THE HEMODYNAMIC-EFFECTS OF ADRENERGIC BLOCKING-AGENTS

The various antihypertensive agents reduce blood pressure by different mechanisms. Alpha-1 receptor blockers reduce vascular resistance and maintain cardiac output. Chronic treatment with beta blockers without intrinsic sympathomimetic activity produces a fall in blood pressure which is associated with a fall in cardiac index and heart rate. Beta blockers with strong intrinsic sympathomimetic activity showed reduced heart rate during exercise. Labetalol reduces cardiac output and peripheral vascular resistance with little or no reduction in peripheral blood flow. Alpha-1 blockers are suitable for patients with active life-styles, with peripheral vascular disorders, or with high blood-cholesterol levels. Beta blockers are useful in patients who have tachycardia, palpitation problems, or angina pectoris, or who have survived a heart attack. They should not be used in patients with bronchial asthma, reduced peripheral blood flow, or heart failure. Labetalol reduces blood pressure in a somewhat larger fraction of patients than the pure alpha- or beta-blocking agents. It is hoped that its long-term results will include regression of cardiovascular damage, improved quality of life, and increased life expectancy.