Fast kinetic phenomena were studied in human subjects exposed to tetrachloroethene (perchloroethylene, PER). The duration of exposure ranged from one to 60 minutes and the concentration of PER in inhaled air ranged from 0.02 to 0.40 mmol/m3. The PER concentration in mixed venous blood (pulmonary artery) was estimated by alveolar concentration (CAlv) measured after a residence time of 10 s. During exposure, stoppage of intake (breath holding up to 50 s) caused a decrease of CAlv down to about 60% of the CAlv at a residence time of 10 s. At the end of exposure, stoppage of intake (breathing fresh air) caused a decrease of CAlv with t1/2 = 15-25 s; after two to four minutes, the decrease slowed down abruptly and the concentration remained more or less constant for about one to three minutes. After this stationary level, the decrease of CAlv continued but at a slower rate. During and after exposure, the decrease of CAlv seems to be caused by large differences in the circulation times of blood flowing through rapid, well perfused tissues and slower, well perfused tissues which may explain the stationary level. From this point of view, the vessel rich group in a compartment model must be split up in order to predict tissue and organ concentrations during peak environmental concentrations.
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