Short- and long-term (six-year) hemodynamic effects of labetalol in essential hypertension.

The acute blood pressure lowering effect of intravenous labetalol (0.2 to 0.8 mg/kg) was studied in 11 patients with severe hypertension. The blood pressure was reduced by 22 percent partly due to a decrease in total peripheral resistance (-14 percent) and partly due to a reduction in cardiac output (-10 percent). Stroke volume was unchanged. Fifteen patients with moderate essential hypertension were studied at rest and during exercise before and after one and six years of labetalol therapy. Blood pressure was reduced approximately 22 percent at rest as well as during exercise, mainly due to a reduction in total peripheral resistance. However, after one year, cardiac index was reduced 10 to 14 percent (p less than 0.01) at rest (sitting) and during exercise due to a reduction in heart rate not compensated for by an increase in stroke volume. During the next five years, blood pressure control was maintained, but cardiac index tended to increase and was not significantly reduced in any situation six years after treatment was started. Total peripheral resistance decreased significantly and was reduced 15 to 20 percent (p less than 0.01) after six years. Stroke index increased about 10 to 15 percent (p less than 0.01). These alterations are the opposite of what is seen in untreated hypertensive patients restudied after 10 and 17 years. The normalization of central hemodynamics could reflect the regression of structural changes in the heart and in the resistance vessels.