Preterm infants with respiratory distress.
Preterm infants have pulmonary immaturity which results in a surfactant deficiency.
Surfactant lowers the surface tension of the alveolar membrane. Without surfactant the alveoli collapse at the end of each expiration. This in turn leads to respiratory failure in the neonate. The patient usually has a decreased lung volume, and vertically oriented ribs leading to a bell shaped thorax. The classical symmetrical appearance will most probably not be present in patients who have received artificial surfactant therapy.