Differential elevation by protriptyline and depression by diazepam of upper airway respiratory motor activity

Effects of systemically administered protriptyline and diazepam on the respiratory activity of the phrenic, hypoglossal, and recurrent laryngeal nerves were investigated in vagotomized, decerebrate cats. Both hypoglossal and recurrent laryngeal nerve activities were consistently increased after protriptyline administration, whereas the phrenic nerve discharge was not systematically altered. Similar changes were observed in cats with bilateral carotid sinus nerve sections. Diazepam induced a reduction of hypoglossal and recurrent laryngeal nerve activities at doses that did not alter phrenic nerve discharge. These results with diazepam were the same in carotid chemodenervated cats. We conclude that neural mechanisms controlling upper airway muscles are much more sensitive to protriptyline and diazepam than are those of the bulbospinal-phrenic system. The selective augmentation of hypoglossal and recurrent laryngeal discharges by protriptyline could account for the reported decrease in the frequency of obstructive sleep apneas in patients receiving this antidepressant. In contrast, diazepam, by depressing motor activity to upper airway muscles, may exacerbate oropharyngeal obstruction during sleep.