MYOCARDIAL RELAXATION IN REGIONALLY STUNNED LEFT-VENTRICLE

Load regulation of pressure fall was analyzed in regionally stunned le ft ventricles (LV) of anesthetized dogs. Stunning delayed and slowed p ressure fall. When partial aortic occlusions elevated systolic pressur e by 12.5 +/- 0.4 mmHg, the rate of pressure fall remained unchanged a t baseline but slowed after stunning. This different response after st unning could be attributed entirely to decreased contractility and dec reased development of peak isovolumetric pressure. Total aortic occlus ions were then performed at various timings during ejection. With earl y occlusions and isovolumetric heartbeats, systolic pressure was lower after stunning, but pressure fall slowed to the same extent. With mid occlusions the stunned LV developed relatively more systolic pressure, and pressure fall slowed more. This suggested a delayed transition fr om contraction to relaxation. With late occlusions pressure fall did n ot slow as with earlier occlusions, but initial pressure fall accelera ted both at base-line and after stunning. The data suggested that load dependence was preserved with stunning and that, even if myocardial i nactivation might be delayed, this delay did not contribute to the obs erved slowing of pressure fall.