I am analyzing a data set of the spinal evoked potentials and have this question in my mind. Why do some of the muscles show high amplitude H reflex as compared to the M wave even at higher intensity of stimulation?
The amplitude of H-Reflexes and M-waves are dependent on the stimulus intensity (current) which depolarizes the afferent and efferent neural axon. Plotting the H-Reflex amplitude and M-wave amplitude against the stimulation current results in a H/M recruitment curve. Dependent on the location of the slopes (descending or ascending) the H-reflex is naturally higher in amplitude than the M-wave as the afferent axon has a lower threshold. However, at high currents that elicit the maximal M-wave, the amplitude of the M-wave should be generally greater than the one of the H-Reflex.
Excellent articles that I recommend to you:
Article Considerations for use of the Hoffmann reflex in exercise studies
Article The Hoffmann Reflex: Methodologic Considerations and Applica...
Best,
Ramona
Stimulation site can cause such "weird" recruitment [1]. Also, I would agree with Ramona Ritzmann, since the recruitment curve can cause this and it depends on a muscle. What is the muscle and what is exactly "high" intensity? It's not the same for soleus and for hamstrings. For hamstrings, I'm not even sure that you can reach Mmax (maybe in some isolated cases...), 'cause it would be way too painful [2]. About stimulation site & H-reflex in hamstrings (in case you need these references):
1. Miljković, N., Malešević, N., Kojić, V., Bijelić, G., Keller, T. and Popović, D.B., 2015. Recording and assessment of evoked potentials with electrode arrays. Medical & biological engineering & computing, 53(9), pp.857-867.
2. Dueholm, S.S. and Rasmussen, J.H., 2013. " Intersession reliability study of Hreflexes in the hamstring muscle group elicited by a novel technique to stimulate the sciatic nerve" Master thesis. Aalborg University.
Ramona Ritzmann Nadica Miljkovic Thank you sharing the information! I should have mentioned in the question that I am analyzing the evoked responses that are generated during spinal cord stimulation with stimulating electrodes implanted on the epidural surface of rats cervical spinal cord. We record evoked responses from several muscles and the responses behave similar to M wave and H-reflex . Its only one muscle that shows high amplitude H reflex as compared to the M wave at higher intensity of 800 microamp. May be its muscle and site of stimulation specific.
Pawan Sharma, I afraid you got totally confused with H-reflex with spinally evoked potentials. Hoffmann's reflex utilizes the afferent pathway to activate the spinal reflex arc and efferent to direct activate the muscle; while the spinal epidural electrical stimulation activates the dorsal (and maybe some lateral and ventral) column of the spinal cord and it's motor pools via mono and polysynaptic pathways. The different responses of the spinal stimulation are called early to late responses. They are NOT H or M waves. You should read the early works from Igor A. Lavrov to learn more about the spinal MEP.
@Monzurul Alam, Thank you for the response and clarifying the difference. I guess, I framed the question wrongly. I was trying to see if anyone has experienced a scenario in which H reflex fails to suppress even at higher intensities of stimulation and I got some interesting replies too. I have read previous work by Dr. Lavrov and Dr. Gerasimenko. I have also learned a lot from your 2015 and 2017 research papers on cervical spinal evoked responses.
Pawan Sharma, are you trying to measure H-reflex during spinal epidural electrical stimulation?
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