Too rapid increase and too much breathlessness are distinct indices of exertional dyspnea in COPD

Abstract

To assess whether different indices of dyspnea can be obtained from cardiopulmonary exercise test and whether these indices correlate with distinct physiological parameters in COPD. Forty-two COPD patients (12 females, median [IQ] age 66 [56-70] years; FEV(1)% predicted: 51 [38-65]) underwent pulmonary function and incremental exercise tests. A power law function described the oxygen consumption (V(O₂)-Dyspnea relationship from which two indices correlated with MRC score: dyspnea score measured at 50% of predicted V(O₂) (too much breathless for that effort) and tangent measured at 50% of peak dyspnea (too rapid increase in dyspnea at this time point). The former independently correlated with ventilation on exercise, while the latter independently correlated with baseline hyperinflation. An upward shift of both (iso)-V(O₂) and -ventilation was evidenced in patients with higher levels of dyspnea (MRC score ≥ 3) and their tangents were significantly different. In conclusion, baseline hyperinflation is associated with the perception of a too rapid increase in dyspnea on exercise in COPD.