Perceived Exertion And Dyspnea While Cycling During A Hypoxic And Hyperoxic Placebo

Abstract

Rating of Perceived Exertion (RPE) is used to subjectively quantify and monitor the perception of physical activity, breathlessness or dyspnea, and leg discomfort (RPElegs) during exercise. However, it is unknown how perceptions of exertion can be influenced by expectation of difficulty. PURPOSE: We asked if the placebo and nocebo effects could alter dyspnea and RPEleg by telling subjects they were receiving different concentrations of oxygen during exercise. We hypothesized that subjects would rate their dyspnea and RPElegs higher when they believed they were breathing hypoxic gas and lower when they believed they were breathing hyperoxic gas relative to room air. METHODS: Thirty healthy, active subjects (19 M, 11 F) with normal pulmonary function participated. Prior to exercise, we read a script to ensure subjects understood hypoxic and hyperoxic gas might make breathing feel more difficult and easier, respectively, but intentionally made no mention about RPEleg. Then during 5-minute submaximal cycling trials (60% peak work rate), we deceived subjects by telling them they were breathing different hypoxic (17% and 15% O2) and hyperoxic (23% O2) gas concentrations, when in fact they breathed room air (21% O2). At the end of each trial, we asked subjects for their dyspnea and RPEleg. RESULTS: Cardiorespiratory variables were similar between the trials, however dyspnea and RPElegs changed in a dose-response manner depending on the O2 concentration participants believed they breathed. When subjects believed they were breathing 15% O2, they significantly increased their dyspnea +0.70 ± 0.2 Borg units (p = 0.03) compared to room air, whereas RPElegs did not significantly change +0.35 ± 0.1 Borg units (p = 0.70). When comparing the most severe hypoxic condition, 15% O2, to the 23% hyperoxic condition, subjects significantly increased their dyspnea +1.05 ± 0.4 Borg units (p = 0.003) but did not significantly change RPElegs + 0.55 ± 0.2 Borg units (p = 0.46). CONCLUSION: We found that dyspnea during exercise is susceptible to expectancy, without any accompanying physiological changes. Given that a single unit in dyspnea is considered a minimal clinically important difference, our findings show that the effect of expectation must be considered when interpreting sensations of breathlessness. Support: NSERC