Expiratory neural activities in gasping induced by pharyngeal stimulation and hypoxia

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The purpose was to characterize expiratory neural activities in gasping elicited during the aspiration reflex (AR) in hyperoxia and during hypoxia-induced gasping. In decerebrate, vagotomized and paralyzed cats, we recorded activities of inspiratory and expiratory cranial and spinal nerves. The AR was elicited by touching the epipharyngeal mucosa. In eupnea, spinal expiratory activities were greatly decreased during AR whereas laryngeal expiratory activities were increased. In hypoxia-induced gasping, both the laryngeal and spinal expiratory activities were reduced. All of the inspiratory activities were increased during both gasping and the AR. In addition, neural activities were below control levels following AR; activities gradually recovered to control levels. We conclude that spinal expiratory activities are inhibited during the AR and gasping. Results are consistent with the concept that medullary mechanisms for gasping are recruited by mechanical stimulation of the epipharynx. In hypoxia-induced gasping, the hypoxia, per se, causes a separate suppression of laryngeal expiratory activities.