Exercise induced bronchoconstriction assessed using the forced oscillation technique

Abstract

Exercise induced bronchoconstriction (EIB) is assessed in the laboratory with an exercise challenge (EC). A ≥10% decline in FEV1 post EC is considered positive. The forced oscillation technique (FOT) is suggested to produce equivalent and more sensitive measures of airway calibre post EC than maximal expiratory manoeuvres. The rate of recovery and effect of raised minute ventilation (VE) post EC is uncertain. We investigated changes in airway mechanics measured with FOT post EC in people with asthma. Method: Inspiratory resistance (R5in) and reactance (X5) at 5Hz were measured prior to FEV1, before and up to 20min after an EC. BHR to the hyperosmolar mannitol test was measured in the asthmatic subjects within one week of the EC. Baseline and sequential FEV1, R5in, X5 and VE post EC were compared using ANOVA and Pearson’s correlation. Results: Subjects with current asthma (n=19, mean[SD] age 28[6] yr) and controls (n=10, 31[5] yr) were studied. Baseline FEV1, R5in, X5 and VE were similar between groups (P>0.09). BHR was present in 12/19 of asthmatic subjects. The %change in R5in (13[10] vs 105[106]% p=0.01) and X5 (16[14] vs 178[188]%, p=0.01) were different to controls in EC-positive but not EC-negative asthmatic subjects. Following EC, max %change FEV1 correlated with R5in and X5 (R>0.8, p 0.3). Conclusion: FOT parameters tracked well with forced manoeuvres following EC and were not influenced by the raised VE. FOT could be used as an end-point in EC in identifying EIB from those with BHR.