Spastic dysphonia is a central nervous system phenomenon of unknown etiology characterized by uncoordinated voice tremor with erratic patterns of laryngeal contraction. Standard treatments have not been entirely satisfactory. The authors propose to apply a concept of selective nerve activity blockage, which leaves normal contractions undisturbed, as the basis for suppression of laryngeal spasticity. Single pulses of constant duration and increasing amplitude were injected into specially designed blocking electrodes placed around six recurrent laryngeal nerves (three dogs). Vocal cord adduction was reduced or arrested within given “windows” of stimulation levels of the blocking electrodes, while it increased with higher amplitudes when the current was injected via standard bipolar electrodes (controls). Although this study demonstrates the feasibility of blocking action potentials passing along recurrent laryngeal nerves, it might eventually allow control of laryngeal spasm from information taken directly from the affected musculature.
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