Exploratory study comparing dysautonomia between asthmatic and non-asthmatic elite swimmers

Abstract

Background: Dysautonomia has been independently associated with training and exercise-induced bronchoconstriction. In addition, neurogenic airway inflammation was recently associated with swimmers-asthma. We aimed to assess the relation between autonomic nervous system and airway responsiveness of asthmatic elite swimmers.

Methods: Twenty-seven elite swimmers, 11 of whom had asthma, were enrolled in this exploratory cross-sectional study. All performed spirometry with bronchodilation, skin prick tests and methacholine challenge according to the guidelines. Pupillometry was performed using PLR-200™ Pupillometer. One pupil light response curve for each eye was recorded and the mean values of pupil's maximal and minimal diameters, percentage of constriction, average and maximum constriction velocities (parasympathetic parameters), dilation velocity, and total time to recover 75% of the initial size (sympathetic parameters) were used for analysis. Asthma was defined using IOC-MC criteria; subjects were divided into airway hyperesponsiveness (AHR) severity according to methacholine PD20 in: no AHR, borderline, mild, moderate and severe AHR. Differences for pupillary parameters between groups and after categorization by AHR severity were assessed using SPSS 20.0 (p ≤ 0.05). In individuals with clinically relevant AHR, correlation between PD20 and pupillary parameters was investigated with Spearman's correlation test.

Results: No statistically significant differences were observed between asthmatic and non-asthmatic swimmers regarding parasympathetic parameters. When stratified by AHR, maximal and minimal diameters and percentage of constriction were significantly lower among those with severe AHR. Among swimmers with clinically relevant AHR (n = 18), PD20 correlated with parasympathetic activity: maximal (r = 0.67, p = 0.002) and minimal diameters (r = 0.75, p<0.001), percentage of constriction (r = -0.59, p = 0.011) and latency (r = 0.490, p = 0.039).

Conclusions: No significant differences were observed between asthmatic and non-asthmatic swimmers regarding parasympathetic parameters, but among those with relevant AHR an association was found. Although limited by the sample size, these findings support the relation between dysautonomia and AHR in asthmatic swimmers.

Keywords: Airway hyperesponsiveness; Autonomic nervous system; Dysautonomia; Exercise-induced asthma; Parasympathetic activity; Swimmers.