CARDIODYNAMICS OF EXPERIMENTAL INTERVENTRICULAR COMMUNICATIONS

Abstract

The manner in which the heart reacts to an interventricular communication was studied in dogs by use of an external shunt which could be opened and closed alternately. The shunt and its application are descr. The constancy of relations between onset of right and left ventricular systole gave evidence that the sequence of ventricular excitation was not disturbed by the apparatus. The dynamic changes, some of a compensatory nature, were deduced from detailed analysis of simultaneously recorded left and right intraventricular pressure curves aided by studies of aortic pressure pulses. Registrations were made by calibrated optical manometers of adequate efficiency. The predominant changes in the left ventricle on opening a shunt consisted of an elevation of initial pressure, a decline in max. pressure, and a prolongation of contraction in relation to cycle length, with modification in the contour of pressure pulses. The predominant effects in the right ventricle on opening the shunt consisted in an elevation of initial and max. pressures. An analysis of results leads to the conclusion that the great elevation of right ventricular pressure is certainly not caused wholly by summation of right and transmitted left ventricular pressures. It is due in part to a more vigorous response of the right myocardium consequent to increased diastolic distension. This compensatory response acts (a) to mobilize larger volumes of blood for return to the left heart and (b) to reduce the fraction of total ventricular discharge, which is transferred to the right ventricle during systole. When the right ventricle fails to respond to the law of initial length and tension, progressive dilation and rapid circulatory failure supervene. Increase in total circulating volume operates as one of the best compensatory mechanisms through additional right ventricular compensation, provided the right ventricle is in good condition.