Clonidine induces upper airway closure in awake goats

In awake goats, clonidine and other a2-adrenoceptor agonists induce profound dysrhythmic ventilatory patterns that are characterized by prolonged and highly variable apneas. Clonidine-induced apneas are accompanied by tonic activation of the thyroarytenoid muscle (TA), a laryngeal adductor. In the present study, we wished to examine the responses of other upper airway abductor and adductor muscles that are important in the control of upper airway patency. Electromyographic activity of the posterior cricoarytenoid muscle (PCA) a laryngeal abductor, the TA, and the middle and inferior pharngeal constrictors were measured simultaneously with ventilation in six awake goats trained to wear a muzzle mask. Apneas induced by clonidine (1.0-11.0 μg/kg IV) were associated with tonic activation of the TA muscle and complete inhibition of phasic PCA activity. These effects persisted throughout the length of the apnea. Preliminary data suggest that these effects are accompanied by tonic activation of the pharyngeal constrictors. These results indicate that apneas induced by α₂-adrenoceptor stimulation are associated with active upper airway closure in awake goats.