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/m(2)) and 18 normal-weight (mean BMI +/- SD, 22 +/- 2 kg/m(2)) patients with moderate to severe COPD.
Measurements and main results: Groups were well matched for FEV(1) (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.