Fixed large airway obstruction
The
inspiratory and expiratory flow-volume curves exhibit a flow plateau
at low flows. Both the expiratory and inspiratory patterns are abnormal.
The overall pattern is compatible with fixed obstruction in large
extra- or intrathoracic airways, e.g. carcinoma of the
larynx, or obstruction due to goiter. Also shown is the flow-volume
curve during normal tidal breathing, and the MEFV-curve (interrupted
line) for a healthy person of the same age, standing height and
gender. It is generally assumed that obstruction is fixed if the
ratio of forced expiratory and inspiratory flow halfway the FVC (MEF50/MIF50)
is between 0.9 and 1.1.
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
Variable extrathoracic airway
obstruction