the diffusion capacity of lung (DL) is decreased in all of the follow ing conditions except -

Ans. is 'b' i.e., Goodpasture's syndrome Gas diffusion tests:o Gas diffusion tests measure the amount of oxygen and other gases that cross the alveoli into the blood.o These tests evaluate how well gases are being absorbed into the blood from lungs. Gas diffusion tests include.a) Carbon monoxide diffusing capacity (transfer factor DLco)b) Arterial blood gasesCarbon monoxide diffusing capacity (DLco)o This measures how well the lung transfers a small amount of carbon monoxide into the blood(r).o Normally, in the lung; a gas has to cross the alveolar membrane, capillary# membrane to reach the blood where it combines with hemoglobin.So quiet obviously the diffusion capacity of gas depends upon -Driving pressure of the gasSurface area of alveolar capillary: membraneThickness of alveolar capillary1 membraneDiffusion coefficient of the gasRed blood cell volume.Reaction rate with hemoglobin and hemoglobin level of patient.Degree of V/Q mismatching.Decrease value of DLco is seen in -o Emphysema-Due to destruction of alveolar wall, the area of alveolar capillary membrane is decreasedo Interstitial lung disease e.g. SLE,Asbestasis pneumonia, sarcoidosis-Due to scarring of alveolar capillary membrane the area of alveolar capillar membrane is diminished.o Recurrent pulmonary emboli or primary pulmonary hypertension-Due to decrease in cross sectional area and volume of pulmonary: vascular bed. the area of alveolar capillary membrane is diminished.o Anemia-Due to decrease in volume of the blood, reduced hemoglobin is available for transfer of gases.Increased level of DLco is seen in-o Congestive heart failure-Due to increase in pulmonary blood volumeo Alveolar hemorrhage-Due to increase in hemoglobino Polycythemia-Due to increase in hemoglobino Left to right shunts-Due to increase in pulmonary volumeo Asthma