Roles of hydration, sodium, and chloride in regulation of canine mucociliary transport system

To gain insight into the homeostatic mechanisms regulating airway ion/water fluxes and mucociliary transport, the canine tracheobronchial airway fluid was perturbed by deposition of hypo- and hyperosmotic aerosols for >1 h. Tracheal ciliary beat frequency (CBF) was measured by using heterodyne laser light scattering. Tracheal mucus velocity (TMV) and bronchial mucociliary clearance (BMC) were measured by using radioaerosols and nuclear imaging. Respiratory tract fluid output (RTFO) was collected by using a secretion-collecting endotracheal tube. In six dogs, CBF increased during water deposition in the airways to 180 +/- 30 mg/min and RTFO increased from 2.2 +/- 0.5 to 18.3 +/- 1.6 mg/min, accounting for <10% of the fluid deposition. TMV and BMC were unchanged. CBF, TMV, and BMC were markedly increased by inhalation of aerosolized 3.4 M NaCl. Aerosolized 0.85 M NaCl, in contrast, decreased BMC. In this case, RTFO represented 24% of aerosol deposition. Aerosolized 0.85 M choline chloride and 0.85 M sodium gluconate enhanced BMC and TMV concurrent with a decrease in CBF. RTFO of sodium gluconate studies exceeded 50% of aerosol deposition. Thus the airways appear to have transepithelial compensatory mechanisms that reduce the impact of a moderate increases in NaCl and hydration load, but when these responses cannot adequately respond because of the delivery of impermeable ions or very high tonicity, removal of the challenges are affected by a stimulation of mucociliary transport.