The Dyspnoea Challenge - a novel approach for measuring exertional dyspnoea

Introduction: Exertional Dyspnoea(ED) is common in heart failure(HF) and chronic obstructive pulmonary disease(COPD). The Dyspnoea Challenge(DC), a 2-min inclined treadmill walk, is a repeatable and valid measure of ED. We aimed to investigate the feasibility of the DC in those with HF and COPD. Methods: Over two visits, participants performed 2x6-min walk tests(6MWT) and multiple DCs to calculate treadmill speed, set at 80% 6MWT, and gradient, which was adjusted between tests, until ED was ≥4 modified Borg scale. Once gradient was confirmed, two DCs were performed with pulmonary gas exchange measured once. Outcome measures included end-exercise ED intensity, oxygen uptake(V̇O2), ventilation(V̇E), and leg fatigue(modified Borg scale). Heart rate(HR) and arterial oxygen saturation(SPO2) were monitored throughout exercise. Results: 25 COPD (68±10yr; forced expiratory volume in 1 second:47.6±11.5%; 6-min walk distance(6MWD): 430±101m) and 21 HF (66±11yr; ejection fraction:45.3±6.1%; 6MWD 520±97m) took part. Both groups attained similar ED (HF:4.3±0.5; COPD:4.5±0.5units,P=.71). Though, the HF group walked at higher treadmill speeds(4.2±0.8 vs. 3.5±0.8km·h-1) and gradients(10.3±2.8 vs. 9.6±2.8%). Consequently, HF patients had higher V̇O2(1.54±0.50 vs. 1.12±0.28L·min-1,P=<.01) and V̇E(56.9±17.8 vs. 38.46±9.6L·min-1,P=<.01); however, end-exercise HR(HF:113±19; COPD:116±19beats·min-1,P=.57), SPO2(HF:95.6±5.8; COPD:93.6±3.6%,P=.08) and leg fatigue(HF: 2.8±1.8; COPD:2.6±1.6units,P=.55) were similar between groups. Intraclass correlation co-efficients for repeat tests were 0.78 (P=<.001) for COPD and 0.79 (P=<.001) for HF. Conclusions: The DC protocol appears to be a feasible and repeatable measure of ED in COPD and HF.