Plastic Surgery Research Council
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PSRC 60th Annual Meeting

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Characterization of Regenerative Peripheral Nerve Device Signaling during Evoked Maximal and Submaximal Fatiguing Conditions
Zachary P. French, HS1, Nicklaus S. Carrothers, HS2, Cheryl A. Hassett, BS1, Jana D. Moon, BS1, Nicholas B. Langhals, PhD1, Paul S. Cederna, M.D.1, Melanie G. Urbanchek, PhD1.
1University of Michigan, Ann Arbor, MI, USA, 2University of Rochester, Rochester, NY, USA.

PURPOSE - Regenerative peripheral nerve interface devices (RPNI devices) transduce signals between remaining peripheral nerves of a residual limb and motorized prostheses. RPNI devices consist of a transferred muscle neurotized by a transected peripheral nerve with electrodes secured to the muscle for RPNI signal transduction. RPNI device maximal twitch signaling has been characterized; however, device function during repetitive signaling has not been studied. Our purpose was to characterize RPNI device continuous submaximal signaling including fatigability with respect to measures of maximal signal.
METHODS - Rats were assigned to RPNI Device (n=5) or Control (n=5) groups. For the Device group, the left extensor digitorum longus (EDL) muscle was transferred to the thigh and neurotized by the transected peroneal nerve. In both groups two fine wire electrodes were secured to the EDL muscle. The EDL muscle was then wrapped with SIS, layered with fascia, and partially covered with silicone sheeting on one side, between the EDL and tibialis anterior muscle. Five months post-surgery, maximal twitch compound muscle action potential (CMAP) and maximal contractile force were measured through evoked peroneal nerve stimulation. A submaximal repeated signaling protocol was administered - 22 minutes of 360 contractions with 300 ms/s duty cycles and 360 contractions with 600 ms/s duty cycles all stimulated at 40 Hz - concluding with a final test of maximal signaling capacity with stimulation 120-180 Hz.
RESULTS - The statistical results are summarized in Table 1. Study animals were matched for body mass and age. A tight correlation was found between maximal twitch CMAP and maximal contractile force (r=0.82, p < 0.01), in this and other RPNI device studies. We thus infer that both measurements indicate RPNI signaling. RPNI Device twitch CMAP signaling was 32% of Controls amplitude. RPNI device maximal contractile force produced 23% the signaling capacity of Controls. This decreased contractile signaling is attributed to limitations for RPNI Devices to maintain contraction signaling over longer signaling times. Contractile force signaling is held for 300 ms while twitch signaling is only 0.1 ms. During repetitive submaximal force signaling, RPNI Devices maintained 22% to 5% of their maximal force. With five minutes of rest, RPNI devices recovered maximal contractile signaling equal to 18% of the recovered Controls. The submaximal repetitive contraction protocol fatigued both RPNI Devices and Controls, with recoveries equal to 53% and 69% maximal contractile signaling respectively (Fig 1).
CONCLUSIONS - RPNI Devices are able to produce signals repetitively during submaximal activation with a rate of fatigue that is similar to Controls; however, RPNI Device signals during repeated activation are of lower amplitude with respect to maximal signaling than Controls. This will be studied further.
Acknowledgements: DARPA N66001-11-C-4190.
Table 1: Summary of RPNI Device Capacity during Maximal and Submaximal Signaling.
DEPENDENT VARIABLESEXPERIMENTAL GROUPSSigni-ficance% Difference
Control Group
(n=5)
RPNI Device Group (n=5)
Body Mass (g)406 ± 45.6364 ± 97.70.40-10%
Muscle Mass (mg)160.00±19.51123.70±66.380.27-23%
Age (days)378 ± 212393 ± 1690.90+4%
Max Twitch CMAP Amplitude (mV)24.23 ± 10.017.98 ± 8.16*<0.01-68%
Max Tetanic Force (mN)2711 ± 645.54627.4 ±493.0*<0.01-77%
Mean Slope Series 1
(% of max per contraction)
-0.086 ± 0.013-0.059 ± 0.0610.41+32%
Mean Slope Series 2
(% of max per contraction)
-0.053 ± 0.017-0.027 ± 0.0140.11+49%
Max Contractile Force Post Fatigue (mN) -1867 ± 488.3330.3 ± 310.3*0.01-82%
Values are shown as mean ± standard deviation. Abbreviations are: g, grams; mg, milligrams; mV, millivolts; mN, milliNewtons, ms, milliseconds. * Indicates significant difference between groups with p < 0.05.



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