RESPIRATORY-RELATED PHARYNGEAL CONSTRICTOR MUSCLE-ACTIVITY IN DECEREBRATE CATS

Respiratory-related activity of the hyopharyngeus (middle pharyngeal c onstrictor) and thyropharyngeus (inferior pharyngeal constrictor) musc les was determined in decerebrate, tracheotomized adult cats and compa red with the electromyographic activity of the thyroarytenoid, a vocal cord adductor. During quiet breathing, the hyopharyngeus and usually the thyroarytenoid exhibited phasic activity during expiration and ton ic activity throughout the respiratory cycle. Respiratory-related thyr opharyngeus activity was absent under these conditions. Progressive hy peroxic hypercapnia and progressive isocapnic hypoxia increased phasic expiratory activity in both pharyngeal constrictor (PC) muscles but t ended to suppress thyroarytenoid activity. Passively induced hypocapni a and the central apnea that followed the cessation of the mechanical hyperventilation were associated with tonic activation of the hyophary ngeus and thyroarytenoid but no recruitment in thyropharyngeus activit y. The expiratory phase of a sigh and progressive pneumothorax were as sociated with an increase in phasic thyroarytenoid activity but no cha nge in phasic PC activity. The results indicate that a variety of stim uli modulate respiratory-related PC activity, suggesting that the PC m uscles may have a role in the regulation of upper airway patency durin g respiration.