Noninvasive assessment of inspiratory muscle neuromechanical coupling during inspiratory threshold loading

Diaphragm neuromechanical coupling (NMC), which reflects the efficiency of conversion of neural activation to transdiaphragmatic pressure (Pdi), is increasingly recognized to be a useful clinical index of diaphragm function and respiratory mechanics in neuromuscular weakness and cardiorespiratory disease. However, the current gold standard assessment of diaphragm NMC requires invasive measurements of Pdi and crural diaphragm electromyography (oesEMGdi), which complicates the measurement of diaphragm NMC in clinical practice. This is the first study to compare invasive measurements of diaphragm NMC (iNMC) using the relationship between Pdi and oesEMGdi, with noninvasive assessment of NMC (nNMC) using surface mechanomyography (sMMGlic) and electromyography (sEMGlic) of lower chest wall inspiratory muscles. Both invasive and noninvasive measurements were recorded in twelve healthy adult subjects during an inspiratory threshold loading protocol. A linear relationship between noninvasive sMMGlic and sEMGlic measurements was found, resulting in little change in nNMC with increasing inspiratory load. By contrast, a curvilinear relationship between invasive Pdi and oesEMGdi measurements was observed, such that there was a progressive increase in iNMC with increasing inspiratory threshold load. Progressive recruitment of lower ribcage muscles, serving to enhance the mechanical advantage of the diaphragm, may explain the more linear relationship between sMMGlic and sEMGlic (both representing lower intercostal plus costal diaphragm activity) than between Pdi and crural oesEMGdi. Noninvasive indices of NMC derived from sEMGlic and sMMGlic may prove to be useful indices of lower chest wall inspiratory muscle NMC, particularly in settings that do not have access to invasive measures of diaphragm function.Peer ReviewedPostprint (published version

Surface mechanomyography and electromyography provide non-invasive indices of inspiratory muscle force and activation in healthy subjects

The current gold standard assessment of human inspiratory muscle function involves using invasive measures of transdiaphragmatic pressure (Pdi) or crural diaphragm electromyography (oesEMGdi). Mechanomyography is a non-invasive measure of muscle vibration associated with muscle contraction. Surface electromyogram and mechanomyogram, recorded transcutaneously using sensors placed over the lower intercostal spaces (sEMGlic and sMMGlic respectively), have been proposed to provide non-invasive indices of inspiratory muscle activation, but have not been directly compared to gold standard Pdi and oesEMGdi measures during voluntary respiratory manoeuvres. To validate the non-invasive techniques, the relationships between Pdi and sMMGlic, and between oesEMGdi and sEMGlic were measured simultaneously in 12 healthy subjects during an incremental inspiratory threshold loading protocol. Myographic signals were analysed using fixed sample entropy (fSampEn), which is less influenced by cardiac artefacts than conventional root mean square. Strong correlations were observed between: mean Pdi and mean fSampEn |sMMGlic| (left, 0.76; right, 0.81), the time-integrals of the Pdi and fSampEn |sMMGlic| (left, 0.78; right, 0.83), and mean fSampEn oesEMGdi and mean fSampEn sEMGlic (left, 0.84; right, 0.83). These findings suggest that sMMGlic and sEMGlic could provide useful non-invasive alternatives to Pdi and oesEMGdi for the assessment of inspiratory muscle function in health and disease.Peer ReviewedPostprint (published version

Noninvasive assessment of neuromechanical and neuroventilatory coupling in COPD

This study explored the use of parasternal second intercostal space and lower intercostal space surface electromyogram (sEMG) and surface mechanomyogram (sMMG) recordings (sEMG para and sMMG para , and sEMG lic and sMMG lic , respectively) to assess neural respiratory drive (NRD), neuromechanical (NMC) and neuroventilatory (NVC) coupling, and mechanical efficiency (MEff) noninvasively in healthy subjects and chronic obstructive pulmonary disease (COPD) patients. sEMG para , sMMG para , sEMG lic , sMMG lic , mouth pressure (P mo ), and volume (V i ) were measured at rest, and during an inspiratory loading protocol, in 16 COPD patients (8 moderate and 8 severe) and 9 healthy subjects. Myographic signals were analyzed using fixed sample entropy and normalized to their largest values (fSEsEMG para%max , fSEsMMG para%max , fSEsEMG lic%max , and fSEsMMG lic%max ). fSEsMMG para%max , fSEsEMG para%max , and fSEsEMG lic%max were significantly higher in COPD than in healthy participants at rest. Parasternal intercostal muscle NMC was significantly higher in healthy than in COPD participants at rest, but not during threshold loading. P mo -derived NMC and MEff ratios were lower in severe patients than in mild patients or healthy subjects during threshold loading, but differences were not consistently significant. During resting breathing and threshold loading, V i -derived NVC and MEff ratios were significantly lower in severe patients than in mild patients or healthy subjects. sMMG is a potential noninvasive alternative to sEMG for assessing NRD in COPD. The ratios of P mo and V i to sMMG and sEMG measurements provide wholly noninvasive NMC, NVC, and MEff indices that are sensitive to impaired respiratory mechanics in COPD and are therefore of potential value to assess disease severity in clinical practice.Peer ReviewedPostprint (published version

Noninvasive assessment of neuromechanical coupling and mechanical efficiency of parasternal intercostal muscle during inspiratory threshold loading

This study aims to investigate noninvasive indices of neuromechanical coupling (NMC) and mechanical efficiency (MEff) of parasternal intercostal muscles. Gold standard assessment of diaphragm NMC requires using invasive techniques, limiting the utility of this procedure. Noninvasive NMC indices of parasternal intercostal muscles can be calculated using surface mechanomyography (sMMGpara) and electromyography (sEMGpara). However, the use of sMMGpara as an inspiratory muscle mechanical output measure, and the relationships between sMMGpara, sEMGpara, and simultaneous invasive and noninvasive pressure measurements have not previously been evaluated. sEMGpara, sMMGpara, and both invasive and noninvasive measurements of pressures were recorded in twelve healthy subjects during an inspiratory loading protocol. The ratios of sMMGpara to sEMGpara, which provided muscle-specific noninvasive NMC indices of parasternal intercostal muscles, showed nonsignificant changes with increasing load, since the relationships between sMMGpara and sEMGpara were linear (R2 = 0.85 (0.75–0.9)). The ratios of mouth pressure (Pmo) to sEMGpara and sMMGpara were also proposed as noninvasive indices of parasternal intercostal muscle NMC and MEff, respectively. These indices, similar to the analogous indices calculated using invasive transdiaphragmatic and esophageal pressures, showed nonsignificant changes during threshold loading, since the relationships between Pmo and both sEMGpara (R2 = 0.84 (0.77–0.93)) and sMMGpara (R2 = 0.89 (0.85–0.91)) were linear. The proposed noninvasive NMC and MEff indices of parasternal intercostal muscles may be of potential clinical value, particularly for the regular assessment of patients with disordered respiratory mechanics using noninvasive wearable and wireless devices.Peer ReviewedPostprint (published version

Evaluación no invasiva del impulso neural respiratorio y su relación con la respuesta mecánica mediante el análisis de señales electromiográficas de músculos respiratorios

Respiratory muscle contraction occurs in response to the electrical stimulation of the muscles. These electrical stimuli originate in the respiratory neurons of the brainstem, are transmitted via motor nerves to the neuromuscular junctions and propagate along muscle fibers. Respiratory electromyography measures the electrical activity of respiratory muscles in response to this nerve stimulation. The neural respiratory drive (NRD) is best expressed in a phrenic neurogram, but this is not feasible in humans. Alternatively, measurements of the diaphragm electromyographic signal (EMGdi) would most likely reflect phrenic neurogram activity. EMGdi signal can be recorded using invasive methods, involving the use of needle electrodes or electrodes positioned in the esophagus at the level of the diaphragm. As a non-invasive alternative, the study of respiratory muscle activity can be addressed by surface electromyography. The onset and offset of the neural inspiratory time (nton and ntoff, respectively) are fundamentally important measurements in studies of patient-ventilator interaction, where the level of assistance delivered by the ventilator is controlled by patient demand. Cardiac artifacts (ECG) often make it difficult to utilize EMGdi. To overcome the shortcoming of the ECG, in this thesis is proposed to use sample entropy with fixed tolerance values (fSampEn), a robust technique against impulsive noise. To evaluate nton and ntoff estimation it has been carried out an experimental study with surface EMGdi signals recorded in healthy subjects during two respiratory protocols designed to evaluate the influence of different breathing patterns on the EMGdi. These protocols consisted of a stepwise increase in respiratory rate (RR) with constant fractional inspiratory time (Ti/Ttot) and a stepwise decrement in the Ti/Ttot with constant RR, respectively. The developed algorithms allowed to determine the nton and ntoff and derive the RR, Ti and Ti/Ttot neural ventilatory parameters. The EMGdi amplitude provides a real-time indirect measure of the NRD, which reflects the load on the respiratory muscles. The NRD, assessed by normalized EMGdi signals, is higher in patients with respiratory disease than in healthy subjects. To evaluate the behavior of the fSamp En, as a method for improving the measurement of NRD from EMGdi signals in the presence of cardiac activity, compared to the average rectified value and root mean square value approaches, first, these methods have been applied to synthetic EMGdi signals . Secondly, we tested the proposed methods in an experimental study with EMGdi signals recorded in healthy subjects during an incremental inspiratory load test. The EMGdi amplitude allowed to evaluate changes in the respiratory muscle activation patterns and estimate the NRD. Also, this thesis contributes to the study of the respiratory activity by the non-invasive recording of mechanomyographic low frequency (BF) activity in healthy subjects and in patients with chronic obstructive pulmonary disease, allowing the study of bilateral asynchrony of the diaphragm and the RR. Finally, we have proposed the use of concentric ring electrodes as an alternative to improve the spatial resolution of electromyographic recordings, and eliminate the problems associated with the location and orientation of the bipolar configuration. The approaches presented in this doctoral thesis based on the analysis of electromyographic and mechanomyographic signals of respiratory museles allow to extract complementary information to current use techniques of and contribute to the study of respiratory function in the clinical setting .La contracción de los músculos respiratorios se produce en respuesta a la estimulación eléctrica. Estos estímulos se originan en las neuronas respiratorias del tronco del encéfalo, se transmiten a través de los nervios motores a las uniones neuromusculares y se propagan a lo largo de las fibras musculares. La electromiografía respiratoria mide la actividad eléctrica de los músculos respiratorios en respuesta a esta estimulación nerviosa. El impulso neural respiratorio (NRD) se expresa mejor a través del neurograma frénico, pero esto no es factible en los seres humanos. Como alternativa, la medida de la señal electromiográfica del diafragma (EMGdi) refleja de forma indirecta la actividad frénica. La señal EMGdi puede registrarse utilizando métodos invasivos, lo que implica el uso de electrodos de aguja o electrodos colocados en el esófago a nivel del diafragma . Como alternativa no invasiva, el estudio de la actividad muscular respiratoria puede abordarse mediante la electromiografía de superficie. El inicio y fin del tiempo neural inspiratorio (nton y ntoff, respectivamente) son medidas de importancia en los estudios de interacción paciente-ventilador, donde el nivel de la asistencia proporcionada por el ventilador es controlado por la demanda del paciente. Los artefactos cardíacos (ECG) a menudo hacen que sea difícil de utilizar la señal EMGdi. Para superar el inconveniente de la interferencia ECG, en la presente tesis se propone utilizar la entropía muestra! con valores de tolerancia fijos (fSampEn), una técnica que es robusta contra el ruido de tipo impulsivo. Para evaluar la estimación del nton y ntoff se ha realizado un estudio experimental con señales EMGdi superficie registrada en sujetos sanos durante dos protocolos respiratorios, diseñados para evaluar la influencia de los diferentes patrones respiratorios sobre la señal EMGdi. Estos protocolos consistieron en un aumento gradual de la frecuencia respiratoria (RR) con un tiempo inspiratorio (Ti) fracciona! constante (Ti!Ttot) y en una disminución gradual en el Ti!Ttot con una RR constante, respectivamente. Los algoritmos desarrollados han permitido determinar el nton y el ntoff y derivar los parámetros ventilatorios RR, Ti, y TifTtot neurales. La amplitud de la EMGdi proporciona una medida indirecta del NRD, que refleja la carga sobre los músculos respiratorios. El NRD, evaluado en señales EMGdi normalizadas, es mayor en pacientes con enfermedades respiratorias que en sujetos sanos. Para evaluar el comportamiento de la fSampEn, como un método para mejorar la medición del NRD a partir de señales EMGdi en presencia de ECG, en comparación con los enfoques basados en el uso del valor rectificado medio y valor cuadrático medio, primero, se han aplicado estos métodos a señales EMGdi sintéticas . En segundo lugar, hemos probado los métodos propuestos en un estudio experimental con señales EMGdi registradas en sujetos sanos durante una prueba de carga inspiratoria incremental. La amplitud de la EMGdi permitió evaluar los cambios en el patrón de activación de los músculos respiratorios y estimar el NRO. Asimismo, esta tesis doctoral contribuye al estudio de la actividad respiratoria mediante el registro no invasivo de actividad mecanomiográfica de baja frecuencia (BF) en sujetos sanos y en pacientes con enfermedad obstructiva crónica, permitiendo el estudio de la asincronía bilateral del diafragma y la RR. Finalmente, hemos propuesto el uso de electrodos de anillos concéntricos como una alternativa para mejorar la resolución espacial de los registros electromiográficos, y eliminar los problemas asociados a la localización y orientación de la configuración bipolar. Los enfoques presentados en esta tesis doctoral basados en el análisis de señales electromiográficas y mecanomiográficas de los músculo

Assessment of inspiratory muscle activation using surface diaphragm mechanomyography and crural diaphragm electromyography

The relationship between surface diaphragm mechanomyography (sMMGdi), as a noninvasive measure of inspiratory muscle mechanical activation, and crural diaphragm electromyography (oesEMGdi), as the invasive gold standard measure of diaphragm electrical activation, had not previously been examined. To investigate this relationship, oesEMGdi and sMMGdi were measured simultaneously in 6 healthy subjects during an incremental inspiratory threshold loading protocol, and analyzed using fixed sample entropy (fSampEn). A positive curvilinear relationship was observed between mean fSampEn sMMGdi and oesEMGdi (r = 0.67). Accordingly, an increasing electromechanical ratio was also observed with increasing inspiratory load. These findings suggest that sMMGdi could provide useful noninvasive measures of inspiratory muscle mechanical activation.Peer ReviewedPostprint (published version

Computational Intelligence in Electromyography Analysis

Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG may be used clinically for the diagnosis of neuromuscular problems and for assessing biomechanical and motor control deficits and other functional disorders. Furthermore, it can be used as a control signal for interfacing with orthotic and/or prosthetic devices or other rehabilitation assists. This book presents an updated overview of signal processing applications and recent developments in EMG from a number of diverse aspects and various applications in clinical and experimental research. It will provide readers with a detailed introduction to EMG signal processing techniques and applications, while presenting several new results and explanation of existing algorithms. This book is organized into 18 chapters, covering the current theoretical and practical approaches of EMG research

Assessment of inspiratory muscle activation using surface diaphragm mechanomyography and crural diaphragm electromyography

The relationship between surface diaphragm mechanomyography (sMMGdi), as a noninvasive measure of inspiratory muscle mechanical activation, and crural diaphragm electromyography (oesEMGdi), as the invasive gold standard measure of diaphragm electrical activation, had not previously been examined. To investigate this relationship, oesEMGdi and sMMGdi were measured simultaneously in 6 healthy subjects during an incremental inspiratory threshold loading protocol, and analyzed using fixed sample entropy (fSampEn). A positive curvilinear relationship was observed between mean fSampEn sMMGdi and oesEMGdi (r = 0.67). Accordingly, an increasing electromechanical ratio was also observed with increasing inspiratory load. These findings suggest that sMMGdi could provide useful noninvasive measures of inspiratory muscle mechanical activation.Peer Reviewe

Surface mechanomyography and electromyography provide non-invasive indices of inspiratory muscle force and activation in healthy subjects

Abstract The current gold standard assessment of human inspiratory muscle function involves using invasive measures of transdiaphragmatic pressure (Pdi) or crural diaphragm electromyography (oesEMGdi). Mechanomyography is a non-invasive measure of muscle vibration associated with muscle contraction. Surface electromyogram and mechanomyogram, recorded transcutaneously using sensors placed over the lower intercostal spaces (sEMGlic and sMMGlic respectively), have been proposed to provide non-invasive indices of inspiratory muscle activation, but have not been directly compared to gold standard Pdi and oesEMGdi measures during voluntary respiratory manoeuvres. To validate the non-invasive techniques, the relationships between Pdi and sMMGlic, and between oesEMGdi and sEMGlic were measured simultaneously in 12 healthy subjects during an incremental inspiratory threshold loading protocol. Myographic signals were analysed using fixed sample entropy (fSampEn), which is less influenced by cardiac artefacts than conventional root mean square. Strong correlations were observed between: mean Pdi and mean fSampEn |sMMGlic| (left, 0.76; right, 0.81), the time-integrals of the Pdi and fSampEn |sMMGlic| (left, 0.78; right, 0.83), and mean fSampEn oesEMGdi and mean fSampEn sEMGlic (left, 0.84; right, 0.83). These findings suggest that sMMGlic and sEMGlic could provide useful non-invasive alternatives to Pdi and oesEMGdi for the assessment of inspiratory muscle function in health and disease

Surface mechanomyography and electromyography provide non-invasive indices of inspiratory muscle force and activation in healthy subjects

The current gold standard assessment of human inspiratory muscle function involves using invasive measures of transdiaphragmatic pressure (Pdi) or crural diaphragm electromyography (oesEMGdi). Mechanomyography is a non-invasive measure of muscle vibration associated with muscle contraction. Surface electromyogram and mechanomyogram, recorded transcutaneously using sensors placed over the lower intercostal spaces (sEMGlic and sMMGlic respectively), have been proposed to provide non-invasive indices of inspiratory muscle activation, but have not been directly compared to gold standard Pdi and oesEMGdi measures during voluntary respiratory manoeuvres. To validate the non-invasive techniques, the relationships between Pdi and sMMGlic, and between oesEMGdi and sEMGlic were measured simultaneously in 12 healthy subjects during an incremental inspiratory threshold loading protocol. Myographic signals were analysed using fixed sample entropy (fSampEn), which is less influenced by cardiac artefacts than conventional root mean square. Strong correlations were observed between: mean Pdi and mean fSampEn |sMMGlic| (left, 0.76; right, 0.81), the time-integrals of the Pdi and fSampEn |sMMGlic| (left, 0.78; right, 0.83), and mean fSampEn oesEMGdi and mean fSampEn sEMGlic (left, 0.84; right, 0.83). These findings suggest that sMMGlic and sEMGlic could provide useful non-invasive alternatives to Pdi and oesEMGdi for the assessment of inspiratory muscle function in health and disease.Peer Reviewe