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Quantification of Extraneous Electromyographic Bio-signal in the Anterior Compartment of the Rat Hind Limb
Shoshana L. Woo, MD, Melanie G. Urbanchek, PhD, Paul S. Cederna, MD, Nicholas B. Langhals, PhD.
University of Michigan, Ann Arbor, MI, USA.
Purpose: High-fidelity signal acquisition is critical for the fundamental control of a neuroprosthesis. Our group has developed a bio-artificial interface consisting of a muscle graft neurotized by a severed nerve in the rat model. This regenerative peripheral nerve interface (RPNI) permits nerve signal transmission, amplification, and detection via in situ electromyography. This study examined the magnitude of extraneous bio-signal during needle electromyography in the anterior compartment of the rat hind limb.
Methods: In six F344 rats, the extensor digitorum longus (EDL) muscle was isolated, and the proximal and distal tendons were transected. The EDL was then wrapped in small intestinal submucosa to fabricate a “simulated” RPNI construct, obviating the need for neurotization and revascularization by preserving the neurovascular pedicle. At three weeks post-implantation, all EDL constructs were isolated. A stimulating hook electrode was placed on the common peroneal nerve, a recording needle electrode in the EDL, and a grounding electrode in the contralateral toe web space. To minimize signal interference within the anterior compartment, the lateral compartment musculature was denervated. Electrophysiological tests were performed on each EDL construct (1) before and (2) after excision of the tibialis anterior (TA) and extensor hallucis longus (EHL) muscles, which comprise the remainder of the anterior compartment musculature.
Results: Average EDL construct mass was 153.3 mg (range 104.7-211.4 mg; SD 44.8). Prior to TA/EHL excision, EDL compound muscle action potentials (CMAPs) displayed an average peak-to-peak amplitude (Vpp) of 23.4 mV (range 14.0-30.7 mV; SD 7.1) with an average threshold stimulation current of 192 μA (range 100-295 μA; SD 72). After TA/EHL excision, average Vpp was 14.1 mV (range 6.8-20.7 mV; SD 5.7), with an average threshold current of 239 μA (range 110-450 μA; SD 114)[Figure 1]. Vpp after TA/EHL excision was overall lower by 23.3 to 57.9% (SD 12.4) compared to Vpp prior to TA/EHL excision [paired t(5) = 6.65; p=0.0012][Figure 2].
Conclusions: Extraneous bio-signal from concomitant stimulation of the anterior compartment musculature was shown to contaminate needle electrode CMAP recordings from various EDL constructs. This signal interference was reduced by TA/EHL excision. Our findings prompt further investigation of CMAP recording methodology (e.g. electrode choice, multi-electrode configurations, and use of bioelectrical insulators) to minimize signal interference from adjacent musculature. Larger studies are warranted to examine the relationship between signals-of-interest and extraneous bio-signal to develop tissue-specific noise-canceling technology in support of high-fidelity neuroprosthetic control.
Acknowledgements: This work was supported by DARPA (N66001-11-C-4190) and the Plastic Surgery Foundation.
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