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Intravenous 133Xe clearance in preterm neonates with respiratory distress. Internal validation of CBF infinity as a measure of global cerebral blood flow.

An intravenous 133Xe clearance technique is described, giving very low values of global cerebral blood flow (CBF infinity) in mechanically ventilated, preterm infants. External monitoring of the chest is used to estimate the arterial input function to the brain, with a modified correction to allow for increased recirculation due to right-to-left shunting. The results compared well in 10 studies in seven infants, where CBF infinity could also be calculated from direct simultaneous blood sampling from the right radial artery (7.9 ml/100 g/min +/- 2.5 SD vs. 8.4 +/- 3.6, p less than 0.05). In 25 studies in 12 infants the results compared well with those calculated from simultaneous 133Xe concentrations in expired air. Fifteen-minute clearance data gave better precision than 8-min data. The modified chest curve correction was partly effective in a case of extreme right-to-left shunting.