Effect of Regional Hypoxia on the Distribution of Pulmonary Blood Flow in Man

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Abstract
In ten patients with chronic lung disease unilateral airway hypoxia was produced by having them breathe 100% nitrogen administered for seven minutes via a Carlens catheter while the other lung received 100% oxygen. The partition of pulmonary arterial blood flow between the two lungs was determined by radioisotope scanning following intravenous injection of I131 macroaggregated human serum albumin (MAA) both during bilateral air breathing and unilateral hypoxia. Unilateral hypoxia produced a 42% decrease in pulmonary blood flow to the hypoxic lung due to ipsilateral vasoconstriction. The response to N2 was greater when given to the diseased lung, suggesting that the pulmonary vascular bed of the involved lung was incapable of accepting a large increase in the proportion of the cardiac output because the vascular bed was already compromised by disease. Ventilation on the hypoxic side increased by 1.4 liters/min while there was no change on the side receiving 100% oxygen. Since unilateral hypoxia produced both a decreased blood flow and an increased ventilation, it is suggested that the lung is capable of altering regional perfusion and ventilation in a manner ideally suited to minimize the change in alveolar and pulmonary capillary oxygen tension.