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Lung Function Tests
Lung Function Tests

Flow-Volume Loops

February 15th, 2021


Flow-volume loops are produced by asking the patient to breath out then in as forcefully as possible, and may reveal a characteristic pattern suggestive of restrictive, obstructive or other pulmonary disease.
  • Procedure

    Performed with the patient breathing into a pneumotachograph:
  • Maximal breath in
  • Forced expiration as hard and fast as possible
  • Maximal breath in as fast as possible
  • Interpretation

  • Normal - symmetric and convex inspiratory limb, with linear expiratory limb
  • Obstructive - 'dipping' or 'steeple' pattern, with reduced flow and expiratory prolongationCOPD, asthma, bronchiectasis, CF, bronchiolitis, α1-antitrypsin deficiency
  • Restrictive - reduced overall volume, with grossly normal shapePulmonary fibrosis, sarcoidosis, chest wall deformity, neuromuscular
  • Fixed upper airway obstruction - flattening of inspiratory and expiratory limbsTracheal stenosis, goitre
  • Variable extrathoracic obstruction - flattening of inspiratory limb only, with no impairment of expirationUnilateral vocal cord paralysis
  • Variable intrathoracic obstruction - diminished expiratory limb with no impairment of inspirationTracheomalacia
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