Does exercise test modality influence dyspnoea perception in obese patients with COPD?

The purpose of this study was to investigate whether differences in physiological responses to weight-bearing (walking) and weight-supported (cycle) exercise influence dyspnoea perception in obese chronic obstructive pulmonary disease (COPD) patients, where such discrepancies are probably exaggerated. We compared metabolic, ventilatory and perceptual responses during incremental treadmill and cycle exercise using a matched linearised rise in work rate in 18 (10 males and eight females) obese (mean ± sd body mass index 36.4 ± 5.0 kg·m(-2)) patients with COPD (forced expiratory volume in 1 s 60 ± 11% predicted). Compared with cycle testing, treadmill testing was associated with a significantly higher oxygen uptake, lower ventilatory equivalent for oxygen and greater oxyhaemoglobin desaturation at a given work rate (p<0.01). Cycle testing was associated with a higher respiratory exchange ratio (p<0.01), earlier ventilatory threshold (p<0.01) and greater peak leg discomfort ratings (p=0.01). Ventilation, breathing pattern and operating lung volumes were similar between tests, as were dyspnoea/work rate and dyspnoea/ventilation relationships. Despite significant between-test differences in physiological responses, ventilation, operating lung volumes and dyspnoea intensity were similar at any given external power output during incremental walking and cycling exercise in obese COPD patients. These data provide evidence that either exercise modality can be selected for reliable evaluation of exertional dyspnoea in this population in research and clinical settings.