 The aim of our study was to delineate the effects of orally administered sildenafil on diffusion capacity absolute value. The significance of this information was twofold. First, it would be helpful clinically to determine the contribution of a pulmonary vasodilator to the change in DLCO to separate this effect from a true clinical change. Second, sildenafils effect on gas exchange may lead to modifications in therapy such as changes in oxygen flow delivered to patients. 