Introduction/Aim: Exertional dyspnea (ED) remains the hallmark of chronic obstructive pulmonary disease (COPD). Current measures of ED rely on recall or on tests that do not adequately control workload. We recently developed the Dyspnea Challenge, a 2-min treadmill walk that allows ED to be measured in real-time while walking on an incline. This study aimed to optimize the Dyspnea Challenge protocol and establish whether end-exercise ED is responsive to progressive, 1% changes in treadmill gradient in individuals with mild–severe COPD.

Method: Thirty (14 female) individuals participated in the study (Age: 69.2 ± 9.2 year; FEV1: 59.3 ± 19.1%). Each participant completed six Dyspnea Challenges at a standardized speed of 3 km h−1 and at 1% increments in treadmill gradient between 3% and 8%, in random order. The intensity of ED and leg fatigue were self-reported at rest and end-exercise using the modified Borg scale (mBorg). Heart rate (HR) and oxygen saturation (SpO2) were monitored continuously.

Results: All participants completed all six gradients. ED intensity increased with treadmill gradient (3%:2.6 ± 1.8; 4%:2.8 ± 2.2; 5%:3.1 ± 2.2; 6%:3.4 ± 2.2; 7%:3.7 ± 1.7; 8%:4.0 ± 2.1 units, p < 0.001). A 1% gradient change corresponded to a mean rise of 0.26 ± 0.22 units. However, we found that a minimum of a 2% gradient increment was necessary to significantly change ED, for example, 3% versus 4%: p = 0.927 versus 3% versus 5%: p = 0.022. Furthermore, while there was a significant increase in end-exercise HR (p = 0.002), no differences were observed in end-exercise SpO2 (p = 0.793) or Leg Fatigue (p = 0.059).

Conclusion: The current study showed that a 1% increase in gradient resulted in a mean increase in ED, but to change ED significantly, a minimum of a 2% gradient increment is necessary in a group of participants with mild–severe COPD. Furthermore, gradient changes in the Dyspnea Challenge may moderate ED independent of both leg fatigue and SpO2.