Coronary Hypertension and Diastolic Compliance in Isolated Rabbit Hearts

Acute pulmonary edema during hypertensive crisis has been attributed to acute left ventriculár systolic failure secondary to increased afterload. We tested the hypothesis that the increase in coronary artery perfusion pressure associated with systemic hypertension could also contribute to increased left ventricular filling pressures by acutely increasing coronary intravascular volume and decreasing left ventricular diastolic compliance. Isolated isovolumic (balloon in left ventricle) normal rabbit hearts (n = 13) with pericardium removed and right ventricle vented were blood perfused at an initial coronary artery perfusion pressure of 100 mm Hg; left ventricular balloon volume was adjusted to produce an initial left ventricular end-diastolic pressure of 15±1 mm Hg; left ventricular systolic pressure was 102±3 mm Hg. When coronary perfusion pressure was increased to 130±l mm Hg to simulate a hypertensive crisis, coronary flow increased from 2.0±0.2 to 3.0±0.2 ml/min/g left ventricle (p < 0.001), left ventricular systolic pressure increased to 116±4 mm Hg, and isovolumic left ventricular end-diastolic pressure increased to 21±1 mm Hg (p < 0.001), which indicated a decrease in left ventricular diastolic compliance. When coronary perfusion pressure was decreased to a physiological level of 70 mm Hg, coronary flow rate decreased to 1.4±0.1 ml/min/g left ventricle (p < 0.001), left ventricular systolic pressure fell to 82±4 mm Hg, and left ventricular end-diastolic pressure fell to 14±1 mm Hg (p < 0.001). The left ventricular diastolic pressure-volume curve was shifted upward and to the left at a coronary perfusion pressure of 130 mm Hg relative to the curve generated at a coronary perfusion pressure of 70 mm Hg, confirming that left ventricular diastolic compliance decreased when coronary perfusion pressure was elevated. Coronary hypertension also resulted in an increase in left ventricular wall thickness as assessed by two-dimensional echocardiogram. Mean endocardial-to-epicardial wall thickness was 5.1±0.6 mm at a coronary perfusion pressure of 130 mm Hg and 4.1±0.4 mm at a coronary perfusion pressure of 70 mm Hg (p < 0.05). Neither peak negative rate of change of pressure (-dP/dt) nor the exponential time constant of ventricular relaxation changed when coronary perfusion pressure was decreased from 130 to 70 mm Hg, which suggests that early diastolic relaxation was unaffected over the range of coronary perfusion pressure studied. The correlation between coronary hypertension, decreased left ventricular diastolic compliance, and increased wall thickness in the normal isolated isovolumic blood-perfused rabbit heart suggests that coronary vascular turgor may be a significant factor altering diastolic compliance of the left ventricle during acute hypertension.