How do changes in blood volume and various physiological or pharmacological interventions affect the degree of obstruction in hypertrophic obstructive cardiomyopathy?
Summarizes known physiological and pharmacological influences on left ventricular outflow tract gradients in hypertrophic obstructive cardiomyopathy.
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).
Shah et al. (1965) studied this question.