Left Ventricular Filling and Diastolic Pressure-Volume Relations in the Conscious Dog

In 7 conscious dogs, left ventricular diastolic volume (V) was estimated by taking biplane cineradiographs with the left ventricular cavity previously outlined by permanent radiopaque markers. Left ventricular pressure (P) was measured with an implanted miniature transducer. There were two rapid filling periods during early and late diastole; little filling occurred during the middle third of diastole (diastasis). The diastolic pressure-volume relationship was approximately exponential and was fitted by the equation P=−a+be, where, a, b, and c are positive constants; the relationship appeared to be determined principally by the elastic properties. The effects of infusions of saline, isoproterenol, calcium gluconate, and methoxamine suggested that viscous and inertial properties are also important determinants of diastolic left ventricular mechanics. No significant series viscosity was observed. Plastic properties were not detected. The elastic properties were not affected by agents having a positive inotropic effect. End-diastolic pressure often differed from that predicted by the exponential equation above, suggesting that it is not a reliable index of enddiastolic volume and left ventricular compliance.