Correlations between physical and physiological properties of various preparations of lung surfactant.

The physical and physiological properties of natural surfactant were investigated after the addition of various synthetic lipids. Three types of surfactant were studied: 1. Bovine surfactant with rapid spreading (1.6 s) and a relatively high minimal surface tension during surface compression (16 mN/m). 2. The same surfactant enriched with dipalmitoylphosphatidylcholine (DPPC), tripalmitin, and palmitic acid showing slow spreading (55 s) and low minimal surface tension (5 mN/m). 3. The same surfactant enriched with DPPC and dipalmitin, showing rapid spreading (1.8 s) and low minimal surface tension (6 mN/m). The physiological properties of these surfactants were evaluated in immature newborn rabbits. All three preparations effectively improved lung expansion and stability in pressure-volume recordings, increased tidal volumes during artificial ventilation, and enhanced alveolar volume density in histological sections. The magnitude of the therapeutic effects was similar for non-enriched and enriched materials. Thus, wide variations in in vitro surface properties do not seem to influence the in vivo activity of the surfactant preparations.