Effects of unilateral bronchoconstriction on distribution of aerosols in ovine airways

The purpose of the study was to assess the effect of unilateral bronchocons triction on the deposition patterns of aerosolized particles in a sheep mod el. Unilateral bronchoconstriction was induced in intubated conscious sheep by placing a protective, obstructing balloon catheter in either main bronc hus, prior to administration of aerosolized carbachol at a dose that increa sed pulmonary resistance by 200-400% above baseline. The catheter was then removed and the animals were positioned under a gamma camera. An equilibriu m image was obtained with xenon (Xe-133), to determine a lung outline that was used to calculate the proportion of counts in each lung. Aerosols, labe led with technetium (Tc-99m) and generated by two jet nebulizers, were inha led tidally by the sheep in serial experiments. (For nebulizer A. mass medi an aerodynamic diameter [MMAD] = 0.39 mum; for nebulizer B, MMAD = 1.1 mum. ) For nebulizer A, percentage deposition in the treated and untreated lungs was not significantly different (50.8% versus 49.2%, respectively), while for nebulizer B, the median deposition in the carbachol treated lung was si gnificantly greater than in the untreated lung (55.8% versus 44.2% respecti vely; p = 0.005). There was a more central pattern of deposition in the tre ated lung than in the untreated lung for both nebulizers, but the degree of central deposition was significantly greater with nebulizer B. The finding s of the present study suggest that regional obstruction does not preclude the delivery of therapeutic aerosols to the airways in such a region, and m ay, depending on the size of the aerosol, result in enhanced airway deposit ion relative to less obstructed regions.