CHANGES IN CANINE LEFT-VENTRICULAR SIZE AND CONFIGURATION WITH POSITIVE END-EXPIRATORY PRESSURE

Previous studies have shown that left atrial pressure increases when measured relative to pleural pressure during positive end-expiratory pressure (PEEP). The authors studied the factors leading to this increase in anesthetized mechanically ventilated dogs. Cardiac output was maintained nearly constant before and during PEEP, and heart rate did not change. Left atrial pressure measured relative to pleural pressure rose by 2.5±0.5 mm Hg (mean ± SE) during PEEP. Pericardial pressure did not rise more during PEEP than did pleural pressure, indications that there was a true increase in transmural left atrial pressure. With PEEP there was no change in left ventricular diastolic volume as measured by cineangiography and cinefluorography of lead markers implanted in the subendocardium. Left ventricular contractile function, as measured by ejection fraction, also was unchanged. Analysis of the ventricular axes showed an increase in the ratio of septal-lateral to apex-base and anterior-posterior axes with PEEP, indicating a shape change in left ventricle. Plots of left ventricular volume against left atrial transmural pressure confirmed that there was a shift in the left ventricular pressure-volume curve during PEEP. Thus, the rise in left atrial transmural pressure during PEEP appears to have been caused by a change in left ventricular diastolic pressure-volume properties. The authors suggest that these changes in the left ventricle may be related to the effects of PEEP on the right ventricle which, in turn, influence the left ventricle.