Clearance of Middle Ear Effusions by the Mucociliary System

Abstract

There are two extreme types of middle ear effusion leading to hearing loss (a) a rubber-like effusion seen in secretory otitis media and (b) a water-like effusion seen in serous otitis media. The possibility is considered that the degree of crosslinking in these two extreme cases is the basis of an altered mucus transport rate that leads to an accumulation of effusions and hence impaired hearing.

It has been shown (King et al., 1974) that the requisite rheological property for transport activity is not unique to mucus structural macromolecules but is found with other polymeric systems that are loosely crosslinked e.g. guaran, polyacrylamide, gelatin and agarose. Studies on one of these systems, guaran, indicate that the transport rate is dependent on the degree of crosslinking with a maximum rate found close to the gel point, i.e. in a region where there are very few crosslinks per macromolecule.

The finding that mucus from different mucociliary epithelial sources involves a chemically similar structural glycoprotein suggests that differences observed in transport rate between various mucus samples are more likely due to differences in crosslinking than chemical variations of the glycoprotein units. By analogy with the model guaran system, it is suggested that the two types of middle ear effusions represent extremes in crosslinking and that their transport rate lie to either side of the optimum presumably represented by the normal secretion. Factors such as charge, concentration and the influence of temperature on mucus crosslinking are discussed.