Ventilatory And Cardiovascular Acclimatization Remains Unchanged Following Active Versus Passive Ascent To 3600 m

PURPOSE: Sympathetic stimulation, induced by intense endurance exercise, may alter the process of ventilatory and cardiovascular acclimatization. The purpose of this study was to examine the magnitude and time course of ventilatory and cardiovascular acclimatization following active and passive ascent to 3600 m. METHODS: Forty-one healthy unacclimatized Soldiers (n = 41, mean ± SD; age = 26 ± 5 yr; body weight = 83.5 ± 11.6 kg; VO2max = 47.9 ± 5.5 ml · kg−1 · min−1) were tested at sea level (SL) in Ft. Leonard Wood, MO, flown to Taos Ski Valley, NM (2845 m) where they arrived around 1400 m, and then either hiked (n = 21; 5.0 km, 15.5% mean grade) or were driven (n = 20; 30-min drive) to a high altitude (HA) ski patrol facility located at 3600 m. Energy expenditure during ascent was measured with an ankle accelerometer. Portable real-time capnography was used to measure end-tidal carbon dioxide partial pressure (PETCO2) after 10 min of sitting at SL, after 19 h (HA2), 43 h (HA3), and 67 h (HA4) at HA. Mean arterial blood pressure (MAP), heart rate (HR), and pulse arterial oxygen saturation (SpO2) were measured at the same time (~0900) as PETCO2 RESULTS: The active group expended a greater (P < 0.05) amount of energy (745 ± 435 kcal) than the passive group (55 ± 10 kcal) during ascent. There were no differences between groups in terms of ventilatory and cardiovascular acclimatization so data were combined. Resting PETCO2 (mmHg) decreased (P < 0.05) from SL (37.5 ± 3.35) to HA2 (33.5 ± 3.71), remained stable from HA2 to HA3 (33.8 ± 3.73) and decreased further (P < 0.05) from HA3 to HA4 (30.8 ± 4.9). Resting MAP and HR, respectively, increased (P < 0.05) from SL (89.9 ± 6.9 mmHg; 65.7 ± 9.8 bpm) to HA2 (100.0 ± 7.2 mmHg; 78.7 ± 10.1 bpm), MAP decreased (P < 0.05) but HR remained unchanged from HA2 to HA3 (96.9 ± 7.1 mmHg; 78.5 ± 15.4 bpm), and both stayed consistent from HA3 to HA4 (98.1 ± 7.1 mmHg; 80.1 ± 12.9 bpm). Resting SpO2 (%) decreased (P < 0.05) from SL (97.6 ± 1.3) to HA2 (88.7 ± 3.1), increased (P < 0.05) from HA2 to HA3 (89.7 ± 2.9), and remained unchanged from HA3 to HA4 (89.1 ± 3.2). CONCLUSION: Ventilatory and cardiovascular acclimatization occurred at HA but sympathetic stimulation and increased metabolic rate due to the active ascent did not change the magnitude or time course of either of these processes. Authors’ views not official U.S. Army or DoD policy. Funding: USAMRDC