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Signal Strength, Reliability, and Validity of Active Regenerative Peripheral Nerve Interface Device Operation during Voluntary Movement
Andrej Nedic, MSE, Daniel Ursu, MS, Jana D. Moon, BS, Cheryl A. Hassett, BS, Richard B. Gillespie, PhD, Nicholas B. Langhals, PhD, Paul S. Cederna, MD, Melanie G. Urbanchek, PhD.
University of Michigan, Ann Arbor, MI, USA.
PURPOSE: Regenerative Peripheral Nerve Interface (RPNI) devices successfully transduce peripheral nerve action potentials to electrical signals suitable for prosthesis control. Voltage changes are the controlling mechanism and can be observed during electromyography (EMG). However, RPNI device signaling has not been characterized during voluntary movements. This study: a) characterizes active RPNI signal strength compared to background activity and b) defines the reliability and validity of RPNI signal function during purposeful movements.
METHODS: Three groups were formed in rats: Control (n=3), RPNI (n=3), 100% Denervated (n=3). Bipolar electrodes were implanted onto the soleus muscles in each group. For RPNI devices, the soleus muscle was freely grafted to the ipsilateral thigh and neurotized by the transected tibial nerve. In the 100% Denervated, the tibial nerve was transected. The Control group was left intact. While walking on a treadmill, rats were videographed and raw EMG signals were simultaneously recorded. Video and EMG recordings were synchronized to stance, swing, and sit (nonactive) gait phases. Rectified EMG was integrated (iEMG) for each gait phase (Fig. 1). iEMG was normalized (NiEMG) to time for each phase. Data represent 16 gait cycles for each of 9 rats. Correlations were performed between iEMG and stance time to determine reliability. RPNI signaling was validated against Control group signal timing for gait phases using Chi Square analysis.
RESULTS: We compared EMG signals to background signal strength in all groups during all gait phases (Fig. 2). Fidelity of RPNI activity (stance) to background signaling (sit) was 5.6 to 1, double the Control signal fidelity (Fig. 2). Significant differences between stance and swing NiEMG activity were confirmed for the Control and RPNI groups. As expected, stance and swing EMG signals were not different for the Denervated group. Correlations between iEMG and stance time for the Control (r=0.74) and RPNI (r=0.76) indicate good RPNI signal reliability (Fig. 3). EMG signals increased at the start of stance and fell to baseline at the start of swing in both Control and RPNI rat gait cycles (Fig. 1). These data comparing gait cycle to EMG activation accuracy between Control, RPNI, and Denervated groups validated RPNI signaling as purposeful peripheral nerve activity appropriate for meaningful control of prostheses (Chi Square; p<0.05).
CONCLUSION: RPNI signal fidelity, reliability, and validity were examined during voluntary movement. With select filtering, signal fidelity was clear. RPNI signal reliability during the gait stance was “good.” RPNI signaling was successfully validated against normal peripheral nerve signaling during walking.
ACKNOWLEDGEMENTS: This work was sponsored by the Defense Advanced Research Projects Agency (DARPA) MTO through Grant/Contract No. N66001-11-C-4190.
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