Figure 8.

Schematic illustration of the impact of dehydration and hyperthermia on cardiovascular function during whole body exercise according to the hydrodynamic equivalent of Ohm's law. This states that perfusion pressure (MAP assuming right atrial pressure is 0 mmHg) equals flow ($\dot{\mathrm{Q}}$) times total peripheral resistance (TPR). Reductions in $\dot{\mathrm{Q}}$ due to diminished SV are associated with increases in TPR, as MAP is maintained. The SV decline in turn is solely the results of lower LV end‐diastolic volume (LVEDV), as LV end‐systolic volume (LVESV) and systolic function are not impaired. Lower total blood volume and peripheral vasoconstriction (and/or reduced peripheral perfusion) diminish venous return to the heart and thereby reduce LVEDV. Concomitant tachycardia‐mediated restrictions in LV filling time also contribute to the reduction in LVEDV. Increases in LV diastolic function blunts the effects of hypovolemia, tachycardia and vasoconstriction thereby preventing greater reductions in LVEDV