REDUCED VENOUS COMPLIANCE IN LOWER-LIMBS OF AGING HUMANS AND ITS IMPORTANCE FOR CAPACITANCE FUNCTION

Venous compliance in the calf of humans and its importance for capacit ance function in relation to age were studied with the aid of 22, 44, and 59 mmHg lower body negative pressure (LBNP). Negative pressure tra nsmission to the calf as well as changes in calf volume were studied, and venous compliance was calculated [change in volume with pressure c hange (dV/dP)]. The change in capacitance response of the calf with ag e (20-70 yr) was evaluated during LBNP 44 mmHg. Transmission of negati ve pressure to the subcutaneous tissue was almost full without any cha nges with age (92%). However, it was reduced to 80% in the underlying muscle tissue, irrespective of depth. Venous compliance in the young w as 0.051 ml.100 ml(-1).mmHg(-1) and was reduced by 45% to 0.029 ml.100 ml(-1).mmHg(-1) in the old (P < 0.05). Accordingly, the capacitance r esponse was reduced by 0.015 ml.100 ml(-1).yr(-1) (P < 0.005). Further more, the hemodynamic response to hypovolemic circulatory stress was a ttenuated with age. The reduced pressure transmission in muscle tissue is probably due to restriction of the muscle fascia envelope. The red uced venous compliance with age and the concomitant reduction in capac itance response during LBNP have implications for both the sympathetic reflex responses as well as the capacitance response during acute hyp ovolemic circulatory stress, which might be defected in aging humans.