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 whole lung in a group of 9 sheep. Submicronic aerosol droplets were delivered to unsedated sheep held in a sling-like frame. Best fits for clearance curves to single- and biexponentials were calculated. The monoexponential T50 for the aerosol clearance was 293 min +/- 74 SD. Background correction was found to have a minimal effect (approx. 10%). Biexponential fitting only marginally improved correlations in the 8 healthy sheep, but in one additional animal with clinical evidence of pneumonia, clearance was faster and biexponential fitting was substantially better. These clearance values in conscious sheep are longer than previous findings with 99mTc-DTPA in anesthetized sheep. There appears to be a wide variation of radioaerosol 99mTc-DTPA lung clearances among different species, sheep exhibiting a comparatively prolonged clearance profile.