Haemodynamic Effects of Changes in Blood Volume in Hypertrophic Obstructive Cardiomyopathy.

Several physiological and pharmacological influences are known to alter the degree of obstruction in hypertrophic obstructive cardiomyopathy (hypertrophic subaortic stenosis, muscular subaortic stenosis). Increased left ventricular-arterial systolic gradients in the beats following a ventricular 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 nitroglycerine administration on the one hand, and diminished gradients with phenylephrine or methoxamine 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 (Braunwald et al., 1964). Cross and Salisbury (1963) succeeded in reproducing some of the hemodynamic features of the disease in dogs by decreasing the cardiac output, provided the pericardium was closed. They first suggested that diminished ventricular volume was the factor responsible for subaortic obstruction. Should diminished cardiac output, blood volume, and ventricular size prove to be important determinants of increased obstruction in patients with hypertrophic obstructive cardiomyopathy then the therapeutic implications are obvious. Since treatment is not yet fully satisfactory or understood and the disease is most hazardous, it was decided to study the hmmodynamic effects of rapid withdrawal followed by reinfusion of blood. These studies were carried out during diagnostic investigations to confirm the clinical diagnosis. The purpose of these studies was to determine the hvmodynamic parameters that affect adversely or beneficially the degree of obstruction in this disease. Knowledge of these is essential as a guide to therapy.