Evaluation of obstructing lesions of the trachea and larynx by flow-volume loops.

Flow-volume loops of forced expiratory vital capacity and forced inspiratory vital capacity maneuvers in 39 of 43 patients with lesions of the major airways fell into 3 characteristic patterns. Each pattern was distinct from that of diffuse airway obstruction (bronchitis, emphysema, or asthma). Four patients had atypical flow-volume. The underlying lesions were strictures of the trachea (16 cases), malignant neoplasms (14 cases), and bilateral vocal cord paralysis (13 cases). Lesions with fixed narrowing were associated with essentially equal decreases of the inspiratory and expiratory loops. Lesions with dynamically variable narrowing were subject to transmural pressure gradients, intrathoracic location distorting primarily the forced expiratory loop, and extrathoracic location distorting the inspiratory loop. The ratio of maximal expiratory to maximal inspiratory flow at midvital capacities was helpful in grouping cases into fixed (average ratio: 0.85), variable extra-thoracic (2.2), and variable intrat...