HAeMODYNAMIC EFFECTS OF CHANGES IN BLOOD VOLUME IN HYPERTROPHIC OBSTRUCTIVE CARDIOMYOPATHY

Abstract

Several physiological and pharmacological influences are known to alter the degree of obstruc- tion in hypertrophic obstructive cardiomyopathy (hypertrophic subaortic stenosis, muscular sub- aortic stenosis). Increased left ventricular-arterial systolic gradients in the beats following a ventri- cular ectopic contraction and following the administration of isoprenaline and of digitalis are probably related to positive inotropic effects (Brockenbrough, Braunwald, and Morrow, 1961; Braunwald, Brockenbrough, and Frye, 1962; Braunwald and Ebert, 1962). The basic mechanism producing increased gradients during the Valsalva manceuvre, amyl nitrite inhalation, and nitro- glycerine administration on the one hand, and diminished gradients with phenylephrine or methox- amine administration are not fully understood. The probable importance of changes in arterial pressure (Wigle et al., 1963) and of changes in ventricular volumes have been emphasized (Braun- wald et al., 1964).