Spirometry Comparison: How do FEV1/FVC ratio, FVC, and Total Lung Capacity (TLC) differentiate Obstructive vs. Restrictive lung disease?
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Spirometry Diagnostic Criteria:
| Parameter | Obstructive (Asthma, COPD) | Restrictive (IPF, Sarcoidosis) |
|---|---|---|
| FEV1/FVC Ratio | < 0.70 (< 70%) (Hallmark!) | Normal or Increased ($\ge 0.70$) |
| FEV1 | Markedly $\downarrow\downarrow$ | $\downarrow$ (proportionate to FVC) |
| FVC | Normal or slightly $\downarrow$ | Markedly $\downarrow\downarrow$ |
| TLC (Gold Standard) | Increased (Air trapping) | $\downarrow < 80%$ predicted |
| Residual Volume (RV) | Increased | Decreased |
Rate recall difficulty to calibrate repetition: