The patients with COPD underwent individualized stress test protocols because they were unable to perform the standard Bruce protocol in which belt speed and inclination are both incremented by a specified amount every three minutes. The individualized protocols began with three minutes of walking at a pace evaluated by the subject as slow. (This speed was used as the starting level for all subsequent tests.) Treadmill speed was then incremented by 0.2 mph during each subsequent three-minute period up to a speed that the patient considered “comfortable.” The healthy group, in contrast, performed the standard Bruce protocol.
During the exercise, subjects’ heart rate and rhythm (measured by telemetry), plus oxygen saturation (measured by oximetry [SoxiOj) were continuously monitored. Stress testing was terminated by any one of the following: (1) subjective complaints (severe dyspnea, fatigue, dizziness, or chest pain); (2) ECG abnormalities (ST changes, frequent ectopic beats); or (3) attainment of target heart rate proposed by the American Heart Association age- predicted maximum. Subjective complaints terminated the stress test in the patients with COPD while heart rate terminated the healthy subjects stress test.
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Oxygen consumption and exercise ventilation could be measured in the healthy group only because the patients with COPD could not tolerate the head-support/breathing valve apparatus. Measurement of postexercise diffusing capacities was similarly limited to the healthy group because the COPD group found the breath- holding time intolerable after exercise. Because all the patients with COPD also took theophylline, assays for plasma levels of theophylline were performed randomly throughout the experimental period.
Data were analyzed for statistical significance using two-way analysis of variance (AN OVA).