DETECTION AND REVERSAL OF PULMONARY ABSORPTION COLLAPSE

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Abstract
Six healthy seated male subjects (aged 36–54 yr) inhaled 100% oxygen for 10 min at normal lung volume and then for a further 5 min with forced maximal expirations. Following this manoeuvre, changes in arterial Po2 ranged from a decrease of 16.7 kPa to an increase of 2 kPa (—125 to +15 mm Hg) while breathing 100% oxygen, and a decrease of 1.8 kPa to an increase of 1.1 kPa (—13.5 to + 8.6 mm Hg) while breathing air. Functional residual capacity (FRC) was unchanged in one subject, but decreased by 0.04–1.15 litre in the others. The chest radiograph was unaltered in the subjects with zero and 0.04 litre decreases in FRC. Three of the other subjects showed line shadows at the bases, while the subject with the largest decrease in FRC showed extensive areas of collapse. There was a good correlation between changes in arterial Po2, FRC and the chest radiograph. Substernal discomfort was felt when those subjects with positive radiographic changes attempted to make a maximal inspiration. All changes were reversed by taking five maximal forced inspirations. Arterial Po2 changes while breathing 100% oxygen provided the most sensitive indication of collapse. Changes in FRC and arterial Po2 while breathing air were generally within the normal reference range of these variables, and therefore of little diagnostic value in the absence of control measurements. Under such circumstances, chest radiography seems to be the most sensitive indication of pulmonary collapse occurring in the upright position.