Acute alterations in left ventricular diastolic chamber stiffness. Role of the 'erectile' effect of coronary arterial pressure and flow in normal and damaged hearts

Abstract

To separate the effects of coronary flow, perfusion pressure, and oxygen delivery on left ventricular diastolic compliance and diastolic wall thickness, isolated buffer and blood-perfused rabbit hearts with left ventricular volume controlled by a fluid-filled intraventricular balloon were subjected to the following interventions: complete global ischemia, hypoxia at constant coronary flow, hypoxia at constant coronary perfusion pressure, adenosine infusion at constant coronary flow, and at constant coronary perfusion pressure. Coronary flow, coronary perfusion pressure, left ventricular compliance curves, and diastolic epicardial circumference were measured during the 3rd minute of each intervention. Circumference changes were directly related to wall thickness changes when the isovolumic balloon was in place. Global ischemia caused a decrease in isovolumic diastolic epicardial circumference, a decrease in diastolic ventricular wall thickness, and an increase in diastolic compliance. Hypoxia with flow held constant caused an increase in diastolic circumference and a decreased diastolic compliance. Hypoxia with constant coronary perfusion pressure caused an increase in coronary flow, a further increase in diastolic epicardial circumference, and a further decrease in diastolic compliance. Hypoxia with constant coronary perfusion pressure caused an increase in coronary flow, a further increase in diastolic epicardial circumference, and a further decrease in diastolic compliance. Adenosine infusion caused an increase in coronary flow, an increase in diastolic circumference, and a decrease in diastolic compliance. Adenosine infusion with constant coronary flow caused a decrease in perfusion pressure but caused no significant change in diastolic circumference or the diastolic pressure-volume curve. The erectile properties of the myocardium (effect of coronary artery pressure and flow on diastolic stiffness) were greater at larger ventricular diastolic volumes and pressures and in the injured heart (after 90 minutes of ischemia). These studies demonstrate a substantial direct 'erectile' or 'hydraulic' effect of the coronary vasculature on left ventricular diastolic properties; such an effect can influence diastolic ventricular filling and overall cardiovascular function and should be considered in interpreting changes in ventricular diastolic pressures in both experimental and clinical situations.