PURPOSE: Epidemiological studies suggest that women with COPD experience greater breathing discomfort (dyspnea) than men for a given FEV1. However, the mechanisms for this difference remain unknown. Accordingly, the purpose of this study was to systematically evaluate sex-differences in exertional dyspnea in patients with mild COPD.
METHODS: We compared minute ventilation (V’ E), operating lung volumes and dyspnea ratings during symptom-limited incremental cycle exercise in 16 females (62±6 years; mean±SD) and 16 males (67±8 years) with mild COPD (post-bronchodilator FEV1/FVC ratio of <0.7 and an FEV1>80% predicted).
RESULTS: Men and women were matched for age and body mass index (p>0.05) but men were taller, heavier and had larger absolute lung volumes (p<0.001). Men and women had an FEV1 of 85±10 and 83±13% predicted and a post-bronchodilator FEV1/FVC of 60±7 and 63±5 %, respectively. Dyspnea intensity (Borg scale) at a given work rate was greater in women compared with men: Borg ratings at 60W were 2.9±1.5 and 1.9±1.5 units, respectively (p<0.05); this difference was further exaggerated at 80W where Borg ratings were 5.7±2.3 and 2.8±1.7 units, respectively (p<0.001). Borg ratings at a given V’ E were also greater in women than men, but were no longer different when V’ E was normalized to predicted ventilatory capacity. Women consistently had higher end-expiratory and end-inspiratory lung volumes (normalized to total lung capacity) relative to men and both groups demonstrated evidence of dynamic hyperinflation throughout exercise.
CONCLUSION: Females with mild COPD reported greater breathing discomfort for a given power output and ventilation than age-matched males. This was associated with a relatively higher ventilatory demand-capacity ratio and greater dynamic mechanical constraints during a standardized physical task in females. By extrapolation, the greater dyspnea intensity in females reflects relatively higher contractile respiratory muscle effort requirements for a given task.
CLINICAL IMPLICATIONS: Future studies examining dyspnea intensity during cardiopulmonary exercise testing need to account for the confounder of reduced ventilatory capacity in females.
DISCLOSURE: Jordan Guenette, University grant monies Spear/Start Fund, Queen’ s University; Grant monies (from industry related sources) GSK; No Product/Research Disclosure Information