The Pericardium Substantially Affects the Left Ventricular Diastolic Pressure‐Volume Relationship in the Dog

We instrumented six dog hearts in vivo to study the relationship between left and right ventricular diastolic pressures with the pericardium closed and open. We measured left ventricular septum-to-free wall and anterior-posterior and right ventricular septum-to-free wall dimensions with implanted ultrasonic crystals, together with simultaneous high fidelity pressures. We varied diastolic pressure by infusing or withdrawing Mood or by increasing right ventricular afterload with transient pulmonary artery constriction. Although left and right ventricular diastolic pressures always correlated, this correlation was significantly higher with the pericardium closed than open. We fit left ventricular dfautolic pressure to an equation whkh included first order right ventricular pressure and fourth order left ventricular dimension terms. With the pericardium closed, the right ventricular pressure term dominated; with the pericardium open, left ventricular dimension terms dominated. Therefore, with the pericardium closed, right ventricular pressure was a more powerful predictor of left ventricular pressure than were left ventricular dimensions. In addition, the left ventricle appears much more compliant with the pericardium open. These results led us to modify the traditional view of the diastolic left ventricle as an unconstrained elastic shell of myocardium and replace it with a concept of the diastolic heart as a composite shell of stiff pericardium and compliant muscle, divided into subcompartments (ventricles) by the relatively compliant septum. The influence of the pericardium on the diastolic pressure-volume relationship should be considered in experiments on animals and patient management when the pericardium is open or closeab.