We measured the oxygen consumption (V̇2) of respiratory muscles in 8 COPD patients and 12 age-matched healthy subjects using a closed circuit device which allows a continuous increase in external dead space and is equipped with a 9-L Collins spirometer. Furthermore, we measured simultaneously mouth occlusion pressure at 0.1 s of inspiration (P0.1), minute ventilation (V̇E), and other ventilatory parameters during the measurement of total V̇O2 (V̇O2tot). We found that the logarithm of V̇O2tot (logV̇O2tot) had a good correlation with V̇E in both groups. The mean slope of the regression line of logV̇O2tot and V̇E (ΔlogV̇O2tot/ΔV̇E) of COPD patients was significantly higher than that of normal subjects (p < 0.001). However, the mean Y-intercept (metabolic V̇O2[V̇O2met]) of the regression lines did not differ between the two groups. The P0.1 in COPD patients was higher than that in normal subjects at the corresponding dead space loading. However, the V̇E did not differ between the two groups except for at rest and the first 1 min after dead space loading. These results suggest that the V̇O2 of respiratory muscles in patients with COPD is higher at given ventilation compared with that in age-matched normal subjects and that this increased V̇O2 partly may be due to an augmented ventilatory drive.
ASJC Scopus subject areas
- Pulmonary and Respiratory Medicine
- Critical Care and Intensive Care Medicine
- Cardiology and Cardiovascular Medicine