Bronchodilation improves endurance but not muscular efficiency in chronic obstructive pulmonary disease

Abstract

Hester van der Vaart1, Dirkje S Postma1, René Grevink1, Willem Roemer2, Nick ten Hacken11University Medical Center, Groningen, The Netherlands; 2Boehringer Ingelheim bv, Alkmaar, The NetherlandsAbstract: We hypothesized that bronchodilator treatment not only improves hyperinflation and endurance capacity but also muscular efficiency in stable chronic obstructive pulmonary disease (COPD). We aimed to demonstrate that tiotropium and salmeterol improve muscular efficiency compared with placebo. Twenty-five COPD patients were studied, including 20 males of mean (standard deviation) age 62 years (7 years) with baseline forced expiratory volume in 1 second of 41% (10%) predicted, and maximal workload of 101 Watt (36 Watt). Subjects were randomized for 6-week treatment with tiotropium 18 µg once daily, salmeterol 50 µg twice daily, or placebo using a double-blind, crossover design. Muscular efficiency and endurance time were measured during cycling at 50% of maximal work load. Resting energy expenditure was measured using a ventilated hood. Muscular efficiency after tiotropium, salmeterol, and placebo treatment was 14.6%, 14.4%, and 14.4%, respectively (P > 0.05), and resting energy expenditure was 1485 kcal/24 hours, 1709 kcal/24 hours, and 1472 kcal/24 hours (P > 0.05), respectively. Endurance time after tiotropium treatment was significantly higher than that after placebo (27.0 minutes versus 19.3 minutes [P = 0.02]), whereas endurance time after salmeterol treatment was not higher than that after placebo (23.3 minutes [P = 0.22]). In this small study, we were not able to demonstrate that bronchodilator therapy improved muscular efficiency. Apparently, reduced costs of breathing relative to total energy expenditure were too small to be detected. Keywords: bronchodilation, chronic obstructive pulmonary disease, energy expenditure, muscle energetics, muscular exercise