Effects of Altered Consciousness on the Protective Glottic Closure Reflex

Abstract

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.

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

“…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 . In awake humans, a longer latency R2 reflex response that causes bilateral vocal fold adduction has been noted using electrical stimulation of laryngeal mucosa or the iSLN, with average response latency of 50 to 80 ms .…”

In search of a longitudinal animal model of evoked swallow function

“…On the one hand, general anesthesia enhances the inhibitory afferent cortical impulses to CPG, opposing the effect of afferent stimuli from iSLN and vagus stimulation in eliciting reflex swallow. Although inhalational anesthetics, such as isoflurane and sevoflurane, increase the reactivity of gamma‐aminobutyric acid (GABA) receptors inhibiting cerebral function and thus suppressing levels of consciousness, they also suppress brainstem activity . Our studies support the observation that even small doses of inhaled sevoflurane at much less than 1.0 MAC can significantly attenuate the swallow reflex.…”

Feasibility of Instrumental Swallowing Assessments in Patients With Prolonged Disordered Consciousness While Undergoing Inpatient Rehabilitation

“…The elimination of this reflex predisposes the subjects to a weakened glottic closure response. 9 Findings from this animal model study suggest that people with disordered consciousness for 4 or more weeks (prolonged) may have a weakened glottic closure response which, in human, is associated with elevated risk for aspiration and/or silent aspiration. 10 Given the limited information currently available regarding treatment and recovery of swallow function in individuals with prolonged disorders of consciousness, the purpose of this case-control, retrospective study was to evaluate the feasibility and potential benefits of conducting an instrumental assessment of the swallow for patients with disordered consciousness admitted to a freestanding rehabilitation hospital.…”