Association between arterial PaCO2 and long-term osteoporosis risk in older patients with chronic obstructive pulmonary disease

Osteoporosis is a highly prevalent disease among older adults. Chronic obstructive pulmonary disease (COPD) and associated hypoxia may contribute to the development of osteoporosis. This study aimed to further investigate the impact of CO₂ retention (another key pathophysiological feature of COPD) on osteoporosis, providing a novel perspective for understanding COPD-related bone metabolic disorders. A total of 611 older patients with acute exacerbation (AE) of COPD were enrolled from the hospital’s emergency department and completed a 1-year follow-up. Arterial PaO₂, PaCO₂, FEV₁% predicted, and FEV₁/FVC were recorded at baseline (AE phase), 2-week recheck (stable COPD phase), and during AECOPD recurrence during follow-up. Lumbar spine bone mineral density (BMD) was measured using dual-energy X-ray absorptiometry at baseline (immediately after AECOPD discharge) and at the end of follow-up. Patients were divided into the BMD-drop group ( n = 231) and BMD-stable group ( n = 380) based on the degree of BMD reduction during follow-up, and multivariate logistic regression was used for analysis. Adverse associations: Elevated PaCO₂ at baseline, 2-week recheck, and during AECOPD recurrence were associated with an increased risk of BMD reduction during follow-up ( P <0.001, P = 0.006, P <0.001, respectively). Favorable associations: Higher PaO₂, FEV₁% predicted, and FEV₁/FVC at these three time points were associated with a decreased risk of BMD reduction during follow-up (all P <0.001). Elevated arterial PaCO₂ may be associated with long-term BMD reduction in older patients with COPD and thus could represent a potential risk factor for osteoporosis in this population.