Role of small airway dysfunction in unexplained exertional dyspnoea

Abstract

BackgroundIsolated small airway abnormalities may be demonstrable at rest in patients with normal spirometry; however, the relationship of these abnormalities to exertional symptoms remains uncertain. This study uses an augmented cardiopulmonary exercise test (CPET) to include evaluation of small airway function during and following exercise to unmask abnormalities not evident with standard testing in individuals with dyspnoea and normal spirometry.MethodsThree groups of subjects were studied: 1) World Trade Center (WTC) dust exposure (n=20); 2) Clinical Referral (n=15); and Control (n=13). Baseline evaluation included respiratory oscillometry. Airway function during an incremental workload CPET was assessed by: 1) tidal flowversusvolume curves during exercise to assess for dynamic hyperinflation and expiratory flow limitation; and 2) post-exercise spirometry and oscillometry to evaluate for airway hyperreactivity.ResultsAll subjects demonstrated normal baseline forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC). Dyspnoea was reproduced during CPET in WTC and Clinical Referral groupsversusControl without abnormality in respiratory pattern and minute ventilation. Tidal flow–volume curves uncovered expiratory flow limitation and/or dynamic hyperinflation with increased prevalence in WTC and Clinical ReferralversusControl (55%, 87%versus15%; p<0.001). Post-exercise oscillometry uncovered small airway hyperreactivity with increased prevalence in WTC and Clinical ReferralversusControl (40%, 47%versus0%, p<0.05).ConclusionsWe uncovered mechanisms for exertional dyspnoea in subject with normal spirometry that was attributable to either small airway dysfunction during exercise and/or small airway hyperreactivity following exercise. The similarity of findings in WTC environmentally exposed and clinically referred cohorts suggests broad relevance for these evaluations.