Maturation of cough and other reflexes that protect the fetal and neonatal airway.

Although aspiration of contaminated amniotic fluid and gastric contents is common at birth, anecdotal evidence indicates that coughing occurs rarely if at all. Studies in which cough and other airway protective responses have been stimulated by introducing a small bolus of water or saline into the pharynx of sleeping infants have found that the predominant responses are swallowing, apnea and laryngeal closure. Coughing is rare. Collectively, these responses are known as the laryngeal chemoreflexes (LCR). These are mediated by receptors in the inter-arytenoid space. The LCR has been studied extensively in animal models. Upper airway infection increases the responses and in this case coughing becomes a common component. Studies in animal models indicate that with maturation, apnea and swallowing components of the LCR decrease while cough becomes increasingly prominent.