Indirect measurement of end-diastolic pressure-volume relation in the in situ canine heart.

We developed a new method to estimate the end-diastolic pressure-volume relation (EDPVR) of the ejecting ventricle without directly measuring the ventricular volume. The following equation is derived from the ventricular elastance concept; Pes = Ees (Ved-Vo-Vj), where Pes is end-systolic pressure; Ees, end-systolic elastance; Ved, end-diastolic volume; Vo, an empirical constant; and Vj, ejected volume at end-systole. Therefore, under a constant preload and contractility; two sets of Pes and Vj, i.e, (Pes 1, Vj 1) and (Pes 2, Vj 2), yield an equation of Ve = (Pes 1 Vj 2-Pes 2 Vj 1)/(Pes 1-Pes 2), where Ve is effective end-diastolic volume, Ved-Vo. Repeated measurements of Ve under various levels of end-diastolic pressure (Ped) allow us to determine the EDPVR. In 8 anesthetized dogs with the chest open, we obtained two sets of Pes and Vj under a given Ped as mentioned above, one in a normally ejecting condition and the other in a clamping condition of the descending aorta to increase afterload of the left ventricle. We then calculated the Ve from the equation mentioned above. We repeatedly determined the Ve varying preload levels to obtain the EDPVR. We compared the EDPVR estimated by the present method with that directly measured by the balloon method in the arrested ventricle. These two EDPVRs were correlated very well. To compare more quantitatively, the chamber stiffness constant was obtained. The chamber stiffness constant derived from the estimated EDPVR was linearily related to that derived from the directly measured EDPVR (y = 1.043x + 0.003, r = 0.987). Furthermore, in order to test whether the EDPVR derived from our present method can detect changes in left ventricular compliance in the in situ ventricle, we obtained the EDPVRs under the three different (intact, opened, and closed) conditions of the pericardium in six dogs. The EDPVR was shifted upward in the closed condition compared with that in the intact condition, while it was shifted downward in the opened condition. Thus, the changes of the left ventricular diastolic compliance were correctly evaluated by the developed method. Therefore, we conclude that the EDPVR obtained using our indirect method is reliable to estimate the ventricular diastolic properties of the in situ heart.