Oxygen desaturation during the 6-min walk test as a risk for osteoporosis in non-cystic fibrosis bronchiectasis

Background: Osteoporosis is a common comorbidity in non-cystic fibrosis (non-CF) bronchiectasis patients. We determined whether desaturation during 6-min walk test (6MWT) can be a predictor for osteoporosis risk. Methods: This was a retrospective cross-sectional study. Sixty-six non-CF bronchiectasis patients were enrolled. Lung function, walking distance, the lowest oxygen saturation (SpO ₂ ), the fall in SpO ₂ (ΔSpO ₂ ), and the distance-saturation product (DSP) were determined during the 6MWT. Desaturators (n = 45) were defined as those with ΔSpO ₂ > 10% or the lowest SpO ₂ < 88%. Bone mineral density (BMD) was determined through dual-energy X-ray absorptiometry. The severity of non-CF bronchiectasis was evaluated using high-resolution computed tomography. Results: Osteoporosis was evident in more desaturators (82%) than non-desaturators (43%, p < 0.01). BMD at the level of the femoral neck was significantly lower in desaturators than in non-desaturators (- 3.6 ± 1.1 vs. - 2.4 ± 0.9, p < 0.01). BMD was correlated positively with the lowest SpO ₂ and negatively with ΔSpO ₂ and severe exacerbations. In multivariate linear regression analysis, desaturation during 6MWT was the most significant predictive factor for osteoporosis (95% confidence interval - 1.60 to - 0.26, p = 0.01). Other risk factors included old age, low body mass index and severe exacerbation. Conclusions: Exertional desaturation during the 6MWT was a significant predictive factor for osteoporosis in Asian non-CF bronchiectasis patients. The 6MWT may be useful in identifying the osteoporotic phenotype of non-CF bronchiectasis and increasing clinician awareness to promote early intervention.