as altitude increases , the weight of air decreases , and the atmospheric pressure decreases . low atmospheric pressure means there is more space between air molecules . as a result , the 
 number of oxygen molecules existing in the same volume of air deceases , so the amount of 
 oxygen intake decreases in the uplands , even if the same amount of air is respired . that is , 
 an increase in altitude reduces oxygen partial pressure in the pulmonary alveoli as well as 
 the blood s ability to carry oxygen due to reduced atmospheric pressure , causing hypoxia . therefore , for an individual to consume the same amount of oxygen in the uplands as is 
 consumed in the lowlands , the volume of air respired needs to increase1 , 2 . exposure to low 
 oxygen due to altitude change acts as a powerful stimulus to induce diverse changes in the 
 lungs3 . when exposed to upland 
 environments , the densities of erythrocytes , hemoglobin , capillary vessels , and myoglobin in 
 the skeletal muscles increase , which may improve the body s ability to transport oxygen4 . since cardiopulmonary function is improved 
 and athletic performance is affected as a result of processes adapting to the 
 characteristics of upland environments1 , 
 upland training is widely used as a method to intensively reinforce physiological functions 
 centering on cardiopulmonary function6 . 
 since respiration supplies oxygen for the performance of activities of daily living ( adl ) , 
 breathing disorders affect the performance of adl6 . that is , the efficiency of the respiratory function is closely 
 related to that of the circulatory function , and is important not only for the performance 
 of athletes , but also for the health of the general population . upland - related studies have mostly dealt with athletes training1 , 7,8,9,10 , and studies conducted among the general population living in the 
 uplands are lacking . in korea , where approximately 70% of the country s area is mountainous , 
 methods for improving respiratory function utilizing upland environments should be 
 particularly useful . accordingly , the authors of this study examined the effects of 
 alternate living experiences in the uplands and the lowlands on respiratory function and 
 oxygen saturation in order to provide basic data for improving cardiopulmonary function 
 exploiting altitude . the study subjects were 100 female students in the 1st through 4th grades of k university , 
 which is located at an altitude of approximately 850  m. the study took place from march 27 
 to april 10 , 2013 . the mean age and height of the study subjects , comprising 25 freshmen 
 ( 18.920.57 years , 163.044.25 cm ) , 25 sophomores ( 19.960.54 years , 161.525.45 cm ) , 25 
 juniors ( 21.040.35 years , 159.844.40  cm ) , and 25 seniors ( 22.120.67 years , 
 160.80  4.17  cm ) , were 20.51  years and 161.30  cm , respectively . the study 
 subjects were selected from among those who had no history of smoking , and had no 
 respiratory organ disease , or symptoms that would have affected their lung capacity . the 
 study s objectives and procedure were explained to the subjects and individual consent to 
 participate was obtained from all of them . the study was approved by the ethical committee 
 of the kangwon national university hospital institutional review board . in korea , one school 
 year is divided into two semesters and each semester consists of 15 or 16 weeks . except for 
 the freshmen , the students who were the subjects of this study took classes at the school 
 located at an altitude above sea level of approximately 850  m for approximately 30 weeks per 
 year . these students spend at least 15 weeks per semester at the school located in the 
 uplands ; they then go home to the lowlands during vacations . when this study was conducted , 
 freshmen had been attending the school for approximately one month , and the students in the 
 more senior grades had already experienced living arrangements alternating between the 
 uplands and the lowlands . in this study , oxygen saturation , heart rate , and cardiopulmonary function were measured at 
 the same time on the 8 floor of a building ( altitude at least 850 m ) located at 
 the highest level of k university , and in the student life center located in the lowlands . oxygen saturation and heart rates ( beats per minute , bpm ) were measured using a heart rate 
 and arterial blood oxygen saturation measuring instrument ( pulse oximeter , mp110p mek - ics 
 co. , korea ) . the pulse oximeter was attached to the subject s middle finger with subjects 
 and the values were measured in a stable state 68 times during five minutes . pulse oximetry is a non - invasive method , 
 using an instrument that can monitor oxygen saturation easily and quickly , and indicate the 
 measured values as spo2 . in this study , forced vital capacity ( fvc ) , forced 
 expiration volume of 1 sec ( fev1 ) , peak forced expiratory flow ( pef ) , forced 
 vital capacity of 1 sec were measured using cardiopulmonary measuring instruments ( microplus 
 spirometer , uk carefusion co. ) , and the fev1/fvc ratio was calculated . when a subject arrived at the location where she was to be measured , she was instructed to 
 rest for approximately five minutes to ensure that she was stabilized . then , oxygen 
 saturation and heart rate were measured using the right index finger . demonstrations and 
 explanations about the posture required were provided before measuring the cardiopulmonary 
 functions , which were measured three times . vital capacity was measured using the method recommended in the chronic 
 obstructive pulmonary disease treatment guidelines11 by referring to the standardized guidelines11 for the implementation and reading of pulmonary function 
 tests published by the american thoracic society and the european respiratory society . when 
 pulmonary functions were measured , the subject was instructed to look forward , standing in 
 an upright position . the subject was instructed to maximally inhale and then exhale as 
 quickly and strongly as possible for the longest time possible , while holding the nose 
 firmly and biting the mouthpiece properly . to obtain better measurement results , the subject 
 was encouraged by the researcher saying ,  more , more , more , hoo~.  the subject was 
 instructed to rest for approximately two seconds after each measurement so as not to record 
 rebound measurements . when measured values could not be properly obtained , because the 
 subject coughed or otherwise , the subject was instructed to rest , after which the 
 measurement was repeated . the data were analyzed using spss 12.0 for windows by conducting one - way anova to test 
 respiratory functions and oxygen saturation according to grade . this study was conducted to examine the effects of living in the uplands and the lowlands 
 on respiratory functions and oxygen saturation . oxygen saturation , heart rate , and 
 respiratory functions of students in different grades at different altitudes were examined . the freshmen showed statistically significant differences between the uplands and the 
 lowlands in all items except pef and fev . heart rates were higher in the uplands , oxygen 
 saturation was higher in the lowlands , fvc was higher in the lowlands , and 
 fev1/fvc was higher in the uplands . significant differences in oxygen saturation 
 were noted in sophomores and significant differences in oxygen saturation and pef were noted 
 in juniors . on the other hand , there were no statistically significant differences in any of 
 the items measured in the uplands and the lowlands among the seniors . therefore , it can be 
 said that alternating living experiences in the uplands and the lowlands affects respiratory 
 functions ( table 1table 1 . differences in oxygen saturation and pulmonary functions with altitudefreshmensophomoresjuniorsseniorsmsdupland hr82.8812.02 * 81.1611.0480.649.83**79.689.78lowland hr78.0410.23 * 76.8411.8575.927.63**80.1211.31upland saturation97.800.96**97.41.04**98.201.0097.881.05lowland saturation98.440.77**98.320.80**98.321.1897.961.24upland pef293.2074.61321.6067.01345.3559.70**356.7757.35lowland pef283.1084.11307.0462.84326.2762.70**356.1557.56upland fvc2.730.48**2.930.502.700.312.890.26lowland fvc2.980.48**2.980.532.660.392.860.38uplandfev2.590.512.690.422.620.282.750.23lowland fev2.650.462.690.402.570.352.700.30upland ratio92.136.60 * 92.097.6897.013.8295.375.40lowland ratio88.928.51 * 91.178.1596.735.3294.935.60*p < 0.05 , * * p < 0.01 ) . to examine the effects of alternating living experiences in the uplands and 
 the lowlands on oxygen saturation , heart rate , and respiratory functions , differences in the 
 values between grades in the uplands and the lowlands were examined separately ( table 2table 2 . differences in vital capacity according to gradeplaceitemgradenmsduplandoxygen saturation ( % ) 12597.800.96297.401.04398.201.00497.881.05hr ( bpm)12582.8812.02281.1611.04380.649.83479.689.78fev1 ( ml)1252.590.5122.690.4232.620.2842.750.23fvc ( ml)1252.730.4822.930.5032.700.3142.890.26pef ( ml)**125293.1874.602321.6067.003345.3559.704356.7757.40fev1/fvc ( % ) * * 12592.136.60292.097.68397.013.82495.375.40lowlandoxygen saturation ( % ) 12598.440.77298.320.80398.321.18497.961.24hr ( bpm)12578.0410.23276.8411.85375.927.63480.1211.31fev1 ( ml)1252.650.4622.690.3932.570.3542.700.30fvc ( ml)*1252.980.4822.980.5332.660.3942.860.38pef ( ml)**125283.0984.102307.0462.803326.2762.704356.1557.60fev1/fvc ( % ) * * 12588.928.51291.178.15396.735.32494.935.60*p < 0.05 , * * p < 0.01 , hr : heart rate , fev1 : forced expiratory 
 volume of one sec , fvc : expiratory flow rate obtained by fastest expiration after 
 maximal inhalation , pef : peak expiratory flow , fev1/fvc : the ratio of 
 forced expiration volume of 1 sec to forced vital capacity . ) . in the uplands , there were no significant differences in oxygen saturation 
 and heart rate between grades . there were statistically significant differences in pef and 
 fev1/fvc ( p < 0.05 ) . pef was shown to be the highest in seniors , followed by 
 juniors , sophomores , and freshmen , in order of precedence , and fev1/fvc was the 
 highest among juniors ( 97.013.82 ) and the lowest among sophomores ( 92.097.64 ) . in the 
 lowlands , there were no significant differences in oxygen saturation and heart rate between 
 grades . there were significant differences in fvc , pef , and fev1/fvc between the 
 grades . fvc was shown to be the lowest among juniors ( 2.660.39 ) , pef was the 
 highest among seniors ( 356.1557.60 ) , and fev1/fvc was the highest 
 among juniors ( 96.735.32 ) and the lowest among freshmen ( 88.928.51 ) ( table 2 ) . * p < 0.05 , * * p < 0.01 * p < 0.05 , * * p < 0.01 , hr : heart rate , fev1 : forced expiratory 
 volume of one sec , fvc : expiratory flow rate obtained by fastest expiration after 
 maximal inhalation , pef : peak expiratory flow , fev1/fvc : the ratio of 
 forced expiration volume of 1 sec to forced vital capacity . cardiopulmonary functions by grade in the uplands and the lowlands were judged after 
 dividing the subjects into lower grade students ( freshmen , sophomores ) , who had less 
 experience of alternating living between the lowlands and the uplands , and upper grade 
 students ( juniors , seniors ) , who had more experience . in the uplands , the cardiopulmonary 
 functions of lower grade students and those of upper grade students showed statistically 
 significant differences ( x = 0.014 ) . upper grade students showed only normal 
 spirometry ( ns ) ( 70% ) and mild restriction ( mr ) ( 30% ) , and some lower grade students showed 
 moderate restriction ( mor ) , mild obstruction ( mo ) , and moderate severe restriction ( mosr ) , 
 indicating that they were experiencing cardiopulmonary function disorders ( table 3table 3 . assessment of on breathing disorders n(%)nsmrmormosrmomoototalupland*a29 ( 58%)10 ( 20%)5 ( 10%)2 ( 4%)4 ( 8%)0 ( 0%)50 ( 100%)b35 ( 70%)15 ( 30%)0 ( 0%)0 ( 0%)0 ( 0%)0 ( 0%)50 ( 100%)lowland**a30 ( 60%)7 ( 14%)0 ( 0%)2 ( 4%)10 ( 20%)1 ( 2%)50 ( 100%)b29 ( 58%)19 ( 38%)1 ( 2%)0 ( 0%)1 ( 2%)0 ( 0%)50 ( 100%)a : freshmen+sophomore , b : juniors+seniors , ns : normal spirometry , mr : mild 
 restriction , mor : moderate restriction , mosr : moderate severe restriction , mo : mild 
 obstruction , moo : moderate obstrction ) . in the lowlands , the cardiopulmonary functions of lower grade students and 
 those of upper grade students showed statistically significant differences ( x = 
 0.005 ) . ns showed the highest proportion in both lower grade and upper grade students . in 
 the lowlands , lower grade students showed ns , mo , mr , mosr , and moderate obstruction ( moo ) , 
 while upper grade students showed ns , mor , mo , and mr ( table 3 ) . a : freshmen+sophomore , b : juniors+seniors , ns : normal spirometry , mr : mild 
 restriction , mor : moderate restriction , mosr : moderate severe restriction , mo : mild 
 obstruction , moo : moderate obstrction this study was conducted to examine the effects of alternating living experiences of the 
 uplands and the lowlands on oxygen saturation and respiratory function in order to provide 
 basic data for improving cardiopulmonary function exploiting altitude . in this study , there were differences in oxygen saturation , heart rate , and most 
 respiratory function items between the uplands and the lowlands among the freshmen ; however , 
 there were no differences in any of the items among the seniors . to take in the same amount 
 of oxygen taken at sea level at 850  m in the uplands , the amount of ventilation would have 
 to increase two - fold . to compensate for this therefore , long - term life in the uplands improves the blood s oxygen carrying 
 capacity2 . this can explain the 
 phenomenon that was apparent in the present study in which freshmen who had just began 
 living in the uplands showed higher oxygen saturation and heart rates , increased fvc , and 
 decreased fev1/fvc . seniors who had long - term experience of alternating life 
 between the uplands and the lowlands did not show differences in any of the items . therefore , it can be said that alternating living experiences in the uplands and the 
 lowlands affects pulmonary functions , even without continuous exposure to the upland 
 environment . when exposed to the upland environment , and the associated low - pressure , low - oxygen 
 environment , the heart rate increases to at a slightly higher level than in the lowlands due 
 to the action of the sympathetic nerve and an increased energy metabolic rate . the heasr 
 rate it returns almost to the original level , after adapting to the upland environment , 
 after approximately one week12 . therefore , the reason why differences in oxygen saturation and heart rate between the grades 
 did not appear in both the upland - and lowland - living students was that even the freshmen had 
 started school at least three weeks earlier , and thus , all of the students had already 
 adapted to their environment . in the uplands , pef and fev1/fvc were shown to be 
 higher among upper grade students , who indicated smooth expiration . this indicates that 
 upper grade students had better adaptability to the uplands than lower grade students . in 
 the lowlands , fvc was shown to be higher among lower grade students , and pef and 
 fev1/fvc were shown to be higher among upper grade students , compared to those 
 from the uplands , indicating that the pulmonary functions of the upper grade students were 
 better . therefore , even alternating living between the uplands ( during semesters ) and the 
 lowlands ( during vacations ) , as opposed to continuous life in the uplands , appears to 
 improve respiratory function . when an individual returns to the lowlands after training in 
 the uplands , his / her maximum oxygen intake increases , aerobic enzymes are activated , 
 mitochondria count increases , glycogen storage ability improves , capillary vessel density 
 increases , hemoglobin concentration increases , and heart functions are activated13 . however , in this study , although there 
 were differences in respiratory function tests between grades , there were no differences in 
 oxygen saturation and heart rate , unlike the findings of the study conducted by bartsch and 
 saltin13 . the degrees of respiratory functional disorders by grade in the uplands and the lowlands 
 were judged after dividing the subjects into the lower grade students ( freshmen , sophomores ) 
 who had less experience of alternating living between the lowlands and the uplands , and the 
 upper grade students ( juniors , seniors ) who had more experience of doing so . in the uplands , 
 the upper grade students showed only ns ( 70% ) and mr ( 30% ) , indicating that their breathing 
 was normal or had slight limitations . on the other hand , some lower grade students showed 
 moderate breathing restrictions , severe breathing restrictions , and mild breathing 
 disorders . in the lowlands , lower grade students showed fewer breathing disorders compared 
 to the uplands , although some had breathing disorders , and upper grade students showed more 
 cases of slight restriction . this was due to 
 large lung capacity , as living in the uplands did not seem to inhibit breathing . the maximum 
 oxygen intake at 1,800 2,300  m corresponds to approximately 8085% of that at sea level and 
 increases by approximately 25% after a 2- to 3-week adaptation periods . the fact that 
 increases in the maximum oxygen intake in the uplands is not shown to be the same as those 
 at sea level indicates the human body s adaptability to low oxygen environments . therefore , 
 upper grade students having longer experience of exposure to upland environments are thought 
 to have shown more breathing disorders in the lowlands than in the uplands because their 
 bodies had adapted to the upland environments . kim et al.5 reported that cardiopulmonary functions improved after upland 
 training . in that study , upper grade students who had been exposed to upland environments 
 for a longer time generally showed better respiratory functions , as in our study . currently , physical strength and the body s abilities based on cardiopulmonary and 
 respiratory functions are known to be insufficient among students as well as in the general 
 population . both athletes and the general population could benefit from upland training . periodic living in the uplands is considered to be an effective method for improving 
 respiratory function ; however , most people can not move on a regular basis . in this study , we 
 were unable to determine the period of upland living required to influence an improvement in 
 respiratory function ; therefore , further studies are necessary . through such studies , 
 researchers may discover methods for improving cardiopulmonary function or breathing 
 disorders exploiting natural environmental conditions , for athletes as well as for the 
 general population .