EFFECTS OF ANESTHESIA AND RECENT SURGERY ON DIASTOLIC FUNCTION

Objective: The aims were to determine the effects and the extent to wh ich 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%) wit h the chest closed, after acute instrumentation with left ventricular pressure transducers, left atrial and aortic catheters, and left ventr icular diameter and wall thickness crystals. The same dogs were then s tudied in the fully conscious state, 2-3 weeks later. An additional fo ur dogs were studied in the conscious state and then again under halot hane anaesthesia remote from acute instrumentation. The left ventricul ar isovolumetric relaxation time constant, tau, as well as myocardial and chamber stiffness constants were used as indices of diastolic func tion. Results: Following halothane anaesthesia and recent surgery, tau was prolonged significantly compared to the conscious state, at 30(SE M 1) v 22(1) ms (p < 0.01), but there were no changes in either myocar dial or chamber stiffness. While tau remained sensitive to increased h eart rate and enhanced contractility and was prolonged by increasing a fterload in both the anaesthetised and conscious states, it was consis tently prolonged following halothane anaesthesia and recent surgery ev en at matched levels of contractile states, heart rates and loading co nditions, compared to the conscious state, at 26(1) v 19(1) ms (p < 0. 01). When the effects of halothane anaesthesia were examined after ful l recovery from surgery, tau was still prolonged under halothane anaes thesia, at 29(2) v 20(1) ms (p < 0.01), compared to the conscious stat e, but in contrast to the findings following halothane anaesthesia and recent surgery, it was fully normalised [19(1) v 19(1) ms] when contr actile state and loading conditions were matched. Conclusions: Left ve ntricular diastolic function is influenced markedly by halothane anaes thesia and recent surgery, and to a degree comparable to many patholog ical states. The effects of halothane anaesthesia and recent surgery a ppear to prolong the isovolumetric relaxation time constant independen tly of heart rate, contractility, and loading conditions and are most likely to be due to the combined direct effects of anaesthetics and ac ute instrumentation.