<prompt> Carbon monoxide diffusion capacity is decreased in all, except:EmphysemaPrimary pulmonary hypertensionAlveolar haemorrhageInfiltrative lung disease  <response>: Flows remain normal, as does the diffusion capacity of the lung for carbon monoxide DlCO, unless obstructive sleep apnea which often accompanies obesity and associated chronic intermittent hypoxemia have induced pulmonary arterial hypertension,in which case DLCO may be low. 