Influence of baclofen on laryngeal and spinal motor drive during cough in the anesthetized cat

Abstract

Objectives/hypothesis: The antitussive properties of (±) baclofen on laryngeal muscle activities have not been determined. The hypothesis of this study was that administration of (±) baclofen would suppress upper airway muscle motor activity in a dose-dependent manner during cough.

Study design: This is a prospective, preclinical, hypothesis-driven, paired design.

Methods: Electromyograms of the parasternal, rectus abdominis, thyroarytenoid, posterior cricoarytenoid, and thyrohyoid were measured, along with esophageal pressure. Cough was elicited by mechanical stimulation of the lumen of the intrathoracic trachea in spontaneously breathing cats.

Results: Baclofen (±) (3-10 μg kg(-1) i.a.) induced decreases in the electromyogram amplitude of the rectus abdominis motor drive during coughing, the inspiratory and active expiratory (E1) phases of cough, and cough number per epoch. There was no effect of (±) baclofen on the EMG amplitudes of any of the laryngeal muscles, the parasternal, or the duration of the passive expiratory (E2) phase.

Conclusions: Results from the present study indicate differential control mechanisms for laryngeal and inspiratory motor drive during cough, providing evidence of a control system regulating laryngeal activity and inspiratory spinal drive that is divergent from the control of expiratory spinal motoneurons.

Keywords: Cough; antitussive; baclofen; larynx; parasternal; posterior cricoid arytenoid; rectus abdominis; thyroarytenoid; thyrohyoid; upper airway.

Fig. 1

Example of thyrohyoid activity during a single cough. EMG signals were recorded for the parasternal, rectus abdominis, posterior cricoarytenoid, thyroarytenoid, and thyrohyoid muscles. The inspiratory phase is from the onset of the inspiratory activity to its peak activity. The active expiratory phase (E1) is from the peak of the inspiratory activity to the end of the rectus abdominis activity. The expiratory phase (E2) is from the end of the active expiratory activity to the onset of the next inspiratory burst.

Fig. 2

Example of the effects of (±) baclofen on cough. EMG signals were recorded for the parasternal (PS), rectus abdominis (RA), posterior cricoarytenoid (PCA), thyroarytenoid (TA), and thyrohyoid (ThHy) muscles. Esophageal pressure (EP) was also recorded. The control period shows repetitive coughing from stimulation of the trachea. Administration of baclofen significantly affected cough number and expiratory drive. Magnitudes of parasternal and posterior cricoarytenoid were relatively unchanged.