Background: 

The oxygenation occurs very rapidly from the alveoli to the erythrocytes because of the large surface area of the lungs and a very small diffusion barrier between blood and air. The surfactant is a compound of the alveolar fluid which function is known so far to lower surface tension. It prevents the alveoli from collapsing as would be expected from the law of LaPlace. Nowhere is the observation described as to be an additional resistance to oxygen diffusion from the alveoli to red cell interior. In a physical model we studied the effect of different oils, in order to quantify them as a diffusion barrier depending on their physical properties such as viscosity and density also in the presence of surfactant.

Method: 

In an especially designed chamber the physical conditions of the alveolar gas exchange were approached. Perfluorocarbons (FC) were used as a blood substitute. These fluids are inert and have high oxygen solubility up to 19 ml/dl and are already used as artificial blood and for liquid ventilation. In the present study FC43 was used. A thin layer of the oil to be investigated was spread upon the FC43 which possesses a high density. The environment over the oil layer was continuously flushed by pure oxygen or air. By a high sensitive O₂-sensor the oxygen partial pressure was continuously measured inside the blood substituting fluid and oxygen bindings curves established for all lamp oils. Additionally a for premature infants clinically used surfactant was applied at various dosages to the "alveolus model chamber". The oxygen diffusion was measured as a function of time.

Results: 

It is shown that all types of oil used demonstrate a significant barrier for oxygen. The resistance amounted up to 15fold of the resistance for a water layer depending upon their physical property. The oil with highest viscosity represented the highest resistance. However, the surprising result is the effect of surfactant on a facilitation of the oxygen diffusion up to 10 times more than without surfactant, which was even dose dependent. The addition of surfactant to the oil but also to a water layer accelerated the dynamic of oxygen uptake, which may be interpreted as a reduction of the diffusion barrier. This observation is the subject of future studies for a definitive explanation for this surprising observation.