Exercise-Induced Bronchoconstriction Identified Using the Forced Oscillation Technique

Objective: Lung mechanics using the forced oscillation technique (FOT) is suggested to be equivalent and more sensitive in determining exercise-induced bronchoconstriction (EIB) than spirometry. Dynamic alterations in minute ventilation (V_E) may affect this measurement. We investigated changes in FOT parameters post exercise challenge (EC) in people with asthma as compared to spirometry. The rate of recovery and any effect of raised V_E following exercise on FOT parameters were also assessed. Method: Airway resistance (R₅) and reactance (X₅) at 5 Hz and V_E were measured prior to forced expiratory volume in 1 s (FEV₁) before and up to 20 min after a standard EC in people with asthma and healthy controls. Airway hyperresponsiveness to the hyperosmolar mannitol test was measured in the asthmatic subjects within 1 week of the EC. Baseline and sequential measures were assessed using repeated measures ANOVA and Pearson's correlation. Group demographics and recovery data were compared using an unpaired t test. Results: Subjects with current asthma (n = 19, mean ± SD age 28 ± 6 years) and controls (n = 10, 31 ± 5 years) were studied. Baseline FEV₁, R₅, X₅, and V_E were similar between groups (p > 0.09). Airway hyperresponsiveness was present in 12/19 asthmatic subjects. The EC max % change of R₅ and X₅ correlated with FEV₁ (r > 0.90) and were only different to controls in those with asthma that responded by FEV₁ criteria (p < 0.01). EC recovery of R₅ was similar to FEV₁; however, X₅ was greater (p = 0.03). Elevated V_E post EC did not affect the % change in FOT parameters across all subjects (p > 0.3). R₅ and X₅ were highly sensitive in determining a positive EC response (80-86%), but X₅ was more specific (93 vs. 80%). Conclusion: FOT parameters tracked with forced maneuvers and were not influenced by increased ventilation following an exercise challenge designed to elicit EIB. FOT identified EIB similarly to spirometry in patients with asthma.