The flow-volume loop in bilateral vocal cord paralysis.

A 38-year-old man with posttraumatic bilateral vocal cord paralysis and a surgically repaired avulsion of the extrathoracic trachea presented with a slight increase of exertional dyspnea (grade 2). Spirometry showed high normal FEV1 for FVC variables, but the F-V loop was characteristic for highly variable UAO with an increased FEV1/PEF ratio of 11 ml/L/min as well as a MEF50/MIF50 of 4.55. Endoscopy during forced respiration showed near total inspiratory obstruction of the larynx due to paradoxical behavior of the vocal cords. In extrathoracic airway obstruction a FEV1/PEF ratio > 10 ml/L/min combined with a MEF50/MIF50 ratio > 4 is suggestive of variable UAO caused by bilateral vocal cord paralysis rather than by a tracheal lesion.