A 68-year-old woman with idiopathic pulmonary fibrosis (IPF) and a 35-year-old man with moderate asthma both undergo spirometry. Both show reduced FEV₁ (65% and 60% predicted, respectively). Which finding best distinguishes the restrictive pattern of IPF from the obstructive pattern of asthma?

Explanation

## Discriminating Restrictive (IPF) from Obstructive (Asthma) Patterns ### Core Distinction **Key Point:** The FEV₁/FVC ratio and TLC together form the diagnostic signature: - **Restrictive disease (IPF):** Reduced FEV₁/FVC is *preserved* (≥ 0.70) because both FEV₁ and FVC fall proportionally; TLC is reduced due to loss of lung parenchyma. - **Obstructive disease (asthma):** FEV₁/FVC is reduced (< 0.70) because FEV₁ falls disproportionately; TLC is normal or increased due to air trapping. ### Comparison: IPF vs Asthma Spirometry | Parameter | IPF (Restrictive) | Asthma (Obstructive) | | --- | --- | --- | | **FEV₁** | ↓ | ↓ | | **FVC** | ↓ | Normal or ↓ | | **FEV₁/FVC** | Normal or ↑ (≥ 0.70) | ↓ (< 0.70) | | **TLC** | ↓ | Normal or ↑ | | **RV** | Normal or ↓ | ↑ | | **DLCO** | ↓↓ (often < 40%) | Normal or mildly ↓ | | **Mechanism** | Fibrosis → ↓ elastic recoil, ↓ compliance | Small-airway collapse → air trapping | **High-Yield:** In IPF, the lungs are stiff and small; both FEV₁ and FVC shrink together, so the ratio stays normal. In asthma, air traps in distal airways, so FEV₁ falls more than FVC, and the ratio drops. ### Why This Patient Has Restriction The IPF patient has pulmonary fibrosis causing: 1. Loss of alveolar units and reduced lung compliance 2. Proportional reduction in both FEV₁ and FVC 3. Preserved FEV₁/FVC ratio (often > 0.75) 4. Reduced TLC (typically 50–70% predicted) 5. Markedly reduced DLCO (hallmark of IPF) The asthma patient has small-airway obstruction causing air trapping, so FEV₁ drops more than FVC, FEV₁/FVC falls, and TLC rises. **Clinical Pearl:** IPF patients often have a restrictive pattern with *preserved* or even *elevated* FEV₁/FVC ratio—a common trap. The diagnosis hinges on reduced TLC and markedly reduced DLCO (< 40% predicted). ### Why Other Options Are Wrong - **Increased RV and increased TLC (Option 0):** This is the obstructive pattern (asthma), not restrictive. IPF shows reduced TLC and normal or reduced RV. - **Reduced FEV₁/FVC with normal or increased TLC (Option 1):** This is the obstructive pattern (asthma), not restrictive. IPF has reduced TLC. - **Reduced FEV₁/FVC with reduced TLC (Option 2):** While TLC is indeed reduced in IPF, the FEV₁/FVC ratio is *preserved* (not reduced) because both FEV₁ and FVC fall proportionally. This option describes a mixed pattern or severe restriction with preserved ratio—not the classic IPF signature.