Phase angle as an indicator of physical activity in patients with stable chronic obstructive pulmonary disease

Phase angle (PhA) reflects cell membrane integrity and vitality and is an indicator of sarcopenia. PhA is associated with physical function in patients with stable chronic obstructive pulmonary disease (COPD). To our knowledge, the association between PhA and physical activity (PA) has not been investigated. Therefore, the aim of this study was to investigate whether PhA reflects PA in patients with COPD.

This single-center, cross-sectional, observational study included 103 patients with stable COPD (87 men; mean age, 74.7 ± 8.1 y; mean forced expiratory volume in 1s %predicted value, 58.9 ± 20.4%). PhA was measured by bioelectrical impedance analysis. Patients were stratified into low (n = 54) and high (n = 49) PhA groups based on median values (4.3° ± 0.6° and 5.4° ± 0.5°, respectively). PA was calculated as the average daily duration of high-intensity light PA (HLPA; 2.0-2.9 metabolic equivalents [METs] of PA) and moderate- to vigorous-intensity PA (MVPA; >3 METs). Correlation and multivariate analyses using multiple regression analysis were performed to confirm the association between PhA and PA.

The high-PhA group demonstrated greater HLPA (104.4 [16.5-332.5] versus 131.3 [61.1-328.7] min, P = 0.005) and MVPA (19.5 [4.7-96.0] versus 46.6 [8.9-139.3] min, P < 0.001) than the low-PhA group. PhA was positively correlated with HLPA (r = 0.32, P < 0.001) and MVPA (r = 0.49, P < 0.001). MVPA (β = 0.178, P = 0.029) and HLPA (β = 0.158, P = 0.026) were associated with PhA independent of age, sex, body mass index, respiratory function, muscle strength, skeletal muscle mass index, and 6-min walking distance.

In patients with COPD, PhA may reflect PA as well as muscle function.