Cardiopulmonary blood volume and plasma renin activity in man: preliminary report

Cardiopulmonary blood volume (CPBV) and plasma renin activity (PRA) were measured simultaneously in five normal subjects and six patients with essential hypertension studied in the following different conditions: supine position, head-down tilt, thigh-cuffs inflation. In each individual, a significant negative correlation (r > or = 0.95) was observed between CPBV and PRA. The slope of the relationship (delta PRA/delta CPBV) was used as an index of sensitivity of the neural control of renin release through cardiopulmonary receptors of the low pressure system. Simultaneously, the sensitivity index of the high pressure baroreflex system (HPB) was evaluated using bolus injections of phenylephrine. In normal subjects and patients with hypertension, the delta PRA/delta CPBV ratio and HBP were strongly correlated. Both indices were negatively correlated to age. It is suggested that the sensitivity of the neural control of renin release as well as the arterial baroreflex sensitivity are influenced by age, and possibly the inflexibility of the vascular system.