A Patient with history of shoness of breath has Decreased FEV1/FVC Ratio, Normal DLCO. A 200 ml increase in baseline FEVI is observed 15 minutes after administration of bronchodilators. The likely diagnosis is

**Core Concept**
The question tests the understanding of pulmonary function tests, specifically the interpretation of FEV1/FVC ratio, DLCO, and the response to bronchodilators. **Chronic obstructive pulmonary disease (COPD)** and **asthma** are key considerations when interpreting these tests.

**Why the Correct Answer is Right**
A decreased FEV1/FVC ratio indicates an obstructive lung disease. The significant increase in FEV1 after bronchodilator administration suggests reversibility of the obstruction, which is more characteristic of **asthma**. Normal DLCO helps to rule out a significant restrictive or parenchymal component.

**Why Each Wrong Option is Incorrect**
**Option A:** Would be incorrect if it suggested a diagnosis that does not typically show reversibility with bronchodilators.
**Option C:** Might represent a condition without significant reversibility or might not fit the pulmonary function test pattern described.
**Option D:** Could be a condition that does not match the obstructive pattern with reversibility seen here.

**Clinical Pearl / High-Yield Fact**
The key point here is the reversibility of the obstructive defect with bronchodilators, which is a hallmark of **asthma**. Remember, an increase of 200 ml in FEV1 is significant and indicates a positive response to bronchodilators.

**Correct Answer:** D. Asthma.

✓ Correct Answer: A. Asthma