Diastolic Pressure-Segment Relations during Early and Later Stages of Experimental Chronic Volume Overload in Dogs

Although the pericardium can exert a restraining effect on filling of the normal left ventricle, it is uncertain to what extent the pericardium influences left ventricular filling during chronic volume overload. We measured left and right ventricular pressure and left ventricular segment dimension before and after pericardiectomy over a range of left ventricular end-diastolic pressure from <5 to >20 mm Hg in open-chest dogs with volume overload due to a prior systemic arteriovenous fistula. In six dogs studied "early" (7-9 days) during volume overload, left ventricular end-diastolic dimension was significantly larger and right ventricular end-diastolic pressure lower following pericardiectomy at matched levels of left ventricular end-diastolic pressure greater than 10-12 mm Hg. In six dogs studied "late" (34-50 days) during chronic volume overload, there were no significant changes in left ventricular end-diastolic dimension after pericardiectomy at comparable levels of end-diastolic pressure. To account for the influence of changes in right ventricular enddiastolic pressure after pericardiectomy, we also compared left ventricular end-diastolic dimensions before and after pericardiectomy at matched "corrected" left ventricular end-diastolic pressure [(left ventricular end-diastolic pressure) — (right ventricular end-diastolic pressure X interventricular septal surface area/total left ventricular surface area)]. This "correction" of the left ventricular enddiastolic pressure did not significantly alter the results in either the "early" or "late" group. These results indicate that restraint to filling by the pericardium in this model of volume overload is present early but becomes markedly diminished during later phases. (Circ Res 50: 501-509, 1982)