Contraction patterns of intrinsic laryngeal muscles induced by orderly recruitment in the canine.

The specific performance of intrinsic laryngeal muscles has been difficult to evaluate, especially in living subjects. To reproduce natural contractions, we artificially induced orderly recruitment of their innervating axons according to the size principle. In 5 dogs, both recurrent laryngeal nerves (RLNs) were stimulated with 50 through 10 Hz, 300 to 1000 microA currents while 600 Hz, 1000 to 0 microA decreasing blocking currents were administered. Surface electromyography electrodes placed on the thyroarytenoid, posterior cricoarytenoid, and lateral cricoarytenoid muscles were used to determine the amplitudes (in mA) of compound muscle action potentials. There was a highly statistically significant 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 rate (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 orderly manner according to their sizes and that the rates are unique to the muscle classes they innervate. The parameters defining these contraction patterns may offer key information for laryngeal pacing.