LARYNGEAL RESPONSE DURING FORCED VITAL CAPACITY MANEUVERS IN NORMAL ADULT HUMANS

Previous investigators have reported that transient forced expiration is accompanied by abduction of the vocal cords. To further investigate the laryngeal response during voluntary forced vital capacity maneuve rs, intramuscular electromyographic recordings were obtained in 25 nor mal adult humans from three intrinsic laryngeal muscles: the posterior cricoarytenoid (PCA), a vocal cord abductor, and the thyroarytenoid ( TA) and arytenoideus (AR), both vocal cord adductors. All three muscle s exhibited sustained activation throughout most of forced expiration from total lung capacity. Forced inspiration from residual volume was associated with a further increase in PCA activity and a marked decrea se in adductor muscle activity. To determine the net effect of these e lectromyographic changes on vocal cord position, simultaneous fiberopt ic recordings of vocal cord movement were obtained in five of the subj ects. The angle formed by the vocal cords at the anterior commissure w as used to assess glottic aperture size. Glottic angle progressively d ecreased from peak expiratory flow to the end of forced expiration. Th e angle was 56 +/- 13 degrees (SD) at peak expiratory flow, 34 +/- 4 d egrees after forced expiration of 90% of the vital capacity, and 7 +/- 7 degrees at end-expiration. The results indicate that forced expirat ion is associated with marked activation of not only the PCA but also laryngeal adductor muscles. During forced expiration, the glottis does not decrease below its size during quiet breathing until exhalation o f about 75% of forced vital capacity.