Vagal Stimulation for Reciprocal Coupling between Glottic and Upper Esophageal Sphincter Activities in the Canine
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Glottic adduction couples with relaxation of the tonically contracted upper esophageal sphincter (UES) to constitute the end point of pharyngeal swallowing. Together with deglutitive laryngeal elevation, this reciprocal relationship contributes to protecting the lungs from aspiration. Degrees of uncoordination between glottic and upper esophageal sphincters can be seen under diverse circumstances of neurologic damage such as stroke, gastroesophageal reflux, and in the growing elderly population presenting with weaker musculature. We hypothesized that reciprocal coupling between glottic closure and UES relaxation may be artificially reestablished through vagal stimulation if the appropriate neural centers and their leading pathways remain capable of exciting a critical number of motor units. Orderly recruitment of the vagus nerve was produced in three dogs with a circuit superimposing 600-Hz, 3800–0-μA blocking over 10–70-Hz, 0–2300-μA stimulating currents. Amplitudes of motor unit or compound muscle action potentials were recorded from the thyroarytenoideus and cricopharyngeus via surface electromyographic electrodes. Stimulation was accompanied by a drop in UES intraluminal pressure. The reciprocal relationship between the two muscles could be time locked within certain stimulus parameters. We submit that electronic coupling between the glottic and UESs may show promise in preventing aspiration under selected circumstances.
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