This work is the continuation of an earlier pilot study in which specially designed electrodes were used to block their own induced action potentials to restrain spasticity. In the current series of experiments, strap muscle and thyroarytenoid contraction (glottic closure) elicited by supramaximal ansa hypoglossi (N = 6) and recurrent laryngeal nerve (N = 4) stimulation (30 to 50 Hz, 0.1 to 6 mA, 0.1 to 1 msec), respectively, allowed afferent information via intramuscular sonomicrometer crystals to trigger a circuit that, in turn, stimulated blocking electrodes passed around the nerves downstream. Simultaneous videorecording of strap and vocal cord motion during direct laryngoscopy with their corresponding excursion tracings demonstrated near-total suppression of contractions within given stimulation "windows." These encouraging results may eventually permit selective restraint of erratic contractions involving laryngeal and other cervical musculatures in the human.
Aspiration can result from muscular weakness or paralysis of laryngopharyngeal muscles after lower motor neuron disorders (e.g., stroke) or unchecked gastroesophageal reflux. We submit that rehabilitation of the finely tuned swallowing mechanism should provide at least restoration of the normal dynamic relationships between glottic closure and cricopharyngeal relaxation. In three dogs under general endotracheal anesthesia, the recurrent laryngeal nerves and the pharyngeal musculature were exposed through a midline cervical incision. A tracheotomy was performed to allow unhindered laryngoscopic exposure of the vocal cords. A no. 9 endotracheal tube passed through the upper esophageal sphincter was used as a pressure transducer by saline inflation of its cuff and linked to an oscilloscope. The cricopharyngeus was placed under baseline tension with pulse trains administered by an intramuscular needle with a circuit previously used for agonist/antagonist coupling of reinnervated facial musculature. A second output channel was linked to the contralateral recurrent laryngeal nerve by a bipolar electrode. As the pulse width of the current to the recurrent laryngeal nerve increased, that to the cricopharyngeus was reciprocally decreased, producing snug glottic closure and synchronous cricopharyngeal relaxation. Results were documented on videotape. These findings were highly reproducible. We believe that the novel approach proposed in the current model offers an attractive solution to long-term aspiration problems resulting from an imbalance between vocal cord and cricopharyngeal activities.
Aspiration can result from muscular weakness or paralysis of laryngopharyngeal muscles after lower motor neuron disorders (e.g., stroke) or unchecked gastroesophageal reflux. We submit that rehabilitation of the finely tuned swallowing mechanism should provide at least restoration of the normal dynamic relationships between glottic closure and cricopharyngeal relaxation. In three dogs under general endotracheal anesthesia, the recurrent laryngeal nerves and the pharyngeal musculature were exposed through a midline cervical incision. A tracheotomy was performed to allow unhindered laryngoscopic exposure of the vocal cords. A no. 9 endotracheal tube passed through the upper esophageal sphincter was used as a pressure transducer by saline inflation of its cuff and linked to an oscilloscope. The cricopharyngeus was placed under baseline tension with pulse trains administered by an intramuscular needle electrode with a circuit previously used for agonist/antagonist coupling of reinnervated facial musculature. A second output channel was linked to the contralateral recurrent laryngeal nerve by a bipolar electrode. As the pulse width of the current to the recurrent laryngeal nerve increased, that to the cricopharyngeus was reciprocally decreased, producing snug glottic closure and synchronous cricopharyngeal relaxation. Results were documented on videotape. These findings were highly reproducible. We believe that the novel approach proposed in the current model offers an attractive solution to long-term aspiration problems resulting from an imbalance between vocal cord and cricopharyngeal activities.
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