Age-related influences of leg vein filling and emptying on blood volume redistribution and sympathetic reflex during lower body negative pressure in humans

To test the hypothesis that leg vein filling and emptying functions could be impaired with advancing age, which would produce less blood volume redistribution toward the lower body and smaller sympathetic reflex response during mild gravitational stress, 9 young and 10 elderly healthy males were exposed to a lower body negative pressure (LBNP) of 15 mmHg. Venous occlusion plethysmography was used to determine the functions of the leg veins. We found that the baseline venous distensibility index (VDI) was lower (0.057±0.004 vs. 0.048± 0.003 ml·100 ml^-1·mmHg^-1, young vs. elderly; p<0.05), and half-emptying time (T_1/2) was shorter (1.6±0.1 vs. 1.3±0.1 s, young vs. elderly; p<0.05) in the elderly. At 15 mmHg-LBNP, VDI was decreased and T_1/2 was shortened significantly in the vounq qroup, but only slightly in the elderly group. Neither blood pressure nor heart rate changed significantly in either group. The reduction in peripheral venous pressure, which was recorded from the left antecubital vein at the cubital fossa, was less in the elderly, indicating a smaller decrease in central blood volume during LBNP; however, the enhancement of muscle sympathetic nerve activity was nearly the same as that in the young. We conclude that leg vein filling and emptying functions are impaired in elderly people, producing less blood pooling in the legs and smaller reduction in peripheral venous pressure during LBNP; the maintained sympathetic reflex response might be attributable to the well-preserved baroreflex function control of sympathetic outflow to the muscle in the elderly.