Abstract
Fixed sample entropy (fSampEn) has been successfully applied to myographic signals for inspiratory muscle activity estimation, attenuating interference from cardiac activity. However, several values have been suggested for fSampEn parameters depending on the application, and there is no consensus standard for optimum values. This study aimed to perform a thorough evaluation of the performance of the most relevant fSampEn parameters in myographic respiratory signals, and to propose, for the first time, a set of optimal general fSampEn parameters for a proper estimation of inspiratory muscle activity. Different combinations of fSampEn parameters were used to calculate fSampEn in both non-invasive and the gold standard invasive myographic respiratory signals. All signals were recorded in a heterogeneous population of healthy subjects and chronic obstructive pulmonary disease patients during loaded breathing, thus allowing the performance of fSampEn to be evaluated for a variety of inspiratory muscle activation levels. The performance of fSampEn was assessed by means of the cross-covariance of fSampEn time-series and both mouth and transdiaphragmatic pressures generated by inspiratory muscles. A set of optimal general fSampEn parameters was proposed, allowing fSampEn of different subjects to be compared and contributing to improving the assessment of inspiratory muscle activity in health and disease.
Highlights
Measuring respiratory muscle function is a key step in the assessment of many respiratory diseases, such as chronic obstructive pulmonary disease (COPD) [1]
The principal aim of the present study is, to provide an in-depth evaluation of the performance of Fixed sample entropy (fSampEn) in myographic respiratory signals, which lead us to propose a set of optimal general fSampEn parameters for inspiratory muscle activity estimation
Measurements of inspiratory muscle force and activation were obtained from twelve healthy subjects (six male, age 33 (30–39) years, body mass index 22.2 (20.6–24.2) kg/m2, forced expiratory volume in 1 second/forced vital capacity 81.9 (74.1–83.9)%), with no history of cardiorespiratory or neuromuscular disease, and from fourteen stable COPD patients (nine male, age 68 (65–72) years, body mass index 25.5 (19.4–28.0) kg/m2, forced expiratory volume in 1 second/forced vital capacity
Summary
Measuring respiratory muscle function is a key step in the assessment of many respiratory diseases, such as chronic obstructive pulmonary disease (COPD) [1]. Respiratory muscle function is typically measured as pressure and lung volume changes [2]. Transdiaphragmatic pressure (Pdi ) is the gold standard measure of the force exerted by the diaphragm, the main inspiratory muscle [3], and depends on the neural drive to the diaphragm and the level of diaphragm electrical activation. The electrical activity generated by the diaphragm can be accurately assessed by crural diaphragm electromyography (oesEMGdi ), using a multipair oesophageal electrode [4]. Invasive measurement of Pdi and oesEMGdi is technically complex and can be uncomfortable for study participants. Inspiratory muscle force and activation can be measured by surface
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