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ESTIMATION OF CLEARANCE RATE OF INHALED XENON‐133 IN THE PLACENTAL REGION OF THE PREGNANT UTERUS

A safe, atraumatic method of measuring clearance of 133Xe in the region of the placenta is described. The gas was inhaled for two minutes, and external monitoring of the placental area and of the expired air was continued for a further 25 minutes. The placental clearance curve was analyzed into two exponential components, with and without correction for recirculation of the tracer. There was a significant difference of 15 per cent between the results of the two methods of analysis. No difference was found between the mean clearance rates of 19 normotensive and 19 hypertensive patients. The birthweights of the babies were used to assess total placental function, and its relationships to the clearance rates is discussed.