Haemodynamic effects of combined alpha- and beta-adrenoreceptor blockade after intravenous labetalol in hypertensive patients at rest and during exercise.

1 The haemodynamic effects of labetalol 50 mg intravenously were studied in 13 hypertensive patients at rest in the supine and upright positions and during exercise using percutaneous right heart and brachial artery catheterization. 2 Labetalol induced immediate significant reductions in systolic and diastolic blood pressures in all conditions. 3 Heart rate, stroke volume and cardiac output were not significantly altered in the supine position at rest but were significantly reduced in the upright position. In addition systemic vascular resistance was significantly reduced. 4 During exercise, heart-rate, cardiac output and vascular resistance were significantly reduced; stroke volume was increased. Left ventriclac filling pressures were unchanged both at rest and during exercise. 5 It was concluded that these changes resulted from blockade to both alpha- and beta-adrenoreceptor.