Artificial control of glottic adduction for aspiration by orderly recruitment in the canine

Abstract

Laryngeal adduction for swallowing chiefly involves contraction of the thyroarytenoid and lateral cricoarytenoid muscles to seal the glottic chink. Vocal cord elongation supplements closure through cricoarytenoid activation. Relaxation of the posterior cricoarytenoid muscle is also involved in the swallowing process. Recent interest has focused on stimulating the laryngeal nerves to protect the lower airway from conditions where normal muscular coordination may be disrupted (e.g., in aspiration following stroke). Unfortunately, electrical stimulation results in a generalized contraction of all the dependent intrinsic laryngeal muscles because the larger, more excitable axons fire before their smaller counterparts can be activated. In the physiological state, however, the smaller fibers are recruited first. The current study focuses on electronic manipulation of force in the glottic muscles involved in deglutition. We used a stimulator that could selectively activate the intrinsic laryngeal muscles based on their specific motor unit architectures. In 5 dogs, the circuit recruited the axons in the recurrent and superior laryngeal nerves from small to large. The muscles were identified according to the differential recruitment rates of their compound muscle action potentials as they appeared on the graph. The smaller axons in the thyroarytenoid recruited faster than the large ones found in the lateral cricoarytenoid muscles, with intermediate figures observed with the cricothyroid. The posterior cricoarytenoid presented with the slowest recruitment rates, as expected from this muscle's highest contingent of larger motor units. Latencies between the onsets of stimulations and muscle saturations also appeared stable. This approach to manipulating glottic force saves energy because it allows stimulating the adductory muscles with minimal interference from their abductor antagonist.