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 evaluate differences in regional deposition patterns of an Evans Blue dye (EB) tracer aerosol. This was done by using different carrier gas composition of either He-O2 (80% helium, 20% oxygen) or air (79% nitrogen, 21% oxygen) in histamine-provoked and nonprovoked rabbits. The ratio of peripheral deposition to total deposition (central + peripheral), in relation to percentage increase in intratracheal pressure (ITP delta %), was used as an evaluation tool. The animals were tracheostomized, cannulated, and ventilated in a volume-controlled mode until they were stable. Saline or histamine was then administrated for 2 min before the tracer aerosol EB was given. The percentage increase in intratracheal pressure before and after provocation was calculated (ITP delta %) and was, on average, 51 +/- 20% for air and 51 +/- 20% for He-O2. EB was extracted from lung tissues and measured with a spectrophotometer. The absorbance in different lung regions was used as a measure of the distribution of aerosol. Bronchial provocation gave a central deposition 0.55 +/- 0.11 (mean +/- SD, ratio = peripheral deposition/central + peripheral deposition) compared to 0.80 +/- 0.09 in the control group. He-O2-ventilated rabbits showed significantly higher peripheral deposition 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-O2, respectively. This study demonstrates the possibility of using a rabbit model and different carrier gases for evaluation of effects of bronchial provocation.