Exertional Dyspnoea responses reported in the Dyspnoea Challenge and measures of disease severity in COPD

Background: The Dyspnoea Challenge has been developed to facilitate the field-based measure of exertional dyspnoea(ED). To further validate the test, we aimed to; investigate the relationship between end-exercise ED, generated by a fixed-intensity Dyspnoea Challenge(DCFIX), and measures of disease severity (Forced expiratory volume in 1 s(FEV1), six-minute walk distance(6MWD), breathing reserve(VE/MVV), modified medical research council dyspnoea scale (mMRC), Body-mass index, airflow Obstruction, Dyspnoea, and Exercise (BODE index) and compare the physiological response of the DCFIX to a six-minute walk test(6MWT). Methods: Thirty-two individuals (15 female) with COPD (GOLD II-IV) (age: 69.7 +/- 9.4 yrs; FEV1: 49.1 +/- 18.2 %) performed 2x6MWT and 2xDC(FIX) at a treadmill speed of 3 km h(-1) and gradient of 4 %. The intensity of ED was measured using the modified Borg dyspnoea scale at baseline and end-exercise with heart rate (HR) and oxygen saturation (SO2)pmonitored continuously. During 1x6MWT and 1xDC(FIX) pulmonary gas exchange, cardiac output (Q) and dynamic hyperinflation were measured. Results: End-exercise ED measured during the DCFIX was not correlated to FEV1, but moderately correlated to; 6MWD(rs =-0.54, P < .01), V-E/MVV (rs = 0.46, P = .02), mMRC(rs = 0.45, P = .01), and the BODE index(rs = 0.53, P < .01). When comparing the DCFIX and 6MWT, participants walked to comparable levels of oxygen consumption(P = .38), ventilation(P = .37), Q(P = .20), VE/MVV(P = .83), maximum HR percentages(P = .67) and dynamically hyperinflated to a similar degree(P = .37). Conclusions: The Dyspnoea Challenge is correlated to different parameters of disease severity and produces a similar physiological and ED response to that of the 6MWT with the added benefit of being appropriate for longitudinal assessment of ED.