Regarding the interpretation of spirometric patterns in obstructive and restrictive lung diseases, all of the following statements are correct EXCEPT:

Question

Accepted Answer

C. In restrictive lung disease, the TLC (total lung capacity) is increased due to loss of elastic recoil of the lungs.. ## Spirometric Pattern Interpretation

### Obstructive vs Restrictive Patterns

| Feature | Obstructive | Restrictive |
|---------|-------------|-------------|
| **FEV₁** | Decreased | Decreased |
| **FVC** | Normal or mildly decreased | Decreased |
| **FEV₁/FVC ratio** | <70% (reduced) | ≥70% (normal or elevated) |
| **TLC** | Increased (air trapping) | Decreased |
| **RV** | Increased | Decreased |
| **Examples** | COPD, asthma, bronchiectasis | Pulmonary fibrosis, ILD, chest wall disease |

### Key Pathophysiology

**Key Point:** The FEV₁/FVC ratio is the gold standard discriminator between obstructive and restrictive patterns. A ratio <70% indicates obstruction; ≥70% indicates restriction (or normal).

**High-Yield:** In **restrictive disease**, TLC is **decreased** (not increased) because:
1. Loss of elastic recoil (fibrosis) reduces lung compliance
2. Chest wall stiffness (kyphoscoliosis) limits expansion
3. Neuromuscular weakness (myasthenia) reduces inspiratory force

All these mechanisms reduce the maximum volume the lungs can hold.

**Clinical Pearl:** In **obstructive disease**, TLC is **increased** due to air trapping from small airway collapse during expiration, leading to residual volume elevation.

### Why Option 4 is Incorrect

Option 4 states that TLC is **increased** in restrictive disease — this is fundamentally wrong. Restrictive diseases reduce TLC. This is the **only false statement** among the four options.

[cite:Harrison 21e Ch 246]

Answer

A. In obstructive airway disease, the FEV₁/FVC ratio is reduced below 70%, whereas in restrictive disease the ratio remains normal or elevated.

Answer

B. Restrictive pattern shows decreased FVC with a normal or elevated FEV₁/FVC ratio, typically seen in pulmonary fibrosis and chest wall disorders.

Answer

D. Obstructive pattern is characterized by decreased FEV₁ with a reduced FEV₁/FVC ratio, commonly observed in COPD and asthma.

Regarding the interpretation of spirometric patterns in obstructive and restrictive lung diseases, all of the following statements are correct EXCEPT:

Explanation

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