The role of bronchospirometry in evaluation of differential left to right congenital shunting from the two lungs is illustrated in an eighteen year old white girl who was found, at cardiac catheterization, to have an interatrial septal defect and anomalous pulmonary venous drainage from the right lung only. During bronchospirometry, administration of pure nitrogen to the right lung (the lung with anomalous pulmonary venous drainage) did not result in a fall in arterial oxygen saturation after ten minutes. However, administration of pure nitrogen to the left lung resulted in a rapid fall in oxygen saturation after a three-minute period. These observations suggest that blood draining the right lung in this patient does not directly reach the periphery at any time, but may only reach the systemic arterial blood after circulation through the left lung. This technic may also be of value in demonstrating differential left to right shunting from the two lungs in patients with interatrial septal defect.
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