Bubbles and computer-aided image analysis for evaluation of surfactant inhibition

Surfactant (Curosurf, diluted to 5 mg/ml) was suspended in normal saline with 3 mM CaCl2 and mixed with different concentrations of albumin or fibrinogen. The samples were vortexed to generate microbubbles, and the equivalent circle diameter of these bubbles was determined with computer-aided image analysis. Bubbles in the original surfactant suspension had an average diameter of 27 microns after 2 min, and their size increased only little during a 15-min period of observation. The diameter of bubbles generated in the presence of albumin (4 or 40 mg/ml) or fibrinogen (4 mg/ml) was 4-5 times larger, indicating surfactant inhibition. We conclude that evaluation of microbubble stability with image analysis provides an objective and rapid assessment of surfactant inhibition, and we speculate that the method could also be used for quantification of surfactant activity in airway samples.