Ozone-induced accelerated lung clearance of ^99mTc-DTPA aerosol in conscious sheep

This study was initiated to determine the rate and characteristics of ^99mTc-DTPA clearance from the lungs of unanesthetized sheep exposed to varying concentrations of O₃ for 4 h in a whole-body exposure chamber. Four sheep exposed to 1 ppm O₃ had a monoexponential T₅₀ of 274 ± 81 min (SD), not significantly different from sham exposures (316±150); 5 sheep exposed to 2 ppm had a T₅₀ of 234 ± 101 min, not significantly different from sham exposures (263±107 min); 3 sheep exposed to 4 ppm showed a T₅₀ of 66 ± 19 min, markedly different from sham exposures (364 ± 131 min). Five additional unanesthetized sheep exposed to 2 ppm for 4 h via a nasotracheal tube had a T₅₀ of 192 ± 55 min, significantly different from sham exposures (300 ± 96 min). The results show that the effect of oxidant pollutants on the permeability of alveolobronchiolar epithelium may be assessed in conscious sheep.