Inhaled menthol for dyspnea relief during cycle exercise in COPD: a randomized trial.

Abstract

Background: Menthol inhalation (MI) lowers dyspnea ratings during loaded breathing in chronic obstructive pulmonary disease (COPD) and cycle exercise in healthy adults. Proposed mechanisms include stimulation of cold receptors in the upper airways, modulating perception of breathing-related effort and airflow.

Research question: Does MI also alleviate exertional dyspnea in COPD?

Study design and methods: Twenty COPD patients (60% male, 68±6 years, FEV₁=47±17 %predicted) completed 2 constant-load cycle exercise tests (73±7 %peak power output) to exhaustion with menthol or placebo (strawberry flavoring) added to the breathing circuit in counter-balanced order and on separate days. Ventilatory and neuromuscular parameters were measured continuously. Dyspnea intensity was serially assessed using the 0-10 category-ratio Borg scale, and dyspnea unpleasantness and related sensory qualities using the Multidimensional Dyspnea Profile at end-exercise. Participants were asked in which test their inspiratory airflow felt easier.

Results: Serial dyspnea intensity ratings were lower with menthol vs. placebo (estimate (Δ/10%peak time): -0.09, 95% CI: -0.15 to -0.02, p=0.01), while ratings of dyspnea unpleasantness, air hunger, and mental breathing effort were lower at end-exercise (all p<0.05). Menthol-related improvements in dyspnea intensity at symptom limitation of the shorter test vs. equivalent time on the other were correlated with higher endurance time (r=-0.73, p<0.001). There were no differences in ventilatory and neuromuscular parameters (p's>0.05). Exercise endurance time was unaffected by menthol (Δ0.3±1.6 minutes with menthol vs. placebo, p=0.50). 85% reported easier inspiratory airflow with menthol.

Interpretation: MI may be useful for management of exertional dyspnea in selected COPD patients. Future work should investigate if MI can improve outcomes of exercise rehabilitation programs.