Peripheral venoconstriction during acceleration and orthostasis.

THE organism exposed to gravitational or accelerative stress would find it advantageous if active venous constriction occurred in the dependent portions of the body. Since the veins contain 60-75 per cent of the total systemic blood volume, a relatively small per cent decrease in capacity of the venous reservoir could yield a considerable increase in the volume of the diastolic cardiac inflow and might contribute a great deal to the support of cardiac output and arterial pressure on the centrifuge or tilt table. •