Effects of acid on the larynx of the maturing rabbit and their possible significance to the sudden infant death syndrome.

Sudden infant death syndrome (SIDS) has been shown to result from a variety of causes. One group of neonates at high risk for SIDS includes those who develop apnea secondary to gastroesophageal reflux (GER). Reflux has been shown to produce apnea in infants, and aggressive treatment results in significant improvement in symptoms. Because it is a site of resistance in the airway, the larynx plays an important role in the development of apnea. Through its sensory innervation, the larynx also serves as the afferent limb for reflexes that regulate respiration. In order to investigate the relationship between obstructive apnea and central apnea induced by the instillation of acid on the larynx, simulating GER, a rabbit model was developed. Maturing rabbits at 15-day intervals up to 60 days of age were studied using saline and acid solutions. Acid solutions produced obstructive apnea in all age groups. With acid solutions, central apnea occurred in all age groups but had a peak incidence at 45 days. Gasping respirations were seen in all groups but were most common at 30 days of age. Although obstructive and central apnea occurred together as mixed apnea, both types of apnea were seen independently of each other. Acid instilled on the larynx of maturing rabbits resulted in significant obstructive, central, and mixed apnea. Gasping respirations and frequent swallowing were frequent associated symptoms. Acid-induced obstructive apnea in rabbits mirrors symptoms seen in human infants with GER. Central apnea in infants with GER is seen less commonly; however, central apnea as the result of laryngeal stimulation has been demonstrated repeatedly in several animal models. Central apnea, culminating in fatal asphyxia, has been described in several animal models. The larynx appears to play a pivotal role in the development of apnea in susceptible infants with GER.