Phrenic‐to‐Intercostal Reflex Activity in Response to High Frequency Spinal Cord Stimulation (HF‐SCS)

Abstract

ObjectiveHF‐SCS is a novel technique of inspiratory muscle activation which results in coincident activation of the diaphragm and inspiratory intercostal muscles via spinal cord pathways and has the potential to provide respiratory support in ventilator dependent persons with spinal cord injury. The purpose of the present study was to examine the phrenic to intercostal reflex during HF‐SCS.MethodsIn 3 anesthetized and C2 spinalized dogs, electrical stimulation was applied via a stimulating electrode located on the ventral surface of the upper thoracic spinal cord at the T2 level before and after cervical phrenicotomy. Fine wire recording electrodes were used to assess single motor unit (SMU) activity of the external intercostal muscles before and after phrenicotomy.ResultsFollowing unilateral phrenic nerve section, mean peak SMU firing frequency of EI ipsilateral to the section was significantly greater when compared to control (15.9±0.7 vs. 12.1±0.5 Hz, p<0.05). However, mean peak SMU firing frequency of the contralateral EI was unchanged (11.1±0.4 vs. 12±0.4 Hz, NS). Section of the contralateral phrenic nerve results in significantly higher mean peak SMU firing frequency of the contralateral EI (15.9±0.7 Hz, p<0.05) when compared to before section.ConclusionThis study demonstrates that during HF‐SCS after C2 spinalization: 1) diaphragmatic afferents reflexly inhibit motor activity to the ipsilateral external intercostal muscles, and 2) the neural circuitry mediating the phrenic‐to‐intercostal reflex is preserved at a spinal level. Consequently, HF‐SCS applied to support ventilation in high tetraplegics with unilateral phrenic nerve injury may elicit increased activity of ipsilateral inspiratory intercostal muscles.Support or Funding InformationSupport: NIH‐NINDS (R01NS064157) and MetroHeath FoundationDisclosure: Dr. DiMarco is a Founder of and has a significant financial interest in Synapse BioMedical, Inc, a manufacturer of diaphragm pacing systems.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.