Am. J. Respir. Crit. Care Med., Vol 150, No. 3, 09 1994, 729-734.
Laryngeal response during forced vital capacity maneuvers in normal adult humans
ST Kuna and CR Vanoye
Department of Internal Medicine, University of Texas Medical Branch, Galveston 77555-0561.
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 maneuvers,
intramuscular electromyographic recordings were obtained in 25 normal 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 muscles 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 decrease in adductor muscle activity.
To determine the net effect of these electromyographic changes on vocal
cord position, simultaneous fiberoptic recordings of vocal cord movement
were obtained in five of the subjects. The angle formed by the vocal cords
at the anterior commissure was used to assess glottic aperture size.
Glottic angle progressively decreased from peak expiratory flow to the end
of forced expiration. The angle was 56 +/- 13 degrees (SD) at peak
expiratory flow, 34 +/- 4 degrees after forced expiration of 90% of the
vital capacity, and 7 +/- 7 degrees at end-expiration. The results indicate
that forced expiration 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 of about 75% of forced vital capacity.
