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Pulmonary Function Tests (PFTs)

Madelaine Behrens

Full PFTs include:

  • Spirometry: FVC, FEV1, with or without bronchodilator

    • Patients with new shortness of breath, chronic cough, or upper airway obstruction

  • Plethysmography: TLC, RV

    • Evaluation of restrictive diseases (ILD, neuromuscular) or hyperinflation (COPD, asthma)

  • Diffusion (DLCO) can be added to plethysmography

  • 'Full PFTs' = Spirometry + Plethysmography + DLCO

Tips for ordering:

  • Initial diagnostic workup: Full PFTs with bronchodilator challenge

  • Chronic Lung disease: Spirometry to track FEV1/FVC over time ± DLCO to evaluate ILD

Interpretation:

  • Distinguish between obstructive and restrictive disease

    • FEV1/FVC \< 0.7 indicates obstructive disease

      • Normal to increased FVC & TLC is consistent with isolated obstructive disease

    • TLC < 80% or < LLN (ATS) is diagnostic of restrictive disease

      • Reduced FVC is suggestive, but not diagnostic of restrictive disease

      • FEV1 commonly too but FEV1/FVC ratio is normal in isolated restrictive disease

    • Decreased FEV1/FVC and TLC suggests a mixed obstructive and restrictive picture

    • Decreased FVC in restriction or air trapping, RV and FRC with restriction, RV and FRC with air trapping

    • ERV ± FRC ̄ in obesity

  • Assess DLCO -- <LLN (ATS) or <80% (GOLD) is low

    • Decreased DLCO can help differentiate between causes of obstructive or restrictive PFTs
    • DLCO >120%: LàR shunt, alveolar hemorrhage, polycythemia
    • Normal DLCO + obstruction: asthma, early COPD/CF
    • Normal DLCO + restriction: pleural disease, chest wall (obesity, scoliosis), neuromusculardisorders)
    • Low DLCO + obstructionàemphysema, CF, bronchiectasis
    • Low DLCO + restrictionàparenchymal lung disease, lung resection
    • Low DLCO + normal spirometry: anemia, early ILD, pulmonary edema, mixed obstruction/restriction pattern (pseudonormalization of PFTs)

  • Bronchodilator response:

    • Asthma: spirometry may be normal, +bronchodilator response (an increase in FEV1 by 12% and 200ml after bronchodilator), +methacholine challenge

    • Though we use FEV1/FVC to diagnose, we track disease severity using FEV1