Vascular pressures and passage of gas emboli through the pulmonary circulation

Anesthetized dogs received venous air infusions at 0.35 ml.kg-1.min-1. In 60% of a group of 15 dogs, venous bubbles spilled over into the arterial circulation and were detected with the ultrasound Doppler technique. The pulmonary vascular pressure gradient (pulmonary artery pressure-pulmonary venous pressure or left atrial pressure) measured at the instant that spillover occurred was 34.7 +/- 4.7 mmHg. In a 2nd group of dogs we raised the pulmonary vascular pressure gradient before the venous air infusions to achieve spillover of bubbles 100% of the time. The resultant pressure gradient at the time of spillover of venous bubbles was 52.0 +/- 2.0 mmHg (P less than 0.05). It is concluded that venous bubbles can cross the lungs of anesthetized dogs when the driving pressures are sufficient to overcome the normal filtering function.