Hydrogen washout in bone cortex and periosteum

Residence time distributions of hydrogen in bone of anesthetized dogs and rabbits were used to estimate local blood perfusion rates and to characterize the important transport processes taking place. The hydrogen was administered by inhalation, and the concentrations in the bone were measured by embedded platinum microelectrodes. Mean residence times varied significantly both with position and time, and it was found preferable to calculate residence time from moments of the residence time distribution rather than the downslope method. Moreover, the downslope on a semilogarithmic scale continued to decrease with the increase in observation time. For the tissue investigated, simple compartmental models are inadequate even for the small regions characterized by the electrodes. This means that a large number of Haldanian compartments are needed even to characterize local washout behavior. The significance of this finding for the selection of decompression schedules is briefly discussed.