High-resolution measurement of electrically-evoked vagus nerve activity in the anesthetized dog.
OBJECTIVE
Not fully understanding the type of axons activated during vagus nerve stimulation (VNS) is one of several factors that limit the clinical efficacy of VNS therapies. The main goal of this study was to characterize the electrical recruitment of both myelinated and unmyelinated fibers within the cervical vagus nerve.


METHODS
In anesthetized dogs, recording nerve cuff electrodes were implanted on the vagus nerve following surgical excision of the epineurium. Both the vagal electroneurogram (ENG) and laryngeal muscle activity were recorded in response to stimulation of the right vagus nerve.


RESULTS
Desheathing the nerve significantly increased the signal-to-noise ratio of the ENG by 1.2 to 9.9 dB, depending on the nerve fiber type. Repeated VNS following nerve transection or neuromuscular block (1) enabled the characterization of A-fibers, two sub-types of B-fibers, and unmyelinated C-fibers, (2) confirmed the absence of stimulation-evoked reflex compound nerve action potentials in both the ipsilateral and contralateral vagus nerves, and (3) provided evidence of stimulus spillover into muscle tissue surrounding the stimulating electrode.


CONCLUSIONS
Given the anatomical similarities between the canine and human vagus nerves, the results of this study provide a template for better understanding the nerve fiber recruitment patterns associated with VNS therapies.
Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON, Canada. paul.yoo@utoronto.ca
Paul B
PB
Yoo
Nathan B
NB
Lubock
Juan G
JG
Hincapie
Stephen B
SB
Ruble
Jason J
JJ
Hamann
Warren M
WM
Grill
D000200:Action Potentials / Q000502:physiology; D000758:Anesthesia; D000818:Animals; D016477:Artifacts; D003627:Data Interpretation, Statistical; D004285:Dogs; D004567:Electrodes, Implanted; D004576:Electromyography; D005071:Evoked Potentials / Q000502:physiology; D005260:Female; D009413:Nerve Fibers, Myelinated / Q000502:physiology; D036421:Nerve Fibers, Unmyelinated / Q000502:physiology; D059906:Neuroimaging; D019148:Neuromuscular Blockade; D010525:Peripheral Nerves / Q000502:physiology; D012018:Reflex / Q000502:physiology; D059629:Signal-To-Noise Ratio; D014630:Vagus Nerve / Q000502:physiology*; D055536:Vagus Nerve Stimulation / Q000379:methods* / Q000706:statistics & numerical data