Respiratory-related pharyngeal constrictor muscle activity in awake goats

Respiratory-related electromyogram (EMG) activities of the middle (MPC) and inferior (IPC) pharyngeal constrictor (PC) muscles were determined simulta neously with up to six additional upper airway abductor and adductor muscle s in awake adult goats. Phasic PC activation began in late inspiration and persisted throughout expiration with a steady, an augmenting or a biphasic pattern of activity. Considerable differences were noted in the EMG respons es of the MPC and IPC muscles to respiratory-related stimuli. During hypoxi a and hypercapnia, phasic MPC activity decreased or was not recruited where as phasic IPC activity was augmented with increased chemical drive. During spontaneous augmented breaths and peripheral chemoreceptor stimulation with sodium cyanide, the pattern of activation of the MPC was similar to that o f the thyroarytenoid muscle (TA), a laryngeal adductor whereas IPC activity was strikingly similar to activity of the laryngeal and pharyngeal dilator s. The expiratory portion of an augmented breath was associated with increa sed phasic MPC and TA but not IPC activities. Dopamine-induced apneas resul ted in tonic activation of the R-IPC and TA at a level equal to or greater than control activity but no recruitment of IPC activity. The marked differ ences in MPC and IPC responses to respiratory-related stimuli suggests that these muscles may have different mechanical effects on pharyngeal airway c aliber in the goal. The results suggest that the MPC may help brake expirat ory flow thus helping to control expiratory timing and lung volume. In cont rast, the IPC may promote pharyngeal airway patency by stiffening or dilati ng the pharyngeal airway. The results demonstrate that a variety of stimuli can influence respiratory-related PC activity and suggest that the PC musc les are important in the regulation of breathing and upper airway patency. (C) 1999 Elsevier Science B.V. All rights reserved.