Humidity prevents the exercise-induced formation of hydrogen peroxide and nitrite in exhaled breath condensate in recreational cyclists

Purpose: The aerobic exercise affects the respiratory redox-state. The influence of different relative humidity (RH) levels on the formation of respiratory reactive chemical species associated with redox-state altered by exercise has been poorly explored. Our aim was to evaluate the effect of two different RH conditions (40% vs. 90%) on the concentration of hydrogen peroxide and nitrite in exhaled breath condensate ([H₂O₂]_EBC and [NO₂⁻]_EBC) and spirometry parameters in recreational cyclists. Methods: Sixteen men and women (12/4) (mean age ± SD: 23.5 ± 2.2 years) completed 60-min of cycling at 166.3 ± 26.9 watts (70% of maximum load of V ˙ O ₂-max. test, 49.3 ± 7.6 mL·min⁻¹·kg⁻¹) at random 40%-RH and 90%-RH conditions separated by 7 days. The two-way RM-ANOVA test was applied to compare [H₂O₂]_EBC, [NO₂⁻]_EBC, [NO₂⁻]_EBC/[NO₂⁻]_Plasma at rest and 80-min post-exercise (80-post); and spirometry parameters at rest, 20-post and 80-post. Results: The interaction of factors (humidity × time) was significant in [H₂O₂]_EBC, [NO₂⁻]_EBC, [NO₂⁻]_EBC/[NO₂⁻]_Plasma (p = 0.005, p = 0.030, p = 0.043, respectively). At 40%-RH conditions, the same parameters were higher in 80-post than at rest (p < 0.001, p = 0.001, p = 0.014, respectively). At the same time, the [H₂O₂]_EBC and [NO₂⁻]_EBC/[NO₂⁻]_Plasma were higher in 40%-RH than 90%-RH (p = 0.010, p < 0.001, respectively). The interaction was significant in FEV₁ (p = 0.013) and FEF_25-75% (p = 0.023), but not in FEV₁/FVC (p = 0.362). At 80-post, the changes are kept in 90%-RH (p < 0.001), diminishing in 40%-RH being similar to rest. Conclusion: In recreational cyclists, 90%-RH prevents the increase of hydrogen peroxide and nitrite in exhaled breath condensate samples observed at 40%-RH and prolonging the bronchodilation until 80-post cycling exercise.