PFTs consist of: 1) Spirometry 2) Lung volumes 3) Diffusion capacity
Spirometry
Stepwise Approach to PFTs
Flow-Volume Loops
Extrathoracic --> inspiratory defect Intrathoracic --> expiratory defect Fixed --> inspiratory and expiratory defect
Cutoff Values
| Severity | FEV1 (% predicted) |
|---|---|
| Mild | > 70 |
| Moderate | 60 – 69 |
| Moderately Severe | 50 – 59 |
| Severe | 35 – 50 |
| Very Severe | < 35 |
| Severity | DLCO (% predicted) |
|---|---|
| Mild | > 60 and < LLN |
| Moderate | 40 – 60 |
| Severe | < 40 |
| Other | |
|---|---|
| Bronchodilator Response (FEV1) | > 200 mL AND 12% |
| Hyperinflation | TLC > 120% predicted or >ULN |
| Gas Trapping | RV > 120% predicted or >ULN |
| ## Diffusion Capacity | |
| Low DLCO: Anemia, recent smoking, parenchymal lung disease, pulmonary hypertension. | |
| Isolated low DLCO: Consider anemia, smoking, early ILD | |
| High DLCO: Obesity, alveolar hemorrhage, polycythemia, asthma |
References
- University of Washington Practive PFTs
- 2005 ATS "Interpretative strategies for lung function tests"