Impaired exercise ventilatory efficiency contributes to dyspnea, exercise limitation in COPD

Impaired exercise ventilatory efficiency above the upper limit of normal was associated with a greater dyspnea burden and low peak VO₂ among never smokers and smokers with or without COPD, researchers reported.

“Activity-related dyspnea and exercise limitation ... are common, even in mild COPD, and are associated with poor health status and increased mortality. The traditional focus of physiological and lung imaging studies in mild COPD has been on small airway dysfunction,” Devin B. Phillips, PhD, in the department of medicine respiratory investigation unit at Queen’s University and Kingston Health Sciences Centre at Kingston General Hospital in Ontario, Canada, and colleagues wrote. “More recently, cardiopulmonary exercise testing has consistently demonstrated a strong link between abnormal dynamic respiratory mechanics and perceived exertional dyspnea in mild COPD.”

The population-based cohort study, published in American Journal of Respiratory and Critical Care Medicine, included 1,250 participants who underwent clinical evaluation, pulmonary function, cardiopulmonary exercise testing and chest CT. Researchers defined impaired exercise ventilatory efficiency as a nadir ventilatory efficiency/VCO₂ above the upper limit of normal.

Overall, 445 participants were never smokers, 381 were ever smokers without airflow obstruction, 224 had Global Initiative for Chronic Obstructive Lung Disease (GOLD) 1 COPD and 200 had GOLD 2-4 COPD.

Those with ventilatory efficiency/VCO₂ above the upper limit of normal had a higher likelihood of activity-related dyspnea (adjusted OR = 1.77; 95% CI, 1.31-2.39) and abnormally low peak VO₂ (aOR = 4.58; 95% CI, 3.06-6.86).

Researchers reported a stronger correlation between carbon monoxide transfer coefficient (KCO) and nadir ventilatory efficiency/VCO2 (P < .001) compared with other relevant lung function and CT metrics.

The prevalence of ventilatory efficiency/VCO₂ was 16% in the entire cohort, and was highest among participants with COPD, both GOLD 1 and GOLD 2-4, compared with never smokers and ever smokers (24% vs. 13% and 12%, respectively).

According to the researchers, participants with COPD were three times more likely to experience impaired ventilatory efficiency compared with never smokers after adjusting for confounding variables.

“The current study is the first to report that impaired ventilatory efficiency was linked to greater dyspnea burden and low VO2 peak among never-smokers and smokers with or without COPD participating in a population-based cohort study. ... Furthermore, our results support the use of cardiopulmonary exercise test-derived ventilatory efficiency and resting KCO for deeper physiological characterization in smokers with troublesome respiratory symptoms,” the researchers wrote.