Viscoelastic properties of canine tracheal mucus: effects of structural inhomogeneities and storage

Tracheal mucus is an inhomogeneous material and thus its viscoelastic properties may vary substantially within a mucus sample. In this study on canine tracheal mucus, we investigated this variation of mucus viscoelasticity and addressed the question whether or not the viscoelasticity is affected by storage of the mucus at low temperatures. Mucus samples were collected from 16 beagle dogs kept under clean air conditions. By means of magnetic rheometry, dynamic viscosity- and elasticity were determined either in the fresh state of these samples or after storage at -80 degrees C. Owing to inhomogeneities within the gel-structure of the mucus, local values of the viscoelastic parameters differed by more than an order of magnitude. Short storage periods (5 d) were found to decrease, long periods (100 d) to increase the viscosity as well as elasticity parameters of the mucus material. These results emphasize the fact that measured viscoelastic properties of mucus are average values depending on the measuring protocol. In addition, these values are modified by storage of the mucus at low temperatures.