MICROATELECTASIS IN PATIENTS WITH SECUNDUM ATRIAL SEPTAL-DEFECT AND ITS RELATION TO PULMONARY-HYPERTENSION

In patients with secundum atrial septal defect, pulmonary hypertension appears to be attributable to microatelectasis of the lung. To confir m this hypothesis, pulmonary arteries in surgical biopsy specimens fro m 72 patients with atrial septal defect and pulmonary hypertension wer e subjected to morphometric examination. Thirty eight of the 72 patien ts (53%) were found to have microatelectasis of the lung, which sugges ts that an even higher frequency would have been found if the entire o rgan had been examined. Atelectatic changes were found in 21 of 39 pat ients with plexogenic pulmonary arteriopathy (54%), 8 of 15 with muscu loelastosis (53%), and 9 of 13 with both of these lesions (69%). No su ch changes were observed in 5 patients with atrial septal defect who s howed thromboembolism-type lesions of the pulmonary arteries. On the o ther hand, microatelectasis was not observed in another 5 patients wit h atrial septal defect who did not exhibit pulmonary hypertension. The medial smooth muscles of pulmonary arteries in ateletatic areas were thicker (16.4+/-4.0 mu m) than those in non-atelectatic areas (10.3+/- 3.3 mu m). The index of pulmonary vascular disease was not significant ly different between atelectatic (2.0+/-0.6) and non-atelectatic areas (1.9+/-0.5). We conclude that in microatelectatic areas, which may te nd to develop after respiratory infections in patients with atrial sep tal defect, hypoxic vasoconstriction of the small pulmonary arteries i s liable to occur, which causes hypertrophy of the media. This is like ly to lead to the elevation of pulmonary arterial pressure and sustain ed pulmonary hypertension.