Haemodynamic adaptation at rest and during exercise to long-term antihypertensive treatment with combined alpha- and beta-adrenoreceptor blockade by labetalol.

Abstract

The effects of labetalol, an .alpha.- and .beta.-adrenoreceptor blocker, on systemic and pulmonary hemodynamics were studied for 20 mo. in 9 hypertensive men aged 49-57 yr, at rest in the supine and upright position and during exercise in the sitting position at 62 and 124 W. Pressures were recorded by catheters inserted percutaneously into the pulmonary and brachial artery, and cardiac output was determined by the Fick method. Systemic systolic, diastolic, and mean pressures were reduced by labetalol under all conditions. Pulmonary mean pressure was slightly higher during exercise and left ventricular (pulmonary artery) diastolic pressure was unchanged. Systemic blood pressure was lowered by reducing systemic vascular resistance alone. Though heart rate was significantly reduced under all conditions, cardiac output was unchanged due to a considerable rise in stroke volume which counterbalanced the reduction in pulse rate. Compared with the hemodynamic pattern induced by i.v. labetalol, prolonged treatment resulted in a greater increase in stroke volume and a further decrease of heart rate, particularly at rest. Systemic vascular resistance showed a tendency towards lower values. Postural hypotension which occurred frequently after i.v. labetalol was not observed after long-term treatment. Plasma renin activity and arterial lactate were consistently reduced. No serious side-effects were seen and there were no significant changes in hematological and biochemical variables. Treatment of hypertension by combined .alpha.- and .beta.-receptor blockade using labetalol offers significant hemodynamic advantages compared with treatment by .beta.-receptor blockade alone.