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Exercise induced bronchoconstriction (EIB) is a frequent and specific symptom of childhood asthma featured by expiratory flow limitation. A recent study showed that exercise can also induce inspiratory flow limitation, independent of EIB.  The aim of this study was to investigate whether salbutamol protects against exercise induced inspiratory flow limitation in asthmatic children.

Methods: The study had a prospective double-blind placebo-controlled randomized cross-over design with two exercise challenge tests preceded by the inhalation of 200µg salbutamol or placebo. Children 8-16 years old with documented exercise induced inspiratory flow limitation performed two exercise challenge tests (ECT’s) to assess EIB. EIB was defined as a fall in forced expiratory volume in 1 second (FEV₁) ≥ 13% whereas inspiratory flow limitation was defined as a fall in mid inspiratory flow (MIF₅₀) ≥ 25%. 

Results: 63% of the children (19/30) with exercise induced flow limitation showed an inspiratory flow limitation. Salbutamol significantly reduced the mean exercise induced fall in MIF₅₀ in children with exercise induced inspiratory flow limitation compared to placebo (17.6% versus 24.9%, p=0.004).

Conclusions: We observed a significant but inconsistent, individually variable protection of salbutamol against exercise induced inspiratory flow limitation in contrast to the consistent protective effect of salbutamol against EIB. We confirmed that a substantial number of the children with exercise induced flow limitation have an inspiratory flow limitation. Asthmatic children who experience persistent exercise induced asthmatic symptoms despite the use of (prophylactic) salbutamol, may suffer from an inspiratory flow limitation as a component of their asthma.