Effects of cardiac oscillations on acinar gas mixing during pulmonary edema

We used a previously reported technique (Mackenzie et al., J. Appl. Physiol. 68: 2013-2018, 1990) to measure the effects of severe pulmonary edema on acinar cardiogenic gas mixing in anesthetized dogs. We also tested how increases in lung volume affected gas mixing in healthy lungs and during pulmonary edema. Cardiogenic gas mixing was evaluated by measurement of the rate of washout of xenon133 injected into an occluded pulmonary artery during apnea. The rate constant of xenon133 washout was 0.40 min-1 (+/- 0.06 SE) in the healthy lung at functional residual capacity. It decreased (P < 0.05) to 0.08 min-1 (+/- 0.03) when lung volume was raised 500 ml. Pulmonary edema was induced by injection of oleic acid (0.06 mg.kg-1) into the right atrium over a 4-min period; clinical signs of severe pulmonary edema were present after 90 min. The rate constant for xenon133 washout (0.07 +/- 0.03 min-1) was less than in the healthy lung (P < 0.05), and was not changed after lung volume was increased (P > 0.05). We conclude that, in the presence of severe pulmonary edema: (1) acinar resistance is increased and/or magnitude of cardiogenic oscillations is decreased; and (2) salutary effects of increased lung volume are not due to enhancement of cardiogenic gas mixing.