Influence of continuous positive airway pressure on EMG activities of the cricothyroid and posterior cricoarytenoid muscles of the canine larynx

Objectives: We investigated the effect of different levels of continuous positive airway pressure (CPAP) on the cricothyroid (CT; a tenser muscle of the vocal folds) and posterior cricoarytenoid (PCA; sole abductor muscle of the vocal folds) muscles in dogs. Design: Prospective, controlled animal study. Subjects: Nine mongrel dogs of both sexes. Setting: University research laboratory. Interventions: After insertion of a cuffed tracheotomy tube low in the neck the compound EMG responses of the CT and PCA muscles during spontaneous respiration were measured simultaneously under different levels (2, 4, 6, and 8 cmH₂O) of positive end-expiratory pressure (PEEP). Measurements and results: The CT showed a progressive increase in phasic expiratory EMG activity with the application of graded levels of PEEP. Application of PEEP over 4 cmH₂O produced significant increases in the phasic CT activity (P < 0.05). In contrast to the CT, the PCA failed to increase phasic inspiratory EMG activity statistically until a 8 cmH₂O of PEEP was applied (P < 0.05). The phasic expiratory CT and inspiratory PCA activities were 297.9 ± 77.6 and 124.5 ± 22.9, respectively, at the application of 6 cmH₂O of PEEP (percentage of control, mean ± SD). Conclusion: This study confirms the difference in sensitivity between adductor and abductor laryngeal muscles, demonstrating that the intrinsic laryngeal muscles do not all behave similarly after the application of CPAP.