OBJECTIVE: To investigate whether segmental phase angle (PhA) is a useful predictor of severe chronic obstructive pulmonary disease (COPD) exacerbation. RESEARCH METHODS AND PROCEDURES: This prospective cohort study enrolled consecutive patients with COPD with a follow-up period of 3 years. The primary outcome was incidence of severe exacerbation. PhA was measured for the whole body and segmental body sites (trunk and upper and lower limbs). We used receiver operating characteristic (ROC) curves to determine the cut-off values and area under the curve (AUC) for predicting exacerbation based on PhA. We applied Cox proportional hazard regression analyses to estimate the independent prognostic effect of PhA on the incidence of severe exacerbation. RESULTS: We analyzed 108 male participants (mean age 75.1±7.9 years) and the median follow-up period was 1082 [643-1103] days, with an annual severe exacerbation incidence rate of 0.23 per person-year. ROC analysis revealed that the AUC for Whole-body and segmental PhA were as follows: Whole-body: AUC = 0.69 (95% confidence interval [CI] = 0.59-0.79)
right arm: AUC = 0.65 (95% CI = 0.53-0.77)
left arm: AUC = 0.68 (95% CI = 0.56-0.79)
right leg: AUC = 0.73 (95% CI = 0.64-0.82)
left leg: AUC = 0.71 (95% CI = 0.62-0.81)
trunk: AUC = 0.58 (95% CI = 0.46-0.69). Cox proportional hazard analysis demonstrated that PhA of the right leg (hazard ratio [HR]=3.50, 95% CI=1.33-9.20), left leg (HR=3.26, 95% CI=1.18-9.04), and left arm (HR=2.61, 95% CI=1.17-6.80) were independently and significantly associated with incidence of severe exacerbation. Whole and trunk PhA were not significantly associated with the incidence of severe exacerbation. CONCLUSIONS: Segmental PhA may serve as a valuable predictive indicator of severe exacerbation in male patients with COPD. Notably, both leg PhA were strongly associated with the occurrence of severe exacerbations. REGISTRY NUMBER: UMIN000044824.