Purpose: A high prevalence of asthma and bronchial hyperresponsiveness (BHR) is reported in swimmers and cross-country skiers. It has been suggested that increased parasympathetic nervous activity is involved in asthma development in endurance athletes. We aimed to assess the associations of BHR to parasympathetic activity in healthy and asthmatic swimmers and cross-country skiers and healthy nonathletes.
Methods: Parasympathetic activity was measured by pupillometry and heart rate variability at the onset of exercise with the cardiac vagal index calculated in 28 cross-country skiers (♂18/♀10), 29 swimmers (♂17/♀12), and 30 healthy nonathlete controls (♂14/♀16) on two different days. All subjects performed a methacholine bronchial challenge with the provocation dose causing 20% decrease in the forced expiratory volume in 1 s calculated (PD20met). Data were analyzed by robust regression analysis and presented as β coefficients with 95% confidence intervals (CI).
Results: PD20met was negatively associated with cardiac vagal index (-13.9, 95% CI = -26.8 to -1.0) in all subjects. When adjusted to the type of sport, this association was stronger in swimmers (-8.3, 95% CI = -13.0 to -3.6) as compared with controls and nonsignificant in cross-country skiers. Percent pupil constriction was significantly associated with PD20met in swimmers (-9.4, 95% CI = -15.4 to -3.4) only after adjusting for the type of sport. Fourteen swimmers (48%) and 16 cross-country skiers (57%) had doctor-diagnosed asthma in combination with current BHR and/or current use of asthma drugs. Seventy-two percent swimmers, 44% cross-country skiers, and 39% controls had a PD20met ≤8 μmol (P = 0.015). Fourteen swimmers had a PD20met ≤2 μmol as compared with one cross-country skier (P < 0.001).
Conclusion: Parasympathetic activity measured in the heart is more closely related to BHR as compared with parasympathetic activity measured in the pupils. The type of sport influences BHR severity and its relationship to parasympathetic activity.