Respiratory muscle activity and patient-ventilator asynchrony during different settings of noninvasive ventilation in stable hypercapnic COPD:Does high inspiratory pressure lead to respiratory muscle unloading?

Introduction: High-intensity noninvasive ventilation (NIV) has been shown to improve outcomes in stable chronic obstructive pulmonary disease patients. However, there is insufficient knowledge about whether with this more controlled ventilatory mode optimal respiratory muscle unloading is provided without an increase in patient-ventilator asynchrony (PVA). Patients and methods: Ten chronic obstructive pulmonary disease patients on home mechanical ventilation were included. Four different ventilatory settings were investigated in each patient in random order, each for 15 min, varying the inspiratory positive airway pressure and backup breathing frequency. With surface electromyography (EMG), activities of the intercostal muscles, diaphragm, and scalene muscles were determined. Furthermore, pressure tracings were derived simultaneously in order to assess PVA. Results: Compared to spontaneous breathing, the most pronounced decrease in EMG activity was achieved with the high-pressure settings. Adding a high breathing frequency did reduce EMG activity per breath, while the decrease in EMG activity over 1 min was comparable with the high-pressure, low-frequency setting. With high backup breathing frequencies less breaths were pressure supported (25% vs 97%). PVAs occurred more frequently with the low-frequency settings (P=0.017). Conclusion: High-intensity NIV might provide optimal unloading of respiratory muscles, without undue increases in PVA

Respiratory muscle activity measured with a noninvasive EMG technique: technical aspects and reproducibility

A new method is being developed to investigate airway obstruction in young children by means of noninvasive electromyography (EMG) of diaphragmatic and intercostal muscles. The purpose of this study was to evaluate the reproducibility of the EMG measurements. Eleven adults, 39 school children (20 healthy, 19 asthmatic), and 16 preschool children were studied during tidal breathing on separate occasions: two for adults with a time interval of 3 wk and three for children with time intervals of 1 and 24 h. Single electrodes were placed on the second intercostal space left and right of the sternum and at the height of the frontal and the dorsal diaphragm. Bipolar electrode pairs were placed on the rectus abdominis muscle. A newly designed digital physiological amplifier without any analog filtering was used to measure the EMG signals. Except for the average dorsal diaphragm EMG derivation in healthy school children on the second occasion, a significant correlation between the mean peak-to-peak inspiratory activity of average diaphragmatic and intercostal EMG was found in the different age groups on the different measurement occasions (P < 0.05). To assess the repeatability, we described the agreement between the repeated measurements within the same subjects. No significant differences were found between the measurements on the separate occasions. Our observations indicate that the EMG signals derived from the diaphragm and intercostal muscles are, in different age groups with and without asthma, reproducible during tidal breathin

Respiratory muscle activity in the assessment of bronchial responsiveness in asthmatic children

We investigated whether an increase in transcutaneous electromyographic (EMG) activity of the diaphragm and intercostal muscles corresponds with the concentration of histamine that induces a 20% fall in the forced expiratory volume in one second (FEV1; PC20). Eleven asthmatic children (mean age 11.9 yr) were studied after they were given histamine challenge. EMG activity at PC20 or at the highest histamine concentration was compared with activity at baseline by calculating the ratio of the mean peak-to-peak excursion at the highest histamine dose to that at baseline [EMG activity ratio (EMGAR)]. In all children reaching PC20, an increase in diaphragmatic and intercostal EMGAR was observed. No increase was found at the dose step before PC20 was reached. In six challenges, no fall in FEV1 was induced, and no increase in EMGAR was seen. In two challenges, no fall in FEV1 was induced, but increase in diaphragmatic or intercostal EMGAR was observed. Increase in the electrical activity of the diaphragm and intercostal muscles in asthmatic children corresponds closely to a 20% fall in FEV1 induced by histamine challeng

A literature review of the methodology of EMG recordings of the diaphragm

Introduction: EMG measurements of the diaphragm (rEMG) provide insight in to ventilatory muscle activity. Applicability of these measurements has improved, but literature of the different rEMG measurement techniques is inconsistent. This makes it difficult to compare studies of rEMG technique. This study summarizes the current available literature on rEMG and focuses on the validation of the techniques. Furthermore, we propose to use validation criteria to improve the quality, for further research. Methods: Pubmed, Ovid Medline and EMBASE were searched for studies describing rEMG experiments with transcutaneous (tc-rEMG) and/or transesophageal (te-rEMG) methods. Validation criteria included feasibility, repeatability, signal disturbance and ECG gating. Results: 650 studies were eligible for reviewing; 211 were excluded, and 39 articles described the measurement technique and were analyzed according to the criteria. 194 studies referred to another paper with a description of the technique and 206 failed to describe the technique nor had references to it. Conclusions: Many studies showed neither a description of the technique used, nor a validation of this technique. Others referred to studies that described the measurement technique. We propose that future studies on rEMG measurements at least meet the above mentioned criteria, in order to be able to compare study results. (C) 2009 Elsevier Ltd. All rights reserve

Respiratory muscle activity and patient&ndash;ventilator asynchrony during different settings of noninvasive ventilation in stable hypercapnic COPD: does high inspiratory pressure lead to respiratory muscle unloading?

Introduction: High-intensity noninvasive ventilation (NIV) has been shown to improve outcomes in stable chronic obstructive pulmonary disease patients. However, there is insufficient knowledge about whether with this more controlled ventilatory mode optimal respiratory muscle unloading is provided without an increase in patient-ventilator asynchrony (PVA). Patients and methods: Ten chronic obstructive pulmonary disease patients on home mechanical ventilation were included. Four different ventilatory settings were investigated in each patient in random order, each for 15 min, varying the inspiratory positive airway pressure and backup breathing frequency. With surface electromyography (EMG), activities of the intercostal muscles, diaphragm, and scalene muscles were determined. Furthermore, pressure tracings were derived simultaneously in order to assess PVA. Results: Compared to spontaneous breathing, the most pronounced decrease in EMG activity was achieved with the high-pressure settings. Adding a high breathing frequency did reduce EMG activity per breath, while the decrease in EMG activity over 1 min was comparable with the high-pressure, low-frequency setting. With high backup breathing frequencies less breaths were pressure supported (25% vs 97%). PVAs occurred more frequently with the low-frequency settings (P=0.017). Conclusion: High-intensity NIV might provide optimal unloading of respiratory muscles, without undue increases in PVA

Respiratory muscle activity and dyspnea during exercise in chronic obstructive pulmonary disease

We aimed to determine by non-invasive EMG, whether during exercise: (1)COPD patients increase scalene and intercostal EMG activity, (2) increased EMG activity is associated with increased dyspnea, and (3) the ratio between EMG activity and volume displacement is increased in COPD compared to healthy subjects (HS). During a maximal incremental cycle test, scalene and intercostal EMG was derived transcutaneously in 17 COPD patients and 10 HS. Dyspnea was quantified using a Borg scale, ranging from zero to 10 (maximal dyspnea). For analyses the ratio between inspiratory muscle activity during exercise and activity during quiet breathing was used (logEMGAR). In COPD patients, scalene and intercostal activity increased at greater rate early in exercise compared to that of the HS. With a doubling of the logEMGAR, in COPD, dyspnea increased with 2.8/3.8 points, while in the HS, dyspnea increased less with 1.1/1.4 points. In COPD, there was a larger increase in EMG activity relatively to tidal volume increases. (C) 2009 Elsevier B.V. All rights reserved