Otitis media with effusion: components which contribute to the viscous properties.

Middle ear effusions from children undergoing myringotomy were classified into thick (mucoid) and thin (serous) on the basis of their flow properties. Their composition was analysed and their rheological properties measured. The viscosity of the effusions was measured using a Contraves low shear viscometer and expressed as specific viscosity per mg/ml of non-dialysable solids present. In order to measure the effusion viscosity it was necessary to solubilize the effusion by mild homogenisation in a phosphate buffer pH 6.7 containing a cocktail of proteolytic inhibitors. The viscosity of mucoid effusions was significantly greater than that of the serous effusions. There was a small but measurable amount of proteolytic activity in the effusions, range 0.05-1.79 micrograms/mg of non-dialysable solids. This proteolytic activity was not significantly different between the thick and thin effusions and was therefore unlikely to explain the difference in viscosity. Analysis of the constituents of the effusions showed that glycoprotein and DNA but not protein nor lipid were significantly higher in the mucoid effusions compared to the serous effusions. The viscosity of the effusions correlated with the glycoprotein concentration but not with the protein or lipid concentration. Under certain circumstances the DNA concentration did correlate with the viscosity of the effusion. However, digestion with a proteinase free DNase did not reduce the viscosity of the effusion. These results demonstrate that classifying effusions as thick and thin based on visual inspection and flow properties is valid and that the only constituent present in the effusions that determines viscosity is mucin.