Flow-Volume Loops
February 15th, 2021
Overview
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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