DECREASED CAPACITANCE RESPONSE WITH AGE IN LOWER-LIMBS OF HUMANS - A POTENTIAL ERROR IN THE STUDY OF CARDIOVASCULAR REFLEXES IN AGING

The cardiovascular regulation in humans depends to a major extent on s ympathetic reflexes originating from volume receptors in the arterial as well as the cardiopulmonary region. With experimental approaches, s uch as lower body negative pressure (LBNP) and tilting, signs of reduc ed efficiency with ageing have been shown. However, a confounding fact or may be an age-related decline in venous capacitance response of the lower limbs, reducing the decrease in central blood volume and thus t he deactivation of baro/cardiopulmonary receptors. This potential erro r was addressed in the present study. Central hypovolaemic stress was produced by LBNP 60 cmH(2)O in 10 young (mean age 23, range 20-25 year s) and 10 old males (mean age 65, range 61-70 years). Changes in tissu e volume of the calf were studied by strain gauge volumetric technique . Transmission of negative pressure to the calf muscle was studied in two young and two old volunteers. The haemodynamic response to hypovol aemic circulatory stress was attenuated in the old as compared with th e young subjects, with a less marked increase in heart rate and periph eral resistance. Further, in the old subjects, the decrease in systoli c blood pressure, pulse pressure and forearm blood flow was attenuated . Transmission of negative pressure to the calf was equal in both grou ps. The capacitance response was reduced with age from 2.27 +/- 0.14 t o 1.64 +/- 0.13 mL 100 mL(-1) (P < 0.005). However, the net capillary fluid filtration was unchanged. The reduced capacitance function might partly explain the declining reflex responses with age in humans, and thus seems to be of considerable importance when studying cardiovascu lar sympathetic reflex responses in ageing.