Epinephrine infusion (2 µg/kg/min) increased peak instantaneous pressure-volume ratio (Emax) from 6.6 to 12.2 mm Hg/ml and shortened Tmax from 191 to 157 msec in the canine left ventricle.
Does epinephrine infusion or altered heart rate change the instantaneous pressure-volume ratio (Emax and Tmax) in the canine left ventricle?
The instantaneous pressure-volume ratio parameters Emax and Tmax explicitly reflect ventricular contractility and are independent of mechanical load.
Absolute Event Rate: 12.2% vs 6.6%
As a means of assessing ventricular performance, we analyzed the time-varying ratio of instantaneous pressure, P(t), to instantaneous volume, V(t), in the canine left ventricle. Intraventricular volume was measured by plethysmography, while the right heart was totally bypassed. The cardiac nerves were sectioned, and an epinephrine infusion was used to alter the contractile state. The instantaneous pressure-volume ratio was defined as E(t) = P(t)/V(t) - V d , where V d is an experimentally determined correction factor. We found that (1) all the E(t) curves thus defined were similar in their basic shape and attained their peak near the end of the ejection phase regardless of the mechanical load, the contractile state, or the heart rate, (2) under a constant heart rate and contractile state extensive changes in preload, afterload, or both did not alter the peak value of E(t), Emax, or the time to Emax from the onset of systole, Tmax, and (3) these parameters of E(t) markedly changed with epinephrine infusion or increases in heart rate. At an epinephrine infusion rate of 2 µg/kg min -1 , Emax increased to 12.2 ± 4.5 ( SD ) mm Hg/ml (N = 9) from its control value of 6.6 ± 1.2 mm Hg/ml before the infusion. Simultaneously, Tmax shortened from 191 ± 29 msec to 157 ± 26 msec. Increases in the paced heart rate proportionally shortened Tmax (45% per 100-beats/min change in heart rate) without any effect on Emax. We concluded that E(t), represented by Emax and Tmax, explicitly reflects the ventricular contractility.
Suga et al. (1973) studied Ventricular performance (canine model) (n=9). Epinephrine infusion vs. Control value before infusion was evaluated on Peak instantaneous pressure-volume ratio (Emax). Epinephrine infusion (2 µg/kg/min) increased peak instantaneous pressure-volume ratio (Emax) from 6.6 to 12.2 mm Hg/ml and shortened Tmax from 191 to 157 msec in the canine left ventricle.