Characteristics of upper airway chemoreflex prolonged apnea in human infants

Water instilled into the pharynx of sleeping human infants elicits a range of chemoreflex responses that, occasionally, includes prolonged apnea (defined as absence of ventilation for at least 20 s, or for a shorter period if accompanied by bradycardia of less than or equal to 100 b.p.m. or cyanosis). To learn more about airway receptors mediating this prolonged apneic response and factors determining its occurrence, we examined the importance of stimulus location and associations between prolonged apnea, bradycardia, and upper airway responses. A total of 29 episodes of prolonged apnea were recorded after water stimulation in 12 infants. Bradycardia (HR less than 100) followed stimulus delivery but was always preceded by apnea and did not appear as an independent chemoreflex response. Behavioral arousal and prolonged apnea were not mutually exclusive responses and recovery from prolonged apnea was not always closely linked with arousal. Occurrence of prolonged apnea was greater after pharyngeal than nasal stimulation, and was frequently associated with coughing, but not with sneezing, suggesting that prolonged apnea is elicited from a sensory site close to, or the same as, one mediating cough. We conclude, using this water stimulus method, that the predominant receptors for chemoreflex-prolonged apnea are located in the pharynx or larynx rather than in the nose.