Noninvasive study of effect of isometric exercise on left ventricular performance in normal man

Abstract

The effect of isometric skeletal muscle contraction on the performance of the normal left ventricle was studied noninvasively in 20 subjects. Studies were conducted at rest and at 3 minutes of isometric hanedrip exercise at 50 per cent of maximum voluntary contraction, and consisted of simultaneous recording of left ventricular echocardiogram, external carotid pulse, phonocardiogram, and electrocardiogram, while blood pressure was measured by sphygmomanometry. These data permitted evaluation of left ventricular performance in terms of left ventricular ejection fraction, mean circumferential fibre shortening velocity, and the ratio pre-ejection period/ejection time. In relation to values at rest, isometric exercise resulted in insigficant change in all three variables. The considerable increase in blood pressure, however, indicated significant increase in left ventricular wall tension, since echocardiographic left ventricular internal dimension remained practically unchanged during exercise. DiastQlic volume reserves were not utilized, and the fact that ejection fraction, mean circumferential fibre shortening velocity, and the pre-ejection period/ejection time period remained unaltered during exercise, despite considerable increase in afterload, supports the hypothesis that isometric exercise leads to enchantment of the inotropic state of the heart.