Pulmonary Function Tests (PFTs)¶
Peter Edmonds
Full PFTs include:¶
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Spirometry: FVC, FEV1, with or without bronchodilator
- Patients with new shortness of breath, chronic cough, or upper airway obstruction
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Plethysmography: TLC, RV
- Evaluation of restrictive diseases (ILD, neuromuscular) or hyperinflation (COPD, asthma)
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Diffusion (DLCO) can be added to plethysmography
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'Full PFTs' = Spirometry + Plethysmography + DLCO
Tips for ordering:¶
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Initial diagnostic workup: Full PFTs with bronchodilator challenge
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Chronic Lung disease: Spirometry to track FEV1/FVC over time ± DLCO to evaluate ILD
Interpretation:¶
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Distinguish between obstructive and restrictive disease
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FEV1/FVC \< 0.7 indicates obstructive disease
- Normal to increased FVC & TLC is consistent with isolated obstructive disease
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TLC \< 80% is diagnostic of restrictive disease
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Reduced FVC is suggestive, but not diagnostic of restrictive disease
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FEV1 commonly too but FEV1/FVC ratio is normal in isolated restrictive disease
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Decreased FEV1/FVC and TLC suggests a mixed obstructive and restrictive picture
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Assess DLCO -- abnormal is \<75%
- Decreased DLCO can help differentiate between causes of obstructive or restrictive PFTs
Causes of common abnormalities:¶
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Obstruction
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Decreased DLCO: COPD, CF, bronchiectasis
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Normal DLCO: asthma, early stages of COPD or CF
- Asthma: spirometry may be normal, +bronchodilator response (an increase in FEV1 by 12% and 200ml after bronchodilator), +methacholine challenge
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Though we use FEV1/FVC to diagnose, we track disease severity using FEV1
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Restriction:
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Decreased DLCO: ILD
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Normal DLCO: pleural disease, chest wall (obesity, scoliosis), neuromuscular disorders
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Decreased DLCO: If PFTs otherwise normal consider pulmonary vascular disease, pulmonary edema, or mixed obstructive/restrictive disease (pseudo-normalization of PFTs)