Detection of upper airway muscle involvement in neuromuscular disorders using the flow-volume loop.

Abnormal contours of the flow-volume loop, ie, flow oscillations and inspiratory flow plateaux, have been noted in disorders affecting upper-airway muscular function. In this study, we assessed the incidence and the value of these contours as a test of bulbar and upper-airway muscular involvement in neuromuscular disease. We therefore compared flow-volume loops and pulmonary function test results between ten patients with (group 1) and 20 patients without (group 2) clinically apparent bulbar muscle involvement in neuromuscular disease. An abnormal flow-volume loop occurred significantly more often in group 1 than in group 2 (9/10 or 90 percent vs 3/20 or 15 percent, respectively; p less than 0.001) and predicted bulbar and upper-airway muscle involvement with high sensitivity (90 percent), specificity (85 percent) and efficiency (87 percent). Based on commonly used spirometric criteria, upper-airway obstruction was not more common in group 1 than in group 2 (1/10 vs 2/20); however, all three patients with upper-airway obstruction suggested by these criteria had an abnormal flow-volume loop. Following this study, three patients incurred severe respiratory complications. All three patients had previously shown an abnormal flow-volume loop. We conclude that in patients with neuromuscular disease, involvement of the bulbar and upper-airway muscles is frequently associated with an abnormal contour of the flow-volume loop. Recognition of flow oscillations or flow plateaux on flow-volume loops in these patients seems important, since they may be potential markers of severe respiratory complications.