Matthew Maddocks|Samantha S.C.Kon|Sarah E. Jones|Jane L. Canavan|Claire M. Nolan|Irene J. Higginson|Wei Gao|Michael I. Polkey|William D-C. Man.
Clinical Nutrition xxx (2015) 1-6
BACKGROUND: Bioelectrical impedance analysis (BIA) provides a simple method to assess changes in body composition. Raw BIA variables such as phase angle provide direct information on cellular mass and integrity, without the assumptions inherent in estimating body compartments, e.g. fat-free mass (FFM). Phase angle is a strong functional and prognostic marker in many disease states, but data in COPD are lacking. Our aims were to describe the measurement of phase angle by assessing its relationship with established markers of function, disease severity and prognosis.
SUBJECTS /METHODS: 502 outpatients with stable COPD were studied. Phase angle and FFM by BIA, quadriceps strength (QMVC), 4-m gait speed (4MGS), 5 sit-to-stand time (5STS), incremental shuttle walk (ISW), and compositive prognostic indices (ADO, iBODE) were measured. Patients were stratified into normal and low phase angle and FFM index.
RESULTS: Phase angle correlated positively with FFM and functional outcomes (r = 0.35-0.66, p <0.001) and negatively with prognostic indices (r = -0.35 to 0.48, p < 0.001). In regression models, phase angle was independently associated with ISW, ADP and iBODE whereas FFM were removed. One hundred and seventy patients (33.9% [95% CI, 29.9-38.1]) had a low phase angle. Phenotypic characteristics included lower QMVC, ISW, and 4MGS, higher 5STS, ADO and iBODE scores, and more exacerbations and hospital days in past year. The proportion of patients to have died was significantly higher in patients with low phase angle compared to those with normal phase angle (8.2% versus 3.6%, p = 0.02).
CONCLUSION: Phase angle relates to markers functions, disease severity and prognosis in patients with COPD. As a directly measured variable, phase angle offers more useful information than fat-free mass indices.