Gas exchange abnormalities in diffuse lung disease.

Pulmonary gas exchange was evaluated in 23 patients with diffuse infiltrative lung disease and 23 patients with chronic obstructive lung disease by measuring alveolar-arterial gradients for oxygen at three levels of oxygenation together with the single breath carbon monoxide diffusing capacity and the alveolar dead space. Results were compared with similar data from 37 normal subjects. “True” right-left shunt and shunt effects due to ventilation-perfusion disturbances were calculated from the alveolar-arterial oxygen gradients. Although patients with diffuse infiltrative lung disease and chronic obstructive lung disease had increased true shunting and increased ventilation-perfusion shunt effect, increased true shunting predominated in those with diffuse infiltrative lung disease and increased ventilation-perfusion shunt predominated in those with chronic obstructive lung disease. Increased alveolar dead space was present in both disease groups. Among the patients with chronic obstructive lung disease, th...