Never-smokers with occupational COPD have better exercise capacities and ventilatory efficiency than matched smokers with COPD

Chronic obstructive pulmonary disease (COPD) in never-smokers exposed to organic dusts is still poorly characterized. Therapeutic strategies in COPD are only evaluated in smoking-related COPD. Understanding how never-smokers with COPD behave during exercise is an important prerequisite for optimal management. The objective of this study was to compare physiological parameters measured during exercise between never-smokers with COPD exposed to organic dusts and patients with smoking-related COPD matched for age, sex, and severity of airway obstruction. Healthy control subjects were also studied. Dyspnea (Borg scale), exercise tolerance, and ventilatory constraints were assessed during incremental cycle cardiopulmonary exercise testing in COPD patients at mild to moderate stages [22 exposed to organic dusts: postbronchodilator forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) z score -2.44 +/- 0.72 and FEV1 z score -1.45 +/- 0.78; 22 with smoking-related COPD: FEV1/FVC z score -2.45 +/- 0.61 and FEV1 z score -1.43 +/- 0.69] and 44 healthy control subjects (including 22 never-smokers). Despite the occurrence of similar significant dynamic hyperinflation, never-smoker COPD patients exposed to organic dusts had lower dyspnea ratings than those with smoking-related COPD. They also had better ventilatory efficiency, higher peak oxygen consumption and peak power output than smoking-related COPD patients, all these parameters being similar to control subjects. Differences in exercise capacity between the two COPD groups were mainly driven by better ventilatory efficiency stemming from preserved diffusion capacity. Never-smokers exposed to organic dusts with mild to moderate COPD have better exercise capacities, better ventilatory efficiency, and better diffusion capacity than matched patients with smoking-related COPD. NEW & NOTEWORTHY It is unknown whether or not neversmokers with chronic obstructive pulmonary disease (COPD) behave like their smoking counterparts during exercise. This is the first study showing that never-smokers with mild to moderate COPD [defined by a postbronchodilator forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) < lower limit of normal] have preserved exercise capacities. They also have lower exertional dyspnea than patients with smoking-related COPD. This suggests that the two COPD groups should not be managed in the same way.