Laryngeal chemoreflex (LCR) responses elicited by fluid irrigation of the larynx have been described repeatedly in animals, whereas evidence for a similar reflex in human infants is extremely limited. Using nasopharyngeal catheters to instill small volumes of warm saline or water into the pharynx, we examined the incidence and characteristics of such a reflex in nine premature infants. Saline and water elicited the same pattern of responses, which frequently included swallows, central apnea, and airway obstruction and less commonly featured coughs, prolonged apnea, and arousal. With the exception of arousal, the incidence of these responses was significantly greater after delivery of water stimuli than after saline bolus administration. We therefore deduce chemoreceptor involvement in generation of these reflex responses and propose a laryngeal site for this sensory system, as in animals. Since greater potency of water compared with saline was demonstrable in all the infants studied, we further conclude that most preterm infants possess an upper airway chemoreflex.

Incoordination of sucking, swallowing, and breathing might lead to the decreased ventilation that accompanies bottle feeding in infants, but the precise temporal relationship between these events has not been established. Therefore, we studied the coordination of sucks, swallows, and breaths in healthy infants (8 full-term and 5 preterm). Respiratory movements and airflow were recorded as were sucks and swallows (intraoral and intrapharyngeal pressure). Sucks did not interrupt breathing or decrease minute ventilation during nonnutritive sucking. Minute ventilation during bottle feedings was inversely related to swallow frequency, with elimination of ventilation as the swallowing frequency approached 1.4/s. Swallows were associated with a 600-ms period of decreased respiratory initiation and with a period of airway closure lasting 530 +/- 9.8 (SE) ms. Occasional periods of prolonged airway closure were observed in all infants during feedings. Respiratory efforts during airway closure (obstructed breaths) were common. The present findings indicate that the decreased ventilation observed during bottle feedings is primarily a consequence of airway closure associated with the act of swallowing, whereas the decreased ventilatory efforts result from respiratory inhibition during swallows.

To learn how increased cervical adipose tissue might affect upper airway function, we studied effects of mass loading on upper airway dimensions, stability, and resistance. Eight rabbits were studied (anesthetized and postmortem) using lard-filled bags to simulate cervical fat accumulation. Additionally, a handheld device was used to apply measured loads at localized sites along the airway. Upper airway resistance and closing pressure (a reflection of airway stability) were determined before and after loading. Endoscopy revealed concentric narrowing of the pharynx during loading in anesthetized and postmortem preparations. Upper airway resistance was increased by mass loads, with larger loads having greater effects. Loading caused decreased airway stability as reflected by closing pressures. The area over the thyrohyoid membrane was more vulnerable to mass loading than adjacent areas. Because mass loading of the upper airway causes changes in its configuration and function similar to those seen in obstructive sleep apnea syndrome (OSA), we speculate that such loading may contribute to the pathogenesis of OSA associated with obesity.

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.

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