Severe hyperthermia during prolonged exercise decreased global cerebral blood flow by 18% compared with normothermic control (43 vs. 51 ml·100 g−1·min−1; P<0.05).
Does severe hyperthermia alter global cerebral blood flow and cerebral metabolism during prolonged exercise in endurance-trained subjects?
Severe hyperthermia during prolonged exercise reduces global cerebral blood flow by 18% while increasing cerebral metabolic rate, likely related to lowered arterial carbon dioxide tension and temperature effects.
Absolute Event Rate: 43% vs 51%
p-value: p=<0.05
The development of hyperthermia during prolonged exercise in humans is associated with various changes in the brain, but it is not known whether the cerebral metabolism or the global cerebral blood flow (gCBF) is affected. Eight endurance-trained subjects completed two exercise bouts on a cycle ergometer. The gCBF and cerebral metabolic rates of oxygen, glucose, and lactate were determined with the Kety-Schmidt technique after 15 min of exercise when core temperature was similar across trials, and at the end of exercise, either when subjects remained normothermic (core temperature = 37.9°C; control) or when severe hyperthermia had developed (core temperature = 39.5°C; hyperthermia). The gCBF was similar after 15 min in the two trials, and it remained stable throughout control. In contrast, during hyperthermia gCBF decreased by 18% and was therefore lower in hyperthermia compared with control at the end of exercise (43 ± 4 vs. 51 ± 4 ml · 100 g −1 · min −1 ; P < 0.05). Concomitant with the reduction in gCBF, there was a proportionally larger increase in the arteriovenous differences for oxygen and glucose, and the cerebral metabolic rate was therefore higher at the end of the hyperthermic trial compared with control. The hyperthermia-induced lowering of gCBF did not alter cerebral lactate release. The hyperthermia-induced reduction in exercise cerebral blood flow seems to relate to a concomitant 18% lowering of arterial carbon dioxide tension, whereas the higher cerebral metabolic rate of oxygen may be ascribed to a Q 10 (temperature) effect and/or the level of cerebral neuronal activity associated with increased exertion.
Nybo et al. (Mon,) conducted a other in Hyperthermia during prolonged exercise (n=8). Severe hyperthermia (core temperature = 39.5°C) vs. Normothermic control (core temperature = 37.9°C) was evaluated on Global cerebral blood flow (gCBF) at the end of exercise (p=<0.05). Severe hyperthermia during prolonged exercise decreased global cerebral blood flow by 18% compared with normothermic control (43 vs. 51 ml·100 g−1·min−1; P<0.05).