A Quantitative Analysis of Left Ventricular Myocardial Function in the Intact, Sedated Dog

Instantaneous contractile element velocity was calculated from left ventricular pressure and its first derivative during isovolumic left ventricular contractions produced by sudden balloon occlusion of the ascending aorta during diastole in closed-chest, sedated dogs. Wall tension was derived from ventricular pressure and volume, the latter being obtained from the pressure-volume relation of the arrested ventricle. During isovolumic contractions, there was an inverse curvilinear relation between tension and velocity, except at the onset of contraction and near peak tension. Increasing diastolic ventricular volume shifted the tension-velocity relations to the right, with increase in mean total isovolumic tension from 188 to 471 g/cm 2 , but without an obvious change in extrapolation to maximum velocity, which averaged 3.0 circumferences/sec. End-diastolic pressure-tension and circumference-tension relations indicated that active tension development continued to increase up to the maximum measured enddiastolic pressures of approximately 20 mm Hg. The normalized data, pooled from 15 animals, showed little scatter in the data for tension and velocity. It is concluded that the contractile properties of left ventricular muscle in the intact, sedated dog may be meaningfully described by tension-velocity relations obtained from single isovolumic contractions. The responses of the intact ventricle to increased diastolic volume and digitalis glycosides are analogous to those of isolated cardiac muscle. The small variability in the normalized tension-velocity relations in the normal dog suggests that it will also be possible to characterize abnormal left ventricular function with this approach.