Expansion pattern of terminal air-spaces in the premature rabbit lung after tracheal deposition of surfactant.

The expansion pattern of the lungs of full-term and premature newborn rabbits was evaluated by direct observation of the lung surface during an inflation-deflation cycle, with particular reference to the effect of tracheal deposition of surfactant before the first breath. In non-treated premature fetuses, aeration of alveoli was initiated at an endotracheal pressure of 35 cm H2O; the mean corresponding 'opening pressure' was 25 cm H2O in both full-term and surfactant-treated premature animals. The process of alveolar aeration was asynchronous in all groups but at maximal inflation pressure (35 cm H2O) the expansion pattern was uniform in full-term and surfactant-treated premature fetuses; these animals also developed residual volume. In non-treated premature animals aeration was patchy, even at maximal inflation, and the lungs emptied at the end of deflation.