Phase angle on bioelectrical impedance analysis and chronic obstructive pulmonary disease-related pathophysiology in smokers

Background

Phase angle on bioelectrical impedance analysis detects impaired skeletal muscle quality, which affects outcomes in patients with chronic obstructive pulmonary disease (COPD) and even smokers without COPD. However, its association with COPD-related pathophysiology remains unclear. We examined whether phase angle is associated with physical function and computed tomography (CT) findings of emphysema, airway disease, and skeletal muscle quantity and density in smokers.

Methods

This cross-sectional study included smokers with and without COPD, categorized into low- and high-phase angle groups based on a previously reported 4.8° cutoff value. Physical function was assessed using grip strength, respiratory muscle strength, and 6-min walk distance (6MWD). Low-attenuation area percentages (LAA%950 for emphysema; LAA%856 for air trapping), wall area percentage (WA%), the erector spinae muscle cross-sectional area and density (ESMA and ESMD) were measured on chest inspiratory/expiratory CT.

Results

Of 172 smokers enrolled, 100 were categorized into the low-phase-angle group. The low-phase angle-group showed lower grip strength, respiratory muscle strength, 6MWD, ESMA, and ESMD, and higher LAA%950, WA%, and LAA%856. In multivariable analyses, the low-phase-angle group was associated with lower ESMD, but not with ESMA, after adjustment for age, sex, body mass index, and smoking history. Higher WA%, but not LAA%950, was associated with the low-phase-angle group after the same adjustment.

Conclusions

A low-phase angle reflected lower skeletal muscle density and was associated with physical dysfunction and severe central airway wall thickening. Phase angle may be a noninvasive biomarker reflecting compromised skeletal muscle conditions, physical function, and airway disease severity in smokers.