Carbon monoxide diffusion capacity decreases in all, Except:

Ans. is 'c' Alveolar hemorrhage (Ref Harrison, 17/e p 1591-1592 & 16/e, p 1505 (15/e, p 1453)).Measurement of DLCO (diffusion capacity of CO) is frequently used to assess the functional integrity of the alveolar capillary membrane.Disease that affect solely the airways generally do not affect DLCO whereas disease that affect the alveolar walls or pulmonary capillary bed will have an effect on DLCO.Three main categories of disease that are associated with lowered DLCO (all of these diseases affect alveolar capillary bed). Interstitial lung disease* - (Scarring of alveolar capillary bed occurs in interstitial lung disease, this diminishes the area of alveolar capillary bed). Emphysema* - (Alveolar walls are destroyed in emphysema so surface area of alveolar capillary bed is diminished).Primary pulmonary hypertension* - (There is decrease in cross sectional area of pulmonary vascular bed).Recurrent pulmonary emboliDisease associated with increased DLCO.Congestive heart failure*Alveolar hemorrhage*