Prevalence and functional impact of respiratory sarcopenia in a COPD-enriched smoking cohort

Respiratory sarcopenia, defined as a combination of respiratory muscle weakness and decreased respiratory muscle mass, is a novel concept with unclear prevalence and clinical relevance in the chronic obstructive pulmonary disease (COPD) population. This study aimed to evaluate the prevalence of respiratory sarcopenia in a COPD-enriched smoking cohort and its association with clinical features.

This prospective observational study included smokers who were categorised into four groups based on respiratory muscle weakness (% maximal inspiratory pressure and/or % maximal expiratory pressure <80%) and low skeletal muscle index (<7.0 kg/m² for men and <5.7 kg/m² for women). Pulmonary function, physical function, and the 6-min walking distance (6MWD) were compared between the groups.

A total of 184 smokers (79% with COPD) were classified into the following groups: normal (n = 77, 42%), muscle mass loss only (n = 32, 17%), respiratory muscle weakness only (n = 53, 29%), and probable respiratory sarcopenia (n = 22, 12%). The probable respiratory sarcopenia group demonstrated a significantly lower %FEV₁ and elevated RV/TLC. Compared with the other groups, the probable respiratory sarcopenia group exhibited markedly impaired physical performance, with reduced gait speed, 6MWD, and knee extension strength. Multivariable regression analysis revealed that probable respiratory sarcopenia (β = -0.24; p = 0.02) was independently associated with a lower 6MWD after adjusting for age, sex, height, body mass index, smoking pack-year, and FEV₁ (adjusted R² = 0.48).

Probable respiratory sarcopenia, which was identified in 12% of elderly smokers, was independently associated with exercise capacity and may be a clinical phenotype requiring early detection and intervention to prevent functional decline. Registered at UMIN (UMIN000049755).