Roberts M F, Wenger C B
Med Sci Sports. 1979 Spring;11(1):36-41.
At any given environmental and mean skin temperature, exercise brings about an increase in internal body temperature and skin blood flow. At high environmental temperatures, when skin temperature is elevated, skin blood flow at any given internal temperature reaches higher levels than at cooler skin temperatures. Increased cutaneous blood flow serves to deliver metabolic heat from the core to the skin, where the heat is lost to the environment by convective, radiative, and evaporative mechanisms. However, at high levels of skin blood flow, peripheral vascular pooling and fluid losses by filtration lead to reduced central venous pressure. This lowers cardiac stroke volume, and requires a higher heart rate to maintain a given cardiac output. Mechanisms which alleviate some of the cardiovascular strain produced by exercise in the heat include the following: acutely, reflexes which arise from receptors in working muscles produce vasoconstriction in a number of central and peripheral vascular beds. Other reflexes, arising from cardiac baroreceptors, produce additional peripheral vasoconstriction when cardiac filling is impaired. In the long term, physical conditioning and heat acclimation lead to increases in sweat output during thermal stress, leading to cooler skin and core temperature during exercise, and decreasing the level of skin blood flow needed for regulation of body temperature.
在任何给定的环境温度和平均皮肤温度下，运动都会导致体内温度升高和皮肤血流量增加。在高温环境中，当皮肤温度升高时，在任何给定的体内温度下，皮肤血流量会比在较低皮肤温度时达到更高水平。皮肤血流量增加有助于将核心部位的代谢热传递到皮肤，在皮肤处热量通过对流、辐射和蒸发机制散失到环境中。然而，在皮肤血流量较高时，外周血管淤血以及通过滤过导致的液体流失会导致中心静脉压降低。这会降低心脏的每搏输出量，并且需要更高的心率来维持给定的心输出量。减轻热环境中运动产生的一些心血管压力的机制如下：急性情况下，工作肌肉中的感受器引发的反射会使许多中枢和外周血管床产生血管收缩。其他反射，源自心脏压力感受器，当心脏充盈受损时会产生额外的外周血管收缩。从长期来看，身体锻炼和热适应会导致热应激期间出汗量增加，使得运动期间皮肤和核心温度降低，并减少调节体温所需的皮肤血流量水平。
