Title: | Time-of-day has no effect on exercise-induced bronchoconstriction in mild to moderate asthma |
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Author(s): | A Rowe N Fleming B Donne N Mahony |
Institution: | Human Performance Laboratory, Discipline of Anatomy, Watt's Building, Trinity College Dublin |
Poster: | Click to view poster |
Category: | COPD/Asthma |
Abstract: | Introduction: Exercise-induced bronchoconstriction (EIB) is defined as a transient, acute narrowing of the airway associated with exercise. ▪ Exercise is therapeutic for asthma, however up to 90% of asthmatics experience exercise-induced bronchoconstriction (EIB) ▪ Diurnal variation in symptoms is characteristic of asthma but few studies have evaluated whether this occurs in EIB. ▪ Eucapnic Voluntary Hypernea (EVH) is a indirect bronchoprovocation test where participants maximally respire a dry gas to stimulate exercise. Objective: ▪ To establish the effect of diurnal variation in EIB in a cohort of recreationally-active males with a diagnosis of mild to moderate asthma. Methods: Asthmatics (n=14) were male, recreationally active, diagnosed with mild to moderate asthma by a physician and used an inhaler with exercise. ▪ Controls (n=9) were recreationally-active volunteers who had no history or symptoms of asthma. ▪ Participants were randomised to either complete an AM (07:00 to 08:00) or PM (17:00 to 18:00) EVH challenge first, followed by the alternate test 34 h to 7 days later. ▪ The EVH protocol comprised of six-minutes of hyperventilation of a 5% CO2 gas at a minimum ventilation rate of 21 × FEV1 min-1. ▪ A 2-way repeated measures ANOVA was performed to assess for AM/PM differences in response to EVH. ▪ The primary outcome measure was FEV1 pre- and post-EVH. Results: No difference between baseline FEV1 in asthmatics (4.21 ± 0.79 vs. 4.25 ± 0.65L) was observed between AM and PM tests. ▪ Significant reductions from baseline FEV1 were noted in both cohorts post-EVH(P<0.001) (Figure 1). ▪ 64% (n = 9) of asthmatics had at least one positive EVH test (10 % drop in FEV1 post-EVH at one time point). ▪ No positive tests were noted in controls. ▪ The mean maximum drop in FEV1 for asthmatics was 15.1 ± 15.4 vs. 15.0 ± 14.6% for AM and PM tests (Figure 2). ▪ No significant differences were observed in controls. ▪ A repeated-measure 2-way ANOVA showed no effect of time-of day on FEV1 post-EVH in asthmatics. Discussion: ▪ We demonstrated diurnal variation has no effect in a cohort of males with mild-to-moderate asthma. ▪ This was the first study to use the gold-standard protocol to test for diurnal variation. ▪ Our study adds to previous work showing no diurnal variation (1) and contrasts with one study which reported more EIB in the evening (2). ▪ Our cohort had milder asthma with no baseline variability in FEV1 – results may have differed in a more severe cohort. ▪ Given the beneficial effects of exercise on asthma, we recommend asthmatics exercise at the time-of-day they are most likely to exercise |