Total daily energy expenditure relative to resting energy expenditure in clinically stable patients with COPD

Background - An elevated resting energy expenditure (REE) commonly occurs in patients with chronic obstructive pulmonary (COPD). The purpose of this study was to investigate the effect of an increased REE on total daily energy expenditure (TDE) in 20 patients with COPD (19 men) with mean (SD) forced expiratory volume in one second of 37 (14)% predicted. Methods - TDE was measured over a two week interval using doubly labelled water. Fat-free mass (FFM) was calculated from total body water assessed by deuterium dilution. REE was measured by indirect calorimetry using a ventilated hood system. Results - The patients (10 men) with a significantly higher REE than those with a normal REE (median difference 205 kcal/24 h, p<0.05) had a comparable TDE (hypermetabolic at rest: median 2593; range 2127-3083 kcal/24 h, normometabolic at rest: median 2629; range 2032-3179 kcal/24 h). There was no difference in mean daily heart rate (HR) between the groups (hypermetabolic at rest: median 92 (range 82-98), normometabolic at rest: median 98 (range 75-116) beats/min) or in the variation in the heart rate during the day. By means of multiple regression analysis it was shown that REE did not correlate significantly with TDE when FFM was taken into account. Conclusions - This study shows that there is no significant difference in free living TDE between clinically stable patients with COPD with a normal REE and those with an increased REE. The variation in TDE in patients with COPD appears to reflect differences in energy expenditure for activities, but not differences in REE.