Cervical posture and nasal breathing in infancy.

Survival of infants born with bilateral choanal atresia or pyriform aperture stenosis who breathe orally, as well as experimental data, challenge the virtually axiomatic theory of 'obligatory' nose breathing of the neonate. The anatomical parameters leading to the infant's airway patency and to airway obstruction were studied on midsagittal anatomical sections of fetal and adult necks as well as in head and neck radiographs of infants. The most important anatomical parameter found to facilitate the switch from nasal to oral ventilation in human infants is a cervical extension, creating a physiological lordosis of the neck that results in an opening of the veloglossal and veloepiglottic sphincters. This mechanism may explain the relationship between the sleeping posture of the infant and sudden infant death syndrome.