Autonomic nervous system function following exercise-induced hyperthermia

Abstract

Exercise in the heat is associated with cardiovascular and thermoregulatory disturbances that can persist postexercise. The effect of orthostasis on autonomic nervous system function following exercise-induced hyperthermia (EIH) remains to date unclear. Insight into the mechanisms of control is beneficial to those encountering orthostatic challenges after activity-induced hyperthermia. We evaluated the short-term postexercise cardiovascular and thermoregulatory responses to repeated orthostatic challenges performed in a hyperthermic state and the effects of EIH on autonomic nervous system function during repeated orthostatic challenges in the early and late-stages of recovery. We conclude that following EIH, the cardiovascular system maintained arterial pressure and cardiac output during repeated 70° head-up tilts. Nonthermal baroreceptor control predominates over thermal control of cutaneous vascular conductance during postural challenges following EIH, but no effect was observed in local sweat rate. The short-term reductions in baroreceptor sensitivity and heart rate variability following EIH were re-established following a 24-h recovery period.