Redistribution of pulmonary blood flow during experimental air embolism

The effect of experimental pulmonary air embolism on pulmonary perfusion was studied in 14 closed-chest, anesthetized, paralyzed dogs. During constant-rate air infusion through a femoral vein, regional distribution of lung perfusion was measured with radioactive xenon boluses injected via a catheter positioned distally to the pulmonary valve. The results obtained from nine prone dogs indicate a large shift of blood perfusion toward the dependent areas of the lung during air embolism; the results obtained in five supine dogs were similar but statistically less significant. Concomitant with the perfusion shift, pulmonary arterial pressure increased, more acutely during the first 30 min. Switching from air to N2O-O2 ventilation accentuated the perfusion shift, which may be reverted towards control values by intravenous administration of 0.4 mg of isoproterenol. Other alterations observed included moderate increase of pulmonary resistance and decrease of cardiac output. It is concluded, based on these results and an adjunct model study, that the observed changes were predominantly due to aggregation of air bubbles in the upper part of the pulmonary vasculature.