Changes in canine left ventricular size and configuration with positive end-expiratory pressure.

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Abstract
Left atrial pressure increases when measured relative to pleural pressure during positive end-expiratory pressure (PEEP). The factors leading to the increase was studied 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; there was a true increase in transmural left atrial pressure. With PEEP left ventricular diastolic volume did not change as measured by cineangiography and cinefluorography of lead markers implanted in the subendocardium. Left ventricular contractile function, as measured by ejection fraction did not change. 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 the 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. The rise in left atrial transmural pressure during PEEP appears to be due to a change in left ventricular diastolic pressure-volume properties. Apparently the changes in the left ventricle may be related to the effects of PEEP on the right ventricle which, in turn, influence the left ventricle.