Dual test gas pulmonary diffusing capacity in patients with idiopathic scoliosis 40 years after diagnosis

There is limited knowledge on diffusing capacity in scoliosis patients. It remains to be determined if impaired pulmonary diffusing capacity is mostly influenced by reduced alveolar-capillary membrane diffusing capacity (D_{M, CO}), reduced pulmonary capillary blood volume (V_C) or both. This study aims to report findings from dual test gas pulmonary diffusing capacity for carbon monoxide and nitric oxide (D_{L, CO, NO}) with quantification of pulmonary diffusing capacity for carbon monoxide corrected for haemoglobin with a five s breath-hold (D_{L, COc, 5s}) and nitric oxide with a five s breath-hold (D_{L, NO, 5s}), D_{M, CO} and V_C. The study included 57 patients with idiopathic scoliosis seen at our department from 1972 to 1983, all of whom underwent radiological assessment and measurement of D_{L, CO, NO} during examination 40 years after diagnosis. One-way ANOVA was performed for between-group differences and Pearson's correlation coefficient was used to assess correlations between D_{L, CO, NO} metrics and Cobb angle. No significant between-group differences based on disease severity were detected. Thirty-nine percent of the patients were presented with either reduced D_{L, COc, 5s} or reduced D_{L, NO, 5s} represented as Z-scores below -1.65. No significant correlations between Cobb angle and Z-scores for D_{L, COc, 5s}, D_{L, NO, 5s}, D_{M, CO} and V_C according to height measurements were found. When using arm span instead, a weak negative correlation between D_{L, COc, 5s} and Cobb angle (r = -0.29; P = 0.04) was detected. In conclusion, approximately 39% of patients with idiopathic scoliosis had either reduced D_{L, COc, 5s} or reduced D_{L, NO, 5s} 40 years after diagnosis with varying contributions from V_C or D_{M, CO}.