Cycle test reliable for dyspnea evaluation in obese COPD patients

By Sara Freeman, medwireNews Reporter

medwireNews: Dyspnea in obese individuals with chronic obstructive pulmonary disease (COPD) can be evaluated reliably by cycle ergometry as well as a treadmill test, researchers have found.

Although physiologic responses differed significantly according to the type of exercise that was chosen, dyspnea intensity, ventilation, and operating lung volumes were unaffected by the mode of exercise.

Obese patients are believed to experience greater dyspnea than normal weight individuals during walking exercises, but questions have been raised as to whether dyspnea measurement during the cycle test, where leg muscles are selectively stressed, accurately reflects normal daily activities, explain Denis O’Donnell (Queen’s University & Kingston General Hospital, Ontario, Canada) and colleagues.

They recruited 10 men and eight women aged a mean of 66 years who had a mean body mass index of 36.4 kg/m² and moderate (post-bronchodilator forced expiratory volume in 1 second [FEV₁] 60% predicted) COPD. Participants performed both treadmill and cycles exercises on separate occasions, at least 48 hours apart.

Compared to cycle testing, treadmill testing was associated with significantly higher peak oxygen uptake (V’O₂; 78 vs 91% predicted), significantly lower ventilatory equivalent for oxygen consumption (V’_E/V’O₂; 32 vs 28 L/min), and significantly higher oxyhemoglobin desaturation (SpO₂; 92 vs 90%). Carbon dioxide production (V’CO₂) was higher on treadmill than cycle testing (1.65 vs 1.49 L/min).

Conversely, cycle testing was associated with a significantly higher respiratory exchange ratio (RER; 0.98 vs 0.92) and an earlier ventilatory threshold.

At peak exercise capacity, patient-rated dyspnea on the Borg Scale was 6.6 during both the walking and cycling tests. A similar level of patient-rated leg discomfort was also experienced until peak exercise capacity made it significantly more intense with cycling than with walking (6.6 vs 5.0). There was no difference between the two exercise modalities and the intensity of dyspnea in relation to the degree of ventilation or inspiratory reserve volume.

“Despite physiological differences, exercise modality has no effect on the dyspnoea/work rate or dyspnoea/V’_E relations in obese patients with COPD,” the researchers report in the European Respiratory Journal.

“Our results provide reassurance that either exercise modality can be selected for the reliable evaluation of dyspnoea in obese COPD patients,” they suggest, adding that this applies to both research and clinical settings.

They conclude that differences in V’O₂ and SpO₂ could have implications for individual assessment of cardiorespiratory fitness and pulmonary gas exchange abnormalities, respectively, and differences in V’CO₂ imply that interventions that reduce CO₂ output during physical activity could relieve exertional dyspnea in obese individuals.

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