Abstract
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 (VE) 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 VE following exercise on FOT parameters were also assessed.Method: Airway resistance (R5) and reactance (X5) at 5 Hz and VE 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 VE 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 VE 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.
Highlights
Exercise-induced bronchoconstriction (EIB) describes increased sensitivity to exercise stimuli that cause airway narrowing via airway smooth muscle contraction (Joos et al, 2003)
Most patients with asthma were mildly symptomatic with an ACT score of 19.7 ± 4.3 and had elevated exhaled nitric oxide (52 ± 46 ppb) as compared to controls (21 ± 13 ppb) that did not reach significance (p = 0.06) (Table 2)
Two thirds (12/19) of subjects demonstrated airway hyperresponsiveness to mannitol with a PD20FEV1M of 165 ± 129 mg
Summary
Exercise-induced bronchoconstriction (EIB) describes increased sensitivity to exercise stimuli that cause airway narrowing via airway smooth muscle contraction (Joos et al, 2003). The presence and degree of EIB can be assessed in the laboratory using an exercise challenge test (EC), a stimulus that releases inflammatory mediators (Anderson et al, 1982; Weiler et al, 2016) via osmotic and thermal effects of respiratory water loss (Anderson et al, 1982). An EC is assessed using forced expiratory volume in 1 s (FEV1), where a ≥ 10% decline from baseline is considered positive (Parsons et al, 2013). Measurement is dependent on the patient’s ability to perform maximal and repeatable efforts, which may be challenging for some and may independently alter airway resistance. The required deep inhalation is known to alter airway caliber in those with airway hyperresponsiveness, affecting airway resistance and the sensitivity of FEV1 to detect EIB. Other lung volume-related responses (such as hyperinflation) are not detectable by spirometry
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