Idiopathic respiratory distress syndrome: acoustic, laryngoscopic and radiological investigation.

The breathing pattern in IRDS has been analysed by sound recording, direct laryngoscopy and chest X-rays. The reflex mechanism operative in IRDS was found to be a modified version of the Hering-Breuer reflex; in a certain phase of inspiration the respiratory muscles relax and passive expiration begins. In IRDS, at the end of the short inspiratory phase accompanied by grunting the glottis is suddenly closed, and collapse of the alveolar space is prevented. The small opening of the glottis before the next inspiration serves the same purpose, and the air passing through it is heard as grunting. As soon as the alveolar space is emptied, the glottis becomes wide open and a quick inspiration follows. The modified Hering-Breure reflex increases the respiratory tract pressure and thus prevents collapse of the alveolar space. When the newborn is no longer capable of the excess extra work required for grunting, the decompensated phase of IRDS sets in. Gas exchange rapidly deteriorates and the white lung pattern is visible on the chest X-ray.