Autonomic and Non-Autonomic Circulatory Components

The circulatory effects of blocking cardiac and peripheral autonomic effectors were studied in 32 subjects with established essential hypertension, and in 15 normotensives. The mean resting arterial pressure, heart rate and total peripheral resistance index (TPRI) were significantly higher in the hypertensives, but cardiac index was the same in both groups. In subjects with blocked cardiac effectors (atropine + beta-blocking drugs, i.v.) the sympathetic constrictor effects on TPRI were estimated from the changes after giving i.v. guanethidine+phentolamine. The autonomic component of TPRI was higher in hypertensives than in normotensives. The residual resistance after 'total' autonomic block (non-autonomic TPRI) was higher in hypertensives, accounting for 60 to 80% of the initial difference in resting TPRI between the two groups. With an increase in non-autonomic TPRI, the increased autonomic TPRI effect in hypertension is not necessarily due to increased sympathetic nerve activity. Vagal and cardiac sympathetic effects on heart rate were compared in the two groups. Each estimate was based on the average of the responses to the appropriate blocking drug (1) in subjects not previously given a blocking drug, and (2) in subjects with the other cardiac effector pathway already blocked. The higher heart rate in established hypertension was predominantly due to change in vagal rather than cardiac sympathetic effects.