INFLUENCE OF CONTINUOUS POSITIVE AIRWAY PRESSURE ON EMG ACTIVITIES OFTHE CRICOTHYROID AND POSTERIOR CRICOARYTENOID MUSCLES OF THE CANINE LARYNX

Objectives:We investigated the effect of different levels of continuou s positive airway pressure (CPAP) on the cricothyroid (CT; a tensor mu scle of the vocal folds) and posterior cricoarytenoid (PCA; sole abduc tor muscle of the vocal folds) muscles in dogs. Design: Prospective, c ontrolled animal study. Subjects: Nine mongrel dogs of both sexes. Set ting: University research laboratory. Interventions: After insertion o f a cuffed tracheotomy tube low in the neck the compound EMG responses of the CT and PCA muscles during spontaneous respiration were measure d simultaneously under different levels (2, 4, 6, and 8 cmH(2)O) of po sitive end-expiratory pressure (PEEP). Measurements and results: The C T showed a progressive increase in phasic expiratory EMG activity with the application of graded levels of PEEP. Application of PEEP over 4 cmH(2)O produced significant increases in the phasic CT activity (P<0. 05). In contrast to the CT, the PCA failed to increase phasic inspirat ory EMG activity statistically until a 8 cmH(2)O 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 c mH(2)O of PEEP (percentage of control, mean+/-SD). Conclusion: This st udy confirms the difference in sensitivity between adductor and abduct or laryngeal muscles, demonstrating that the intrinsic laryngeal muscl es do not all behave similarly after the application of CPAP.