Repeated Measurement of Respiratory Muscle Activity and Ventilation in Mouse Models of Neuromuscular Disease

Abstract

Accessory respiratory muscles help maintain ventilation when diaphragm function is impaired. The following protocol describes a method for repeated measurements over weeks or months of accessory respiratory muscle activity while simultaneously measuring ventilation in a non-anesthetized freely behaving mouse. The technique includes surgical implantation of a radio transmitter and insertion of electrode leads into the scalene and trapezius muscles to measure electromyogram activity of these inspiratory muscles. Ventilation is measured by whole body plethysmography and animal movement is assessed by video and synchronized with electomyogram activity. Measurements of muscle activity and ventilation in a mouse model of amyotrophic lateral sclerosis are presented to show how this tool can be used to investigate how respiratory muscle activity changes over time and to assess the impact of muscle activity on ventilation. The described methods can easily be adapted to measure activity of other muscles or to assess accessory respiratory muscle activity in additional mouse models of disease or injury.

V2a Neurons Constrain Extradiaphragmatic Respiratory Muscle Activity at Rest

“…Telemetry devices [either single (TAE-F10) or double channel (F20-EET) transmitters from Data Sciences International] were implanted as early as eight weeks of age to chronically record EMG from respiratory muscles of V2a-(G i )DREADD and non-DREADD control mice. Surgeries to implant devices subcutaneously for recording EMG from the trapezius and scalene muscles were performed as previously described (Jensen et al, 2017; Romer et al, 2017). Briefly, a 3-cm-long incision was made between the right shoulder and ear and the transmitter was placed subcutaneously on the back of the mouse.…”

“…Plethysmography, EMG acquisition, and digital video recording was performed as described previously (Jensen et al, 2017; Romer et al, 2017) using DSI Ponemah Physiology Platform Acquisition software v.5.20. Briefly, mice were placed in a plethysmography chamber on top of a transmitter receiving pad and allowed to acclimate for 30 min.…”

“…The Ponemah Physiology Platform Analysis software v.5.20 was used to mark individual resting breaths to be analyzed for breathing frequency (f), tidal volume (V T ), minute volume (MV), peak inspiratory flow (PIF), inspiratory time (T i ), expiratory time (T e ), and total breathing cycle time (T t ) as described previously (Jensen et al, 2017; Romer et al, 2017). V T /T i , a measure of respiratory drive, was calculated from these derived values.…”

“…The raw EMG signal was high pass filtered at 1.5 Hz and the root mean square (RMS) was calculated using a 30-ms window. The frequency of bouts of trapezius or scalene activity was counted as described previously (Jensen et al, 2017). Briefly, ARM EMG activity is scored as a “bout” if it satisfies the following three criteria: (1) the RMS EMG trace must exhibit at least three consecutive points that are at least 50% higher than the surrounding baseline (each point represents a 30-ms window), (2) EMG activity occurs during resting breaths (i.e., sighs and movement artifacts are excluded), and (3) EMG activity occurs when the mouse is still (i.e., no movement or changes in posture) based on the synchronized video recordings.…”

Respiratory capacity is maintained despite Duchenne muscular dystrophy‐related diaphragm weakness

“…Because of these findings, Burns et al (2019) suggest that accessory respiratory muscle activation is probably responsible for this preserved ventilatory behaviour. A study by Jensen et al (2017) assessed the impact of accessory respiratory muscle activity on respiration by recording scalene and trapezius EMG in rats with amyotrophic lateral sclerosis. The inclusion of additional measurements of accessory inspiratory or expiratory muscles should be considered in the future to clarify the mechanism(s) responsible for mechanical compensation.…”