Variable extrathoracic airway obstruction
The
pattern of the expiratory flow-volume curve is normal, but the inspiratory
flow reaches a low plateau value. This pattern is characteristic
of variable extrathoracic airway obstruction (an upper airway abnormality
which may cause airway obstruction), for example due to paralysis
of the vocal cords. Typically the FVC and FEV1
are in the normal range, as there is no intrathoracic airway obstruction,
and the high pressure in extrathoracic airways distends the airway
(see literature),
unless there is fixed obstruction. However, the FIV1
and FIV1/VC are typically
abnormally low. Also shown is the flow-volume loop during normal
tidal breathing.
Poor co-operation does not lead to reproducible curves. In general, therefore, if the patient appears to produce satisfactory efforts leading to a reproducible flow-volume curve with an abnormal pattern, take this seriously. Check carefully whether there is an inspiratory or expiratory stridor.
See also:
Flow-volume curve during tidal
breathing
Fixed large airway obstruction
Extrathoracic
airway obstruction:
Miller RD, Hyatt RE. Obstruction lesions of larynx
and trachea: clinical and physiologic characteristics. Mayo
Clin Proc 1969; 44: 145-161.
Miller RD, Hyatt RE. Evaluation of obstructing lesions of
the trachea and larynx by flow-volume loops. Am Rev Respir Dis
1973; 108: 475-481.
Hyatt RE. Evaluation of major airway lesions using the flow-volume
loop. Ann Otol Rhinol Laryngol 1975; 84: 635-642.