Parasternal intercostal muscle activity during methacholine-induced bronchoconstriction
Victoria MacBean, Claire L. Pringle, Alan C. Lunt, Keith D. Sharp, Ashraf Ali, Anne Greenough, John Moxham and Gerrard F. Rafferty
Published in the journal Experimental Physiology, February 2017
Neural respiratory drive (NRD) is commonly used as a measure of respiratory function, as it measures the overall muscular effort required to breathe in the presence of the changes that occur in lung disease. Both bronchoconstriction (airway narrowing) and hyperinflation (over-inflation of the chest, caused by air trapped in deep parts of the lung) occur in lung disease and are known to have detrimental effects on breathing muscle activity. Electromyography (EMG) is a measure of electrical activity being supplied to a muscle and can be used to measure the NRD leaving the brain towards respiratory muscles (in this study the parasternal intercostals – small muscles at the front of the chest). This study aimed to research the individual contributions of bronchoconstriction and hyperinflation on EMG and the overall effectiveness of the EMG as an accurate marker of lung function.
A group of 32 young adults were tested as subjects for this study, all of which had lung function within normal limits at rest, prior to testing. The subjects inhaled increasing concentrations of the chemical methacholine to stimulate the contraction of airway muscles – imitating a mild asthma attack. Subjects’ EMG, spirometry (to measure airway narrowing) and IC (inspiratory capacity) was measured to test for hyperinflation. Detailed statistical testing was used to assess the relationships between all the measures.
The results show that obstruction of the airway was closely related to the increase in EMG, however inspiratory capacity was not related. The data suggests that the overinflation of the chest had less of an effect on the EMG than the airway diameter (bronchoconstriction). This helps advance the understanding of how EMG can be used to assess lung disease.
This summary was produced by Talia Benjamin, Year 13 student from JFS School, Harrow, as part of our departmental educational outreach programme.