Convertino V A
The Bionetic Corporation, Biomedical Operations and Research Office, NASA, Kennedy Space Center, Florida, USA.
Can J Sport Sci. 1987;12(Suppl 1):136S-139S.
During exercise, increased capillary hydrostatic pressure caused by elevation of arterial pressure produces plasma volume shifts from the vascular space to the interstitial fluids. Following a rapid efflux of vascular fluid within minutes of exercise, there is very little further reduction in plasma volume during long-term exercise, suggesting protective mechanisms against loss of circulating blood volume. These mechanisms probably include increasing plasma protein oncotic pressure, differences in peripheral vasoconstriction in active muscles and inactive tissues, and elevated lymph flow. The interaction of these factors provides optimal thermoregulatory and cardiovascular stability. The dynamics of fluids shifts during long-term exercise are altered by hydration state. The hypovolemia caused by dehydration acts to conserve blood volume by reducing the amount of plasma shift and sweat loss during exercise. The consequence is less heat dissipation and greater cardiovascular stability. In contrast, the hypervolemia produced by hyperhydration promotes greater shifts of fluid and sweat loss, resulting in lower body temperature and heart rate during prolonged work. The beneficial effects of hyperdydration and subsequent hypervolemia are manifest in the adaptation of body fluids and electrolytes to exercise training. Thus, with regard to fluid shifts during long-term exercise, training is an effective way to become hyperhydrated and to reduce the limiting effects of working in 'hostile' environments.
运动期间，动脉压升高导致毛细血管流体静压增加，促使血浆容量从血管腔转移至组织间液。运动开始几分钟内血管内液体迅速外流后，长期运动期间血浆容量几乎不再进一步减少，这表明存在防止循环血容量丢失的保护机制。这些机制可能包括增加血浆蛋白胶体渗透压、活跃肌肉与非活跃组织外周血管收缩的差异以及淋巴液流量增加。这些因素的相互作用可提供最佳的体温调节和心血管稳定性。长期运动期间液体转移的动态变化受水合状态影响。脱水导致的血容量不足通过减少运动期间的血浆转移量和汗液流失量来保存血容量。结果是散热减少，心血管稳定性增强。相反，过度水合导致的血容量过多会促使更多的液体转移和汗液流失，从而在长时间工作期间导致体温和心率降低。过度水合及随后的血容量过多的有益作用体现在体液和电解质对运动训练的适应性方面。因此，就长期运动期间的液体转移而言，训练是实现过度水合并减轻在“恶劣”环境中工作的限制作用的有效方法。
