Positional Hypoxemia in Unilateral Lung Disease

BODY position may affect gas exchange by altering the matching of ventilation to perfusion within the lungs._{1 2 3} In normal subjects breathing normally, both blood flow and ventilation are greater in the dependent lung zones. When subjects breathe deeply so that lung volume falls below that present at the end of normal expiration, the nondependent lung zones are preferentially ventilated.₄ These considerations may assume clinical importance in unilateral lung disease, in which alterations in lung volume and regional perfusion complicate the predictability of the gravitational effects on gas exchange.₅ We have encountered positionally related cardiac arrhythmias and dyspnea induced by lying. . .