RING DISTRACTION TECHNIQUE FOR MEASURING SURFACE-TENSION OF SPUTUM - RELATIONSHIP TO SPUTUM CLEARABILITY

Poor sputum clearance has been related to sputum adhesion tension. In this study, we describe a modified du Nouy ring method for measuring t he surface tension (gamma) of small samples of sputum and for comparin ge the calculated work of adhesion (W-ad) for sputum specimens with th e measured mucociliary transportability (MCTR) and cough transportabil ity (CTR). The gamma, as measured by this method, correlates with gamm a measured by sputum contact angle on a low-surface-energy solid (R(2) = 0.368, P = 0.03). There is a small but significant difference in me asurements made by these two methods (P = 0.03). W-ad calculated from the surface tension ring method is inversely correlated with CTR (R(2) = 0.181, P = 0.004) but has no correlation with MCTR in this study. T he miniaturized ring method gives accurate and reproducible measuremen ts of the surface tension of small amounts of respiratory secretions. Because sputum behaves enough Like a liquid that the assumptions made in using the Young equation to calculate W-ad appear valid, we also sh owed that the Neumann equation can be used to determine the surface te nsion of sputum by its contact angle on tetrafluoroethylene (Teflon).