Lung Function Tests
Lung Function Tests

Flow-Volume Loops



  • 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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