Ipratropium bromide (IB) has been used to prevent exercise-induced bronchoconstriction (EIB), but its effect varies among individuals. We hypothesized that such variability may reflect individual differences in vagal activity (VA), and therefore determined whether a correlation exists between VA and the effect of IB on EIB in 13.0 (±0.8)-yr-old children with asthma and documented EIB.
Subjects served as their own control and were tested on three occasions in an ambient temperature of 5°C. Visit I included no treatment. In visits II and III (counterbalanced sequence) subjects inhaled either 500 μg IB or 0.9% NaCl as a placebo, 45 min before exercise provocation. Investigators and the subjects were blinded to the inhaled substance. VA was assessed by a 4-s exercise test (3). The ratio of resting ECG R-R-interval at full inspiration to the lowest R-R interval during 4-s cycling was taken as an index of VA. Eight-minute cycling at constant work rate (HR = 173 ± 4 bpm) at 5°C was used to provoke EIB. A two-factor (treatment × time) repeated-measures ANOVA was used.
The exercise-induced drop in FEV1 was similar in the three sessions. However, because the IB caused a 15.7 ± 4.1 increase in FEV1 preexercise, the postexercise values after a placebo or no treatment were consistently lower than after IB. The beneficial response to IB, compared with no treatment and with placebo, was positively correlated to VA (for FEV1: r = 0.91, P = 0.002; and r = 0.90, P = 0.002, respectively).
We suggest that the therapeutic effect of IB on exercise-induced asthma may be related to vagal activity.
1 Alpine Children’s Hospital Davos, Davos, SWITZERLAND; 2Children’s Exercise and Nutrition Centre, McMaster University, Hamilton, CANADA; and 3Graduate Program in Physical Education, Gama Filho University, Rio de Janeiro, BRAZIL
Address for correspondence: Bruno Knöpfli, M.D., Head and Medical Director, Alpine Children’s Hospital Davos, Scalettastrasse 5, Postfach 118, CH-7270 Davos 2 Holauben, Switzerland; E-mail: firstname.lastname@example.org.
Submitted for publication June 2004.
Accepted for publication October 2004.
Professor Martin Schöni’s initiative and support for this study is greatly appreciated. We are grateful to the volunteers and their parents for taking part in the study.