Faculty of Health and Sports Science, University of Juntendo, Inzai, Japan.
Graduate School Department of Medicine and Engineering Sciences, University of Yamanashi, Kofu, Japan.
High Alt Med Biol. 2021 Jun;22(2):201-208. doi: 10.1089/ham.2020.0142. Epub 2021 Feb 16.
Takezawa, Toshihiro, Shohei Dobashi, and Katsuhiro Koyama. Cardiorespiratory response and power output during submaximal exercise in normobaric versus hypobaric hypoxia: a pilot study using a specific chamber that controls environmental factors. . 22: 201-208, 2021. Many previous studies have examined hypoxia-induced physiological responses using various conditions, e.g., artificially reduced atmospheric oxygen concentration [normobaric hypoxia (NH) condition] or low barometric pressure at a mountain [hypobaric hypoxia (HH) condition]. However, when comparing the results from these previous studies conducted in artificial NH and HH including real high altitude, we must consider the possibility that environmental factors, such as temperature, humidity, and fraction of inspired carbon dioxide, might affect the physiological responses. Therefore, we examined cardiorespiratory responses and exercise performances during low- to high-intensity exercise at a fixed heart rate (HR) in both NH and HH using a specific chamber where atmospheric oxygen concentration and barometric pressure as well as the abovementioned environmental factors were precisely controlled. Ten well-trained university students (eight males and two females) performed the exercise test consisting of two 20-minute submaximal pedaling at the intensity corresponding to 50% (low) and 70% (high) of their HR reserve, under three conditions [NH (fraction of inspired oxygen, 0.135; barometric pressure, 754 mmHg), HH (fraction of inspired oxygen, 0.209; barometric pressure, 504 mmHg), and normobaric normoxia (NN; fraction of inspired oxygen, 0.209; barometric pressure, 754 mmHg)]. Peripheral oxygen saturation (SpO) to estimate arterial oxygen saturation and partial pressure of end-tidal carbon dioxide (PCO) were monitored throughout the experiment. SpO, PCO, and power output at fixed HRs (i.e., pedaling efficiency) in NH and HH were all significantly lower than those in NN. Moreover, high-intensity exercise in HH induced greater decreases in SpO and power output than did high-intensity exercise in NH (NH vs. HH; SpO, 78.2% ± 5.0% vs. 75.1% ± 7.1%; power output, 120.7 ± 24.9 W vs. 112.4 ± 23.2 W, both < 0.05). However, high-intensity exercise in HH induced greater increases in PCO than did high-intensity exercise in NH (NH vs. HH; 54.2 ± 5.9 mmHg vs. 57.2 ± 3.4 mmHg, < 0.01). These results suggest that physiological responses and power output at a fixed HR during hypoxic exposure might depend on the method used to generate the hypoxic condition.
Takezawa 等人研究了在常压低氧（NH）和低海拔 hypobaric 缺氧（HH）条件下，亚极量运动时心肺反应和功率输出的差异。许多先前的研究使用各种条件（如人工降低大气氧浓度[常压低氧（NH）条件]或在山上降低气压[低海拔 hypobaric 缺氧（HH）条件]）来研究缺氧引起的生理反应。然而，当比较这些在 NH 和 HH 条件下进行的研究结果时，我们必须考虑到环境因素（如温度、湿度和吸入二氧化碳分数）可能会影响生理反应。因此，我们使用特定的室来研究在固定心率（HR）下进行的低到高强度运动期间的心肺反应和运动表现，该室可以精确控制大气氧浓度和气压以及上述环境因素。十名训练有素的大学生（八男二女）在三种条件下进行了 20 分钟的亚极量踏车运动测试[NH（吸入氧分数，0.135；气压，754 mmHg）、HH（吸入氧分数，0.209；气压，504 mmHg）和常压低氧正常（NN；吸入氧分数，0.209；气压，754 mmHg）]，强度分别对应于 HR 储备的 50%（低）和 70%（高）。整个实验过程中监测外周血氧饱和度（SpO2）以估计动脉血氧饱和度和呼气末二氧化碳分压（PCO2）。NH 和 HH 中的固定 HR 时的 SpO2、PCO2 和功率输出（即踏车效率）均显著低于 NN。此外，HH 中的高强度运动比 NH 中的高强度运动引起更大的 SpO2 和功率输出下降（NH 与 HH；SpO2，78.2%±5.0%比 75.1%±7.1%；功率输出，120.7±24.9 W 比 112.4±23.2 W，均 < 0.05）。然而，HH 中的高强度运动比 NH 中的高强度运动引起更大的 PCO2 增加（NH 与 HH；54.2±5.9 mmHg 比 57.2±3.4 mmHg，均 < 0.01）。这些结果表明，在缺氧暴露时，固定 HR 下的生理反应和功率输出可能取决于产生缺氧条件的方法。
