ABSTRACT
The first breaths result in an enormous expansion of the air-liquid interface of the respiratory system, from about 2 cm2 (estimated surface area of the larynx) to some 2-3 m2 in a full-term newborn baby when all alveoli have become recruited.4 The work required to expand the inner respiratory surface is directly related to surface tension.123 Gruenwald,31 on the basis of port-mortem pulmonary pressure-volume recordings and histological observations of lung expansion patterns, postulated that ‘the addition of surface active substances to the air or oxygen which is being spontaneously breathed in or introduced by a respirator might aid in relieving the initial atelectasis of newborn infants’. These observations anticipated the physicochemical demonstration of surfaceactive material in lung tissue by Pattle86 and Clements.13
