Phasic reflux of pulmonary blood flow in atelectasis: influence of systemic PO2

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Abstract
In 16 dogs ventilated with 100% O2, control blood flow to the left lung was 35 .+-. 2% of aortic flow. When left lung atelectasis was induced, left pulmonary artery flow fell to 19 .+-. 2% of aortic flow. A large retrograde component of flow developed in this pulmonary artery, suggesting that blood flows into the pulmonary arteries of both lungs during systole, but flows back out of the collapsed lung and into the uncollapsed lung during disatole. Systemic PaO2 arterial O2 tension remained above 78 mmHg. Subsequently, when the ventilation of the right lung was changed from O2 to room air, systemic PaO2 fell to 64 .+-. 3 mmHg, and atelectatic left lung flow rose from 19 .+-. 2% to 28 .+-. 2% of aortic flow. This was associated with a reduction in reflux from the ateletatic lung. The attenuation of flow to an atelectatic lung is apparently more pronounced if systemic normoxemia is maintained by adequate oxygenation of the normal lung.

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