Effects of mechanical vibration on left ventricular diastolic properties during global ischemia.

To examine the effect of mechanical vibration on ventricular relaxation and diastolic chamber stiffness under global ischemia, we studied eight coronary perfused, isolated, isovolumic canine left ventricles (LV). To produce varying degrees of impaired relaxation, graded coronary flow reduction and paced tachycardia were imposed. A mechanical 50-Hz, 2-mm-amplitude vibration was applied during diastole and was turned off during systole. Without diastolic vibration, the relaxation time constant of LV pressure (tau) increased with the severity of ischemia. The chamber stiffness index (K) from the diastolic pressure-volume relationship showed a slight increase during ischemia; tau decreased with diastolic vibration. The change in tau with vibration increased with ischemia and was dependent on vibration amplitude but not heart rate. The ratio of tau to the diastolic interval (DI, the time from peak negative rate of LV pressure change to end diastole) always decreased with vibration and was linearly correlated with K (r = 0.93; P less than 0.01). K decreased with vibration when tau/DI was greater than 0.3. We conclude that diastolic vibration improves impaired relaxation and chamber stiffness under myocardial ischemia.