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Lung Function Tests
 
 
Lung Function Tests
Pulmonary function tests including spirometry, flow-volume loops, lung volumes and diffusion capacity can be used to diagnose and grade obstructive or restrictive lung disease.
 

Obstructive vs Restrictive Disease

 
 

Overview

  • A major role of pulmonary function testing is to distinguish between obstructive lung disease and restrictive lung disease. This may be done using simple spirometry, flow volume loops and lung volume assessment.

Obstructive Disease

  • A reduced FEV₁:FVC ratio of <0.7 is diagnostic of obstructive lung disease.
    • Pulmonary Function Test Findings

    • FEV₁ reduced (<80% predicted)
    • FVC mildly reduced
    • FEV₁:FVC ratio reduced (<0.7)
    • ‘Scooped’ or ‘dipped’ flow-volume loop
    • Obstructive Disease
    • Causes of Obstructive Disease

    • COPD
    • Asthma
    • Bronchiectasis
    • Cystic fibrosis
    • Bronchiolitis
    • α1-antitripsin deficiency
    • Severity of Obstructive Disease

      Based on FEV₁:
    • Mild - >70% predicted
    • Moderate - 60-69% predicted
    • Moderately severe - 50-59% predicted
    • Severe - 35-49% predicted
    • Very severe - <35% predicted

Restrictive Disease

  • While spirometric values such as FEV₁ and FVC can be suggestive of restrictive lung disease,  a reduced total lung capacity (TLC) of 80% predicted is diagnostic.
    • Pulmonary Function Test Findings

    • FEV₁ reduced (<80% predicted)
    • FVC reduced (<80% predicted)
    • FEV₁:FVC ratio normal (>0.7)
    • Reduced volume in flow-volume loop
    • TLC <80% predicted
    • DLCO normal (extrapulmonary) or decreased (parenchymal)
    • Restrictive Disease
    • Causes of Restrictive Disease

    • Parenchymal

    • Pulmonary fibrosis
    • Sarcoidosis
    • Atelectasis
    • Extrapulmonary

    • Pleural - pleural effusion, pneumothorax
    • Chest wall deformity - kyphosis, scoliosis, morbid obesity
    • Neurologic / neuromuscular / muscular disorder - motor neurone disease, Guillain-Barre, muscular dystrophy, myasthenia gravis
    • Severity of Restrictive Disease

      Based on TLC:
    • Mild - 70-80% predicted
    • Moderate - 60-70% predicted
    • Moderately severe - 50-60% predicted
    • Severe - <50% predicted
Last updated on January 17th, 2019
 
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