Non-stationarity and power spectral shifts in EMG activity reflect motor unit recruitment in rat diaphragm muscle |
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Authors: | Yasin B Seven Carlos B Mantilla Wen-Zhi Zhan Gary C Sieck |
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Institution: | 1. Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN 55905, USA;2. Department of Anesthesiology, Mayo Clinic, Rochester, MN 55905, USA |
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Abstract: | We hypothesized that a shift in diaphragm muscle (DIAm) EMG power spectral density (PSD) to higher frequencies reflects recruitment of more fatigable fast-twitch motor units and motor unit recruitment is reflected by EMG non-stationarity. DIAm EMG was recorded in anesthetized rats during eupnea, hypoxia-hypercapnia (10% O2–5% CO2), airway occlusion, and sneezing (maximal DIAm force). Although power in all frequency bands increased progressively across motor behaviors, PSD centroid frequency increased only during sneezing (p < 0.05). The non-stationary period at the onset of EMG activity ranged from ∼80 ms during airway occlusion to ∼150 ms during eupnea. Within the initial non-stationary period of EMG activity 80–95% of motor units were recruited during different motor behaviors. Motor units augmented their discharge frequencies progressively beyond the non-stationary period; yet, EMG signal became stationary. In conclusion, non-stationarity of DIAm EMG reflects the period of motor unit recruitment, while a shift in the PSD towards higher frequencies reflects recruitment of more fatigable fast-twitch motor units. |
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Keywords: | DIAm diaphragm muscle ECG electrocardiogram EMG electromyogram/electromyography fc centroid frequency H/L ratio ratio of power in high frequency vs low frequency bands IRL inspiratory resistive loading MUAP motor unit action potential Pdi transdiaphragmatic pressure PSD power spectral density RAT reverse arrangements test RMS root-mean-squared |
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