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

Abstract

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, apnoea 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, apnoea and swallowing components of the LCR decrease while cough becomes increasing prominent.

Expert opinion on the cough hypersensitivity syndrome in respiratory medicine

“…This ''cough cry sequence'' appears at about 1-2 months and is possibly a protective clearing of the airway of secretions prior to the inspiration of crying [92]. In the first months of life, coughing typifies airway infections such as respiratory syncytial virus (RSV).…”

Apnea of prematurity: challenges and solutions

“…Reflexes such as the laryngeal chemoreflex and the lung inflation (Hering-Breuer) reflex are also involved in the control of breathing, and the brain further controls the basic respiratory pattern. 10,11 The breathing pattern of a preterm infant, with the presence of periodic breathing, paradoxical ventilation, and immature responses to hypercapnia and hypoxia, resembles that present during fetal life. Fetal respiratory efforts do not influence arterial oxygen and carbon dioxide, so the fetal response to hypoxia is mainly aimed at reducing the consumption of oxygen, resulting in a reduction in respiratory activity.…”

Chronic cough and irritable larynx

“…6 In the upper airway there are many sensory nerve receptors 7 that are central to protecting the lungs from exogenous noxious agents. An important defensive reflex is the laryngeal chemoreflex, which in the newborn consists of vocal cord adduction and apnea aimed at preventing the aspiration of liquids, 8 whereas in the adult it consists of cough and airway constriction. The nociceptive nerve endings involved in these reflexes are unmyelinated, unencapsulated C-fibers and myelinated Ad-fibers, 9 which lay beneath and between the mucosal epithelial cells of the epiglottis, aryepiglottic folds, and interarytenoid space.…”