Non-invasive measures of neural respiratory drive in children: the utility of respiratory muscle electromyography

Abstract

Background and aims: Surface electromyography (sEMG) recording of the inspiratory muscles is a potential non-invasive method of assessing neural respiratory drive (NRD) in children. This thesis explored the application of inspiratory muscle sEMG to assess NRD in healthy children and in children with sleep-disordered breathing. The relationship between sEMG and lung function variables of volume and pressure, and other factors affecting interpretation of sEMG were also evaluated. Method: The reliability of a developed method to quantitatively assess sEMG of the diaphragm (sEMGdi) recorded using a commercial sleep study set up was examined. Surface EMG of the diaphragm recorded from snoring children with and without obstructive sleep apnoea, and also from children with sleep-disordered breathing before and after treatment with pressure support were compared. Inspiratory muscle (scalene, parasternal intercostal, and diaphragm) sEMG recorded from healthy children during tidal breathing and maximal inspiratory ramps were evaluated. Variability in peak inspiratory muscle sEMG recorded during different maximal inspiratory manoeuvres were assessed. Linear mixed models were used to assess factors affecting sEMG magnitude. Results: A reliable method using sEMGdi to assess NRD was developed and demonstrated that NRD was significantly higher in children with obstructive sleep apnoea and increased work of breathing compared to healthy snorers. Provision of positive airway pressure support decreased NRD as reflected by decreased sEMGdi from baseline in children with sleep-disordered breathing. Inspiratory muscle sEMG had a curvilinear/linear relationship with increasing lung volume and pressure. Inspiratory muscle tidal sEMG had a negative linear relationship with age and body mass index (BMI), but not biological sex. Postural changes can affect inspiratory muscle sEMG. Peak sEMG of the inspiratory muscles were recorded from the majority of the children when performing the maximal sniff inhalation manoeuvre. Normalising sEMG to a maximal value abolished the influence of BMI, but not age, on sEMG. Conclusion: Diaphragm sEMG recorded from children with and without sleep-disordered breathing using commercial equipment can be quantitively measured to evaluate NRD. Inspiratory muscle sEMG in children is affected by age and BMI. Future work needs to address standardisation of the methodology in order to translate this application into routine clinical practice.