Electronic control of laryngeal spasm. II. Selective blockage of glottic adduction by a closed-loop circuit in the canine.

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.