THE HEMODYNAMIC EFFECTS OF HYPOTENSIVE DRUGS IN MAN. III. HEXAMETHONIUM 123

Abstract

Hexamethonium admn. to hypertensive and normal subjects produces the following hemodynamic effects: In hypertensive patients who do not have heart failure reduction of systemic arterial pressure (sys. art. pres.) is accompanied by a decrease in right heart pres. and cardiac output. The total peripheral resistance (per. res.) does not change significantly. It is suggested that these alterations are the result of a combination of "venous pooling" and failure of reflex vasoconstriction (vasocon.). In pts. with ht. failure the fall in sys. art. pres. appears to be accompanied by a reduction of right ht. pres., an increase in cardiac output, and a significant decrease in total per. res. These alterations may be due to unloading of the congested right side of the ht. as well as to inhibition of vasocon. reflexes activated by the low output ht. failure. In contrast to the marked increase in blood flow in the foot observed previously, blood flow through the muscles increases only moderately. Since the arterial pres. falls after hexameth. admn., a significant decrease in per. res. is assumed to occur in this area. Despite a moderate reduction of hepatic vascular res., estimated hepatic-portal blood flow usually decreases after hexameth. Renal plasma flow decreases paralleling the initial fall in arterial pres. and then rises to approx. control levels despite a contined hypotensive response. This is consistent with previous observations indicating an autonomy of tone of the renal arterioles. In most cases the changes in glomerular filtration rate follow a pattern similar to the alterations in renal plasma flow, but occasionally filtration may remain below control values. Oliguria with increased concn. of urine usually occurs. All these renal effects begin to diminish after 30-60 min. despite continued significant hypotension. The studies to date suggest that sympathetic vasocon. nerves blocked by hexameth. exert the controlling influence no homeostatic adjustments to postural change and maintain the tone of the vessels of the distal part of the extremities. However, in resting supine subjects such nerves appear to exert a much less important influence on arteriolar tone in the hepatic-portal, renal and muscle areas.