Diffusion capacity of lung is increased by?
**Core Concept**
The diffusion capacity of the lung (DLCO) is a measure of the lungs' ability to transfer gas from inhaled air to the blood. It is primarily dependent on the surface area available for diffusion, the thickness of the alveolar-capillary membrane, and the solubility of the gas in the blood.
**Why the Correct Answer is Right**
One of the factors that can increase DLCO is an increase in the surface area available for diffusion. This can occur due to the presence of pulmonary edema, which increases the number of alveoli in contact with the capillaries, thereby increasing the surface area for gas exchange. Another factor that can increase DLCO is the administration of certain medications, such as aminophylline, which can increase the surface area available for diffusion by causing bronchodilation and increasing the number of alveoli in contact with the capillaries.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect, as pulmonary embolism decreases DLCO by reducing the number of alveoli in contact with the capillaries.
**Option B:** Incorrect, as chronic obstructive pulmonary disease (COPD) decreases DLCO by thickening the alveolar-capillary membrane and reducing the surface area available for diffusion.
**Option C:** Incorrect, as pneumonia decreases DLCO by increasing the thickness of the alveolar-capillary membrane and reducing the surface area available for diffusion.
**Clinical Pearl / High-Yield Fact**
Remember that DLCO is a sensitive indicator of pulmonary edema, and an increased DLCO can be a sign of pulmonary edema, even in the absence of symptoms.
**Correct Answer:** C.