Peak isovolumic pressure-volume relation of puppy left ventricle.

We studied peak isovolumic pressure-volume (PV) relation of the left ventricle in 3-mo-old mongrel puppies. A puppy heart was excised and cross circulated with an adult dog. Left ventricular pressure and volume were measured with a water-filled balloon. Peak isovolumic PV curve in control contractile state was convex upward, reaching a maximum pressure of 130 mmHg. Epinephrine (0.6 microgram/min intracoronary) shifted the curve leftward and up to a maximum pressure of 160 mmHg. Propranolol (0.8 mg intracoronary) shifted it rightward and down to a maximum pressure of 110 mmHg. These PV curves were reasonably fitted by an asymptotic equation: P = A (1 - exp[-B (V - Vd)]), where V was normalized volume for 100 g left ventricle and Vd (6 ml/100 g) was V at which peak pressure was zero. A and B are regression coefficients. A was 149, 169, and 120 mmHg, and B was 0.16, 0.19, and 0.06 ml, respectively, in control, enhanced, and depressed contractile states. These changes in A and B were statistically significant. We conclude that the puppy left ventricular peak isovolumic PV curve is convex upward and shifts sensitively with inotropic changes.