Effective pulmonary blood flow was measured in 32 normal infants by an indicator gas technique. To check the accuracy of this technique in the absence of shunts, we obtained 39 pairs of measurements of pulmonary blood flow in anesthetized rabbits by the gas technique and dye dilution. The results showed a high degree of correlation between the two methods of measurement (r = 0.986). Effective pulmonary blood flow was 1.1% less than total pulmonary flow (p < 0.005); this difference was attributed to venoarterial shunting through non- ventilated parts of the lung.
Measurements of effective pulmonary blood flow in normal newborn infants increased with age. Before 24 hours of age, mean effective pulmonary flow averaged 138 ml/min/kg or less and gradually rose to a mean value of 166 ml/min/kg (±25.6 SE) at a mean age of 81 hours. It is possible that our measurements of effective pulmonary blood flow before 24 hours of age were falsely low because of the presence of clinically undetectable left-to-right shunts.
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