Diffusion capacity of carbon monoxide is decreased in all except:
Polycythemia
Interstitial lung disease
Emphysema
Pulmonary vascular disease
Ans: A. Polycythemia(Ref Ganong 25/e p635. 24/e p635)Diffusion capacity of carbon monoxide is increased in polycythemia.Diffusing capacity of lung:Directly propoional to surface area of alveolo-capillary membrane.Inversely propoional to alveolo-capillary membrane thickness.Diffusing capacity for- CO (DICO):Measured as an index of diffusing capacity.Due to diffusion-limited uptake. Factors Affecting DLCOIncreased DLCODecreased DLCOExerciseSupine positionMuller maneuver (inspiration against closed mouth & nose after forced expiration)Pulmonary hemorrhagePolycythemiaLeft-to-right shunt (e.g. atrial septal defectdeg)ObesityAsthmaChronic bronchitis without major'PregnancyPost-exerciseStandingValsalva maneuveLung resectionPulmonary emphysemaPulmonary emphysema hypeension & chronic venous thromboembolism)Interstitial lung diseasesAnemiaDrugs: Amiodarone, bleomycin, Pulmonary lymphangitic carcinomatosis