Hemodynamic and hormonal effects of propranolol on patients with essential hypertension during head-up tilting: a comparison between normal and low cardiac index groups.

Twelve outpatients with essential hypertension who showed a normal cardiac index (CI) (between 2.5 and 3.6 1/min/m2) or low CI (2.5 and less 1/min/m2) were studied. Head-up tilting (70 degrees) was performed for 15 min before and 2 weeks after treatment with propranolol (90 mg/day). Before treatment, the normal CI group showed a fall in systolic blood pressure (SBP) associated with a decrease in CI and an increase in the total peripheral resistance index (TPRI) during tilting. Conversely, the low CI group showed a rise in SBP associated with an increase in CI and a decrease in TPRI. There was a negative correlation (r = -0.69, P less than 0.05) between the basal CI and the change caused by the tilting. During treatment with propranolol, on the other hand, both groups showed decreases in CI. There was a greater increase in plasma renin activity (PRA) in the normal than in the low CI group before treatment with propranolol. The rise in PRA was significantly (P less than 0.05) suppressed by propranolol in the normal CI group only. It was demonstrated that the low CI group showed a different hemodynamic response to the tilting than the normal CI group. The lower rise in PRA may have partially contributed to the lack of increase in TPRI in the low CI group, compared with the normal CI group. Such hemodynamic differences may be abolished by propranolol which has a cardioinhibitory and/or renin-suppressive effect.