Abstract / Summary
Background Exertional dyspnoea is largely explained by excessive or (mechanically) constrained ventilation. Although the severity of resting lung function impairment is commonly used to estimate whether self-reported activity-related dyspnoea can be attributed to these abnormalities, the optimal use of routine pulmonary function tests in this context remains unclear in tobacco-exposed subjects. Methods Lung function and exercise testing data from 1105 males and females (523 “at-risk” smokers with FEV 1 /FVC and FEV 1 ≥−1.645 z-score and 582 patients with COPD, of whom 189 were non-obstructed with FEV 1 <−1.645). The burden of exertional dyspnoea and its proximate mechanical-ventilatory determinants were determined across the whole exercise test. Severe-to-very severe dyspnoea plus “excessive” and/or “constrained” breathing indicated ventilation-related dyspnoea. Results Ventilation-related dyspnoea was identified in ∼40% (433/1105) of subjects, who typically exhibited poorer exercise tolerance ( p <0.001). In addition to FEV 1 , only the transfer coefficient (K CO ) independently predicted exercise intolerance and ventilation-related dyspnoea across cohorts; moreover, inspiratory capacity (IC) was independently associated with these negative outcomes in obstructed subjects with low FEV 1 . The odds of ventilation-related dyspnoea increased markedly as these abnormal findings compounded. When FEV 1 was controlled for, “excessive” breathing was predicted by a low K CO (odds ratio [95% confidence interval]=3.68 [2.30–6.41]), whereas “constrained” breathing was predicted by a low IC (9.96 [4.53–21.92]) ( p <0.001). Conclusion Selected variables indicating poor gas-exchange efficiency (low K CO ) and restraints to tidal expansion (low IC) provide independent information beyond FEV 1 for estimating the burden of exertional dyspnoea attributable to ventilation in tobacco-exposed subjects with a highly variable pre-test likelihood of abnormality.