Impaired Ventilatory Efficiency, Dyspnea, and Exercise Intolerance in Chronic Obstructive Pulmonary Disease: Results from the CanCOLD Study.

Abstract

<b>Rationale:</b> Impaired exercise ventilatory efficiency (high ventilatory requirements for CO₂ [[Formula: see text]e/[Formula: see text]co₂]) provides an indication of pulmonary gas exchange abnormalities in chronic obstructive pulmonary disease (COPD). <b>Objectives:</b> To determine <i>1</i>) the association between high [Formula: see text]e/[Formula: see text]co₂ and clinical outcomes (dyspnea and exercise capacity) and its relationship to lung function and structural radiographic abnormalities; and <i>2</i>) its prevalence in a large population-based cohort. <b>Methods:</b> 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 [Formula: see text]e/[Formula: see text]co₂ above the upper limit of normal (ULN), using population-based normative values. <b>Measurements and Main Results:</b> 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 [Formula: see text]e/[Formula: see text]co₂ 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 [Formula: see text]o₂ ([Formula: see text]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 [Formula: see text]e/[Formula: see text]co₂ (<i>r</i> = -0.38; <i>P</i> < 0.001) than other relevant lung function and computed tomography metrics. The prevalence of [Formula: see text]e/[Formula: see text]co₂ 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%). <b>Conclusions:</b> [Formula: see text]e/[Formula: see text]co₂ above the ULN was associated with greater dyspnea and low [Formula: see text]o_2peak 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.