PERICARDIAL DISEASE Left ventricular pressure-volume relations shift to the left after long-term loss of pericardial restraint

The short-term effect of pericardiectomy is to shift the in vivo left ventricular (LV) pressure-volume curve to the right. We studied nine weight-matched pairs of male guinea pigs 28 to 39 days (mean 35) after complete pericardiectomy or sham thoracotomy to determine the long-term effects of pericardiectomy on LV pressure-volume relations. Hemodynamic and in vitro LV pressure-volume data were collected in matched pairs on the same day, 2 to 3 hr after catheter placement and recovery from anesthesia. Cardiac output was measured by the microsphere reference sample method. Postsurgical weight gain was similar in both groups: 823 + 6 (mean + SD) to 925 + 6 g in the pericardiectomy group and 829 7 to 927 + 7 g in the sham thoracotomy group. We found no difference in LV weight: 1.555 ± 0.145 g in the pericardiectomy group vs 1.564 + 0.148 g in the sham thoracotomy group, nor any difference in heart rate, mean arterial, right atrial, or left ventricular end-diastolic pressures, cardiac outputs, or stroke volumes (p = NS). LV pressure-volume relations, however, were shifted to the left in the pericardiectomy group (p < .005). At 10 mm Hg, LV volume in the pericardiectomy group (0.85 + 0.22 cc) was less than that in the sham thoracotomy group (1.02 + 0.15 cc; p < .025). The LV stress-elastic modulus relationship was not different between groups (p > .30). One month after pericardiectomy, LV pressure-volume relations in vitro were shifted to the left without a change in LV weight, LV elastic modulus, or hemodynamics. We speculate that this shift compensates for the lack of pericardial restraint and returns LV volume Circulation 68, No. 1, 155-163, 1983. MORE than 50 years ago, Wilson and Meek' demonstrated a constraining effect on the heart by the pericardium at physiologic filling pressures. Although several investigations have suggested that pericardial constraint of the heart is important only at elevated filling pressures,24 others have demonstrated that the pericardium affects the diastolic pressure-volume relationship of the left ventricle both at normal and elevated filling pressures.58 One concludes from these data that short-term pericardial removal shifts the left ventricular pressure-volume relationship to the right. Glantz and Parmley9 stressed the importance of pericardial restraint to left ventricular performance, and Misbach and Glantz'0 later demonstrated this importance. Short-term pericardial removal shifts the left ventricular function curve upwards; stroke volume is From the Heart Research Laboratory, Division of Cardiology, Department of Medicine and the Department of Physiology, Oregon Health Sciences University, Portland. Supported in part by U.S.P.H.S. NRSA Fellowship HL06409, PPG HD10034, American Heart Association, Oregon Affiliate, and the N. L. Tartar Trust Fund. Address for correspondence: Jeffrey D. Hosenpud, M.D., Oregon Health Sciences University, Division of Cardiology, 3181 S.W. Sam Jackson Park Rd., Portland, OR 97201. Received Jan. 3, 1983; revision accepted March 24, 1983. Vol. 68, No. 1, July 1983 and hemodynamics to normal in vivo. increased at any given filling pressure. Nevertheless, Holt" observed that "human beings with congenital absence of the pericardium and pericardiectomized animals survive indefinitely and appear to carry out their gross physiologic functions in a more or less normal manner." Evaluation of heart size by x-ray in these same groups has produced conflicting results. 12-15 Studies of myocardial or circulatory adjustments to long-term pericardial removal have not been reported. Accordingly, we investigated the effect of 1 month of pericardial removal on left ventricular pressure-volume relations and hemodynamics in the guinea pig.