Acute and long-term effects of labetalol on systemic and pulmonary haemodynamics in hypertensive patients

Abstract

The effects of the combined adrenergic alpha- and beta-receptor blocking compound labetalol on the systemic and pulmonary circulation were studied after its acute and long-term administration to patients with essential hypertension (WHO grade I–II). Nine men and one woman (mean age 46 years) participated in the acute study. Cardiac index, systemic blood pressure, pulmonary artery pressure and heart rate were measured at rest in the supine and upright positions, and during supine exercise at two work loads (50 and 100 watt), before and after intravenous administration of labetalol 50 mg. Eight of the men were re-examined after three months oral treatment with labetalol 600–900 mg daily. In the acute study cardiac index was unchanged by labetalol, except at the work load of 100 watt, when it decreased by 18.7%. The mean blood pressure decreased under all conditions; 11.6 mm Hg at supine rest, 22.3 mm Hg in the upright position, and by 15.9 mm Hg and 16.9 mm Hg at the two work loads. Heart rate was unchanged at supine rest, but was reduced in the upright position 9,0% and during exercise — at 50 watt by 9.3%, and at 100 watt by 10.3%. Systemic vascular resistance decreased at rest in the supine and upright positions, but not during exercise. The pulmonary artery pressure remained unchanged both at rest and during exercise. In the long-term study cardiac index was unchanged except at the heavy work load, when it decreased by 11.4%. Mean blood pressure was reduced significantly under all circumstances, by 14.6 mm Hg at supine rest, 16.8 mm Hg in the upright positions, and by 13.9 mm and 13.4 mm, respectively, at the two work loads. Heart rate was reduced both at rest 13.6% and during exercise at the two work loads 9.6% and 12.4%. Systemic vascular resistance decreased at rest, but not during exercise. The pulmonary artery pressure were unchanged. Thus, the haemodynamic patterns after acute and long-term administration of labetalol were essentially similar, which suggests that the agent is suitable both for acute and long-term treatment of hypertension, at least from a haemodynamic point of view.