Carbon dioxide labeled with oxygen-15 has been used to study the regional blood flow in the lungs of patients with pulmonary stenosis. The upper and lower zone flows were normal in patients with isolated pulmonary stenosis, but both were low in patients with the tetralogy of Fallot. A comparison of the two upper zones showed a significantly higher blood flow through the left upper zone in patients with both isolated pulmonary stenosis and the tetralogy of Fallot. A significantly higher flow was also found through the left upper zone than the right of normal subjects. By contrast, patients with atrial septal defect had a higher flow through the right upper zone than the left. Neither difference was as large as in the patients with right ventricular outflow tract obstruction. Patients with ventricular septal defect and those with patent ductus arteriosus had almost identical flow through the two upper zones.
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Dollery et al. (1961) studied this question.