USE OF A STEP TEST TO CHARACTERIZE ACCLIMATION TO HIGH ALTITUDE IN THE HIMALAYAS

1. ► ▼ ◄ ▲ USE OF A STEP TEST TO CHARACTERIZE ACCLIMATION TO HIGH ALTITUDE IN THE HIMALAYAS J. S. Han*, K. M. Wells*, A.D. Miller♦, T. Wilson* *Department of Biology, Winona State University; ♦Division ofCardiovascular Diseases, Mayo Clinic College of Medicine ABSTRACT # 3089 Acclimation to high altitude was characterized in nine non athletic college aged students aged 19 to 24 during a trek in the Himalayas. A three minute step test (40.6 cm step and a 24 step/minute rate) was performed at 1654 (am, day 1), 3696 (pm, day 1), 3865 (day 8), 3688 (day 10), 4115 (day 13) and again at 3688 meters (day 14). Resting heart rate and oxygen saturation (SaO2) was measured prior to the step test and 20 seconds after exercise cessation (recovery). The heart rate difference (percent change) between pre- and post-exercise cessation was used to measure hypoxic stress at altitude and significant acclimation could not be documented until day 14 (3688 m). The percent difference between pre- and post-step test SaO2 at 1654 m was significantly different from tests performed at 3696, 3865, 3688, and 4115 m. However, at day 14 (3688 m) the percent change in SaO2 was no longer significantly different from the 1654 m value at day 1. Pre-trip response to acute hypoxia (12.5 % O2) was examined by performing the same step test at 402 m, with inconclusive results. This study suggests that 14 days are required for non-athletic students to achieve acclimation to a step test. INTRODUCTION: Previous studies have evaluated the physiological reactions and the acclimation processes of military trainees and endurance professional athletes during exercise at high altitude. However, little is known on the reaction of non-athletic subjects to exercising at high altitude. Most travelers to high altitude are tourists and not soldiers or athletes. Acclimation is the body's way of adjusting to hypoxic conditions at high altitude. Acclimation occurs over a variable period of time (Ward et al 2000). Measuring changes in heart rate and oxygen saturation (SaO2) can help characterize acclimation in an individual. A previous study on military trainees suggested that as acclimation progresses heart rate decreases and oxygen saturation increases (Gupta 1980). The current study was conducted to follow the acclimation of non-athletic college aged participants on a trek at high altitude. These non-athletic participants were expected to show a similar trend in acclimation as military trainees. In this study we used a step test to characterize the time required to achieve acclimation among participants. Prior to trip departure (April 2006), subjects performed two step tests at 402 m 30 minutes apart. The first test was performed at atmosphericO2 pressure and the second test at 12.5% PaO2,modeling acute hypoxia. The pre-test heart rate at atmospheric pressure was higher than expected, and may have been caused by participants’ performance anxiety. The general trend of the heart rates were correct, with pre-test being lower and post-test being higher. However, high resting heart rates at atmospheric pressure were similar to resting heart rate values at 12.5% PaO2, making contrasts difficult to distinguish. Therefore, the data was not incorporated in this study. METHODS: Nine non-athletic college students participated (19-24 years of age; 4 female, 5 male). In this study, non-athletic was defined as running no more than five miles a week during the two months prior to the study. A three minute modified version of the Queen’s step test was performed. The test consisted of a 40.6 cm step at a 24 step/minute rate. Prior to starting the test, resting oxygen saturation (SaO2) and heart rate were recorded using a finger pulse oximeter. Measurements were taken prior to (pre-) and 20 seconds (post-) after cessation of the step test. Step test data was analyzed as percent change. Percent change was defined as the difference between the pre- (P1) and post- (P2) test values, divided by the pre-test value to give the percent ([(P2 - P1)/P1]*100). RESULTS: Figure 1: Percent change ([(P2 - P1)/P1]*100) in pre- to post-step test heart rates observed at different elevations during a 14 day trek. Significant: Gangtok (day 1) vs Thangsing 2 (day 14) (p < 0.0241). * * • MAIN POINTS OF DISCUSSION: • The highest percent change in heart rate was observed • at 3696m (day 1), while the lowest was at 3688m • (day14). This data concludes that the subject’s heart • rates improved over the 14 days as part of acclimation. • 2. Percent change in oxygen saturation increased until • 3688 m (day 10) and, there after percent change inSaO2 • decreased. At 3688m (day 14), percent change in SaO2 • was no longer significantly different from 1654m • (day1). This data concludes that the subject’s oxygen • saturation improved over the 14 days as part of • acclimation. • 3. The elevations for day one (3696m) and day 14 • (3688m) were similar, however, the time lapse between • the two allowed for acclimation to occur. A rapid • accent from 1654m (day 1) to 3696 m (day 1) without • acclimation caused the oxygen saturation to • significantly decrease compared to baseline (1654m). • However, after spending 14 days in high altitude, the • descent from 4115m to 3688m (day 14) was associated • with an increase in oxygen saturation as part of • acclimation. • OVERALL CONCLUSION: • 14 days are required for non-athletic college aged • students to acclimate to high altitude in the Himalayas. Figure 2: Percent change ([(P1 – P2)/P1]*100) in pre- to post-step test heart ratesin oxygen saturation observed at different elevations during a 14 day trek. Significant: ▲ Gangtok (day 1) vs Tsomgo Lake (1 pm) (p = 0.0012) ► (p < 0.0001); ▼ (p < 0.0001); ◄ (p < 0.0001). The step test was repeated six times over the course of 14 days during a trek in the Himalayas of India. The tests were conducted at 1654 (day 1 am), 3696.5 (day 1 pm), 3865 (day 8), 3688 (day 10), 4115 (day 13) and 3688 meters (day14). Additional tests at 402 m three weeks prior to the departure were performed while breathing normal atmospheric air and while breathing 12.5% O2. However, data is not shown. Table 1: Trek itinerary including altitude and atmospheric pressure. Figure 3: Percent change ([(P2 - P1)/P1]*100) in pre- to post-step test heart rate observedat 1654m (baseline), 3696m (day 1), and 3688m (day 14). Significant: Gangtok vs Thangsing 2 (p = 0.0241) Figure 4: Percent change ([(P1 – P2)/P1]*100)in pre- to post-step testSaO2 observed at 1654m, 3688m, and 3696m. Significant: Gangtok vs Tsomgo Lake (p = 0.0012) ACKNOWLEDGEMENTS: Thanks for a research development grant from the WSU foundation, a travel grant from WSU office of Academic Affairs and to Dr. Christopher Malone for statistical analysis assistance.