Ring distraction technique for measuring surface tension of sputum: relationship to sputum clearability

Albers, G. M., R. P. Tomkiewicz, M. K. May, O. E. Ramirez,and B. K. Rubin. Ring distraction technique for measuring surfacetension of sputum: relationship to sputum clearability. J. Appl. Physiol. 81(6):2690-2695, 1996.Poor sputum clearance has been related to sputumadhesion tension. In this study, we describe a modified du Noüyring method for measuring the surface tension () of small samples ofsputum and for comparinge the calculated work of adhesion(W_ad) for sputum specimens withthe measured mucociliary transportability (MCTR) and coughtransportability (CTR). The , as measured by this method, correlateswith  measured by sputum contact angle on a low-surface-energy solid(R² = 0.368, P = 0.03). There is a smallbut significant difference in measurements made by these two methods(P = 0.03).W_ad calculated from the surfacetension ring method is inversely correlated with CTR(R² = 0.181, P = 0.004) but has nocorrelation with MCTR in this study. The miniaturized ring method givesaccurate and reproducible measurements of the surface tension of smallamounts of respiratory secretions. Because sputum behaves enough like aliquid that the assumptions made in using the Young equation tocalculate W_ad appear valid, wealso showed that the Neumann equation can be used to determine thesurface tension of sputum by its contact angle on tetrafluoroethylene(Teflon).