Regional distensibility, chamber stiffness, and elastic stiffness constant in halothane and propofol anesthesia

Nine mongrel dogs were acutely instrumented in order to investigate cardiac stiffness at end-diastole while left ventricular circumferential lengths were measured at two different sites (near-apical region and near-basal region). Two hundred mL of autologous blood were infused and then withdrawn to create different volume loading conditions. Four different anesthetic settings were tested: two concentrations (0.7% and 1.7%) of halothane, and two infusion rates (0.2 mg/min/kg, and 0.4 mg/min/kg) of propofol. Three parameters of cardiac stiffness were calculated: distensibility, chamber stiffness (Kp), and elastic stiffness constant (k). Chamber stiffness and elastic stiffness constant were smaller in the apical region than the basal region under halothane anesthesia at both the 0.7% and 1.7% concentrations. There were no regional differences in elastic stiffness constant (k) under propofol anesthesia at either infusion rate. However, Kp was smaller in the apical region at the low propofol infusion rate. There were no significant differences in Kp and k between the anesthetic agents, or with the increase in concentration of either agent. However, when both agent and concentration were taken into consideration, an increase in stiffness was observed with deepening halothane, but not propofol anesthesia. These results show that assessment of diastolic function must take into consideration both regional differences and the anesthetic agent, because the latter may alter such differences and, thus, alter diastolic function.