THE CAPTIVE BUBBLE METHOD FOR THE EVALUATION OF PULMONARY SURFACTANT - SURFACE-TENSION, AREA, AND VOLUME CALCULATIONS

For measuring the properties of lung surfactant, we provide formulas f or calculating the surface tension, area, and volume of captive air bu bbles in aqueous media. Only measurements of bubble height (h) and dia meter (d) are required. Data processing has been automated using stand ard video capture hardware and software, and our own image-processing and -analyzing programs. Our polynomials in h/d describe the ratios of actual bubble surface area and volume to that of a spherical bubble h aving the same diameter. For surface tension, a polynomial in h/d desc ribes the ratio of the surface tension of a flat semi-infinite bubble to the surface tension of the measured bubble of the same height. Coef ficients for the area and volume polynomials were obtained from h and d, and measured areas and volumes of revolution of calibrating bubbles . Coefficients for the surface tension polynomial were obtained analyt ically from a published polynomial in h/d [3]. Results using these pol ynomials agree satisfactorily with those obtained independently [4] us ing bubble perimeter measurements.