Cardiovascular drift during prolonged exercise and the effects of dehydration.

Reductions in SV are the most striking component of "classic" CV drift as well as "dehydration induced" CV drift. Direct data for the widespread notion that increased skin blood flow causes SV to be reduced during "classic" CV drift is rather scarce. Reductions in SV due to dehydration and concomitant hyperthermia are clearly not due to increases in skin blood flow. Instead, skin blood flow declines as skin and systemic vascular resistance increase as the CV system attempts to cope with the severe challenge of large reductions in cardiac output. Approximately one-half of the reduction in SV is due to reduced blood volume from dehydration during exercise which produces hyperthermia. The remaining reduction in SV with dehydration and hyperthermia appears to be related to additional factors such as hyperthermia and their interaction with factors that further reduce ventricular filling, such as heart rate acceleration.