Effects of volatile anesthetics on stiffness of mammalian ventricular muscle

To assess the effects of halothane, isoflurane, and sevoflurane on cross br idges in intact cardiac muscle, electrically stimulated (0.25 Hz, 25 degree sC) right ventricular ferret papillary muscles (n = 14) were subjected to s inusoidal load oscillations (37-182 Hz, 0.2-0.5 mN peak to peak) at the ins tantaneous self-resonant frequency of the muscle-lever system. At resonance , stiffness is proportional to in * omega (2) (where in is equivalent movin g mass and omega is angular frequency). Dynamic stiffness was derived by re lating total stiffness to values of passive stiffness at each length during shortening and lengthening. Shortening amplitude and dynamic stiffness wer e decreased by halothane > isoflurane greater than or equal to sevoflurane. At equal peak shortening, dynamic stiffness was higher in halothane or iso flurane in high extracellular Ca2+ concentration than in control. Halothane and isoflurane increased passive stiffness. The decrease in dynamic stiffn ess and shortening results in part from direct effects of volatile anesthet ics at the level of cross bridges. The increase in passive stiffness caused by halothane and isoflurane may reflect an effect on weakly bound cross br idges and/or an effect on passive elastic elements.