Energy expenditure and impact of bronchodilators in COPD patients

28 Consecutive COPD patients performed four 6-minute walking tests (6-MWTs) in 2 different days before and 2, 4 and 6h after the inhalation of formoterol 12microg or tiotropium 18microg, respectively. Physical activity during each 6-MWT was assessed by the SenseWear Armband. At each time also spirometry was performed. Both formoterol and tiotropium induced a significantly sustained bronchodilation and influenced hyperinflation. Formoterol significantly increased distance walked in 6min at 2h and at 4h, whereas tiotropium significantly increased it at all time points. There was a trend to an increase in calories and metabolic equivalents of task (METs) after formoterol and a decrease after tiotropium, but changes were not statistically significant. Total energy expenditure for each 6-MWT was not changed by formoterol, but decreased in significant manner 6h after the inhalation of tiotropium. Active energy expenditure at physical activity level of more than 3 METs decreased significantly after tiotropium at each 6-MWT, but not after formoterol. We did not find any significant correlation between the changes in lung function and those of parameters recorded with SenseWear Armband. Our study seems to indicate that tiotropium, but not formoterol, is able to reduce energy expenditure in COPD patients, although both drugs elicit significant bronchodilation and are able to increase the distance walked in 6min.