Low Fat-free Mass in Prognosis of People With Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a heterogeneous lung condition characterized by chronic respiratory symptoms (dyspnea, cough, sputum production and \\ or exacerbations) due to abnormalities of the airways (bronchitis, bronchiolitis) and\\ or alveoli (emphysema) that cause persistent, often progressive, airflow obstruction. COPD is characterized by a progressive and irreversible decline in lung function. In addition, COPD is recognized as a systemic disease with significant extra pulmonary effects. Loss of skeletal muscle mass is a well described and clinically relevant systemic consequence of COPD. Across the disease severity spectrum of COPD, the prevalence of abnormally low muscle mass (i.e. sarcopenia or cachexia) is estimated to be ∼23%. The etiology of muscle dysfunction in COPD is complex and multifactorial. Proposed pathophysiological mechanisms include 1) disease-related factors such as systemic inflammation; 2) ageing; and 3) behavior modification, particularly less time spent physically active and more time spent sedentary. The rate of age-related decline in skeletal muscle function is accelerated in people with COPD compared to that of otherwise healthy adults (Limpawattana et al., 2018). Additionally, loss of muscle function begins early in the disease course, with ostensible muscle dysfunction observed in people with mild COPD. Importantly, low muscle mass is not just a systemic manifestation affecting people with COPD who are underweight, but also those who are pre-obese or obese, termed sarcopenic obesity, which is similarly associated with poor health outcomes in COPD (Machado et al., 2023). People with COPD who possess higher muscle or fat-free mass have a better quality of life and prognosis. In addition, a significant positive association between muscle or fat-free mass and exercise tolerance in COPD has been also shown. This has led to low muscle mass being recognized as a treatable trait of COPD to help alleviate disease burden and improve clinical health outcomes.