Optimising the Dyspnoea Challenge: exertional dyspnoea responses to changing treadmill gradients

The Dyspnoea Challenge is a two-minute treadmill walk designed to measure exertional dyspnoea(ED). To efficiently individualise workload, we aimed to assess; 1) whether the Dyspnoea Challenge is responsive to 1% changes in treadmill gradient and 2) the minimum gradient variation necessary to generate a clinically meaningful change in ED (≥1 modified Borg scale).

Thirty individuals with COPD(GOLD II-IV) (age: 69.2 ± 9.2 years; FEV₁: 49.3 ± 19.1%) completed six Dyspnoea Challenges at a fixed treadmill speed of 3 km·h^-1 and at a gradient of between 3% and 8%, performed in random order. ED intensity and leg fatigue were measured using the 0-10 modified Borg scale. Heart rate(HR) and oxygen saturation(S_pO₂) were monitored continuously. A multidimensional dyspnoea profile(MDP) was used to quantify the discomfort, physical, e.g., work/effort and breathing frequency, and emotional components of ED.

Higher treadmill gradients generated stronger intensities of ED (3%:2.6 ± 1.8; 4%:2.8 ± 2.2; 5%:3.2 ± 2.2; 6%:3.4 ± 2.2; 7%:3.7 ± 1.8; 8%:4.0 ± 2.1units). Statistical changes were observed in ED(e.g.,3 vs. 5%: P = .03) and the MDP discomfort data(e.g.,4 vs. 6%: P = .04) at ≥ a 2% variation in treadmill gradient. Linear regression found a 4% variation in treadmill gradient corresponded to a rise in ED ≥ 1unit. Increases in ED intensity corresponded to heightened sensations of work/effort(P < .01) and breathing frequency(P < .01). There were no changes in emotional constructs(P = .27). While there was an increase in HR with increasing gradient(P < .01), no differences were observed in end-exercise S_pO₂(P = .79) or leg fatigue(P = .06).

To significantly change ED, the treadmill gradient must be manipulated by ≥ 2%, with a ≥ 4% change in gradient required to induce a clinically meaningful change in ED.