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Combined Effects of Obesity and Chronic Obstructive Pulmonary Disease on Dyspnea and Exercise Tolerance

¹ Respiratory Investigation Unit, Department of Medicine, Queen's University and Kingston General Hospital, Kingston, Ontario, Canada

Correspondence and requests for reprints should be addressed to Denis E. O'Donnell, M.D., F.R.C.P.(I), F.R.C.P.(C), 102 Stuart Street, Kingston, ON, K7L 2V6 Canada. E-mail: odonnell{at}queensu.ca

Rationale: Severity of lung hyperinflation is known to influence the extent of dyspnea and exercise intolerance among patients with chronic obstructive pulmonary disease (COPD) with similar degrees of airway obstruction. Lung volume components are consistently affected by body mass index (BMI) in health and in disease.

Objectives: To explore the complex interactions between obesity, lung hyperinflation, dyspnea, and exercise performance in COPD.

Methods: We compared dyspnea intensity ratings and ventilatory responses (breathing pattern, operating lung volumes, and gas exchange) during symptom-limited incremental cycle exercise in well-characterized groups of 18 obese (mean BMI ± SD, 35 ± 4 kg/m²) and 18 normal-weight (mean BMI ± SD, 22 ± 2 kg/m²) patients with moderate to severe COPD.

Measurements and Main Results: Groups were well matched for FEV₁ (mean 49% predicted) and diffusing capacity (means >70% predicted), but resting lung hyperinflation (end-expiratory lung volume [EELV]) was significantly reduced in association with increasing BMI (P < 0.005). In the obese patients, peak symptom-limited oxygen uptake was increased (P < 0.01) and dyspnea ratings at a standardized ventilation were decreased (P < 0.01) compared with normal-weight patients. Ratings of dyspnea intensity at a standardized ventilation during exercise correlated well with the concurrent dynamic EELV/total lung capacity (TLC) ratio (r = 0.68; P < 0.00001) and with the resting EELV/TLC (r = 0.67; P < 0.00001).

Conclusions: The combined mechanical effects of obesity and COPD reduced operating lung volumes at rest and throughout exercise with favorable influences on dyspnea perception and peak oxygen uptake during cycle ergometry.

Key Words: lung hyperinflation • lung volumes • respiratory mechanics • cycle ergometry

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject Obesity and COPD frequently coexist and are increasing in prevalence. The impact of obesity on dynamic respiratory mechanics, dyspnea and exercise intolerance in patients with COPD is unknown. What This Study Adds to the Field Despite having greater metabolic and ventilatory requirements, obese COPD patients do not experience greater dyspnea and exercise limitation than normal-weight patients with comparable airway obstruction. This, in part, reflects the mechanical advantage of breathing at relatively lower lung volumes in obesity.