Cardiovascular responses to lower body negative pressure in the elderly: role of reduced leg compliance.

BACKGROUND

It is warranted to test the hypothesis that the orthostatic tolerance does not diminish in the aging process per se in healthy individuals.

OBJECTIVE

The purpose of the present study was to examine the effects of aging on cardiovascular response and baroreflex sensitivity during lower body negative pressure (LBNP) with a special reference to leg compliance.

METHODS

Fifteen healthy old male subjects [mean age 68.2 +/- (SE) 0.8 years] and 22 young male subjects [mean age 21.4 +/- (SE) 0.3 years] underwent a 21-min bout of ramped LBNP (from 0 to -60 mm Hg, 10 mm Hg each for 3 min). Heart rate (HR), blood pressure, stroke volume (SV), forearm blood flow, and leg volume were measured throughout the experimental period. The arterial baroreflex sensitivity was calculated from spontaneous changes in beat-to-beat arterial pressure and HR during LBNP.

RESULTS

The leg compliance was lower, and the orthostatic tolerance index was higher in old than in young participants. The LBNP-associated increases in leg volume and HR and the decreases in SV were lower in old subjects, suggesting that the reduction of venous return was less in magnitude in old subjects during LBNP. The baseline value of baroreflex sensitivity evaluated by the sequence analysis was smaller, and no LBNP-related change was observed in old subjects, whereas a gradual LBNP-related reduction was observed in young subjects. The slope of regression between DeltaSV and change in forearm vascular resistance during LBNP was identical in both age groups.

CONCLUSIONS

We conclude that: (1) aging per se does not increase the intolerance to orthostatic stress induced by LBNP; (2) a low magnitude of venous return reduction during LBNP contributes to a higher tolerance in the old because of lower leg compliance, and (3) the sensitivity of baroreflex control of the HR is attenuated in the old; however, there is no deterioration of the sensitivity of the peripheral vasoconstriction during LBNP.