Noninvasive Assessment of Inspiratory Muscle Neuromechanical Coupling During Inspiratory Threshold Loading

Abstract

Diaphragm neuromechanical coupling (NMC), which reflects the efficiency of conversion of neural activation to transdiaphragmatic pressure (P di), 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 P di and crural diaphragm electromyography (oesEMG di), 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 P di and oesEMG di , with noninvasive assessment of NMC (nNMC) using surface mechanomyography (sMMG lic) and electromyography (sEMG lic) 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 sMMG lic and sEMG lic measurements was found, resulting in little change in nNMC with increasing inspiratory load. By contrast, a curvilinear relationship between invasive P di and oesEMG di 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 sMMG lic and sEMG lic (both representing lower intercostal plus costal diaphragm activity) than between P di and crural oesEMG di. Noninvasive indices of NMC derived from sEMG lic and sMMG lic 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. INDEX TERMS Electromyography, inspiratory threshold loading, mechanomyography, neuromechanical coupling, respiratory muscles. The associate editor coordinating the review of this manuscript and approving it for publication was Venkata Rajesh Pamula .

Combining Bioimpedance and Myographic Signals for the Assessment of COPD During Loaded Breathing

“…Inspiratory threshold loading protocols are associated with changes in breathing pattern and, particularly, with an increase of tidal volume with respect to baseline in healthy subjects [22], [27], [28], [37]. The increase in ∆bioZ can only be observed in the mild group of which the median values were higher than median values of the other two groups (Fig.…”

“…On the other hand, clinical evidence is still limited, only a few studies have investigated and showed the applicability of the use of bioimpedance in respiratory diseases, focusing on infants suffering from reduced lung function [14]- [16]. Other noninvasive measurements such as surface electromyography (sEMG) and surface mechanomyography (sMMG) have been investigated for assessment of muscle function in healthy and diseased state [9], [10], [17]- [22]. These studies showed strong correlations between sEMG and sMMG and classical invasive measurements of respiratory muscle function [17]- [19].…”

Noninvasive Assessment of Neuromechanical Coupling and Mechanical Efficiency of Parasternal Intercostal Muscle during Inspiratory Threshold Loading

“…All recordings were obtained from 12 healthy subjects, including 6 male and 6 female, with no medical history of neuromuscular or cardiorespiratory disease and with the following characteristics (median (interquartile range)): age 33 (30–39) years, body mass index (BMI) 22.2 (20.6–24.2) kg/m 2 , forced expiratory volume in 1 second 98% (95–106%) % of predicted, and forced expiratory volume in 1 second/forced vital capacity 82% (74–84%) % of predicted [ 19 ]. Written consent was provided by all subjects prior to study participation.…”

“…In the respiratory system, sMMG and pressure represent different mechanical states of inspiratory muscles, the latter being a more global measure of respiratory muscle mechanical output. We have recently used sMMG and sEMG measurements from lower chest wall intercostal spaces (sMMG lic and sEMG lic , respectively) to provide noninvasive indices of lower chest wall inspiratory muscle NMC [ 19 ], which did not change significantly with increasing inspiratory load due to the linear relationship between sMMG lic and sEMG lic measurements. Measurements of sMMG lic have also been used, in combination with measurements of mouth pressure (P mo ), to calculate the mechanical efficiency (MEff) of lower chest wall inspiratory muscles, that is the transformation of muscle mechanical activation into pressure generation, in healthy subjects and patients with chronic obstructive pulmonary disease (COPD) [ 20 ].…”

“…Gold standard P di measurements are derived from simultaneous measurements of gastric (P gas ) and esophageal (P oes ) pressures (P di = P gas – P oes ). Since P di is specific to the diaphragm, P di has been widely used, together with oesEMG di , for the assessment of diaphragm NMC [ 4 , 12 , 19 , 23 , 24 , 25 , 26 ]. Measurements of P oes alone are, however, not specific to the diaphragm and are influenced by the activation of all inspiratory muscles [ 1 ].…”