ELECTRONIC CONTROL OF LARYNGEAL SPASM .2. 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 speci ally designed electrodes were used to block their own induced action p otentials to restrain spasticity. In the current series of experiments , strap muscle and thyroarytenoid contraction (glottic closure) elicit ed by supramaximal ansa hypoglossi (N = 6) and recurrent laryngeal ner ve (N = 4) stimulation (30 to 50 Hz, 0.1 to 6 mA, 0.1 to 1 msec), resp ectively, allowed afferent information via intramuscular sonomicromete r crystals to trigger a circuit that, in turn, stimulated blocking ele ctrodes passed around the nerves downstream. Simultaneous videorecordi ng of strap and vocal cord motion during direct laryngoscopy with thei r corresponding excursion tracings demonstrated near-total suppression of contractions within given stimulation ''windows.'' These encouragi ng results may eventually permit selective restraint of erratic contra ctions involving laryngeal and other cervical musculatures in the huma n.