-
digest state. The implications of this are huge. It means that stimulating the
vagus nerve can activate the PNS, subduing or balancing out the fight-or -
flight reaction of the SNS. This “Vagusstuf f” (ACh) released by the vagus nerve is a
neurotransmitter—a chemical messenger released by nerve cells to send
messages to other cells. This neurotransmitter is found in all motor neurons,
where it stimulates smooth muscles to contract, slows the heart rate, and
dilates the blood vessels. It is also present in many brain neuro ns where it
has a role in vital mental processes such as cognition and mem ory. Severe
depletion of acetylcholine has been associated with conditions such as
Alzheimer ’s. 12
STRESS, INFLAMMA TION, AND ILLNESS
From a health perspective, if we define stress as a disruption of
homeostasis, inflammation often begins as the body’ s natural response to
stress. What’s more, chronic, low-grade inflammation has been proven to
indicate an overactive fight-or -flight response. 10 It makes sense, therefore,
to deduce that inhibiting the fight-or-flight reaction (as the ACh released by
the vagus nerve does) could reduce inflammation. Inflammation is a defense mechanism triggered by injury or infection. It
is at the extreme  end of the spectrum that ranges from homeosta sis to stress
response to inflammatory response. 10 It combines different immune
mechanisms that work to neutr alize invading pathogens such as bacteria
and viruses, repair injured tissues, and heal wounds. However, when out of
balance, inflamm ation plays a key role in the development and persistence
of many diseases. It can be triggered by extreme internal imbalances or byexternal challen ges that disturb homeostasis. After a stressor occurs, the
inflammatory response kicks in. While modern life has its benefits, including a much longer life span,13
advanced technology, and home  grocery deliveries, the nature of stress has
changed dramat ically. When stress is severe and prolonged, it causes the
body to compensate, physiologically and behaviorally, to maintain
homeostasis. Long term, this can put an unsustainable load on the body’ s
systems. There is increasing evidence that chronic stress increases the risk of
both physical and mental health disorders. It can play a critical role in the
onset and progress of stress-rela ted illness, including diseases of the heart,
digestive system, brain, and many forms of cancer. Chronic stressors are
known to suppress immune function. In fact, while not yet fully understood,
studies show that stress is a common risk factor in 75% to 90% of human
diseases. 13 That’ s nearly all of them. Scientists at Carnegie Mellon University discovered a direct
relationship betw een chronic mental stress, the body’ s inability to regulate
inflammation, and the progression of disease. 14 Their study, which used the
common cold as a model, found that prolonged stress decrease s the body’ s
sensitivity to the stress hormon e cortisol in such a way that the immune
cells become insensitive to it. This negatively affects the ability of cortisol
to regulate inflammation. Inflam mation gets out of control, and disease sets
in. The research demonstrated that the symptoms of a cold are not actually
caused by the virus. They are a side effect of the body’ s inflammatory
response, which is designed to fight infection. People who suf fer most when
they have a cold don’t have “Man Flu”—they are actually experiencing a
more extreme inflammatory reaction. The study also confirmed that stress led to the immune cells being less
able to respond to signals that normally regulate inflammation. Participants
who were stressed were much more likely to develop colds when exposed
to the virus than those who weren’ t stressed, and those people also
produced more cytokines —the chemical messengers that trigger
inflammation. Because inflamm ation is pivotal in so many illnesses, this
offers a valuable  window into the impact that psychological stress can have
on health. VAGAL STIMULA TION AND THE IMMUNE SYSTEM
A clear connection between the nervous system and the immune system
was discovered by neurosur geon Kevin Tracey in 1998. In an experiment
on a rat, he investigated the idea that stimulating the vagus nerve could
alleviate harmful inflammation. 4 He found that the nervous system could be
used almost like a computer to trigger commands that stop a problem in its
tracks. The results of his expe riment were so unexpected that Tracey’ s
colleagues were apparently in the corridor outside his lab, running bets
against his theor y even as he was in the middle of testing it. 4 Further trials
confirmed Tracey’ s findings. Using electronic implants to stimulate the
vagus nerve in humans, he produced a dramatic reduction and even
remission in rheumatoid arthriti s, a condition with no known cure. 15 This
helped illuminate the vagal system’ s close interrelationship with the
inflammatory system. The first steps of an inflammatory reaction involve the release of those
pro-inflammatory chemicals called cytokines. 8 When the body produces too
many cytokines,  they can cause more damage than the invading  pathogens. For exam ple, in sepsis, the body’s own immune reaction can cause tissue
injury, dangerously low blood pressure, and even death. Chronic
inflammation can also feature in many diseases where no infection or injury
is present. In obesity, for examp le, an overload of storage in fat cells leads
to a stress response that causes the release of inflammatory cytokines. 10
The conversatio n between the immune system and the brain that
moderates this inflammatory response relies, in part, on the vagus nerve,
which, in turn, is important due to the anti-inflammatory role of
Vagusstuf f/ACh. Crucially, ACh, the neurotransmitter secreted by the vagus
nerve, blocks the release of many of the pro-inflammatory cytokines. In
studies of diseases characterized by an excessive immune reaction,
including sepsis and pancreatiti s, vagus nerve stimulation was found to be
sufficient to block cytokine activity. When the vagus nerve is stimulated
electronically, the body’ s level of inflammatory cytokines decreases. 16
As it turns out, the breath also provides a (natural) gateway to influence
the vagu s nerve and the ANS— through the role of carbon dioxide (CO 2)
levels in mainta ining the body’ s acid-base balance. 17 One of the functionsof breath ing is to regulate the level of blood CO2 to maintain the blood’ s
acid balance (or pH). When levels of CO2 in the blood are too high, over
time, CO2 diffuses  into the red blood cells as carbonic acid, making the
blood too acidic, a condition called acidosis. When CO2 levels are too low,
respiratory alkalosis  occurs. Both acidosis and alkalosis are serious,
potentially life-t hreatening in their acute forms and damaging to health if
they persist long term. Therefore, the proper management of CO2 through
the breath is crucial. When blood pH changes even subtly, respiration will automatically
decrease or increase to compensate. One example of this is ketoacidosis, a
serious complication which can occur in diabetes. Ketoacidosis increases
acidity in the blood, stimulating corrective overbreathing. This fast, upper
chest breathing  is also commonly seen after the acidosis following
prolonged diarrhea and as a response to increased progesterone levels in
women. Conversely, alkalosis can be induced by vomiting or the use of
steroids or diuretics. The respiratory drive is then suppressed as the body
works to restore homeostasis. 17 Information about blood CO2 is sent to the
respiratory center so that breathing can adjust via pathways involving the
vagus nerve. Therefore, breathing exercises to increase CO2 have a “vagotropic
effect. ”18 CO 2 directly influences the sensitivit y of the vagus nerve’ s nuclei. This slows the pulse and improves the blood-filling of the heart. 19 Increased
blood CO2 is the most likely mechanism  to enhance the vagus nerve’ s
slowing effect on the heart during exhalation. Increased CO2 (hypercapnia)
and exhalation are both vital in stimulating the vagus nerve. 18
What’ s particularly exciting is that the effects of vagu s nerve
stimulation don’t stop when treatment is finished. They are ongoing. Over
time, the vagus system develops and maintains much greater resilience to
stressors. This long-term condit ioning of the vagus nerve, its functionality,
and ability to react to maintain homeostasis is known as vagal tone. This
vagal tone is key not just to reducing inflammatory responses but also to a
healthy and resilient functioning of the heart. VAGAL T ONE AND HEART RA TE V ARIABILITYWhile we often associate heartbeats with rhythm and may believe an
absolutely regul ar heartbeat is a healthy one, heartbeats are not all the
same. 9 In fact, they change constantly, and the more coherent the
fluctuations are in speed and intensity, the healthier you are likely to be,
both mentally and physically. 16 The heart is not a metronome. Its
oscillations are complex and constantly changing. The cardiovascular
system needs to adjust to external and internal stimuli to maintain
homeostasis. Heart rate variability  (HRV) measures the difference between
consecutive heartbeats. In clinical settings, readings are taken to the
millisecond with the help of an ECG signal. With modern technology, you
can now measu re your own HRV using a smart watch or other wearable
fitness tracker. Results are presented as time series data, a way of recording
information collected over a period of time to show variations  within that
period. Daily high and low tide data is a familiar use of a data time series. Using HRV as an objective indicater of fitness and resilience has been
gaining traction among fitness enthusiasts. While many people enjoy using
gadgets and apps to measure their own HRV, remember that technology
doesn’ t change HRV; it simply provides the information that allows you to
assess it. HRV is predominantly controlled by the ANS. Growing evidence
associates an ANS imbalance with a higher prevalence of disease and death,
which makes HRV a useful tool in predicting and assessing illness. When
you are in a fight-or -flight state, HRV changes. As the system restores
homeostasis, those changes settle down. However, if the body is under
constant stress, the heart rate becomes less resilient and less flexible. The
variation between oscillations decreases, and the body can’t shift gears as
easily. The potential impact is massive. Because lower HRV can be caused
by stress, emoti onal distress and chronic stress directly impact wellness. Studies indicate,  for example, that stress increases the risk of heart attack in
people who have no prior heart disease and that emotions like anger,
hostility, and aggressiveness can contribute to coronary artery disease. 10
HRV declines significantly with poor health. 20,21 People who are
emotionally sick, older, or less physically fit often have a lower HRV. 16
High concentrations of cortisol are associated with low HRV,8 and HRV isan estab lished tool in diagnosing diabetic neuropathy, the nerve damage,
often to the legs and feet, suffered by diabetics. Correlations have also been
found between changes to HRV and many high-mortality conditions,
including heart disease, cancer, stroke, Alzheimer ’s, diabetes, chronic lower
respiratory diseases, and intentional self-harm. Low HRV is related to a wide range of physical and mental illnesses
and a lower life expectancy. 8 Even the stress caused by a single significant
life event can have an impact. Scientists looking at the health of divorced
people discovered that particip ants who had gone through a marriage
breakdown had a lower resting HRV than those who were married. 22 The
upset caused by divorce actually made those people less healthy. While low HRV is associated with disease, people with high HRV are
likely to be healthier, both physically and mentally. All of this explains why
some people seem to be more resilient to stress, better able to field
challenging situations and take difficulties in their stride, while others get
thrown off balance. Scientists have so far failed to find satisfying answers
about the genetics of the stress response,23 but inherited conditions can
certainly contri bute to aspects of health that result in low HRV. For
example, studies  have shown that vagal tone is passed on from mother to
child. 24 Mothers who are depressed,  anxious, and angry during their
pregnancy have lower vagal activity. Once the baby is born, he or she also
displays a low vagal tone. The good news is that it is possible to build better vagal tone. Just one
note of caution: it is not always better to increase vagal tone. 25 For instance,
parasympathetic hyperactivity can occur in athletes who overtrain. Several
studies indicate that symptoms  of overreaching may be relate d to down-
regulation of the SNS and/or changes in the balance between  vagal and
sympathetic tone. This can cause fatigue and adversely affect performance
during periods of regular competition. 26 The key is to optimize  HRV, not
just blindly augment it. Slow breathing at 4. 5 to 6. 5 breaths per minute has
been found to optimize sympathovagal balance, creating an ideal balance
between the two branches of the autonomic nervous system. 27
Because it is closely connected with the working of the ANS, especially
the parasympathetic branch (PNS), HRV is considered a reliable measure of
how well the vagus nerve is working, that is, of vagal tone. Scientistsbelieve that vagal tone in the heart forms one of the connectio ns between
breathing and emotion. 28 It is influenced by the breath and is essential to the
stimulation of the vagus nerve, which is closely tied to aspects of human
connection such as emotional regulation, reactivity, expression, empathy,
and attachment. At the other end of the emotional spectrum, dysfunction of
the ANS is common to people suffering from anxiety, depression, PTSD,
panic disorder, and other stress-related mental and physical conditions. Parallels have even been found between vagal tone and cognitive functions
such as visual recognition memory and alertness. HRV, used as a measure
of vagal tone, provides doctors with a way to physically quantify stress and
vulnerability to stress. That means that stress can be defined by its effect on
the function of systems like the heart, rather than just on the way a
challenging life event makes you feel. RSA: THE HEAR T-BREA TH CONNECTION
The activity of the vagus nerve can be accurately measured using HRV and
the way the heart interacts with the breath. When vagal tone is healthy,
there are small differences in heart rate during the in-breath (when it speeds
up) and out-brea th (when it slow s down). Inhaling, an increase in heart rate
is caused by a rhythmic partial withdrawal of vagal tone. Exhaling, a
release of acetylcholine causes the heart to slow, just as it did in Loewi’ s
frog. This phenomenon is called respiratory sinus arrhythmia  (RSA). It’s a
good indicator of how well the nervous system is functioning. In simple
terms, HRV measures rhythmic changes between heartbeats, whereas RSA
is HR V in synchronicity with the breath. For most of us, breathing frequency is around 9 to 24 breaths per
minute. 16 Corresponding oscillations in heart rate that produce respiratory
sinus arrhythmia can be regarded as the effects of breathing on the region of
the heart that initiates the electrical impulses for it to contract. The
oscillations of RSA can be affected by stress, alterations in breathing
patterns, or sudden bouts of exercise. RSA controls the rate of gas exchange
inside the alveo li, the tiny air sacs in the lungs. 16 The heart beats faster
when the air in the lungs is richest with oxygen, whereas the impulse to
exhale is triggered when CO2 in the lungs is highest. Gas exchange is mostefficient when the heart rate is synchronized with the breath such that the
heartbeat begins  to increase at the start of an inhalation and begins to
decrease at the start of an exhalation. RSA is controlle d entirely by the vagus nerve. Mirroring the function of
the ANS,16 it reveals how well the parasympathetic (or rest and digest)
branch is working. 29 Because the vagus nerve activates during the
exhalation, many studies have explored whether longer exhalations and
slower breathing  would produce greater differences in RSA and HRV. HRV
is linked to breathing frequency, and greater changes occur when the breath
is controlled and slower. Reducing the rate of respiration, increasing the
amount of air delivered to the lungs with each breath, and breathing from
the diaphragm have all been shown to increase RSA significantly. The best
results for HRV, RSA, barore flex sensitivity (more on this later), and
optimal gas exchange are achiev ed with a breathing rate of 5. 5 or 6 breaths
per minute. 27 It has also been  suggested that RSA has a central role in the
resting state of the cardiorespira tory system. RSA maximizes during sleep,
relaxation, and slow, deep breathing but is reduced in states of anxiety. 27
Energy expenditure is naturally minimized with improved pulmonary gas
exchange. HRV BIOFEEDBACK
In the 1990s, clinician and research psychologist Paul Lehrer and his
colleagues began to experiment with heart rate variability biofeedback
(HRVB). The central focus of the technique is on slowing the breath to
obtain beat-by-beat heart rate data so the participant can maximize RSA and
match it to heart rate patterns. The participant uses feedback or a breath-
pacing device to produce a heartbeat more rhythmically “in tune” with the
breath. This synchronization provides the best conditions for gas exchange
in the lungs. Significant evidence supports the benefits of HRVB for a variety of
common disorders,16 as well as for enhancing athletic performance. While
controlled studies are still needed for many specific conditions, scientists
believe that training to optimiz e the rhythms of the breath and heart has
potential applications for illnesses as varied as asthma, irritable bowelsyndrome, COPD, cyclic vomiti ng, recurrent abdominal pain, fibromyalgia,
cardiac rehabilitation, hypertension, chronic muscle pain, pregnancy-
induced hyperte nsion, depress ion, anxiety, PTSD, and insomnia. The
improved gas exchange achievable with HRVB training may help people
with respiratory diseases and stress-induced hyperventilation. 16 HRVB has
been proven to restore the balance of the nervous system to combat
inflammation. 30 It may also have advantages as a diagnostic tool for
cardiovascular system dysfunction and its resulting illnesses. 31
While most research in the field focuses on helping people who are sick,
HRVB can also be used to reduc e stress in otherwise healthy individuals. A
study of young athletes who were taking their university exams found that
the breath training resulted in long-term improved resistance to stressful
situations (i. e. , better vagal tone). 32 Another small study of women
suffering from fibromyalgia concluded that actively participating in HRVB
treatment restored a level of control to the patient, improving self-esteem
and feelings of empowerment. 33
RSA, THE BAROREFLEX, AND BLOOD PRESSURE
Respiratory sinus arrhythmia (RSA) is also significantly connected to blood
pressure. Remember, RSA describes changes in the heart rate during the
respiratory cycle. Its functionin g is highly dependent on the flexibility of
the vagus nerve, or the heart’ s vagal tone, as measured using HR V. One of the most important mechanisms of RSA is the baroreflex, a
homeostatic function that helps maintain blood pressure at healthy, near-
constant levels. The baroreflex is a reflex mediated by blood pressure
sensors in the aorta (the largest artery in the body) and carotid arteries (the
ones that supply  blood to the brain, neck, and face). 34 Even during rest,
blood pressure constantly fluctu ates as breathing causes the pressure in the
chest cavity to change. Scientist s consider the strengthening of homeostasis
in the baroreceptors to be the most obvious mechanism at play during
HRVB training. 16
All major blood vessels contain pressure receptors. These detect the
stretching of the arteries as blood pressure increases. When blood pressure
rises, the barore flex immediatel y causes the blood vessels to dilate and theheart rate to drop. Conversely, when blood pressure falls, the baroreflex
ensures that the blood vessels constrict and heart rate increas es. 16 Under
stress, the baroreflex reduces sympathetic outflow and increases vagal tone
to protect the heart against unhealthy arrhythmias. 34
The baroreflex is optimized when the relationship between breathing
and heart rate is at its most efficient with regard to blood gas exchange. This means that breathing is a natural way to provide the external
stimulation to increase HRV. At the same time, each breath stimulates the
baroreflex. Hear t rate and blood  pressure are linked to the amount of air we
breathe and to the exchange of oxygen between the lungs and the blood. During HRV biofeedback, the baroreflex works more effectively. This is
associated with better mental and physical health, because as with higher
oscillations in RSA and HR V, the body is more adaptable. The sensitivity of the baroreceptors is also a good indicator of the
body’ s response to a buildup of CO2. 35 The respiratory system reacts to
CO2 buildup  with involuntary contractions of the breathing muscles after an
exhalation, triggering an inhalat ion. The stronger the reaction to blood CO2,
the harder it is to hold your breath after exhaling and the sooner you need to
breathe in. The baroreceptors are most functional when the body is less
sensitive to CO2. Imagine being able to wait much longer before needing to
breathe in. A high BOL T score, indicating comfort with slower breathing,
signifies a reduced sensitivity to CO2 in the blood. A healthy baroreflex
with less sensitivity to CO2 results in more frequent reflex es, slower heart
rate, and increased vagal tone. The cardiovascular and respira tory systems are tightly interconnected
by the ANS which controls major functions of the body without conscious
direction. 8,36 Blood pressure receptors are triggered by the workings of
RSA, which can be measured through HRV, providing strong indicators of
mental and physical health. The fight-or -flight reaction (SNS) causes blood
vessels to constrict, increasing heart rate and blood pressure, while ACh,
the neurotransmitter released by the PNS-controlled vagus nerve, slows
heart rate, dilates blood vessels, and suppresses the inflammatory response. The baroreflex system is more than just a control mechanism involving
heart rate and blood pressure. The activity of the baroreflex affects vascular
tone—the sensitivity with which blood vessels expand and contract. 31 HRValso changes when there is inflammation. There is a clear relationship
between various pro-inflammatory cytokines and lower HRV. The impact of
the immune system on HRV, and the implications of that for health and
disease, is probably underestimated. 8
The common denominator in all these systems is the breath, especially
slow breathing. Reducing the number of breaths per minute improves vagal
tone, reduces stress, and suppo rts health and cognition. The practices of
slow breathing and relaxation benefit the heart and respiratory system in
many ways. The baroreceptors become more responsive to changes in blood
pressure, the heart rate becomes more lively and elastic, the vagus nerve
more reactive, and the ANS shifts away from fight and flight toward less
stress—which supports social interaction and enables the body to thrive. BETTER BRAIN FUNCTION: SLOW V AGAL
BREA THING
It may seem obvious that it is easier to think when we are less stressed, and
that when we concentrate on a breathing exercise, there is less room for the
brain to worry. However, there is also evidence that slow breathing
exercises have a direct impact on the way the brain works. In one Belgian study, scientists discovered that vagus nerve stimulation
(VNS) in rats clearly produced a memory-enhancing effect. 37 The rats
performed a gambling task in which they could learn to use reasoning to
maximize their food reward. Those that were treated with VNS developed
better decision-making. Further trials, from another Belgian lab, found that
vagal breathing could be used as a possible intervention agains t stress and
its negative effects on decision-making in humans. 38 Other experiments
have shown a connection between the vagus nerve and enhanced working
memory. 39 Patients given inhalant anesthetics experience an increase in
vagal tone as they regain consciousness9. Diaphragmatic  breathing can
directly lower cortisol levels,28 reducing the negative physiological
responses to stress and improving cognitive function. Research into the connection between the breath and the brain in nasal
breathing found that the breath directly affects neural activity in the brain. 40
Breath actively promotes oscillatory synchronicity, which produces theconditions for optimal gas exchange and information processing in areas of
the brain that mediate goal-directed behaviors. Nasal breathing offers an
entry point to areas of the limbic brain that modulate cognitive function,
which has interesting implica tions for mental agility given that the
structures in the limbic syste m are involved in motivation, emotion,
learning, and memory. 41 For example, experiments demonstrated that
breathing influenced a participant’ s ability to identify fearful emotions in
other people and their memory of visual objects. Passive inhalation of air
through the nose enhanced reaction time to scary stimuli. While there is a need for more research into the applications of VNS,
slow breathing, and activation of the PNS on cognition, these correlations
have been studied to some  extent in other fields. For example,
investigations into the impact of yogic breathing exercises have produced
interesting insig hts into the connection between breath and brain. A study
looking at Nadi Shodhana, yogic alternate nostril breathing, used EEG
measurements (from scalp electrodes) to assess the balance between the two
halves of the brain. It found that the practice generated more beta and alpha
brain waves. 42 Beta waves are characteristic of a strongly engaged mind. A
person who is in active conver sation or focused on their work is in beta. Alpha represents nonarousal. It is associated with down time and relaxation. This suggests that the breathing practice allows participants to become
more mentally active while remaining calm and clear headed. Another
study looked at the way a combined practice of breathing and meditation
improved memory and influenced academic performance. 43
We will look in more detail at the correlation between these
contemplative practices and the science of slow breathing, but it’s worth
noting that even meditation that doesn’ t focus on the breath can have the
effect of reducing the respira tory rate. Scientists have concluded that
regular yogic practices might improve cognitive functions, largely because
they tilt the autonomic balance in favor of the PNS. Further experiments
reported that EEG readings showed increased beta brainwave s under all
conditions in advanced meditators, that long-term meditati on practice
improves gray matter atrophy, that attention and working memory improve,
and that these techniques improve brain function in multiple pathways and
may even of fset age-related cognitive decline. 43Perhaps even more important, severe depletion of ACh, the
neurotransmitter secreted by the vagus nerve when it is stimulated, has been
associated with Alzheimer ’s. Parallels have been found between the
working of the PNS and visual recognition memory and alertness. It has
also been observed that both stress and inflammation can factor in the
development of Alzheimer ’s13 and Parkinson’ s disease. Breathing
dysfunction can be related to impairments of attention or vigilance in
patients with dementia. 28
VAGUS NER VE STIMULA TION: THE SECRET T O
BETTER HEAL TH
Many clinical applications of vagus stimulation, including those approved
to treat mental conditions like depression, bipolar disorder, and anxiety,
involve a small surgical implant that electronically activates the nerve. 44
However, there are less-invas ive, readily accessible option s available. Countless studie s, including those into HRVB, have shown that the power
of the vagus nerve can be accessed indir ectly  to relieve imba lances in the
nervous system. 25 This is particularly helpful with stress. When the vagus
nerve is activated, the messages received by the brain become calmer. This
begins a top-dow n feedback loop where the brain reports back to the body
that it is safe, perpetuating a feeling of relaxation. Techniques to stimulate
the vagus nerve include humm ing, laughing, and any sort of conscious
breathing practice, including holding the breath, diaphragm breathing, nose
breathing, and slow, relaxed exhalations. 45
To recap quickly, fibers from the vagus nerve innervate systems that
include the heart and lungs. When you breathe in, the sympathetic nervous
system (SNS) facilitates a brief acceleration in heart rate. 46 On the out
breath, the vagus nerve secretes Vagusstuf f/ACh. ACh slows down the heart
rate via the PNS. Section summary: 

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**Summary:**



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* **Mouth breathing**: Continuous or intermittent mouth breathing weakens Nitrous Oxide(NO)'s effectiveness, allowing "virulent replication". *   Rebuttal


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The topic revolves primarily around promoting nasal breathing versus mouth/bottom-air-passage usage amid growing concern regarding COVID-19 pandemic severity enhancement attributed partly to inadequate nitrogen monoox ide/NOS-based defenses weakened owing continuous/noir-solitary mouth breather-ing action impacting unfavorable outcomes compared-to-natural-COVID-responses-sequence-of-action-rules-vary-between-degre-effects-collaboratively-with-the-heartbeat-rate-measured-through-Electroencephalo graphicaled-electrophysics-using-an-applesauce-device-. Overall-SUMMARY-is-as-follows:-. * [Removed irrelevant lines]* MOUTH BREATHING IS BAD FOR YOUR HEALTH*

Keep adjusting according to preferences. Feel free share thoughts/questions/suggestions below;
Thank you kindly.
The article suggests that mouth breathing may worsen the symptoms of COVID-19.
What is the relationship between mouth breathing and COVID-19 symptoms?
The vagus nerve is responsible for many functions, including the release of acetylcholine, which slows down the heart rate and dilates blood vessels.
What is the primary function of the vagus nerve?
The vagus nerve plays a crucial role in maintaining homeostasis, regulating blood pressure, and influencing the immune system.
What is the purpose of the vagus nerve in the body?
Yes, chronic stress can lead to chronic inflammation, which can have severe consequences on the body.
Can stress lead to chronic inflammation?
The text does not explicitly state a recommended breathing rate, but it does mention that a rate of 5.5-6.5 breaths per minute is beneficial for optimal brain function and cognitive performance.
What is the recommended breathing rate for optimal brain function?