REGIONAL DEPOSITION OF INHALED EVANS BLUE-DYE IN MECHANICALLY VENTILATED RABBITS WITH AIR OR HELIUM OXYGEN MIXTURE

An animal model has been used and further developed to examine and eva luate differences in regional deposition patterns of an Evans Blue dye (EB) tracer aerosol. This was done by using different carrier gas com position of either He-O-2 (80% helium, 20% oxygen) or air (79% nitroge n, 21% oxygen) in histamine-provoked and nonprovoked rabbits. The rati o of peripheral deposition to total deposition (central + peripheral), in relation to percentage increase in intratracheal pressure (ITP Del ta%), was used as an evaluation tool. The animals were tracheostomized , cannulated, and ventilated in a volume-controlled mode until they we re stable. Saline or histamine was then administrated for 2 min before the tracer aerosol EB was given. The percentage increase in intratrac heal pressure before and after provocation was calculated (ITP Delta%) and was, on average, 51 +/- 20% for air and 51 +/- 20% for He-O-2. EB was extracted from lung tissues and measured with a spectrophotometer . The absorbance in different lung regions was used as a measure of th e distribution of aerosol. Bronchial provocation gave a central deposi tion 0.55 +/- 0.11 (mean +/- SD, ratio = peripheral deposition/central + peripheral deposition) compared to 0.80 +/- 0.09 in the control gro up. He-O-2-ventilated rabbits showed significantly higher peripheral d eposition ratio (0.67 +/- 0.12) compared with air-ventilated rabbits ( 0.55 +/- 0.11). The latter finding may be due to the difference in the degree of turbulent flow. There were significant correlations between intratracheal peak pressure and peripheral deposition, r = -.60 and r = -.71 for air and He-O-2, respectively. This study demonstrates the possibility of using a rabbit model and different carrier gases for ev aluation of effects of bronchial provocation.