Post-ischemic cardiac chamber stiffness and coronary vasomotion: the role of edema and effects of dextran

Abstract

Contributions of edema to left ventricular (LV) chamber stiffness and coronary resistance after ischemia were studied in isolated buffer-perfused rabbit hearts, with constant LV chamber volume, subjected to 30 min global ischemia and 60 min reperfusion. During reperfusion hearts were perfused with standard buffer or with 3% dextran to increase oncotic pressure and decrease water content. LV chamber volume was adjusted to an initial diastolic pressure (LVEDP) of 10 mmHg. In nonischemic hearts (n = 6) LVEDP was 11 +/- 0.3 mmHg and water content was 5.0 +/- 0.1 ml/g dry weight after 90 min of perfusion. In untreated ischemic hearts (n = 8) LVEDP was 51 +/- 4 mmHg and water content was 6.0 +/- 0.1 ml/g dry weight after 60 min reperfusion (P less than 0.001 v. nonischemic). In dextran-treated ischemic hearts (n = 8) LVEDP was 38 +/- 3 mmHg (P less than 0.05 v. untreated ischemic) and water content was 5.2 +/- 0.1 ml/g dry weight (P less than 0.001 v. untreated ischemic). Coronary resistance in untreated ischemic hearts increased by 26% from 2.0 +/- 0.06 to 2.6 +/- 0.06 mmHg/ml/min after 60 min reperfusion. In treated hearts coronary resistance increased by 16% from 1.9 +/- 0.09 to 2.2 +/- 0.09 mm/Hg/ml/min (P less than 0.01 v. untreated ischemic). To determine whether the decrease in coronary resistance with dextran could be ascribed to active vasodilation, dilator responses to 2 min hypoxia or 10(-4)M adenosine were tested in nonischemic and reperfused ischemic hearts. Dilator responses were stable in nonischemic hearts or hearts reperfused after 15 min ischemia but after 30 min ischemia the dilator response to hypoxia was reduced by 72% (P less than 0.025) and the dilator response to adenosine was eliminated (P less than 0.02). Thus the response to dextran was unlike that of a direct vasodilator. These data suggest that myocardial edema plays a significant role in maintaining increased ventricular chamber stiffness and coronary resistance during reperfusion after ischemia.