Tsuji Bun, Honda Yasushi, Kondo Narihiko, Nishiyasu Takeshi
Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, Japan; Department of Health Sciences, Prefectural University of Hiroshima, Hiroshima, Japan; and.
Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, Japan;
Am J Physiol Regul Integr Comp Physiol. 2016 Aug 1;311(2):R401-9. doi: 10.1152/ajpregu.00484.2015. Epub 2016 Jun 22.
We investigated whether heat-induced hyperventilation during exercise is affected by time of day, as diurnal variation leads to higher core temperatures in the evening. Nineteen male subjects were divided into two experiments (protocol 1, n = 10 and protocol 2, n = 9). In protocol 1, subjects performed cycle exercise at 50% peak oxygen uptake in the heat (37°C and 50% RH) in the morning (0600) and evening (1800). Results showed that baseline resting and exercising esophageal temperature (Tes) were significantly (0.5°C) higher in the evening than morning. Minute ventilation (V̇e) increased from 54.3 ± 7.9 and 54.9 ± 6.8 l/min at 10 min to 71.4 ± 8.1 and 76.5 ± 11.8 l/min at 48.5 min in the morning and evening, respectively (both P < 0.01). Time of day had no effect on V̇e (P = 0.44). When V̇e as the output response was plotted against Tes as thermal input, the Tes threshold for increases in V̇e was higher in the evening than morning (37.2 ± 0.7 vs. 36.6 ± 0.6°C, P = 0.009), indicating the ventilatory response to the same core temperature is smaller in the evening. In protocol 2, the circadian rhythm-related higher resting Tes seen in the evening was adjusted down to the same temperature seen in the morning by immersing the subject in cold water. Importantly, the time course of changes in V̇e during exercise were smaller in the evening, but the threshold for V̇e remained higher in the evening than morning (P < 0.001). Collectively, those results suggest that time of day has no effect on time course hyperventilation during exercise in the heat, despite the higher core temperatures in the evening. This is likely due to diurnal variation in the control of ventilation in response to rising core temperature.
我们研究了运动期间热诱导的过度通气是否受一天中时间的影响，因为昼夜变化会导致傍晚时核心体温升高。19名男性受试者被分为两个实验（方案1，n = 10；方案2，n = 9）。在方案1中，受试者于上午（06:00）和傍晚（18:00）在热环境（37°C，相对湿度50%）中以峰值摄氧量的50%进行自行车运动。结果显示，傍晚时的基线静息和运动时食管温度（Tes）显著高于上午（高0.5°C）。分钟通气量（V̇e）在上午从10分钟时的54.3±7.9升/分钟和54.9±6.8升/分钟分别增加到48.5分钟时的71.4±8.1升/分钟和76.5±11.8升/分钟（均P < 0.01）。一天中的时间对V̇e没有影响（P = 0.44）。当以V̇e作为输出反应，以Tes作为热输入进行绘图时，傍晚时V̇e增加的Tes阈值高于上午（37.2±0.7对36.6±0.6°C，P = 0.009），表明傍晚时对相同核心体温的通气反应较小。在方案2中，通过将受试者浸入冷水中，将傍晚时出现的与昼夜节律相关的较高静息Tes调整到与上午相同的温度。重要的是，傍晚时运动期间V̇e的变化时间进程较小，但V̇e的阈值傍晚时仍高于上午（P < 0.001）。总体而言，这些结果表明，尽管傍晚时核心体温较高，但一天中的时间对热环境中运动期间过度通气的时间进程没有影响。这可能是由于对核心体温升高的通气控制存在昼夜变化。
