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The airway protective mechanisms evoked after infusion of fluids into the pharynx were examined in the intact and healthy newborn piglet during sleep. Thirteen healthy normothermic piglets (3-6 days of age) were examined on 4 consecutive days during sleep. The fluids infused (0.05-1.5 ml) were 0.9% saline, distilled water, and HCl (pH 3 and pH 2). Respiratory rate, heart rate, oxygen saturation (SaO2), swallowing, and arousal were compared pre- and postinfusion during active (AS) and quiet sleep (QS) for each test fluid. The most common response in AS and QS was swallowing (90%) and then arousal (24%); however, no apnea occurred, and respiratory rate and SaO2 were always maintained. A significant difference occurred between HCl infusions of pH 2 and pH 3; at pH 2, the frequency of swallows and latency to the first swallow were reduced (P < 0.05) and the frequency of arousal was reduced in AS compared with that in QS (P < 0.01). Airway protection after pharyngeal fluid stimulation is achieved primarily by swallowing and arousal, without any effect on respiratory rate and SaO2. Attenuation of protective mechanisms occurred, however, when the infusate was at pH 2.

This study was designed to evaluate upper airway protective mechanisms in response to pharyngeal fluid stimulation in healthy term and preterm infants at term equivalent age. Five term and seven preterm infants were studied and the following recorded: sleep state, cardiorespiratory function, and swallowing. Infusions of 0.9% saline and sterile water of volumes of 0.04, 0.2, and 0.35 mL were made during active (AS) and quiet sleep (QS). The effect of these variables on apnea (> or = 2 and > or = 5 s), swallowing, and arousal was examined. After pharyngeal infusion, apnea of > or = 2 and > or = 5 s did not change from spontaneous rates for both term and preterm infants. The most common response to pharyngeal infusion was swallowing. In AS, swallowing occurred after 65 and 73% and in QS after 40 and 64% of infusions in term and preterm infants, respectively. Swallowing was volume-related and occurred significantly more often in term infants after larger infusions of 0.35 and 0.2 mL (83 and 67%) compared with the 0.04 mL (19%) and after 0.2 mL compared with 0.04 mL for preterm infants (94 and 44%). At 0.2 mL, this was significantly higher in preterm compared with term infants (p < 0.01) and was the only significant difference between these infants. In response to pharyngeal fluid stimulation, airway defense in both full-term and preterm infants is maintained primarily by swallowing with no evidence of apnea.

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