flow-volume loop

Indications

• upper airway obstruction
• chronic obstructive lung disease
• reactive airway disease, i.e. asthma

Clinical significance

Characteristic patterns occur for certain respiratory disorders:

• a plateau during forced inspiration is characteristic of extrathoracic upper airway obstruction (paradoxical vocal cord motion)
• a plateau during forced expiration is characteristic of intrathoracic upper airway obstruction (tumor compressing trachea)
  • MKSAP20 offers variable intrathoracic airway obstruction
• a plateau during both forced inspiration & expiration is characteristic of a fixed upper airway obstruction such as tracheal stenosis*
• low flow rates with minimal change with bronchodilation occur with chronic obstructive lung disease
• low flow rates that improve with bronchodilation characterize reactive airway disease, i.e. asthma

* beware of inspiratory loop being rounded, but insufficiently dome shaped

Procedure

• graphic displays of lung volume & airflow.
• inspiration is represented in the flow-volume loop below the x axis

* ref shows classic flow-volume loop.

* refs show other (less useful) flow-volume loops.

Radiology

• Chest CT to confirm an intrathoracic airway obstruction
  • allows visualization of intrathoracic airways
• any patient with a focal wheeze should undergo chest CT to rule out an endobronchial lesion

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 flow-volume loop

More general terms

• pulmonary function test (PFT)
• loop