Brief, Daily Diaphragm Pacing Increases Satellite Cell Expression in Diaphragm Muscle Following Spinal Cord Injury

The diaphragm muscle undergoes profound morphological changes following cervical spinal cord injury (cSCI). Chronic mechanical ventilation, the standard treatment for respiratory insufficiency following cSCI, further exacerbates these deleterious effects on the diaphragm muscle. Diaphragm pacing (DP) utilizes electrical stimulation to elicit a contraction of the diaphragm muscle and has been used to replace mechanical ventilation in a subset of individuals with cSCI. We have previously shown that 4 days of DP (1hr/day) improves tidal volume through phrenic afferent mediated mechanisms in adult male Sprague Dawley rats following cSCI. However, the impact of our DP protocol on the cellular and morphological properties of the diaphragm muscle is unknown. We hypothesized that after cSCI, DP would 1) attenuate diaphragm muscle atrophy, and 2) increase expression of diaphragm muscle satellite cells ipsilateral to stimulation. To test these hypotheses, we examined the diaphragm muscle 3 days after rats received DP (n=5), DP and dorsal rhizotomy (n=5) to prevent phrenic afferent signaling, or controls not receiving DP (n=5). All animals were instrumented with diaphragm electromyography wires and received a left C2 hemisection (C2Hx). We delivered DP (30Hz, 0.8 mA, 80μs pulse width) to the paralyzed hemidiaphragm for 1 hour/day over 4 consecutive days beginning 1 week after injury. We found no differences in ipsilateral diaphragm muscle fiber cross sectional area (p=0.9276) or fiber type distribution (p=0.3826). Compared to controls, animals receiving diaphragm pacing alone (p=0.0347) and diaphragm pacing after dorsal rhizotomy (p=0.0169) show an increase in ipsilateral diaphragm muscle satellite cell density. This data suggests that brief, daily DP does not induce morphological changes in the diaphragm muscle as measured through cross sectional area or fiber type distribution, but does increase satellite cell expression which is critical for muscle regeneration and repair. We conclude that in addition to activating phrenic afferents and improving breathing, DP can have a direct and beneficial effect on the diaphragm muscle itself. Future studies are needed to explore the effect of long-term stimulation protocols on ventilation and diaphragm function after cSCI. This work was supported by the National Institute of Health, grant numbers: R00 HL143207-01 (KAS) and 2TL1 TR001437 (TCH) and Craig H Neilsen Pilot Grant #993667 (KAS). This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.