Exercise‐induced bronchoconstriction assessed by a ratio of surface diaphragm EMG to tidal volume

Exercise‐induced bronchoconstriction (EIB) is usually assessed by changes in forced expiratory volume in 1 s (FEV(1)) which is effort dependent. The purpose of this study was to determine whether the diaphragm electromyogram (EMG(di)) recorded from chest wall surface electrodes could be used to reflect changes in airway resistance during an exercise challenge test and to distinguish patients with EIB from those without EIB. Ninety participants with or without asthma history were included in the study. FEV(1) was recorded before and 5, 10, 15, and 20 min after exercise. EIB was defined as an FEV(1) decline greater than 10% after exercise. A ratio of root mean square of EMG(di) to tidal volume (EMG(di)/V (T)) was used to assess changes in airway resistance. Based on changes in FEV(1), 25 of 90 participants exhibited EIB; the remainder were defined as non‐EIB participants. EMG(di)/V (T) in EIB increased by 124% (19%–478%) which was significantly higher than that of 21% (−39% to 134%) in non‐EIB participants (p < 0.001). At the optimal cutoff point (54% in EMG(di)/V (T)), the area under the ROC curve (AUC) for detection of a positive test was 0.92 (p < 0.001) with sensitivity 92% and specificity 88%. EMG(di)/V (T) can be used to assess changes in airway resistance after exercise and could be used to distinguish participants with EIB from those without EIB.