Mucociliary function deteriorates in the clinical range of inspired air temperature and humidity

Objective. To test whether a reduction in air temperature within the clinical range [37 degreesC to 30, 100% relative humidity (RH)] altered mucus transport velocity (MTV) and ciliary beat frequency (CBF) in an in vitro ovine tracheal model. Design. Controlled laboratory study. Setting. University research laboratory. Subjects. Farm-reared sheep. Interventions. Tracheae were mounted flat in an organ bath. Krebs Henseleit bathed the serosal surface and air at 100% (RH) was passed over the mucosal surface at 4 l/min. Cilial beat frequency (CBF) was measured photo-electrically and mucus transport velocity (MTV) by timing movement. After 2 h at 37 degreesC (100% RH) the tissue was either maintained with those settings (controls), or the air temperature reduced to 34 degreesC or 30 degreesC. Tissue was taken for histology before and after each experiment. Measurements and results. CBF was 19.8+/-2.7 beats/s and MTV 5.7+/-2.6 mm/min in tissue exposed to air at 37 degreesC. Cilial activity continued for up to 6 h in the controls but mucus transport was more fragile. Reduction of the air temperature to either 34 degreesC or 30 degreesC led to a decrease in both CBF and MTV and, frequently, total mucociliary failure. There was a reduction in epithelial mucous cell numbers in all preparations. Tissues exposed to low temperature had additional abnormal histology. Conclusions. Delivery of inspired gas at 30 degreesC, or even 34 degreesC, with 100% RH may not be sufficient to prevent epithelial damage occurring during 6 h exposure.