17. Pulmonary Function Tests

Measurements

 

Restrictive Lung Disease

Obstructive Lung Disease

FVC

↓/Normal

FEV1

↓/Normal

FEV1/FVC

Normal/↑

TLC

↑/Normal

VC

Slightly ↓

  • DLCO: diffusing capacity for carbon monoxide. Reduced in PCP, interstitial lung disease, emphysema, pulmonary hypertension or any other process that causes pulmonary capillary bed obliteration.
  • MIF: maximum inspiratory force. Decreased in progressive neuromuscular dysfunction (e.g., spinal cord injury) and can help predict which patients need mechanical ventilation.

Diagnostic Approach

  • Obstructive defect: FEV1/FVC <70% or flow volume loop is curvilinear.
    • Asthma: improvement in FEV1 of 12% and >200ml following albuterol; obstruction is responsive to bronchodilators.
    • COPD: no improvement in FEV1 following albuterol; check DLCO, lung volume measurements. 
      • Emphysema: DLCO is low.
      • Air trapping: TLC is high.
  • Restrictive defect: TLC low.
    • DLCO low: interstitial process. 
    • DLCO normal: chest wall process such as anatomic defect, pleural pathology, or diaphragmatic weakness.
  • Isolated low DLCO: consider anemia, early ILD, pulmonary vascular disease.

 

Evans SE, Scanlon PD.  Current practice in pulmonary function testing.  Mayo Clin Proc 2003;78:758-763.

Pellegrino R, Viegi G, Brusasco V, et al.  ATS/ERS Standardization of Lung Function Testing: Interpretative strategies for lung function tests. Eur Respir J 2005;26:948-968.