Definition: An exaggerated drop in systemic arterial pressure during inspiration (>10mmHg)
Inspiration is performed by decreasing intrathoracic pressure
Because the heart is in the thorax, this pressure is transmitted to the heart and causes a bigger gradient between the pressure in the veins outside of the thorax and the right atrium/ventricle
As such, with each inhalation, more blood flows into the right side of the heart
When this occurs, the interventricular septum subtly bulges into the LV cavity, lowering LV filling, and therefore lowering systemic stroke volume/BP
Because the ventricle can normally also expand outward, this septal shift is usually small, and the difference in the blood pressure is therefore small between inspiration and expiration (<10 mmHg)
In states in which the ventricle cannot expand outward (e.g. tamponade) or in which the drop in intrathoracic pressure with inspiration is profound (e.g. status asthmaticus), the septal shift is exaggerated and the difference in BP is larger
Pulsus paradoxus
Moderate to severe cardiac tamponade
Low ECG voltage
Constrictive pericarditis
AVR ST elevation
Active COPD/asthma exacerbation
Chest wall pain
Paradoxical vocal fold motion