The respiratory function of the cricothyroid muscle: An electromyographic investigation in dogs

The activity of the cricothyroid (CT) muscle during phonation has been well studied electromyographically in several species. Its activity during respiration, however, has been the source of numerous discrepant reports. In order to determine whether the CT muscle has respiratory function, nine dogs were used for this study. In the majority of the muscle, there was continuous activity during quiet respiration. Although motor unit activity was recorded from the muscle during both inspiration and expiration, more muscle potentials were observed during the first half of the expiratory phase. During artificially induced inspiratory dyspnea, the CT muscle discharged during inspiration and at the beginning of expiration. During expiratory dyspnea, the EMG pattern was basically the same as that observed during inspiratory dyspnea, but there appeared to be more unit activity during inspiratory dyspnea. A special change in EMG recordings was observed in two of the nine animals, i.e., inspiratory activity was strongly increased during inspiratory dyspnea, whereas expiratory activity was strongly increased during expiratory dyspnea. The increased activities returned to normal levels immediately after dyspnea was relieved. The authors believe that the CT muscle has respiratory function. The function of the muscle is dependent on the state of respiration. The CT and the posterior cricoarytenoid (PCA) muscles have a synergistic effect during dyspnea; however, each of them has its own major role in other functions of the larynx.