Aortic pressure during ventricular ejection as a determinant of cardiac performance

¹ Research Division, St. Vincent Charity Hospital, Cleveland, Ohio

In the isolated, supported, canine heart preparation, the left ventricle was subjected to brief, repetitive, identical increases in outflow resistance. By varying the timing of the application of the augmented resistance, it was possible to subject the ventricle to a series of different aortic pressures during the ejection phase of systole, in the face of a virtually constant change of arterial impedance. The aortic diastolic pressure, the minimum pressure during the preceding beat, was used as an index of the aortic pressure range against which the ventricle contracted during each experimental beat with increased resistance. For any given increment of resistance, peak systolic pressure was an approximately linear, direct function of aortic diastolic pressure, and peak flow velocity and stroke volume were approximately linear, inverse functions of the diastolic pressure over the range of variations which was studied. Peak power generation and stroke work were also affected both by the magnitude of the resistance and by the level of the diastolic pressure. However, the direction in which these changes occurred was variable. Presumably this was dependent upon the position on the load-power and load-work curves at which the heart was operating during the control beats, as well as upon the magnitude of the changes in resistance and diastolic pressure which were imposed.

Note:
With the Assistance of Geraldine Nelson

Key Words: dog • outflow resistance • arterial impedance • flow velocity • stroke-volume

Submitted on April 5, 1963