The pattern of ldye dilution curves and the cardiac output was studied in 29

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The arterial oxygen saturation was determined in 135 healthy newborn infants during sleep and while crying with a direct reading single scale oximeter. In the first group, consisting of infants from one hour and 30 minutes to 3 days of age, 66% showed a decrease of oxygen saturation with crying, 27% an increase and 6.8% no change. In the second group, which includes all infants between 4 and 9 days of age, 59% showed an increase in saturation with crying, 21% a decrease and 22.4% no change. In comparison, the mean results in these two groups are in the opposite direction. These changes are statistically significant. Twenty-eight infants were studied also while breathing oxygen (73%-98.5%), and the results compared with those in room air were found to show an identical trend. It is concluded that increases in arterial oxygen saturation with crying, which occur most frequently in older infants, are probably due to an increase in alveolar oxygen tension secondary to improved pulmonary ventilation during crying. The paradoxic decrease in saturation during crying, which was found in a large percentage of infants of the younger group, is suggestive of the presence of a transitory venous-arterial shunt. This shunt could be either through atelectatic areas of the lung or through the foramen ovale, which is only functionally closed and can open whenever the pressure in the right auricle exceeds the left auricular pressure. There is some available evidence to support the latter possibility.

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