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 tensor 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.