The airways are lined with a thin film consisting of two layers. A watery layer, the airway surface liquid (ASL) surrounds the cilia and its major function is to serve as a medium for ciliary boating of mucus out of the respiratory system. The other layer is a viscous mucus layer consisting mainly of airway cellular secretions and cellular debris.
The composition and effects of altered concentrations of the constitutive elements in the ASL and mucus layer remain a mystery. in human patients, attempts have been made to determine the composition of these layers by sampling with a filter paper by touching it to the mucosa and wetting it by capillary action. This material was then removed from the filter paper and quantitative analyses using energy dispersive x-ray spectrometry (EDS) and a Hall’s thin film correction routine performed on the residue. Although differences were detected between normal and pathological material, these results did not reflect the composition of the individual layers but an average of both.
Attempts have been made to determine the elemental composition of these layers in intact and in cultured rabbit trachea, bovine trachea and hamster trachea.