Pericardial and Ventricular Pressure

In anesthetized open-chest and closed-chest dogs subjected to plethora and hemorrhage, pressures were measured simultaneously in the right atrium, right and left ventricles, and the pleural and pericardial spaces. It was found that an increase in ventricular end-diastolic pressure above approximately 1 mm. Hg was associated with a rise in pericardial pressure of nearly the same amount. Thus, the practice of defining "effective" ventricular end-diastolic pressure as the difference between the ventricular and intrapleural pressure gives erroneous values when ventricular end-diastolic pressure is greater than a few mm. Hg. The true ventricular transmural pressure is the difference between ventricular end-diastolic and pericardial end-diastolic pressure and has a value of no more than 2 or 3 mm. Hg under all except the most abnormal circumstances. When ventricular end-diastolic pressure is greater than a few mm. Hg, the pericardial pressure at the end of systole is likewise elevated, but to a lesser degree. Thus, when ventricular end-diastolic pressure is elevated, the measured ventricular end-systolic pressure is greater than the pressure developed by ventricular muscular contraction because end-systolic pressure is the algebraic sum of the pressure developed by ventricular muscular contraction and the pressure in the pericardial space. This error in ventricular systolic pressure may be relatively large for the right and small for the left ventricle. Pericardial pressure decreases during ventricular systole, lowers the pressure on the outside of the atria, and thus, tends to draw blood into the right atrium during ventricular systole.