Sources of variation in 133Xenon washout after subcutaneous injection on the abdomen.

The washout of 133Xenon injected locally in three subcutaneous regions on three volunteers was in a repeated latin square design analyzed regarding flow values and initial clearance. Blood flow showed no dependence on injected volumes (.02-.5 ml), but there was a significant day-day variation and regional and personal differences in subcutaneous blood flow. The initial fast washout was related to the injected volumes due to trauma and dilution of the tissue. From these results precautions are described to increase the validity of the local 133Xenon washout method for measurement of subcutaneous blood flow. In repeated clinical studies it remains important even on the same individuals to record sources of variation apart from the variable to be investigated.