Abstract
The investigations reported in this paper were designed to determine the greatest magnitude of regurgitation possible in the relaxing mammalian heart under optimal conditions and to study the mechanisms by which such volumes are accommodated. These questions have previously been studied chiefly with the aid of artificial circulation machines. But, as Allan 1 properly concludes, conditions are manifestly so different in the mammalian heart that it would be unwise to transfer such values to the human circulation. A number of physical factors enter into relaxation of the mammalian heart which are difficult to reproduce in an artificial model. Ventricular diastole begins with a phase of isometric relaxation during which the intraventricular pressure is reduced from that existing in the aorta to a level below that in the auricle. During this early diastolic phase, averaging 0.07 second in the dog and 0.12 second in man, the ventricular cavity remains in the state of obliteration reached at the end of ejection. Consequently, by far the greatest backflow and possibly all of it must occur during the subsequent inflow phases. Whether the rapid filling from the auricles hinders aortic regurgitation or, vice versa, whether regurgitating blood reduces the filling from the auricles remains a debatable question. The extent to which a backflow from the aorta is accommodated by replacing inflow from the auricle or by stretching of the ventricle has also not been satisfactorily settled.
Procedure. Our experiments were carried out on cats' hearts arranged to contract isometrically and supplied through the aorta and coronary vessels with nutrient fluid under adjustable pressure. The special arrangements consisted (1) in the introduction of a plunger cannula through the aortic valves for the purpose of producing an aortic insufficiency at will, and (2) in the insertion of a thin rubber balloon into the left ventricle by way of the mitral orifice.
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