EFFECTS OF ANESTHESIA AND RECENT SURGERY ON DIASTOLIC FUNCTION

Objective: The aims were to determine the effects and the extent to which halothane anaesthesia affects diastolic function both immediately after and remote from surgery and to investigate whether the effect is due to alterations in loading conditions. Methods: Eight mongrel dogs were studied under halothane anaesthesia (0.5-1.5 end tidal vol%) with the chest closed, after acute instrumentation with left ventricular pressure transducers, left atrial and aortic catheters, and left ventricular diameter and wall thickness crystals. The same dogs were then studied in the fully conscious state, 2-3 weeks later. An additional four dogs were studied in the conscious state and then again under halothane anaesthesia remote from acute instrumentation. The left ventricular isovolumetric relaxation time constant, tau, as well as myocardial and chamber stiffness constants were used as indices of diastolic function. Results: Following halothane anaesthesia and recent surgery, tau was prolonged significantly compared to the conscious state, at 30(SEM 1) v 22(1) ms (p < 0.01), but there were no changes in either myocardial or chamber stiffness. While tau remained sensitive to increased heart rate and enhanced contractility and was prolonged by increasing afterload in both the anaesthetised and conscious states, it was consistently prolonged following halothane anaesthesia and recent surgery even at matched levels of contractile states, heart rates and loading conditions, compared to the conscious state, at 26(1) v 19(1) ms (p < 0.01). When the effects of halothane anaesthesia were examined after full recovery from surgery, tau was still prolonged under halothane anaesthesia, at 29(2) v 20(1) ms (p < 0.01), compared to the conscious state, but in contrast to the findings following halothane anaesthesia and recent surgery, it was fully normalised [19(1) v 19(1) ms] when contractile state and loading conditions were matched. Conclusions: Left ventricular diastolic function is influenced markedly by halothane anaesthesia and recent surgery, and to a degree comparable to many pathological states. The effects of halothane anaesthesia and recent surgery appear to prolong the isovolumetric relaxation time constant independently of heart rate, contractility, and loading conditions and are most likely to be due to the combined direct effects of anaesthetics and acute instrumentation.