Left ventricular diastolic relaxation and pressure-diameter relations during ischaemic left ventricular failure in the dog.

The significance of severe ischaemic left ventricular (LV) failure on the LV isovolumic relaxation process and diastolic chamber stiffness has been investigated in nine open-chest pentobarbital-anaesthetized dogs. LV failure was induced by bolus injections of 50 micron microspheres into left coronary vascular bed until LV minor axis diameter had increased about 25% and end-diastolic pressure about 20 mmHg. Such ischaemic LV failure did not shift the relation between diastolic LV pressure and minor axis diameter compared with pressure-diameter curves obtained before induction of failure. Neither inotropic nor chronotropic stimulation evoked such shifts. Assuming exponential pressure decline, LV relaxation was significantly slower during failure, but proceeded in all experimental conditions at rates which indicated complete relaxation in late diastole. Analysis of the pressure decline during LV relaxation demonstrated that this process proceeded faster than assumed by an exponential function both before and during LV failure.