Relationship between exercise performance and water distribution measured by new bioelectrical impedance analysis in patients with chronic obstructive pulmonary disease.

Body composition analysis is useful for objective evaluation of malnutrition in patients with chronic obstructive pulmonary disease (COPD). The purpose of this study was to evaluate the influence of body composition on exercise performance by patients with COPD using a new method of bioelectrical impedance analysis. Twenty patients with COPD performed incremental exercise ramp tests to the symptom-limited maximum and constant work rate tests for 10 min. Their body compositions were measured by bioelectrical impedance analysis with eight electrodes and four frequencies, which could estimate the amount of intra- and extracellular water (ICW, ECW) and water distribution of the extremities separately. Some pulmonary function parameters of airflow limitation or hyperinflation and body composition parameters were significantly correlated with peakVO2. Stepwise multiple regression analysis revealed that independent predictors of peakVO2 included ECW/ICW ratio, lower extremity water and FEV1.0 (P<0.0001, R = 0.892), which explained 27, 31 and 21% of peakVO2, respectively. Furthermore, there was a significant correlation between ECW/ICW ratio and time constant of oxygen consumption in constant work rate tests. These findings indicate that increased ECW/ICW ratio and lower extremity water correlated with exercise intolerance independent of pulmonary function, and that changes in cellular hydration state might affect oxygen utilization of skeletal muscle in patients with COPD. In conclusion, the BIA used in our study, which can easily and simultaneously evaluate the water distribution of the extremities and cellular hydration state, is useful for the evaluation of exercise performance in COPD patients.