Mucus transportability: the bovine trachea and frog palate models compared.

For nearly 30 yrs, the mucus-depleted frog palate has been used to measure the ciliary transportability of respiratory and other mucus gels, but the data obtained from this amphibian digestive system may not be applicable to human airway mucociliary clearance. This study compared this model with the mucus-depleted bovine trachea, a mammalian respiratory system. Assessments were made of the reproducibility of each model, and of the behaviour of sputum subjected to changes to its salinity or hydration. The bovine tracheal model was more reproducible than the frog palate. On the trachea but not the frog palate, sputum was transported more slowly than mucus from healthy animals. Increasing the salinity of sputum caused it to be transported 129% more quickly by the trachea (p=.001), but made no significant change to its transportability by the frog palate. Removal of water by evaporation led to an 83% increase in its bovine tracheal transportability but a 60% fall in its frog palate transportability (p<0.001). Therefore, the models make opposite predictions for the clinical value of altering mucus osmolality. The applicability of the frog palate model in the study of airway mucociliary clearance should be seriously questioned.