Skin blood perfusion (BP) changes under ischial tuberosity (IT) during gluteal neuromuscular stimulation (GNMS) in spinal cord injury (SCI)

Introduction: The IT is one of the most vulnerable site for pressure ulcer (PrU) development in SCI who use wheelchairs [1]. Previous studies suggest that decreased volume of blood in the tissues below the injury in SCI contributes to their susceptibility to PrU [2,3]. Electrical stimulation (ES) was reported to increase tissue blood flow in SCI [4,5]. Various techniques are available to measure tissue/skin blood parameters, yet most of them utilise rigid probes, which could potentially cause local tissue damage. Therefore we aimed to assess gluteal skin blood perfusion changes using a thin flexible optical probe during GNMS in seated SCI. Methods: A total of 18 adults with suprasacral complete SCI were included. GNMS was delivered via sacral nerve root stimulation (SNRS) or surface ES. Skin BP was measured using a tissue reflectance spectrometer (TRS) to measure index of hemoglobin (IHB) and oxygenation (IOX) under the ITs. We used a two-tailed paired t-test to compare IHB and IOX before and during stimulations. Results: The IHB and IOX during stimulation were significantly higher than baseline in 6 participants who had SNRS using magnetic stimulator (IHB 1.05±0.01 before vs. 1.08±0.01 during stimulation, P=0.03; IOX 0.18 ± 0.08 before vs. 0.46 ± 0.12, P=0.01 during stimulation). Similarly, the significant difference in IHB and IOX were obtained in 6 participants who had SNRS via a SARS implant (IHB (1.01 ± 0.01 before vs. 1.07 ±0.01 during stimulation, P=0.004), IOX (0.79±0.3 before vs. 2.2±0.5 during stimulation, P=0.03). Although IHB and IOX increased in those 6 participants who had surface ES, the difference of both indices were not significant between baseline and during FES.(IHB 1.05 ± 0.003 before vs. 1.06 ±0.01 during stimulation, P=0.07, and oxygenation (IOX 0.59±0.19 before stimulation vs. 0.93±0.24 during stimulation, P=0.12). Conclusion: SNRS or surface FES of gluteal muscles can induce sufficient gluteus maximus contraction and significantly increase skin blood perfusion. Clinical relevance: Using such thin flexible probe has advantages of avoiding local tissue damage. Moreover, the SNRS via a SARS implant may be more convenient and efficient for frequently activating the gluteus maximus in SCI population for PrU prevention