Study objective: To investigate differences in work capacity for the arms and legs in patients with moderate-to-severe COPD.
Design: Cross-sectional investigation.
Patients: One hundred twenty-four patients (90 men and 34 women) aged 45 to 81 years with moderate-to-very severe COPD. FEV1 ranged from 0.70 to 2.79 L/min (FVC, 1.73 to 5.77 L; FEV1/FVC, 24 to 69%). All patients were in stable condition at the time of testing and receiving a stable drug regime.
Measurements: Each patient completed a demographic and medical history questionnaire, pulmonary function studies (spirometry, lung volumes, and diffusion capacity), peak exercise ergometry with gas exchange for the arms and legs; they also rated their subjective assessment of perceived dyspnea and extremity fatigue using Borg scores during exercise.
Results: Patients were of comparable age, with men taller and heavier than women. Smoking history was significantly less for women (47.9 pack-years vs 66.6 pack-years for men) even though each group presented with equivalent age (p > 0.05). Women were less obstructed than men, with FEV1/FVC (mean ± SD) of 46.5 ± 10.9% vs 40.2 ± 9.3%, respectively. Ventilatory limitation during exercise was noted for all patients studied. Peak work capacity was greater for men, and leg peak responses were greater than arm values for each gender. As airway obstruction increased, work capacity became more limited. Peak arm work achieved was 38.9 ± 19.6 W, oxygen uptake (V̇o2) was 903.9 ± 263.5 mL/min, and minute ventilation (V̇e) was 33.7 ± 9.5 L. Peak leg work value was 62.9 ± 24.8 W, V̇o2 was 1,091.4 ± 321.5 mL/min, and V̇e was 39.3 ± 12.0 L. Hence, arm values were 62%, 83%, and 85% of the measured leg values, respectively. Dyspnea and extremity effort scores were similar for men and women, and for arms and legs. Regression analysis was used to derive prediction equations for arm work from measured leg ergometry testing. For watts of work, a three-variable model emerged explaining 66% of the variance; V̇o2 yielded a four-variable model with 80% of the variance explained; and V̇e yielded a three-variable model explaining 72% of the variance.
Conclusion: Arm work is reduced by 38% that of the legs, while more modest reductions are noted for V̇o2 and V̇e, suggesting greater mechanical efficiency for leg work as compared to arm work. These data also suggest greater metabolic demand for respiratory muscles and arm ergometry. Dyspnea and extremity Borg scores were equivalent for each modality and level of airway obstruction studied, suggesting that perception plays an important role in limiting exercise, and that a threshold for termination of exercise may exist. Further, peak leg ergometry results can be used with pulmonary function indexes to predict peak arm workload in watts, V̇o2, and V̇Ve. These data may be used to assist the clinician in prescribing rehabilitation or estimating arm exercise ability when arm testing is unavailable.