Diffusing capacity in idiopathic scoliosis and its interpretation regarding alveolar development.

We measured lung volumes, diffusing capacity by the single breath method (DL), membrane permeability (DM), and capillary blood volume (Vc) in 22 subjects with idiopathic scoliosis (mean angle of curvature, 66 degrees). Compared with an age-matched group, vital capacity, total lung capacity, and functional residual capacity were respectively, 21% (p less than 0.0001), 18% (p less than 0.01), and 15% (p less than 0.05) lower. The DL was 17% lower (p less than 0.01), but specific DL (DL divided by alveolar volume = DLVA) was the same. For both groups, DLVA was inversely correlated with VA. The same qualitative relationship existed between DM, Vc, their specific values, and VA except for a larger spread of Vc in the scoliotic group. The data show that DL and its components, DM and Vc, are normal in idiopathic scoliosis when reduced lung volumes are allowed for. These findings are consistent with partial failure of alveolar enlargement as a result of the thoracic deformity rather than any atrophy of the alveoli or pulmonary vasculature. Thus scoliosis results in a delay of lung development, such that in a group of symptomatic patients with moderate degrees of deformity (mean angle of curvature, 66 degrees), lung volumes and DL are about 80% of that of an age-matched control group; the alveolar characteristics of a 12-yr-old with scoliosis are therefore similar to those of a 9-yr-old normal child.