Direct assessment of right ventricular transmural pressure.

Although the measurement of transmural pressure is important, calculation of transmural pressure is complicated by the difficulties in measuring pericardial pressure. Recently, flat balloons have been proposed to measure pericardial pressure. Over a wide range of volumes, right ventricular diastolic pressure and pericardial balloon pressure were similar in diastole, suggesting that the right ventricle is unstressed at physiologic volumes and that right atrial pressure can be used to estimate pericardial pressure. To evaluate these concepts and to assess indirectly the accuracy of measuring pericardial pressure using flat balloons, six canine hearts were examined postmortem. The pericardium was removed and the hearts were submerged in cold cardioplegic solution. Balloons were inserted into the right and left ventricles, and right and left ventricular pressure-volume curves were obtained. Right ventricular transmural pressures of 2.6 +/- 0.5, 3.9 +/- 0.9, 5.9 +/- 1.4, and 8.9 +/- 2.4 mm Hg were required to distend the right ventricle to 10, 20, 30, and 40 ml, respectively. For the left ventricle, transmural pressures of 3.4 +/- 0.7, 5.4 +/- 1.2, 8.6 +/- 2.1, and 14.1 +/- 3.8 mm Hg were recorded at volumes of 10, 20, 30, and 40 ml, respectively. Although the right ventricular transmural pressures were less than the left ventricular transmural pressures over the physiologic range, right ventricular transmural pressures were always positive and increased with increments in ventricular volume. Thus the right ventricle is not unstressed over the entire range of physiologic volumes, suggesting that pericardial balloon pressures may overestimate pericardial pressure and that right atrial pressure cannot be used to estimate pericardial pressure.