Yonsei Med J.  2009 Jun;50(3):380-384. 10.3349/ymj.2009.50.3.380.

Characteristics of Glottic Closure Reflex in a Canine Model

• Kim YH
• Kang JW
• Kim KM

• KMID: 1758566
• DOI: http://doi.org/10.3349/ymj.2009.50.3.380

Abstract

PURPOSE: The most important function of the larynx is airway protection which is provided through a polysynaptic reflex closure triggered by the receptors in the glottic and supraglottic mucosa, evoking the reflex contraction of the laryngeal muscles especially by strong adduction of vocal cords. Based on the hypotheses that central facilitation is essential for this bilateral adductor reflex and that its disturbance can result in weakened laryngeal closure, we designed this study to elucidate the effect of central facilitation on this protective reflex.
MATERIALS AND METHODS
Seven adult, 20 kg mongrel dogs underwent evoked response laryngeal electromyography under 0.5 to 1.0 MAC (minimum alveolar concentration) isoflurane anesthesia. The internal branch of the superior laryngeal nerve was stimulated through bipolar platinum-iridium electrodes, and recording electrodes were positioned in the ipsilateral and contralateral thyroarytenoid muscles.
RESULTS
Ipsilateral reflex closure was consistantly recorded regardless of anesthetic levels. However, contralateral reflex responses disappeared as anesthetic levels were deepened. Additionally, late responses (R2) were detected in one animal at lower level of anesthesia.
CONCLUSIONS
Deepened level of anesthesia affects central facilitation and results in the loss of the crossed adductor reflex, predisposing to a weakened glottic closure response. Precise understanding of this effect may possibly provide a way to prevent aspiration in unconscious patients.

Keyword

Glottic closure reflex; anesthesia; central facilitation; aspiration

MeSH Terms

Anesthesia/methods
Animals
Dogs
Glottis/*physiology
Laryngeal Nerves/physiology
*Reflex

Figure

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  Fig. 1 Stimulation of the left internal branch of SLN. Compound muscle action potential (CMAP) recordings obtained from ipsilateral thyroarytenoid muscle at (A) 0.5 MAC, and (B) 1 MAC, from contralateral thyroarytenoid muscle at (C) 0.5 MAC, and (D) 1 MAC.

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  Fig. 2 Presence of R2 at 0.5 MAC. Late response (R2) was detected at lowest level of anesthesia in one experimental animal.

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  Fig. 3 Organizational model of the crossed adductor reflex pathway in a dog.

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