THE RIGHT AND LEFT-VENTRICULAR INTRACAVITARY AND TRANSMURAL PRESSURE-STRAIN RELATIONSHIPS

The magnitude of pericardial pressure and therefore the shape of the right ventricular end-diastolic transmural pressure-volume relationship remains controversial. To investigate ventricular compliance, eight dogs anesthetized with fentanyl were instrumented as follows. Right and left ventricular intracavitary pressures were measured with micromanometer-tipped catheters. Right and left ventricular free wall segment lengths were measured by sonomicrometry. Pericardial pressure was measured over the right and left ventricles by means of flat liquid-containing balloon transducers, and transmural pressures were calculated as the difference between intracavitary and pericardial pressures. After defining the pressure-segment length relationship by vena caval constriction followed by release and blood transfusion, the pericardium and chest were opened widely and the cardiac volume manipulation was repeated; this allowed direct measurement of transmural right ventricular end-diastolic pressure for each level of strain recorded with the chest and pericardium closed. When intracavitary right or left ventricular end-diastolic pressure was raised from zero to 20 mm Hg, the respective transmural pressures increased from 0.2 +/- 0.6 (SD) mm Hg to 2.5 +/- 1.8 mm Hg and from 0.3 +/- 0.7 mm Hg to 6.0 +/- 2.5 mm Hg. Ventricular segmental strain increased by 7.0 +/- 0.8% and 6.0 +/- 0.2%, respectively. No statistically significant differences were found between right ventricular calculated (intracavitary minus pericardial pressure) and measured (open pericardium, open chest) transmural pressures at a given strain, thereby confirming the accuracy of our pericardial pressure measurements. In addition, there was a linear relationship between the pressure measured over the right and left ventricles: right ventricular pericardial pressure = 1.00 (left ventricular pericardial pressure) - 0.53 (r = 0.98, p < 0.0005). In conclusion, the right ventricle has a small but measurable end-diastolic transmural pressure, which increases slightly over a wide range of intracavitary pressures and myocardial segmental strain. The compliance of the right ventricle is three to four times that of the left ventricle. Furthermore, the pericardial pressures measured over the right and left ventricles are similar.