Heat acclimation (HA) may improve the regulation of cardiac output (Q̇) through increased blood volume (BV) and left ventricular (LV) diastolic filling, and attenuate reductions in Q̇ during exercise-induced dehydration; however, these hypotheses have never been directly tested. Before and following 10-days exercise HA, eight males completed two trials of submaximal exercise in 33°C and 50% relative humidity while maintaining pre-exercise euhydrated body mass (EUH; -0.6±0.4%) or becoming progressively dehydrated (DEH; -3.6±0.7%). Rectal (T_re) and skin (T_sk) temperatures, heart rate (HR), LV volumes and function, systemic hemodynamics and BV were measured at rest and during bouts of semi-recumbent cycling (55% V̇O_2max) at 20, 100 and 180 min, interspersed by periods of upright exercise. T_re, BV, HR, LV volumes, LV systolic and diastolic function and systemic hemodynamics were similar between trials at rest and during the first 20 min of exercise (all P>0.05). These responses were largely unaffected by HA at 180 min in either hydration state. However, DEH induced higher T_re (0.6±0.3°C) and HR (16±7 beats^.min^-1) and lower stroke volume (26±16 ml), end-diastolic volume (29±16 ml) and Q̇ (2.1±0.8 L^.min^-1) compared to EUH at 180 min (all P<0.05), yet LV twist and untwisting rate were increased or maintained (P=0.028 and 0.52, respectively). Findings indicate HA has minimal effects on LV volumes, LV mechanical function and systemic hemodynamics during submaximal exercise in moderate heat where HR and BV are similar. In contrast, DEH evokes greater hyperthermia and tachycardia, reduces BV, and impairs diastolic LV filling, lowering Q̇, regardless of HA state.

中文翻译：

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运动热量适应对训练有水和脱水的人的左心室容积，功能和全身血流动力学影响最小。

热适应（HA）可以通过增加血容量（BV）和左心室（LV）舒张期充盈来改善心输出量（Q̇）的调节，并减弱运动引起的脱水过程中Q̇的降低；但是，这些假设从未得到过直接检验。在进行HA运动10天之前和之后，八名男性完成了两项在33°C和50％相对湿度下进行次最大运动的试验，同时保持了运动前的水合体重（EUH; -0.6±0.4％）或逐渐脱水（DEH; -3.6±0.7％）。直肠（T_重）和皮肤（T _SK）的温度下，心脏速率（HR），LV体积和功能，全身血流动力学和BV分别在休息和在半卧位循环的发作（55％VO测量_2MAX），在20、100和180分钟时穿插一些直立运动。在休息和运动的最初20分钟之间，试验的T _re，BV，HR，LV量，LV收缩和舒张功能以及全身血流动力学相似（​​所有P> 0.05）。在任一水合作用状态下，HA在180分钟时这些反应在很大程度上不受HA影响。然而，DEH诱导高于或等于该_重（0.6±0.3℃）和HR（16±7次^。分钟^-1）和较低的每搏输出量（26±16毫升），舒张末期容积（29±16毫升）和Q（ 2.1±0.8升^。分钟^-1）与EUH在180分钟时相比（所有P <0.05），但左心室的扭转和解捻率增加或维持（分别为P = 0.028和0.52）。研究结果表明，HA在HR和BV相似的中等热量的次最大运动中对LV体积，LV力学功能和全身血流动力学的影响最小。相反，DEH引起更高的热疗和心动过速，降低BV，并损害舒张压LV充盈，降低Q̇，而与HA状态无关。