Is non‐normalized chest wall electromyogram activity a reliable index of respiratory neural drive? On the surface – yes!

Abstract

Respiratory EMG recordings provide a useful measure of the pattern and magnitude of respiratory muscle recruitment at rest and in circumstances of altered respiratory neural drive. The measures can also sometimes serve as useful surrogates for the assessment of respiratory mechanics and, when married with measures of respiratory-related pressures, flows and volumes, provide a comprehensive portrait of neuromechanical coupling, affording wideranging application in the study of the performance of the respiratory system in health and disease. Quantification of EMG activity as a measure of motor drive is most often standardized to allow for comparisons between participants. It is common to normalize EMG activity across the spectrum of behaviour in a single recording session to a reference value, typically themaximal activity recorded. For example, in assessments of upper airway EMG activity it is common to express respiratory-related activity relative to the peak activity during a swallow. For thoracic respiratory EMGs, activity can be expressed relative to the peak activity recorded during a volitional manoeuvre. It is argued that the standardization of measures with such approaches allows for a faithful comparison of EMGactivities between individuals, allaying concerns regarding potential inconsistencies in electrode placement. It is recognized too, however, that true differences between individuals in themaximal activity can potentially confound interpretations across various behaviours normalized to the maximum, with increased risk of arithmetic anomaly in comparisons between control and disease states. As such, the reporting of absolute non-normalized EMG activity is also potentially valuable. Indeed, in a variety of participant cohorts, maximal EMG activity cannot be determined reliably, owing to an inability to perform volitional measures, which necessitates other approaches to the quantification of respiratory EMGs. In this issue of Experimental Physiology, Chuang et al. (2019) describe the use of chest wall surface EMG in children during sleep,