An analysis of the components of the pulmonary shunt equation: significance of the alveolar-arterial oxygen gradient, arterio-venous oxygen content difference, and mixed venous oxygen pressure.

Pulmonary shunt calculated by the Berggren method is commonly used as an indicator of pulmonary function. Although there is usually a good correlation between the shunt and the A-aDO2, other physiologic parameters involved in the shunt equation may significantly alter pulmonary function. The purpose of this study is to show the contribution of the PVO2 and a--v diff to the shunt equation. Data from eight selected patients with A--aDo2 values ranging from 300 to 395 torr and calculated shunts ranging from 6 to 35% were selected for this purpose. In patients with significant changes in PVO2 and a--v diff, the A--aDO2 is more reliable as an indicator of pulmonary function than is the calculated shunt.