D30-15 Thoracic Bone and Muscle Health in Relation to Diaphragmatic and Rib Cage Respiratory Mechanical Biomarkers in COPD

Rationale Osteoporosis and sarcopenia are common in COPD and negatively affect thoracic bone and muscle health. These musculoskeletal impairments alter thoracic geometry and compromise respiratory function, accelerating disease progression. However, the interplay between thoracic bone, muscle, and body composition metrics with respiratory mechanics in COPD remains poorly understood. We retrospectively examine the linkages of thoracic musculoskeletal (MSK) metrics with respiratory mechanical biomarkers of the thoracic cavity in COPD. Methods The study cohort included participants in the Genetic Epidemiology of COPD (COPDGene) Iowa cohort at baseline visits after excluding never smokers and BMI outside the range of 20-35 kg/m2. Respiratory mechanical biomarkers were automatically derived from inspiratory (TLC: total lung capacity) and expiratory (RV: residual volume) CT scans, quantifying lung-volume-dependent craniocaudal diaphragm deformation (Δdia-CC; Figure 1(a)) and transverse areal expansion of the rib cage (Δrib-A; Figure 1(b)). Thoracic musculoskeletal (MSK) metrics included pectoral muscle (PM) and posterior subcutaneous adipose tissue (SAT) areas, normalized by body cross-sectional area, and spine bone mineral density (BMD), all measured from TLC CT. For the reference group, consisting of smokers with preserved lung function (COPD GOLD stage 0), metric-specific expectation models were built using linear regression and age, sex, and BMI as predictors. For each metric, a standard residual (z-score) was computed for each participant using their observed and model-derived expected values. Pearson correlations between z-scores of MSK measures and Δ-metrics were assessed among smokers with impaired lung function, including PRISm and GOLD stages 1-4. Results 434 participants (213 females, age: 61.5±8.6 years) had preserved lung function, while 674 participants (332 females, age: 65.6±7.9 years) had compromised lung function. Correlation of Δ-metric z-scores with the z-scores of MSK measures in the compromised lung function group are presented in Figure 1(c). PM was significantly positively associated with both diaphragm (r = 0.16) and chest wall (r = 0.11) respiratory mechanics. SAT was significantly negatively associated with chest wall expansion (r=-0.19). Spine BMD showed significant positive association with Δdia-CC (r = 0.08). Conclusion The study findings suggest that muscle health is positively associated with respiratory mechanics of the thoracic cavity, including both diaphragm and rib cage, while posterior fat is negatively associated with rib cage during respiration. Bone density showed relatively weaker association with respiratory mechanics. This study examines the roles of thoracic MSK health on respiratory mechanical impairments in COPD, which may contribute to clinical outcomes, especially, in the presence of comorbid conditions such as osteoporosis and sarcopenia.