Laryngeal Muscle-Evoked Potential Recording as an Indicator of Vagal Nerve Fiber Activation
(2022) Neuromodulation — Vol. 25, n° 3, p. 461-470 (2022)
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Delbeke, Jean 
- Abstract
- (en) BACKGROUND: Vagus nerve stimulation (VNS) is an adjunctive therapy for drug-resistant epilepsy. Noninvasive evoked potential recordings in laryngeal muscles (LMEPs) innervated by vagal branches may provide a marker to assess effective vagal nerve fiber activation. We investigated VNS-induced LMEPs in patients with epilepsy in acute and chronic settings. MATERIALS AND METHODS: A total of 17 of 25 patients underwent LMEP recordings at initiation of therapy (acute group); 15 of 25 patients after one year of VNS (chronic group); and 7 of 25 patients were tested at both time points (acute + chronic group). VNS-induced LMEPs were recorded following different pulse widths and output currents using six surface laryngeal EMG electrodes to calculate input/output curves and estimate LMEP latency, threshold current for minimal (Ithreshold), half-maximal (I50), and 95% of maximal (I95) response induction and amplitude of maximal response (Vmax). These were compared with the acute + chronic group and between responders and nonresponders in the acute and chronic group. RESULTS: VNS-induced LMEPs were present in all patients. Ithreshold and I95 values ranged from 0.25 to 1.00 mA and from 0.42 to 1.77 mA, respectively. Estimated mean LMEP latencies were 10 ± 0.1 milliseconds. No significant differences between responders and nonresponders were observed. In the acute + chronic group, Ithreshold values remained stable over time. However, at the individual level in this group, Vmax was lower in all patients after one year compared with baseline. CONCLUSIONS: Noninvasive VNS-induced LMEP recording is feasible both at initiation of VNS therapy and after one year. Low output currents (0.25-1.00 mA) may be sufficient to activate vagal Aα-motor fibers. Maximal LMEP amplitudes seemed to decrease after chronic VNS therapy in patients.
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Bouckaert, C., Raedt, R., Larsen, L. E., El Tahry, R., Gadeyne, S., Carrette, E., Proesmans, S., Dewaele, F., Delbeke, J., De Herdt, V., Meurs, A., Mertens, A., Boon, P., & Vonck, K. (2022). Laryngeal Muscle-Evoked Potential Recording as an Indicator of Vagal Nerve Fiber Activation. Neuromodulation, 25(3), 461-470. https://doi.org/10.1016/j.neurom.2022.01.014 (Original work published 2022)