Surface activity in situ, in vivo, and in the captive bubble surfactometer

For studies of the mechanical effects of lung surfactants, the captive bubb le surfactometer (CBS) combines the advantages of the continuous film of Pa tties bubbles with the feasibility of the Langmuir-Wilhelmy balance to prod uce surface tension-area hysteresis loops. The CBS allows the compression o f films to very low and stable surface tensions of 1-2 mN/m. Such low and s table surface tensions are in line with results obtained from pressure-volu me studies on excised lungs. In addition, the CBS is useful to test other e ssential physical properties of the surfactant system, including: (1) rapid film formation (within seconds) through adsorption from the hypophase, (2) low film compressibility with a fall in surface tension to very low (< 2 m N/m) values during surface compression; and (3) effective replenishment of the surface film on expansion by the incorporation of surfactant material f rom material associated with the surface (the surface associated surfactant reservoir). Morphological observations of films fixed in situ or in vitro reveal frequently their multilayered structure, which is consistent with th e concept of the surface reservoir. The deviation of the bubbles from a Lap lacian shape at very low surface tension and the morphological observations suggest that the surfactant film cannot be considered a simple monolayer. (C) 2001 Elsevier Science Inc. All rights reserved.