Lundby C, Araoz M, van Hall G
Copenhagen Muscle Research Centre, Rigshospitalet, Copenhagen, Denmark.
High Alt Med Biol. 2001 Fall;2(3):369-76. doi: 10.1089/15270290152608543.
The purpose of the present study was to investigate the degree to which peak heart rate is reduced during exhaustive exercise in acute hypoxia. Five sea-level lowlanders performed maximal exercise at normobaric normoxia and at three different levels of hypobaric hypoxia (barometric pressures of 518, 459, and 404 mmHg) in a hypobaric chamber and while breathing 9% O(2) in N(2). These conditions were equivalent to altitudes of 3300, 4300, 5300, and 6300 m above sea level, respectively. At 4300 m, maximal exercise was also repeated after 4 and 8 h. Peak heart rate (HR) decreased from 191 (182-202) (mean and range) at sea level to 189 (179-200), 182 (172-189), 175 (166-183), and 165 (162-169) in the acute hypoxic conditions. Peak HR did not decrease further after 4 and 8 h at 4300 m compared to the acute exposure at this altitude. Between barometric pressures of 518 and 355 mmHg (approximately 3300 and 6300 m), peak HR decreased linearly: peak HR(hypobaria) = peak HR(sea level) - 0.135 x [hypobaria(3100) - hypobaria (mmHg)]; or peak HR(altitude) = peak HR(sea level) - 0.15 x (altitude - 3100 m). This corresponds to approximately 1-beat x min(-1) reduction in peak HR for every 7-mmHg decrease in barometric pressure below 530 mmHg (approximately 130 m of altitude gained above 3100 m). At termination of exercise, maximal plasma lactate and norepinephrine concentrations were similar to those observed during maximal exercise in normobaric normoxia. This study clearly demonstrates a progressive decrease in peak HR with increasing altitude, despite evidence of similar exercise effort and unchanged sympathetic excitation.
本研究的目的是调查在急性低氧环境下力竭运动期间心率峰值降低的程度。五名海平面地区的低海拔居民在低压舱内，于常压常氧以及三种不同程度的低压低氧环境（气压分别为518、459和404 mmHg）下，同时呼吸含9%氧气的氮气进行最大运动。这些条件分别相当于海拔3300、4300、5300和6300米。在4300米处，最大运动在4小时和8小时后也重复进行。心率峰值（HR）在海平面时为191（182 - 202）（平均值及范围），在急性低氧条件下分别降至189（179 - 200）、182（172 - 189）、175（166 - 183）和165（162 - 169）。与该海拔的急性暴露相比，在4300米处4小时和8小时后心率峰值没有进一步下降。在气压518和355 mmHg（约3300和6300米）之间，心率峰值呈线性下降：心率峰值（低压环境）=心率峰值（海平面）- 0.135×[低压环境（3100）- 气压（mmHg）]；或心率峰值（海拔）=心率峰值（海平面）- 0.15×（海拔 - 3100米）。这相当于在气压低于530 mmHg（约海拔高于3100米每升高130米）时，气压每降低7 mmHg心率峰值约降低1次/分钟。运动结束时，最大血浆乳酸和去甲肾上腺素浓度与常压常氧下最大运动时观察到的浓度相似。本研究清楚地表明，尽管运动强度相似且交感神经兴奋未改变，但随着海拔升高心率峰值逐渐降低。
