González-Alonso J, Mora-Rodríguez R, Coyle E F
Human Performance Laboratory, Department of Kinesiology and Health Education, The University of Texas at Austin, Austin, Texas 78712, USA.
Am J Physiol. 1999 Aug;277(2):H576-83. doi: 10.1152/ajpheart.1999.277.2.H576.
We determined whether the deleterious effects of dehydration and hyperthermia on cardiovascular function during upright exercise were attenuated by elevating central blood volume with supine exercise. Seven trained men [maximal oxygen consumption (VO(2 max)) 4.7 +/- 0. 4 l/min (mean +/- SE)] cycled for 30 min in the heat (35 degrees C) in the upright and in the supine positions (VO(2) 2.93 +/- 0.27 l/min) while maintaining euhydration by fluid ingestion or while being dehydrated by 5% of body weight after 2 h of upright exercise. When subjects were euhydrated, esophageal temperature (T(es)) was 37. 8-38.0 degrees C in both body postures. Dehydration caused equal hyperthermia during both upright and supine exercise (T(es) = 38. 7-38.8 degrees C). During upright exercise, dehydration lowered stroke volume (SV), cardiac output, mean arterial pressure (MAP), and cutaneous vascular conductance and increased heart rate and plasma catecholamines [30 +/- 6 ml, 3.0 +/- 0.7 l/min, 6 +/- 2 mmHg, 22 +/- 8%, 14 +/- 2 beats/min, and 50-96%, respectively; all P < 0. 05]. In contrast, during supine exercise, dehydration did not cause significant alterations in MAP, cutaneous vascular conductance, or plasma catecholamines. Furthermore, supine versus upright exercise attenuated the increases in heart rate (7 +/- 2 vs. 9 +/- 1%) and the reductions in SV (13 +/- 4 vs. 21 +/- 3%) and cardiac output (8 +/- 3 vs. 14 +/- 3%) (all P < 0.05). These results suggest that the decline in cutaneous vascular conductance and the increase in plasma norepinephrine concentration, independent of hyperthermia, are associated with a reduction in central blood volume and a lower arterial blood pressure.
我们研究了通过仰卧位运动增加中心血容量是否能减轻脱水和高温对直立运动期间心血管功能的有害影响。七名训练有素的男性[最大耗氧量（VO₂ max）4.7±0.4升/分钟（平均值±标准误）]在高温环境（35℃）下分别以直立位和仰卧位进行30分钟的骑行运动（VO₂ 2.93±0.27升/分钟），期间通过摄入液体保持正常水合状态，或在直立运动2小时后脱水5%体重。当受试者处于正常水合状态时，两种体位下食管温度（Tₑₛ）均为37.8 - 38.0℃。脱水在直立和仰卧运动中均导致同等程度的体温过高（Tₑₛ = 38.7 - 38.8℃）。在直立运动期间，脱水降低了每搏输出量（SV）、心输出量、平均动脉压（MAP）和皮肤血管传导率，并增加了心率和血浆儿茶酚胺[分别为30±6毫升、3.0±0.7升/分钟、6±2毫米汞柱、22±8%、14±2次/分钟和50 - 96%；所有P < 0.05]。相比之下，在仰卧运动期间，脱水并未引起MAP、皮肤血管传导率或血浆儿茶酚胺的显著变化。此外，仰卧运动与直立运动相比，减弱了心率的增加（7±2%对9±1%）以及SV（13±4%对21±3%）和心输出量（8±3%对14±3%）的降低（所有P < 0.05）。这些结果表明，皮肤血管传导率的下降和血浆去甲肾上腺素浓度的增加，与高温无关，与中心血容量减少和动脉血压降低有关。
