Laryngeal adductor function in experimental models of recurrent laryngeal nerve injury

Abstract

Objectives/Hypothesis Most patients with unilateral vocal fold paralysis experience some degree of spontaneous reinnervation, which depends upon the type and severity of recurrent laryngeal nerve (RLN) injury. After partial recovery, the paretic vocal fold may or may not adduct adequately to allow glottic closure, which in turn affects phonatory and swallowing outcomes. This process was studied in a series of canine laryngeal nerve injury models. Study Design Animal (canine) experiments. Methods Maximum stimulable laryngeal adductor pressure (LAP) was measured pre-treatment (baseline) and at 6 months following experimental RLN injuries (total n=59). The 9 study groups were designed to simulate a range of severities of RLN injury. Results The greatest LAP recovery, at 108% of original baseline, was seen in a 50% transection model; the least recovery was seen when the RLN underwent complete transection with repair, at 56% with precise alignment and 50% with alignment reversed. Intermediate models (partial RLN injuries) gave intermediate results. Crush models recovered 105% of LAP, while a half-transection, half-crush injury recovered 72% and cautery injuries recovered 61%. Controls (complete transection without repair) had no measurable recovery. Conclusions The injured RLN has a strong tendency to recover. Restoration of adductor strength, as determined by the LAP, was predictably related to the severity of RLN injury. The model RLN injuries studied provide a range of expected outcomes that can be used for future experiments exploring interventions that may improve post-injury adductor function.

Reversing Age Related Changes of the Laryngeal Muscles by Chronic Electrostimulation of the Recurrent Laryngeal Nerve

“…The lowest current amplitude at which changes in the LAP could be observed was defined as the adductor muscle twitch threshold. We initially set the stimulation burst frequency to 20 Hz, where activity of the slow-twitch abductor posterior cricoarytenoid muscle (PCAM) predominates [19]. We could not detect a clear abduction movement here.…”

Effect on Laryngeal Adductor Function of Vincristine Block of Posterior Cricoarytenoid Muscle 3 to 5 Months After Recurrent Laryngeal Nerve Injury

“…The RLN was transected 4cm inferior to the cricothyroid joint, and then immediately re-anastomosed end-to-end using an operating microscope and 9-0 nylon sutures. The orientation of the stumps was random (in a previous study, the same result was obtained with a precise realignment as with a 180° rotation of the stumps{12}). The stoma was matured and the wounds were closed.…”

Toxicity trial of canine posterior cricoarytenoid intramuscular vincristine injections

“…Stimulation of each RLN resulted in movement of the vocal fold, which varied by stimulus intensity and frequency; these movements were documented by videoendoscopy through the laryngoscope. Strength of adduction was measured using laryngeal adductor pressure as previously described . Briefly, the squeezing force exerted on an endotracheal balloon passed between the vocal folds was measured with a force transducer and compared with historic controls.…”