Diaphragm Stimulation Enhances Respiratory Function After Cervical Spinal Cord Injury

Purpose/Hypothesis Cervical spinal cord injury (CSCI) causes severe respiratory impairment and respiratory complications are a leading cause of illness and death. Although mechanical ventilation (MV) is lifesaving, MV use is associated with diaphragm atrophy and high respiratory infection rates. Intramuscular diaphragm stimulation, or diaphragm pacing (DP), is now used acutely to promote MV weaning. Preliminary reports suggest that DP may improve diaphragm activation, respiratory function, and promote recovery of independent respiration. The effects of DP, however, have not been systematically evaluated. Our purpose was to test the hypothesis that DP leads to an increase in voluntary diaphragm activation and improvements in respiratory function. Subjects Eleven adults with acute, traumatic CSCIs (6 males, mean age 40.8±12 years) who underwent implantation of DP wires due to failure to wean from MV participated (mean time on MV until DP wire implantation 16±10 days). Injuries were classified as C1 to C4 based on the ASIA Impairment Scale A or B (motor complete, n=10) and C (motor incomplete, n=1). Materials/Methods Respiratory function and diaphragm activation were assessed within 3 days post implantation of the DP wires and assessments were repeated at regular intervals up to four months post DP implantation. Respiratory function was assessed using standard measures of tidal volume (Vt), forced vital capacity (FVC), and maximal inspiratory and expiratory pressures (MIP, MEP). Diaphragm activation was assessed by recording electromyograms (EMGs) from the intramuscular DP wires during maximal inspiratory maneuvers. All tests were conducted without assistance from DP and with the lowest ventilator setting tolerated. Results Following onset of DP, 9 of 11 individuals weaned from MV (mean time 35±24 days) and 6 individuals resumed independent respiration without use of DP. All measures of respiratory function increased over time (p<0.05). Average gains in respiratory function were: Vt, +24±31% (range −31 – 77%); FVC, +37±16% (range 17 – 63%); MIP, +43±56% (range −45 – 124%); MEP +67±64% (range −31 – 176%). Mean peak EMG burst amplitude during maximal inspiratory maneuvers increased 20% (range 0 – 92%). Conclusions During an extended period of DP, adults with severe CSCIs demonstrated gains in respiratory function and volitional diaphragm activation. Nearly all individuals weaned from MV and over half progressed to independent respiration following onset of DP. Stimulation of the diaphragm is likely to promote muscle health which would contribute to weaning. In addition, the increased diaphragm muscle activation in many subject raises the possibility that DP and associated activation of sensory afferents evokes beneficial plasticity in the respiratory neural control system. Support or Funding Information Craig H. Neilsen Foundation (EJF); NIH/NICHD K12 HD055929 (EJF); T32‐HD043730 (MDS) This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .