CONTRACTION PATTERNS OF INTRINSIC LARYNGEAL MUSCLES INDUCED BY ORDERLY RECRUITMENT IN THE CANINE

The specific performance of intrinsic laryngeal muscles has been diffi cult to evaluate, especially in living subjects. To reproduce natural contractions, we artificially induced orderly recruitment of their inn ervating axons according to the size principle. In 5 dogs, both recurr ent laryngeal nerves (RLNs) were stimulated with 50 through 10 Hz, 300 to 1000 mu A currents while 600 Hz, 1000 to 0 mu A decreasing blockin g currents were administered. Surface electromyography electrodes plac ed on the thyroarytenoid, posterior cricoarytenoid, and lateral cricoa rytenoid muscles were used to determine the amplitudes (in mA) of comp ound muscle action potentials. There was a highly statistically signif icant difference (P<.004) between the thyroarytenoideus which had the fastest rate of recruitment (8.38%), and posterior cricoarytenoideus, which had the slowest (4.81%). There was an intermediate recruitment r ate (6.72%) of the lateral cricoarytenoideus, a divergence attributed to a more equal distribution in fast and slow types of myofibers and a smaller sample. We submit that RLN axons can be recruited in an order ly manner according to their sizes and that the rates are unique to th e muscle classes they innervate. The parameters defining these contrac tion patterns may offer key information for laryngeal pacing.