Parasternal intercostal muscle activity during methacholine‐induced bronchoconstriction

Abstract

What is the central question of this study? The parasternal intercostal electromyogram (EMGpara) is known to provide an accurate, non-invasive index of respiratory load-capacity balance. Although relationships between EMGpara and both airflow obstruction and hyperinflation have been shown, the independent contribution of each factor has not been examined. What is the main finding and its importance? Reductions in airway calibre and inspiratory capacity along with increases in EMGpara were induced via methacholine challenge. A strong inverse relationship was observed between EMGpara and airway obstruction, with no influence of inspiratory capacity. These data suggest that EMGpara is more strongly influenced by airway calibre than by changes in end-expiratory lung volume during airway challenge testing. Neural respiratory drive, measured via the parasternal intercostal electromyogram (EMGpara), provides a non-invasive index of the load-capacity balance of the respiratory muscle pump. Previous studies in patients with obstructive lung disease have shown strong relationships between EMGpara and the extent of both airflow obstruction and hyperinflation. The relative influence of the two factors has not, however, been described. Airflow obstruction was induced via methacholine challenge testing in 25 adult humans. Forced expiratory volume in 1 s (FEV ) and surface EMGpara during tidal breathing were measured after each dose, with 20 of the participants also undergoing measurements of inspiratory capacity (IC) at each stage. Linear mixed model analysis was used to assess dose-wise changes in FEV and EMGpara, and thereafter to determine the influence of changes in FEV and IC on change in EMGpara. Median (interquartile range) FEV decreased significantly [from 96.00 (80.00-122.30) to 67.80 (37.98-92.27)% predicted, P < 0.0001] and EMGpara increased significantly [from 5.37 (2.25-8.92) to 6.27 (3.37-19.60) μV, P < 0.0001] from baseline to end of test. Linear mixed model analysis showed a significant interaction between methacholine dose and induced change in EMGpara, with an increase in EMGpara of 0.24 (95% confidence interval 0.11-0.37) μV per methacholine dose . Change in FEV further influenced this relationship [increase in slope of 0.002 (0.004-0.001) μV dose per % predicted fall in FEV , P = 0.011], but not with change in IC. These data suggest that bronchoconstriction exerts a more potent influence on levels of EMGpara than changes in end-expiratory lung volume during methacholine challenge.

Quantitative assessment of nocturnal neural respiratory drive in children with and without obstructive sleep apnoea using surface EMG

“…Even when children are school‐aged, reproducible volitional effort may still not be achievable (MacBean et al., ). Recently, non‐normalized respiratory muscle EMG has been reported as an outcome measure in adults and children with various clinical conditions, including patients ventilated on respiratory support (Kallio et al., ), wheezy preschool children (MacBean et al., ), adults undergoing methacholine‐induced bronchoconstrictions (MacBean et al., ) and adults with OSA (Luo et al., ). We have demonstrated in our cohort that non‐normalized sEMGcw as an index of NRD was significantly higher in children with OSA and a group of children with subjectively increased respiratory effort compared with primary snorers.…”

“…To minimize the effect of interindividual differences in muscle‐to‐electrode distance, sEMGcw is typically expressed as a percentage of a maximal value, limiting its use to those who can perform consistent maximal inspiratory efforts (Lin et al., ). Recent studies in both children and adults have supported the reporting of raw respiratory muscle EMG (not normalized to a reference value; Kallio et al., ; Luo et al., ; MacBean et al., , b, ), demonstrating greater variability in normalized EMG compared with the raw signal both within and between occasions (MacBean et al., ). However, further studies are required to ascertain the clinical utility of the non‐normalized EMG to facilitate translational use of respiratory muscle EMG.…”

The influence of affective state on respiratory muscle activity

“…To our knowledge, this is the first study to demonstrate an influence of non-physiological stimuli on parasternal intercostal muscle activity. The responsiveness of EMGpara to altered respiratory load is well documented (Reilly et al, 2011;Suh et al, 2015;MacBean et al, 2017), but consideration has not previously been given to subjects' affective state in interpreting the elevated EMGpara and derived indices observed in previous studies. We attributed our previous finding (MacBean et al, 2016) of a significant reduction in healthy adults' EMGpara between first and second measurements within a single testing session to acclimatization to the laboratory environment and a reduction in the anxiety associated with entering an unfamiliar environment; the results from the current study lend weight to this hypothesis by demonstrating a relationship between perceived 'tension' and 'relaxation' and measures of EMGpara.…”

The influence of posture on parasternal intercostal muscle activity in healthy young adults

“…Accurate measurement of respiratory function is a vital aspect of respiratory disease management. Parasternal intercostal electromyography (EMGpara) has been shown to be a robust measure of respiratory load, responsive to spontaneous and induced changes in pulmonary function (Reilly et al 2013, Suh et al 2015, MacBean et al 2017. Reference values have been established for EMGpara in healthy adult subjects (MacBean et al 2016b), allowing data from clinical populations to be expressed relative to predicted.…”