Ventilatory Demand During Stepping and Running: Implications for Exercise-Induced Bronchoconstriction in Children

BACKGROUND: Single-step tests have been proposed as simple and inexpensive challenges to diagnose exercise-induced bronchoconstriction (EIB) in the pediatric population. Work performed and the resulting ventilation, however, might be substantially lower in stepping than running. This might decrease the diagnostic yield of step-based challenges. METHODS: In a cross-sectional study, 53 children with asthma with exercise-related symptoms (34 boys, age 6-18 y) underwent an incremental stepping test, a 6-min constant stepping test, and a treadmill running test on different days. RESULTS: Constant and incremental stepping tests presented with lower metabolic demands ((V) over dotO(2) 1.42 +/- 0.48 and 1.34 +/- 0.55 L/min, respectively), ventilatory demands ((V) over dotO(2) 45 +/- 14 and 43 +/- 16 L/min, respectively), and cardiovascular demands (160 +/- 20 and 161 +/- 19 beats/min, respectively) than the treadmill running test (1.65 +/- 0.60 L/min, 54 +/- 17 L/min, and 172 +/- 7 beats/min, respectively) (P <.05). Between-test agreement in diagnosing EIB was poor (kappa 0.217-0.361). Although EIB prevalence was higher after the treadmill running test (60%) compared to constant (53%) and incremental (47%) stepping tests, 7 subjects developed EIB only in stepping. Clinical and resting functional characteristics did not differ in discordant subjects (ie, EIB negative in a given test but positive in another) versus concordant subjects (ie, EIB negative or positive in both tests). EIB was not related to individual test ability in eliciting high to very-high ventilation (>= 40% or >= 60% maximum voluntary ventilation, respectively). Moreover, a negative stepping test but a positive treadmill test (and vice versa) was not associated with greater ventilatory demands. CONCLUSIONS: Lower prevalence of EIB in stepping compared to treadmill running is not related to less ventilation demand in the former modality. Although stepping might be useful as a screening EIB test due its portability and low cost, a negative test should be confirmed with a running-based test in symptomatic children.