Changes In Oxygenation Of Peripheral Muscle During Aerobic Exercise In Persons With COPD

Abstract

Studies on exercise intolerance in persons with chronic obstructive pulmonary disease (COPD) have primarily focused on limitations in ventilation and gas exchange. However, recent studies have suggested that peripheral skeletal muscle is mechanically compromised in this group, and may play an additional role in the inability of persons with COPD to exercise. PURPOSE The purpose of this study was to compare changes in peripheral muscle oxygen utilization in persons with COPD compared to healthy controls. METHODS Eight persons with moderate COPD (68±15 yrs; FEV1 = 1.0±0.3 l/min, 44±11% predicted) and eight healthy age, weight and activity matched controls (69±12 yrs; FEV1 = 1.8±0.6 l/min, 70±12% predicted) performed a submaximal (∼70% of maximal heart rate) graded exercise test (GXT), and a six-minute steady state exercise test at 50% of the workload obtained during the submaximal GXT. Measurements included oxygen uptake (VO2), heart rate (HR), arterial oxygen saturation (SaO2) and peripheral muscle oxygenation (StO2) at rest, during exercise, and recovery. RESULTS Independent t-tests revealed significantly greater workloads for controls at peak (73.8±36.2 vs. 36.9±11.9 watts) and steady state exercise (36.9±18.1 vs. 18.1±6.5 watts) when compared to COPD. Results of a repeated measures ANOVA (group × time) did not reveal any significant differences in StO2 between the groups (Control vs. COPD): at rest (29.5±22.8 vs. 30.4±17.3 %), during peak (29.4±19.4 vs. 26.5±15.9%) and constant load exercise (28.1±12.8 vs. 34.8±23.9%) and during the first (48.0±28.9 vs. 42.6±19.4%) and fifth (46.6±29.1 vs. 44.3±21.7%) minute of recovery from exercise. A significant main effect for group was demonstrated for SaO2 during the submaximal GXT and steady state exercise test. Individuals with COPD demonstrated significantly lower SaO2 values for the GXT at rest (96.8±1.0 vs. 93.5±1.7%) and during the first minute of recovery from exercise (96.0±1.3 vs. 92.8±2.4%). During steady state exercise, SaO2 was significantly higher in control participants at rest (96.3±1.3 vs. 93.6±1.5%), at 3 minutes of exercise (95.8±2.1 vs. 92.9±2.6%) and during the fifth minute of recovery from exercise (96.8±0.7 vs. 94.9±1.0%). Regression analysis was utilized to examine the relationship between measures of pulmonary function (FEV1, FVC, % FEV1/FVC), StO2 and SaO2, however no significant correlations were found. CONCLUSION These results suggest that peripheral skeletal muscle oxygenation is not compromised in individuals with moderate COPD during submaximal aerobic exercise, and that limitations in exercise capacity are most likely a result of muscle disuse and poor lung function.