Pharyngeal fluid clearance and aspiration preventive mechanisms in sleeping infants

We sought to characterize ventilatory and airway protective responses to pharyngeal stimulation in young infants during sleep. We studied the various responses with respect to frequency of occurrence, effect of increased stimulus intensity, and relation of stimulus fluid to laryngeal structures. Two groups of infants were studied: healthy full-term infants (n = 5) and preterm infants with a history of prolonged apnea (n = 9). We used a nasopharyngeal catheter to deliver small boluses of warm saline (0.02-0.35 ml) to the oropharynx. Responses repeatedly observed in both infant groups included swallows, obstructed respiratory efforts, brief apnea, prolonged apnea, and cough. In both infant groups, swallows and obstructed breaths occurred frequently and cough and prolonged apnea infrequently. The functional significance of some response patterns was clear, whereas that of others was obscure. Larger stimulus volumes yielded more frequent responses (P less than 0.01), and preterm infants responded much more frequently than full-term infants (P less than 0.01). Prolonged apnea was a composite of the other responses and was much more common in preterm than full-term infants (P less than 0.01). The stimulus technique was performed under direct visualization of the airway in two deceased infants. The findings suggested that the relation of the piriform fossae to the interarytenoid notch is important in determining response frequency. Implications for regulation of the removal of upper airway secretions during sleep are discussed.