Efects of propofol on left ventricular mechanoenergetics in the excised cross-circulated canine heart

Although propofol is commonly used for general anesthesia, its direct effects on left ventricular (LV) contractility and energetics remain unknown. Accordingly, we studied the effects of intracoronary propofol on excised cross-circulated canine hearts using the framework of the Emax (a contractility index)-PVA (systolic pressure-volume area, a measure of total mechanical energy)-V0₂ (myocardial oxygen consumption per beat) relationship. We obtained 1) the V0₂-PVA relationship ofisovolumic contractions with varied LV volumes at a constant Emax, 2) the V0_2-PVA relationship with varied LV volumes at aconstant intracoronary concentration of propofol, and 3) the Vo_2-PVA relationship under increased intracoronary concentrations of either propofol or CaCl₂ at a constant LV volume to assess the cardiac mechanoenergetic effects of propofol. We found that propofol decreased Emax dose-dependently. The slope of the linear V0_2-PVA relationship (oxygen cost of PVA) remained unchanged by propofol. The PVA-independent Vo_2-Emax relationship (oxygen cost of Emax) was the same for propofol and Ca²⁺. In conclusion, propofol showed a direct negative inotropic effect on LV. At its clinical concentrations, decreases incontractility by propofol were relatively small. Propofol shows mechanoenergetic effects on the LV that are similar to those of Ca²⁺ blockers or B-antagonists-i.e., it exerts negative inotropic effects without changing the oxygen costs of Emax and PVA.