Effects of altered consciousness on the protective glottic closure reflex.
OBJECTIVE
The sphincteric function of the larynx, essential to lower airway protection, is most efficiently achieved through strong reflex adduction by both vocal folds. We hypothesize that central facilitation is an essential component of a bilateral brain stem-mediated adductor reflex and that its disturbance by altered consciousness or physiologic sleep could result in weakened sphincteric closure.


METHODS
In 10 adult pigs the glottic closure response was evaluated under light and deep isoflurane anesthesia. The internal branch of the left superior laryngeal nerve was stimulated through bipolar platinum-iridium electrodes, and recording electrodes were positioned in the ipsilateral and contralateral thyroarytenoid muscles. The force of evoked glottic closure was measured with a pressure transducer positioned between the vocal folds.


RESULTS
Consistent threshold responses (>90%) were obtained ipsilaterally from 0.5 to 2.0 minimal alveolar concentration (MAC) anesthesia. However, the contralateral reflex responses declined to 6.4% in successive trials as anesthetic levels approached 1.5 to 2.0 MAC. Furthermore, glottic closing force closely reflected these electromyographic changes, declining from 383 mm Hg at 0.5 to 1.0 MAC to 114 mm Hg at 1.5 to 2.0 MAC.


CONCLUSIONS
Alteration of central facilitation by progressively deeper loss of consciousness abolishes a lower brain stem-mediated crossed adductor reflex, predisposing the subject to a weakened glottic closure response.
Sasaki
Clarence T
CT
Section of Otolaryngology, Yale School of Medicine, New Haven, Connecticut 06520-8041, USA.
Yu
Ziwei
Z
Xu
Jiajun
J
Hundal
Jagdeep
J
Rosenblatt
William
W
D000769:Anesthesia, Inhalation; D018685:Anesthetics, Inhalation / Q000008:administration & dosage; D000818:Animals; D003679:Deglutition / Q000502:physiology*; D004195:Disease Models, Animal; D004558:Electric Stimulation; D004576:Electromyography; D005071:Evoked Potentials; D005931:Glottis / Q000503:physiopathology*; D007530:Isoflurane / Q000008:administration & dosage; D007823:Laryngeal Nerves / Q000502:physiology*; D008297:Male; D012018:Reflex / Q000502:physiology*; D013552:Swine
D018685:Anesthetics, Inhalation; D007530:Isoflurane