Effects and interactions of myocardial ischaemia and alterations in circulating blood volume on canine left ventricular diastolic function.

We have determined the effects of alterations in preload on ischaemia-induced diastolic dysfunction in anaesthetized beagles instrumented to measure left ventricular pressure and regional dimensions. Low-flow regional ischaemia decreased peak lengthening rates in ischaemic (mean -26 (SEM 6) mm s-1, P < 0.01) and non-ischaemic (-8.6 (3.4) mm s-1, P < 0.05) myocardium. Peak lengthening rates and the time constant of iso-volumic relaxation (tau) were not affected by alterations in preload. Absolute values of tau failed to distinguish between ischaemia and control. The ischaemia-induced decrease in peak negative dP/dt was preload dependent and caused mainly by a concomitant decrease in peak left ventricular pressure. We conclude that indices derived from segmental lengthening are sensitive to ischaemia and insensitive to preload, in contrast with indices derived from left ventricular pressure. It remains to be determined if monitoring of early segmental lengthening will improve detection and assessment of perioperative myocardial ischaemia.