Influence of the pericardium on left ventricular diastolic pressure-volume curves in dogs with sustained volume overload.

The pericardium is largely responsible for displacement of the left ventricular diastolic pressure-volume curve observed after acute volume loading in dogs. Likewise the pericardium has been considered likely to play a role in displacement of the curve in patients with acute cardiac failure and in shifts following manipulation of afterload. This study was designed to examine the influence of the pericardium on the diastolic pressure-volume relation of the left ventricle when volume load is more sustained, a setting relevant to observations made in patients with heart failure. We measured left ventricular pressure and volume in six conscious dogs with sustained volume overload (mean left ventricular end-diastolic pressure 21 mm Hg, left ventricular end-diastolic volume 149% of the upper limit of normal for our laboratory) produced by aortocaval shunt created 7 to 29 days earlier. Simultaneous left ventriculograms and pressures were obtained before and during nitroprusside infusion with the pericardium intact and in four dogs the studies were repeated 7 to 15 days after pericardiectomy. In all six dogs with intact pericardium, nitroprusside displaced the entire pressure-volume curve downward whereas after pericardiectomy, the pressure-volume data points obtained before and during nitroprusside infusion fell on a single curve. These results were similar to those previously reported for acute volume overload. Nitroprusside did not alter the time course of left ventricular pressure fall during the isovolumic period of diastole either before pericardiectomy (28.8 +/- 10.2 sec,-1, 28.4 +/- 11.9 sec-1) or after (28.8 +/- 6.7 sec-1, 26.1 +/- 7.2 sec-1). These data indicate that in dogs subjected to volume overload sustained for periods of up to 29 days, the pericardium affects the left ventricular diastolic pressure-volume curve and contributes to the elevation of left ventricular filling pressure through upward displacement of this curve.