Authors: V. L. ARVANIAN, H. A. PETROSYAN, A. TESFA, M. FAHMY, C. ZOU, S. SISTO
H-reflex is recognized as an important neurophysiology tool used in evaluation of spino-muscular circuitry. H-reflex is sensitive to conditions and activity. For example, H-reflex diminishes after several days in zero gravity and is modulated differently depending on muscle activity. Spinal cord injury (SCI) reportedly affects threshold intensity and frequency dependent depression (FDD) of H-reflex. We examined 4 healthy and 3 SCI participants; study was approved by the IRB and conducted in accordance with the Declaration of Helsinki. We measured soleus M-wave and H- reflex recruitment curves using peripheral tibial nerve stimulation after each following condition: (i) baseline, (ii) initial 25 min session of EMS over spinal L5 level (SEMS; 0.2 Hz frequency, 70% coil intensity), (iii) additional 15 min session of SEMS, (iv) 15-min session of EMS at leg muscles. FDD of H-reflex (stim current was set to evoke 40% of H-max, using 0.2, 1, 2 and 5 Hz stim rate) was examined after taking baseline measures and then after end of muscle stimulation. Baseline measurements (prior SEMS] ) revealed a less steep (flatter) rise phase and more prolonged plateau of the recruitment curve of H-reflex, as well as a lesser depression rate of FDD in SCI vs healthy participants. In both healthy and SCI subjects, 1stapplication of SEMS for 25mins induced substantial facilitation of both M-response and H-reflex; this associated with a significant leftward shift of the recruitment curves for M- and H-responses and a marked decrease in the threshold currents to evoke H- and M-responses. 2nd follow-up application of SEMS for 15 min did not induce further changes, thus indicating that effects of SEMS reached its maximum after initial 1st 25 min of SEMS. However, EMS application over leg muscles induced further facilitation of M-wave and H-response. These results suggest that EMS over spinal level and leg muscles exert their effects on H-reflex through different mechanisms. Results also revealed improvement of FDD rate following SEMS/leg stimulation in SCI participants. Importantly, one SCI participant was engaged in 20 min exercise training sessions (NUSTEP exercise machine) after completion of SEMS/leg stimulation protocols; after 5 sessions the subject, who is 12 years post SCI, reported an increase in sensation and function for the first time. It is important to note that this subject had been performing similar exercise on a regular basis prior to this study without functional changes. Results suggest that spinal/leg EMS stimulation combined with exercise may be a potential approach in clinics for a variety of spinal or peripheral nerve conditions.
*V. L. ARVANIAN1, H. A. PETROSYAN1, A. TESFA1, M. FAHMY1, C. ZOU2, S. SISTO3;
1Res. Services, Northport VAMC, Northport, NY; 2StonyBrook Univ., Stony Brook, NY; 3Univ. of Buffalo, Buffalo, NY. Combined administration of electro-magnetic stimulation (EMS) at spinal level and at leg muscles to modulate neurophysiological properties at spino-muscular circuitry in healthy and SCI humans. Program No. 298.12. 2018 Neuroscience Meeting Planner. San Diego, CA: Society for Neuroscience, 2018. Online.