Impaired Ventilatory Efficiency, Dyspnea, and Exercise Intolerance in Chronic Obstructive Pulmonary Disease: Results from the CanCOLD Study
Devin B. Phillips, Amany F. Elbehairy, Matthew D. James, Sandra G. Vincent, Kathryn M. Milne, Juan P. de‐Torres, J. Alberto Neder, Miranda Kirby, Dennis Jensen, Michael K. Stickland, Jordan A. Guenette, Benjamin M. Smith, Shawn D. Aaron, Wan C. Tan, Jean Bourbeau, Denis E. O’Donnell
Abstract
Abstract Rationale Impaired exercise ventilatory efficiency (high ventilatory requirements for CO2 [V̇e/V̇co2]) provides an indication of pulmonary gas exchange abnormalities in chronic obstructive pulmonary disease (COPD). Objectives To determine 1) the association between high V̇e/V̇co2 and clinical outcomes (dyspnea and exercise capacity) and its relationship to lung function and structural radiographic abnormalities; and 2) its prevalence in a large population-based cohort. Methods Participants were recruited randomly from the population and underwent clinical evaluation, pulmonary function, cardiopulmonary exercise testing, and chest computed tomography. Impaired exercise ventilatory efficiency was defined by a nadir V̇e/V̇co2 above the upper limit of normal (ULN), using population-based normative values. Measurements and Main Results Participants included 445 never-smokers, 381 ever-smokers without airflow obstruction, 224 with Global Initiative for Chronic Obstructive Lung Disease (GOLD) 1 COPD, and 200 with GOLD 2–4 COPD. Participants with V̇e/V̇co2 above the ULN were more likely to have activity-related dyspnea (Medical Research Council dyspnea scale ⩾ 2; odds ratio [5–95% confidence intervals], 1.77 [1.31 to 2.39]) and abnormally low peak V̇ o 2 (V̇ o 2peak below the lower limit of normal; odds ratio, 4.58 [3.06 to 6.86]). The Kco had a stronger correlation with nadir V̇e/V̇co2 (r = −0.38; P < 0.001) than other relevant lung function and computed tomography metrics. The prevalence of V̇e/V̇co2 above the ULN was 24% in COPD (similar in GOLD 1 and 2 through 4), which was greater than in never-smokers (13%) and ever-smokers (12%). Conclusions V̇e/V̇co2 above the ULN was associated with greater dyspnea and low V̇o2peak and was present in 24% of all participants with COPD, regardless of GOLD stage. The results show the importance of recognizing impaired exercise ventilatory efficiency as a potential contributor to dyspnea and exercise limitation, even in mild COPD.