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flow-volume loop

Indications: 1) upper airway obstruction 2) chronic obstructive lung disease 3) reactive airway disease, i.e. asthma Procedure: - graphic displays of lung volume & airflow. - inspiration is represented in the flow-volume loop below the x axis [2] * ref [2] shows classic flow-volume loop. * refs [3,4] show other (less useful) flow-volume loops. Clinical significance: Characteristic patterns occur for certain respiratory disorders: 1) a plateau during forced inspiration is characteristic of extrathoracic upper airway obstruction (paradoxical vocal cord motion) 2) a plateau during forced expiration is characteristic of intrathoracic upper airway obstruction (tumor compressing trachea) - MKSAP20 offers variable intrathoracic airway obstruction [1] 3) a plateau during both forced inspiration & expiration is characteristic of a fixed upper airway obstruction such as tracheal stenosis* 2) low flow rates with minimal change with bronchodilation occur with chronic obstructive lung disease 3) low flow rates that improve with bronchodilation characterize reactive airway disease, i.e. asthma * beware of inspiratory loop being rounded, but insufficiently dome shaped Radiology: - Chest CT to confirm an intrathoracic airway obstruction - allows visualization of intrathoracic airways [1] - any patient with a focal wheeze should undergo chest CT to rule out an endobronchial lesion [1] Management: - MKSAP20 does not address management of inspiratory vs expiratory wheezes, or management of fixed obstruction since only the expiratory phase of the flow-volume loop is shown [1] flow-volume loop

General

pulmonary function test (PFT) loop

References

  1. Medical Knowledge Self Assessment Program (MKSAP) 11, 14, American College of Physicians, Philadelphia 1998. 2006 - Medical Knowledge Self Assessment Program (MKSAP) 20 American College of Physicians, Philadelphia 2025
  2. Lung Function Tests. Flow-Volume Loops. MedSchool. Feb 15, 2021 https://medschool.co/tests/lung-function/flow-volume-loops
  3. Vitalograph. May 21, 2025 Spirometry - Understanding the Flow Volume Loop. https://vitalograph.com/vital-insights/respiratory-insights/spirometry-understanding-the-flow-volume-loop
  4. Karkhanis VS, Desai U, Joshi JM Flow volume loop as a diagnostic marker Lung India. 2013 Apr-Jun;30(2):166-168 PMID: 23741103 PMCID: PMC3669562 Free PMC article