Mechanisms of dyspnoea and exercise intolerance in smokers with preserved ratio impaired spirometry

Smokers with preserved ratio impaired spirometry (PRISm) present reduced forced expiratory volume in the first second (FEV₁ < 80% predicted) but preserved FEV₁/forced vital capacity (FVC) ≥ 0.7.  Although they do not meet diagnostic criteria for chronic obstructive pulmonary disease (COPD), they often report respiratory symptoms and exercise intolerance. We aimed to compare sensory and physiological responses to exercise between smokers with PRISm and matched healthy controls. Patients with mild-to-moderate COPD were included as a reference group.

In this cross-sectional study, smokers (> 10 pack-years) from a specialized outpatient clinic were evaluated. Thirteen participants (11 females; 62.4 ± 7.7 years) with PRISm and 13 age- and sex-matched patients with mild-to-moderate COPD (FEV₁/FVC < 0.7; FEV₁ > 50% predicted) underwent incremental cardiopulmonary exercise testing on a cycle ergometer. Data from healthy nonsmoking controls were obtained from previous studies.

PRISm and COPD groups had similarly reduced FEV₁ (~ 72% predicted) compared to controls (97% predicted), whereas FVC was lower in PRISm (73% predicted) than in COPD and controls (~ 95% predicted). Both patient groups showed higher ventilation, reduced ventilatory reserve, and greater dyspnoea at a given submaximal workload versus controls. Increased tidal volume/inspiratory capacity ratios were also observed, contributing to greater dyspnoea for a given ventilation and lower peak work rate (42 ± 16 vs. 68 ± 11 vs. 94 ± 17% predicted, respectively; all P < 0.05).

Smokers with PRISm exhibit increased dyspnoea and reduced exercise tolerance compared to healthy controls, largely driven by excessive ventilatory demand and reduced ventilatory capacity during submaximal exercise.