Myocardial relaxation in regionally stunned left ventricle.

Load regulation of pressure fall was analyzed in regionally stunned left ventricles (LV) of anesthetized dogs. Stunning delayed and slowed pressure fall. When partial aortic occlusions elevated systolic pressure by 12.5 +/- 0.4 mmHg, the rate of pressure fall remained unchanged at baseline but slowed after stunning. This different response after stunning could be attributed entirely to decreased contractility and decreased development of peak isovolumetric pressure. Total aortic occlusions were then performed at various timings during ejection. With early occlusions and isovolumetric heartbeats, systolic pressure was lower after stunning, but pressure fall slowed to the same extent. With midocclusions the stunned LV developed relatively more systolic pressure, and pressure fall slowed more. This suggested a delayed transition from contraction to relaxation. With late occlusions pressure fall did not slow as with earlier occlusions, but initial pressure fall accelerated both at baseline and after stunning. The data suggested that load dependence was preserved with stunning and that, even if myocardial inactivation might be delayed, this delay did not contribute to the observed slowing of pressure fall.