Nybo Lars, Secher Niels H, Nielsen Bodil
Department of Human Physiology, Institute of Exercise and Sport Sciences, University of Copenhagen, Denmark.
J Physiol. 2002 Dec 1;545(2):697-704. doi: 10.1113/jphysiol.2002.030023.
Brain temperature appears to be an important factor affecting motor activity, but it is not known to what extent brain temperature increases during prolonged exercise in humans. Cerebral heat exchange was therefore evaluated in seven males during exercise with and without hyperthermia. Middle cerebral artery mean blood velocity (MCA V(mean)) was continuously monitored while global cerebral blood flow (CBF) and cerebral energy turnover were determined at the end of the two exercise trials in three subjects. The arterial to venous temperature difference across the brain (v-aD(temp)) was determined via thermocouples placed in the internal jugular vein and in the aorta. The jugular venous blood temperature was always higher than that of the arterial blood, demonstrating that heat was released via the CBF during the normothermic as well as the hyperthermic exercise condition. However, heat removal via the jugular venous blood was 30 +/- 6 % lower during hyperthermia compared to the control trial. The reduced heat removal from the brain was mainly a result of a 20 +/- 6 % lower CBF (22 +/- 9 % reduction in MCA V(mean)), because the v-aD(temp) was not significantly different in the hyperthermic (0.20 +/- 0.05 degrees C) compared to the control trial (0.22 +/- 0.05 degrees C). During hyperthermia, the impaired heat removal via the blood was combined with a 7 +/- 2 % higher heat production in the brain and heat was consequently stored in the brain at a rate of 0.20 +/- 0.06 J g(-1) min(-1). The present results indicate that the average brain temperature is at least 0.2 degrees C higher than that of the body core during exercise with or without hyperthermia.
脑温似乎是影响运动活动的一个重要因素，但在人类长时间运动过程中脑温升高的程度尚不清楚。因此，对7名男性在有或无体温过高情况下运动时的脑热交换情况进行了评估。在三名受试者的两次运动试验结束时，测定全脑血流量（CBF）和脑能量代谢的同时，持续监测大脑中动脉平均血流速度（MCA V(mean)）。通过置于颈内静脉和主动脉的热电偶测定脑的动静脉温差（v-aD(temp)）。颈静脉血温度总是高于动脉血温度，表明在正常体温以及体温过高的运动状态下，热量通过脑血流量被释放。然而，与对照试验相比，体温过高时通过颈静脉血的散热降低了30±6%。从脑内散热量的减少主要是由于脑血流量降低了20±6%（大脑中动脉平均血流速度降低了22±9%），因为在体温过高时（0.20±0.05℃）与对照试验（0.22±0.05℃）相比，动静脉温差没有显著差异。在体温过高时，通过血液的散热受损与脑内产热增加7±2%同时出现，因此热量以0.20±0.06 J g(-1) min(-1)的速率在脑内蓄积。目前的结果表明，无论有无体温过高，运动过程中平均脑温比体核温度至少高0.2℃。
