Effect of thermal stress on cardiac function.

Whole-body heating decreases pulmonary capillary wedge pressure and cerebral vascular conductance and causes an inotropic shift in the Frank-Starling curve. Whole-body cooling increases pulmonary capillary wedge pressure and cerebral vascular conductance without changing systolic function. These and other data indicate that factors affecting cardiac function may mechanistically contribute to syncope during heat stress and improvements in orthostatic tolerance during cold stress.