Association Between Phase Angle, Muscle Mass Distribution, and Quality of Life in Patients with Chronic Obstructive...

Background: Chronic obstructive pulmonary disease (COPD) is associated with systemic alterations in body composition, including muscle mass loss and fat redistribution, which may influence patient-reported outcomes. However, the independent contribution of bioimpedance-derived parameters, particularly phase angle, to quality of life (QoL) remains unclear. Methods: This exploratory pilot study included 75 clinically stable patients with moderate-to-severe COPD (GOLD stages II-III). Body composition was assessed using segmental multi-frequency bioelectrical impedance analysis with the InBody 770 system. Evaluated parameters included fat-free mass (FFM), skeletal muscle mass (SMM), percent body fat (PBF), visceral fat area (VFA), extracellular water-to-total body water ratio (ECW/TBW), bone mineral content (BMC), and phase angle (PhA). Quality of life was assessed using the WHOQOL-BREF questionnaire. Associations between body composition parameters and QoL domains were analyzed using Spearman correlation analysis and multivariable linear regression models. Results: Despite a median body mass index (BMI) within the normal range (23.4 kg/m²), body fat mass exceeded reference values in both men and women. Fat-free mass and skeletal muscle mass were located near the lower range of expected values. Correlation analysis demonstrated predominantly weak associations between body composition parameters and QoL domains. Significant positive correlations were identified between the psychological QoL domain and fat-free mass (ρ = 0.238, p = 0.041), skeletal muscle mass (ρ = 0.240, p = 0.040), basal metabolic rate (ρ = 0.236, p = 0.043), and bone mineral content (ρ = 0.249, p = 0.033). In multivariable regression models, fat-free mass and skeletal muscle mass demonstrated consistent positive associations with both physical and psychological QoL domains. Whole-body and segmental phase angle parameters did not demonstrate significant associations with QoL outcomes. Conclusions: In patients with COPD, BMI alone may inadequately reflect underlying alterations in body composition. Muscle-related parameters, particularly fat-free mass and skeletal muscle mass, demonstrated more consistent associations with physical and psychological aspects of quality of life than obesity-related indicators. These findings suggest that bioelectrical impedance analysis may provide additional clinically relevant information beyond BMI when assessing body composition and quality of life in patients with COPD.