Contrasting dynamic and peak exercise inspiratory constraints: Implications for dyspnoea and exercise tolerance in chronic obstructive pulmonary disease

BACKGROUND: Exertional dyspnoea is linked to inspiratory constraints to tidal volume expansion in chronic obstructive pulmonary disease (COPD). Dynamic assessment of these constraints via serial inspiratory capacity (IC) maneuvers across incremental cardiopulmonary exercise testing (CPET) might provide information regarding dyspnoea severity and exercise intolerance beyond the conventional peak IC-only approach. METHODS: Pulmonary function tests and cycle ergometer CPET in 360 patients with COPD of varied severity. In addition to using peak-exercise cutoffs for critically high inspiratory constraints (CIC), a novel AI-based algorithm quantified dyspnoea and dynamic inspiratory constraints throughout progressively higher exercise intensities. RESULTS: Among the CIC variables, end-inspiratory lung volume (EILV)/total lung capacity (TLC) ≥ 0.9 correlated best with dyspnoea and exercise intolerance. CIC and dynamic constraints (≤ 25th centile relative to sex- and age-adjusted norms) disagreed significantly: whereas ∼ a third of patients without CIC exhibited inspiratory constraints, ∼ a fifth of those with CIC did not (P < 0.05). Dynamic constraints, regardless of CIC, were significantly associated with abnormalities in submaximal mechanical-ventilatory responses, higher operating lung volumes, higher dyspnoea scores, and lower exercise tolerance. Of note, the prevalence of "high" dyspnoea-work rate and -ventilation (≥ 75% centile) was more than fourfold higher in patients with dynamic constraints, regardless of CIC (P < 0.05). CONCLUSIONS: Clinicians interested in assessing the presence and severity of dyspnoea attributable to ventilatory responses to exercise should consider serial IC measurements in patients with COPD. Novel AI-based approaches to quantify these dynamic abnormalities are poised to increase the sensitivity of this analytical approach.