Exogenous surfactant enhances mucociliary clearance in the anaesthetized dog

Abstract

Therapy with exogenous surfactants is currently used for the treatment of respiratory distress syndrome of the newborn (RDS) and is under investigation for treatments related to adult RDS. However, the possible use of exogenous surfactant as a means of enhancing mucus clearance in other respiratory diseases has not been addressed. We therefore studied the effects of an artificial surfactant (Curosurf) on in vivo tracheal mucus velocity in intubated pentobarbital-anaesthetized dogs. Five dogs were randomly administered, on separate occasions, either vehicle (saline) or 10 mg Curosurf by means of local instillation via a catheter into the right lung. Tracheal mucus was collected by inserting a soft-bristled cytology brush to the level of the carina, and analysed for viscoelasticity by microrheometry. Mucociliary clearability in vivo, tracheal mucus velocity (TMV) in mm · min-1, was determined by bronchoscopic observation of charcoal marker particle transit times. The initial placement of charcoal was at the same level of the lower trachea that mucus was collected from. The effect of ciliary beat frequency was assessed on the frog palate assay by a videoscopic technique. In the dog, TMV was significantly increased after administration of surfactant. The values of TMV in the vehicle- and surfactant-treated dogs were 6.3 ± 4.0 vs 25.6 ± 6.5 mm · min-1 (SD), respectively. There were no discernible differences between prevehicle and postvehicle TMV values, and no significant differences in any mucus viscoelastic parameter, as determined by magnetic rheometry. There were also no significant changes in the viscoelastic or surface properties of mucus incubated with surfactant in vitro; however, ciliary beat frequency increased following administration of surfactant in the frog palate assay (from 3.6 ± 0.4 to 8.5 ± 3.2 Hz). The stimulation of TMV may be due either to a direct effect on ciliary function, to a reduction in the viscosity of the periciliary fluid, or to a more efficient interaction between the mucus and the cilia. In view of these results, we suggest that exogenous surfactant administration may provide a new therapeutic approach in treating conditions of impaired mucus clearance.