Peak exercise response in relation to tissue depletion in patients with chronic obstructive pulmonary disease

In several studies a correlation between body weight and peak exercise capacity has been found in patients with chronic obstructive pulmonary disease (COPD). In the present study a thorough analysis of the relationship between body composition and peak exercise performance was executed in 62 patients with clinically stable COPD. This was based on the hypothesis that particularly muscle mass, as the largest constituent of both fat-free mass (FFM) and body cell mass, is related to exercise capacity. Body composition was assessed using deuterium and bromide dilution techniques, to measure total body water (TBW) and extracellular water. From these measurements FFM:TBW/0.73, the ratio of ECW/intracellular water (ICW) and ICW-index (ICW/height2) were calculated. Peak exercise performance was measured using an incremental cycle ergometry test. The transfer factor of the lung for carbon monoxide (TL,CO) intrathoracic gas volume (ITGV), maximal expiratory and inspiratory mouth pressure, forced expiratory volume in one second (FEV1), FFM-index (FFM/height2), body mass index (weight/height2) and ICW-index correlated strongly (p<0.01) to peak oxygen consumption (V'O2). The ratio ECW/ICW correlated only weakly, but significantly, with peak V'O2 (r=-0.25, p<0.05). Stepwise regression analysis demonstrated that FFM-index and TL,CO explained 53% of the variation in peak V'O2. The results of this study furthermore indicate that severe FFM depletion is related to a blunted tidal volume response to peak exercise, a decreased peak oxygen pulse and an early anaerobic metabolism in patients with COPD. Depletion of muscle mass, measurable by assessment of fat-free mass, significantly effects peak oxygen consumption, ventilatory response, the oxygen pulse and anaerobic energy metabolism in patients with chronic obstructive pulmonary disease.