ASSESSMENT OF PULMONARY SURFACTANT FUNCTION USING A CAPTIVE-BUBBLE SURFACTOMETER

A captive-bubble surfactometer was built to measure the surface proper ties of reconstituted pulmonary surfactants (L-alpha-dipalmitoyl phosp hatidylcholine (DPPC), Exosurf, Alveofact) and whole lung surfactants obtained from normal and injured rat lungs (silica induced Lipoprotein osis). Whole surfactants from normal or injured rats were further char acterized by protein and phospholipid measurements. We used soluble te st substances (ethanol, water) to ascertain the precision, reliability , and cleanliness of the captive-bubble surfactometer. We performed th ree types of experiments by controlling the system pressure on the air bubble: adsorption, dynamic, and quasi-static cycling. Lateral views of the bubble were continuously recorded. The bubble height and diamet er were determined by image analysis and were used for the calculation of bubble tension and related parameters. Adsorption was slow with DP PC, faster with Exosurf and Alveofact, and fastest with whole lung sur factants. During the dynamic cycling experiments, DPPC immediately exh ibited low bubble tension. The bubble tension for Exosurf, Alveofact, and whole lung surfactants showed both decreasing values at minimum ar ea and increasing values at maximum area during dynamic cycling. In in itial cycles of the quasi-static cycling experiments, isotherm hystere ses were different for the various surfactants, and the bubble tension and compressibility were least with pure DPPC as compared to Exosurf and Alveofact. In contrast to all other surfactants, DPPC showed minim al refinement of film characteristics after repeated cycling. Whole lu ng surfactants exhibited surface properties comparable to those of rec onstituted surfactants, albeit at only half the phospholipid concentra tion. Whole lung surfactant from injured rat lungs was characterized b y increased lipid and protein content, whereas changes in the phosphol ipid composition and surface activity were only subtle compared to sur factant obtained from normal rat lungs. The characterization of the su rface properties of biological substances using the captive-bubble sur factometer is feasible and discriminates between different reconstitut ed and whole surfactants. This method is useful for studying biologica l materials because it enables measurements of surface properties unde r dynamic non-equilibrium conditions without him leakage, which is in contrast to other methods.