Menthol inhalation relieves dyspnoea through the brain

Background Menthol inhalation (MI) relieves dyspnoea in healthy individuals and people with respiratory disorders, independent of changes in breathing patterns and respiratory muscle electromyography activity. Thus, the underlying working mechanism of MI is unknown. We tested whether MI reduces dyspnoea by attenuating the neural processing of afferent respiratory sensations, without altering respiratory patterns and the efferent neural drive to breathe. Methods Thirty healthy adults completed four 5-min trials of strong inspiratory resistive loaded breathing: two with MI and two with strawberry scent inhalation (SI; placebo control), in counterbalanced order. Paired inspiratory occlusions (150 ms) were randomly administered every 2–6 breaths to evoke respiratory-related evoked potentials (RREPs) in the electroencephalogram, reflecting neural processing of respiratory signals. Respiratory parameters were measured continuously, and neural drive to breathe was assessed via inspiratory occlusion pressure (P0.1). Dyspnoea intensity and unpleasantness were rated using the modified Borg scale, and five sensory dyspnoea qualities were rated using the Multidimensional Dyspnoea Profile. Results Dyspnoea intensity (Δ=−0.67 modified Borg units, p=0.003, d=−0.56), air hunger (p