Quantitation of volatile anesthetic-induced depression of myocardial contractility using a single beat index derived from maximal ventricular power.

Development of an index of myocardial contractility that is load independent and that can be derived from a single cardiac cycle in vivo has important intraoperative ramifications. Recently, a new index of contractile state based on maximal ventricular power (the rate of ventricular work) has been proposed that appears to fulfill these requirements. This investigation compared the efficacy and sensitivity of this novel method of measurement of myocardial contractility to the slope (Mw) of the preload recruitable stroke work (PRSW) relationship, an established measure of left ventricular function derived from left ventricular pressure-segment length loops in dogs before and during volatile anesthetic-induced cardiac depression. Sixteen experiments in two groups were performed using eight dogs chronically instrumented for measurement of aortic and left ventricular pressure, left ventricular dP/dt, subendocardial segment length, intrathoracic pressure, and thoracic aortic blood flow. The maximal ventricular power index (PWRmax/EDL2) was calculated as the product of peak aortic blood pressure and peak aortic blood flow divided by the square of end-diastolic segment length. Mw was obtained from a series of left ventricular pressure-segment length loops generated by abrupt vena caval occlusion. Systemic hemodynamics and myocardial contractility using these two methods were recorded in the conscious state and after 30 minutes of equilibration at 1.25, 1.5, or 1.75 MAC isoflurane or halothane.(ABSTRACT TRUNCATED AT 250 WORDS)