Bronchodilator Response Assessed by Surface Respiratory Muscle EMG in Children

An increase of ≥ 12% in forced expiratory volume in the first second (FEV₁) after inhalation of bronchodilator indicates airway reversibility. However, it is difficult to measure FEV₁ in children. The aim of the study is to determine whether respiratory muscle electromyograms recorded from chest wall surface electrodes can be used to distinguish children with uncontrolled asthma from healthy subjects.

Fourteen children with uncontrolled asthma [aged 6.1 (3 ~ 13) years] and 28 healthy children [aged 7.6 (3 ~ 13) years] were recruited. Uncontrolled asthma was defined as having poorly controlled symptoms, along with an increase in FEV₁ of at least 12%, or presenting with a wheezing symptom that improved after inhaling a bronchodilator. Diaphragm electromyogram (EMG_di), parasternal intercostal EMG (EMG_para), airflow, FEV₁, and wheezing were recorded before and after inhalation of bronchodilator.

Good-quality EMG_di and EMG_para could be recorded in all subjects. However, 18 of 42 children could not perform the spirometer properly. Changes in EMG_di [-24.6% (-43.5 ~ -12.4%) vs -0.1% (-13.2 ~ 16.9%), p<0.001] and EMG_para [-11.2% (-31.5 ~ 32.4%) vs -0.5% (-24.9 ~ 13.0%), p<0.05] in children with asthma were, respectively, significantly larger than those in healthy subjects during bronchodilator response. The area under the receiver operating characteristic curves for the changes of EMG_di and EMG_para were 0.995 (95% CI 0.906 to 1.000) and 0.755 (95% CI 0.598 to 0.874).

Surface respiratory muscle EMG could be feasible and useful to assess bronchodilator response to differentiate children with uncontrolled asthma from healthy subjects.