Human subjects were 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. Alveolar air was sampled after several residence times (t*) in the lung. Both during and after exposure, the concentration of PER in alveolar air (C Alv) as a function of the residence time was studied to estimate the concentration in the pulmonary artery (C Ven: mixed venous blood) and in the pulmonary vein (C Art: arterial blood). During exposure C Alv decreased as function of t*. At t* = 10 s C Alv was 70-75% of the value presented at t* = 5 s; this decrease approximates an exponential curve. C Alv seemed to stabilise at t* = 10-12 s, whereas it decreased more rapidly at t* greater than 12 s; this decrease continued up to at least t* = 55 s when C Alv was about 40% of the value it represented at t* = 5 s. In the postexposure period C Alv increased as function of t* from 5 to 10 s. Both during and after exposure, no difference was observed between C Alv at t* = 10 s and C Alv in the exhaled part of the expiratory reserve volume. A simple gas exchange model showed that the decrease or increase of C Alv at t* less than 10 s could be explained by either absorption or excretion by mixed venous blood. C Alv at t* = 10-12 s provided a valid estimate of C Ven. To estimate C Art, its fluctuating character due to the discontinuous breathing with a breathing frequency had to be taken into account. It is shown that C Alv during normal breathing (t* = 5 s) provides a reasonable estimate of the time weighted concentration in arterial blood.
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