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#PHARYNGEAL CONSTRICTOR MUSCLES PC#
The purpose of the present study was to extend this previous work by providing a quantitative analysis of respiratory-related PC activity in response to a variety of respiratory-related stimuli, including progressive changes in chemical drive and lung volume. These previous studies are largely qualitative and report the response to only one level of hypercapnia. Murakami and Kirchner ( 21) report that the chondropharyngeus and keratopharyngeus portions of the HP have the same activation patterns. From electromyogram (EMG) studies in anesthetized cats, it has been found that 1) the HP and TP exhibit phasic activity in expiration and tonic activity throughout the respiratory cycle during quiet breathing, 2) phasic HP activity increases under hypercapnic conditions (5% inspired CO 2), and 3) passively induced hypocapnia is associated with the emergence of tonic PC activation ( 21, 23). Inspiratory units with a steady, late augmenting, or tonic discharge pattern were also present. Most units fired only in expiration and exhibited a steady, a decreasing, or a late augmenting discharge pattern. ( 6) recorded the discharge of motor axons supplying the PC muscles in decerebrate, paralyzed, artificially ventilated cats. Sherrey and Megirian ( 24) performed whole nerve recordings in anesthetized, spontaneously breathing cats and found expiratory activity in the nerve branches innervating the TP and HP. Previous investigators have examined the respiratory-related activity of the PC muscles in cats. Respiratory-related PC activity is of interest because previous investigators have speculated that PC muscle activation may promote pharyngeal airway closure during sleep in patients with obstructive sleep apnea ( 25). The PC muscles are activated after the oral phase of swallowing and are believed to promote pharyngeal airway closure. The pharyngeal branch of the vagus nerve supplies motor output to the PC muscles in cats ( 4, 6, 21, 24). The inferior PC is termed the thyropharyngeus (TP). In animals, the middle PC is termed the hyopharyngeus (HP) and consists of the chondropharyngeus and keratopharyngeus muscles. They arise from the dorsal midline pharyngeal aponeurosis and attach to various anterior structures in the ventral wall of the pharyngeal airway. The superior, middle, and inferior pharyngeal constrictors (PCs) are saillike muscles that help form the lateral and posterior walls of the pharyngeal airway. The results indicate that a variety of stimuli modulate respiratory-related PC activity, suggesting that the PC muscles may have a role in the regulation of upper airway patency during respiration. The expiratory phase of a sigh and progressive pneumothorax were associated with an increase in phasic thyroarytenoid activity but no change in phasic PC activity. Passively induced hypocapnia and the central apnea that followed the cessation of the mechanical hyperventilation were associated with tonic activation of the hyopharyngeus and thyroarytenoid but no recruitment in thyropharyngeus activity. Progressive hyperoxic hypercapnia and progressive isocapnic hypoxia increased phasic expiratory activity in both pharyngeal constrictor (PC) muscles but tended to suppress thyroarytenoid activity. Respiratory-related thyropharyngeus activity was absent under these conditions. During quiet breathing, the hyopharyngeus and usually the thyroarytenoid exhibited phasic activity during expiration and tonic activity throughout the respiratory cycle. Physiol.83(5): 1588–1594, 1997.-Respiratory-related activity of the hyopharyngeus (middle pharyngeal constrictor) and thyropharyngeus (inferior pharyngeal constrictor) muscles was determined in decerebrate, tracheotomized adult cats and compared with the electromyographic activity of the thyroarytenoid, a vocal cord adductor. Vanoye.Respiratory-related pharyngeal constrictor muscle activity in decerebrate cats.