A mechanism for shifts in the diastolic, left ventricular, pressure-volume curve: the role of the pericardium.

Attempts to explain acute shifts in the pressure-volume relationship by changes in myocardial stiffness have been unsupported by animal experimentation and discouraged by calculations showing that making half the ventricle rigid would hardly account for the clinically observed upward shifts in the curve. Data collected in open-chest anesthetized dogs during volume loading with the pericardium open and closed indicate that when the pericardium is closed, left ventricular enddiastolic pressure is better predicted by right ventricular pressure than by left ventricular dimensions. These data support the hypothesis that acute, upward shift in the pressure-volume curve may be caused by an increase in pericardial pressure, in turn caused by an increase in the volume of the intrapericardial contents. This follows from the fact that measured left ventricular diastolic pressure is equal to the sum of the pressure differences accross the myocardium and the pericardium. Thus, increases in pericardial pressure raise measured ventricular diastolic pressure without change in ventricular volume: hence, an upward shift in the pressure-volume curve.