Pressure Pulses and Blood Pressure Values in Unanesthetized Dogs

At present two views are held concerning the relationship between left ventricular and aortic pressure curves as regards contour and ordinate value. The one, sponsored by Wiggers (5) on the basis of experiments on anesthetized dogs with open chests and subscribed to by many others, holds that the systolic portions of both curves are parallel and of approximately the same height, whereas the other, most recently sponsored by Hamilton and associates (2,3,4), maintains on theoretical grounds and experimental work on unanesthetized dogs that during systole the apical intraventricular pressure must and does exceed the aortic to insure that blood shall flow from the ventricle to the aorta. Failure to obtain curves showing such pressure differences (indicating low or zero velocity in the ventricular apex and high velocity in the aorta) is ascribed to various factors which tend to reduce the kinetic factor and hence minimize the excess ventricular pressure; such as reduction of cardiac output through anesthesia and surgical shock and connection of the intraventricular manometer to the upper portion of the ventricle, a region in which the blood has nearly attained the aortic velocity. PROCEDURE. To obtain an answer to the question, attention was directed first of all toward devising ways and means of determining accurately the pressure pulses from the heart and arterial system of normal well-trained dogs, and secondly, toward making the circulatory system more accessible so that we could be sure of the exact location of our cannulae. For this purpose the Wiggers universal manometer cannot be used because attachment to it of the necessary, long, small-bore cannula results in an inefficient instrument of low frequency. The small, hypodermic manometer of Hamilton (2) overcomes these difficulties and represents a distinct contribution to the tools available for investigating circulatory