Evaluation of Surfactant Function: In Vitro and In Vivo Techniques in Experimental Respirology
Pulmonary surfactant is present as the thin film of surface active material in the terminal airspaces and conducting airways. The major function of the surfactant film is to reduce the surface tension at the alveolar surface. Deficiency or dysfunction of pulmonary surfactant cause severe respiratory diseases that make the study of pulmonary surfactant not only of physiological but also of clinical importance.
There are three main categories of methods for assessing the properties of pulmonary surfactant: in vitro, in situ and in vivo techniques. Pulsating bubble surfactometer (PBS) and captive bubble surfactometer (CBS) enables to study surfactant properties at spherical air-liquid interphase. Capillary surfactometer in contrast to alveolar models mimics the human terminal airways and evaluates surface properties required for airway patency. Each of above-mentioned methods enables to study exogenous surfactants, as well as surface activity of lavage fluids or tracheal aspirates.
Biophysical characteristics should be reflected by lung compliance and, as a consequence, by improved blood oxygenation. Various animal models have been developed to evaluate the efficacy of surfactant replacement therapy on preterm and term animals. In vivo models can be divided in those, primarily involving surfactant deficiency, such as premature animal model, and those with secondary surfactant dysfunction or inactivation, such as meconium or acid aspiration models.
This review is restricted to the in vivo and in vitro techniques handled by the authors in their research performed within the last years at both domestic and external laboratories.