Acquisition and Semi-Automated Analysis of Respiratory Muscle Surface Electromyography

Summary

Here, we describe a protocol to record and analyze respiratory electromyography (EMG) signals. It includes the anatomic references for placing the EMG electrodes over several respiratory muscles, removing electrocardiographic noise from the EMG signals, and acquiring the EMG root mean square (RMS) and onset timing of activity.

Abstract

Evaluating respiratory drive presents challenges due to the obtrusiveness and impracticality of current methods like functional magnetic resonance imaging (fMRI). Electromyography (EMG) offers a surrogate measure of respiratory drive to the muscles, allowing the determination of both the magnitude and timing of muscle activation. The magnitude reflects the level of muscle activation, while the timing indicates the onset and offset of muscle activity relative to specific events, such as inspiratory flow and activation of other muscles. These metrics are critical for understanding respiratory coordination and control, especially under varying loads or in the presence of respiratory pathophysiology. This study outlines a protocol for acquiring and analyzing respiratory muscle EMG signals in healthy adults and patients with respiratory health conditions. Ethical approval was obtained for the studies, which included participant preparation, electrode placement, signal acquisition, preprocessing, and postprocessing. Key steps involve cleaning the skin, locating muscles via palpation and ultrasound, and applying electrodes to minimize electrocardiography (ECG) contamination. Data is acquired at a high sampling rate and gain, with synchronized ECG and respiratory flow recordings. Preprocessing includes filtering and transforming the EMG signal, while postprocessing involves calculating onset and offset differences relative to the inspiratory flow. Representative data from a healthy male participant performing incremental inspiratory threshold loading (ITL) illustrate the protocol's application. Results showed earlier activation and prolonged duration of extradiaphragmatic muscles under higher loads, correlating with increased EMG magnitude. This protocol facilitates a detailed assessment of respiratory muscle activation, providing insights into both normal and pathophysiologic motor control strategies.

Introduction

Respiratory drive (i.e., the output of respiratory centers to respiratory muscles) is challenging to evaluate due to the obtrusive, often impractical nature of evaluative methods such as functional magnetic resonance imaging (fMRI). Moreover, the small size of the respiratory centers located in the brain stem is difficult to localize and is sensitive to alterations by physiologic noise^1,2. Measurements of respiratory drive are important because of their association with important clinical outcomes such as dyspnea, an indication of respiratory distress. Electromyography (EMG) is a surrogate of respiratory ....

Protocol

Studies employing this technique have received ethical approval from the University of Toronto and St. Michael's Hospital located in Toronto, Canada, and the University Hospital Gasthuisberg, Leuven, Belgium. One specific protocol is described here. General discussion about several alternative surface EMG (sEMG) approaches have been proposed for the respiratory muscles and are reported elsewhere¹².

1. Participant preparation and placement of sEMG electrodes

Discussion

Removal of cardiac activity artifacts from the EMG signal is complex due to their overlapping bandwidth spectrums. The majority of the EMG frequency spectrum is between 20 and 250 Hz, while the ECG frequency spectrum is between 0 Hz and 100 Hz. For some analyses (i.e., timing), it is essential to derive the EMG signal without ECG contamination to achieve accuracy and interpretability of the EMG magnitude and timing. The least mean square (LMS) adaptive filter by utilizing frequencies, is an algorithm that recognizes a pa.......

Materials

Name	Company	Catalog Number	Comments
Adjustable table	Amazon	VIVO Electric Height Adjustable 102 cm x 61 cm Stand Up Desk	Enables fine adjustment for trunk and mouthpiece position
Air filters	Cardinal	https://cardinalfilters.com/
Analog output cable	A-Tech Instruments Ltd.	25 pin D-sub Female to 16xBNC male; 16xRG-174 -16 x 3ft cable	To connect EMG (Noroxan) to data acquisition system (PowerLab)
Bioamp for ECG	ADInstruments	ML138
Desktop or Laptop	N/A	N/A	Capacity for data acquisition system including EMG
Double sticks for EMG probes	Noraxon	https://shop.noraxon.com/products/dual-emg-electrodes
Electromyography	Noraxon	Noraxon Ultium Myomuscle with 8 smart leads. https://www.noraxon.com/our-products/ultium-emg/
EMG electrodes	Duotrode	N/A
Gas analyzer	ADInstruments	ML206
Gloves	Medline	https://www.medline.com/jump/category/x/cat1790003
Metricide or protocol to disinfect valves & mouthpieces	Medline	https://www.medline.com/product/MetriCide-28-Disinfectant/Disinfectants/Z05-PF27961?question=metricide
Oximeter pod	ADInstruments	ML320/F	https://www.adinstruments.com/products/oximeter-pods
Pneumotach	ADInstruments	MLT3813H-V	https://www.adinstruments.com/products/heated-pneumotach-800-l-heater-controller
Powerlab and Labchart Data Acquisition System	ADInstruments, Inc.	https://m-cdn.adinstruments.com/brochures/Research_PowerLab _Brochure_V2-1.pdf	Acquires mouth pressure, ECG, end-tidal CO2, flow (to derive respiratory rate, tidal volume, minute ventilation) and EMG.
Pressure transducer with single or dual channel demodulator	Validyne.com	Www.Validyne.Com/Product/Dp45_Low_Pressure_ Variable_Reluctance_Sensor/	Range depends on population being tested i.e. patients or healthy (Www.Validyne.Com/Product/Cd280_Multi_Channel_Carrier_ Demodulator/; www.Validyne.Com/Product/Cd15_General_Purpose_Basic _Carrier_Demodulator/)
Silicone mouthpieces	Hans Rudolph	https://www.rudolphkc.com/	Small bite size
Table model chin rest	Sacor Inc.	Model 600700	https://sacor.ca/products/head-chin-rest-table-model-with-white-chin-rest-cup
Two-way t-piece nonrebreathing valve with sampling port	Hans Rudolph	1410 Small
Ultrasound	GE Healthcare	Vivid i BT12 Cardiac system with Respiration and 12L-RS Linear Array Transducer	Requires resolution to landmark respiratory muscles including appositional region of diaphragm