Central Facilitation of the Glottic Closure Reflex in Humans

Abstract

The sphincteric function of the larynx, essential to lower airway protection, is most efficiently achieved through strong reflex adduction by both vocal cords. We hypothesize that central facilitation is an essential component of a bilateral adductor reflex and that its disturbance could result in weakened sphincteric closure. Five patients during supraglottic laryngectomy underwent evoked response laryngeal electromyography under 0.5 and 1.0 minimal alveolar concentration (MAC) 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. Consistent threshold responses were obtained ipsilaterally from 0.5 to 1.0 MAC anesthesia. However, the contralateral reflex responses approached 0% in successive trials as anesthetic levels approached 1.0 MAC. In human subjects, alteration of central facilitation by deepening anesthesia abolishes the crossed adductor reflex, predisposing to a weakened glottic closure response. A precise understanding of this effect may improve the prevention of aspiration in patients emerging from prolonged sedation or under heavy psychotropic control.

Contralateral R1 and R2 components of the laryngeal adductor reflex in humans under general anesthesia

“…This suggests that, under general anesthesia, the R1 component of the LAR may be the predominant contractile force. cR1 latencies were comparable to cR1 latencies reported by Sasaki et al and were 4 ms to 6 ms longer than previously reported iR1 responses in awake and anesthetized states, consistent with the additional time required for impulses to cross to the contralateral side of the brainstem. cR2 latencies in this series were within the range of R2 latencies noted for awake patients in prior studies The consistency of response latencies across all studies, despite different stimulation strategies and consciousness states, implies that TIVA anesthesia has minimal effect on conduction time of the reflex and attests to the robust nature of these responses.…”

“…cR2 latencies in this series were within the range of R2 latencies noted for awake patients in prior studies The consistency of response latencies across all studies, despite different stimulation strategies and consciousness states, implies that TIVA anesthesia has minimal effect on conduction time of the reflex and attests to the robust nature of these responses. Regarding the strength of mucosal stimulus, the current range (3–8 mA) used in this study was comparable to that utilized by other authors, with no perioperative or postoperative complications noted in this or other studies …”

“…The LAR is a primitive brainstem reflex that can be elicited by a number of supraglottic irritants . In anesthetized and awake humans, supraglottic stimulation results in an early iR1‐evoked response with a latency between 16 and 18 ms . In anesthetized cats and in humans under light inhalational anesthesia (MAC = 0.5), a second short‐latency contralateral‐evoked response, cR1, has been reported .…”

Characteristics of Glottic Closure Reflex in a Canine Model

“…In our model, we propose that the iSLN projects to motor neurons of nucleus ambiguus through at least two synapses, the first within ipsilateral nucleus tractus solitarius, and the second likely within nucleus ambiguus ipsilaterally and contralaterally within the reticular formation in a manner supported by Sessle's observations. 26 In recent studies, it was suggested that the pig model has equivalent numbers of ipsilateral and contralateral interneurons,22 and that humans have 2 to 3 more contralateral interneurons compared to ipsilateral side 27. However, in our current study with canine model, the fact that the contralateral latency was about 2 msec longer than ipsilateral one leads us to suggest the presence of one more interneuron possibly in the reticular formation (Fig.…”

Laryngeal Reflexes

“…The late bilateral thyroarytenoid response occurred in awake humans but was rare in the anesthetized cat. A study of changes in the laryngeal closure response in patients at different anesthesia levels demonstrated that the bilateral response only occurred when the level of anesthesia was reduced (Sasaki, Jassin, Kim, et al, 2003). The late responses in the cat only occurred when ketamine was not administered demonstrating that this late component is a glutaminergic pathway (Ambalavanar, Purcell, Miranda, et al, 2002).…”