The Impact Of Electrical Pulse Waveform Modulation On H-reflex Response In Rat

Neuromuscular electrical stimulation(NMES)is commonly used to enhance muscle movement and maintain motor or sensory function.It has been widely applied to multiple biomedical applications such as neural prosthetic hands and clinical rehabilitation for restoring motor function from stroke,hemiplegia and spinal cord injury.It is believed that the NMES was able to activate muscle contraction based upon a central mechanism which recruited the motor units through the spinal pathway by the electrically evoked sensory volley.Studies suggested that the central pathway activities enhanced by the electrically evoked sensory fiber response played a key role to improve the efficiency of NMES.And the contraction generated by NMES can sequentially recruit motor units of target muscles through a central pathway in terms of the Henneman's size principle,which is similar to voluntary contractions.Muscle contractions generated through this way could induce the rebuilding of fatigue-resistant contractions in rehabilitation,improve the long-term motor function and reduce muscle atrophy.Therefore,modulation of the sensory neural responses by NMES through central mechanism is of great importance for motor function rehabilitation.The efficiency of NMES on activation of motor units depends on tissue properties and various stimulus parameters such as amplitude,frequency and pulse width.Recently,wide-pulse electrical stimulation(0.5-1 ms)has attracted increasing interests for its advantage in facilitating sensory axons recruitment.And the pulse-modulated of stimulus waveform is one important widely-accepted technical strategy to modulate the vagal nerve fibers.However,how the pulse-modulated waveforms enhance peripheral afferent pathways still remains an open question.Supported by an NSFC project(31771069),this research investigated the effect of pulse-modulated of wide-pulse stimulus on sensory fiber activation of the tibial nerve.Firstly,considering advantages of wide-pulse priority activation of afferent fibers and the higher charge efficiency of short pulse,we uniformly modulated the wide-pulses(1 ms)to improve the stimulation efficiency of afferent fibers.Eleven SD rats were used in the experiments.Modulation wide-pulse(mWP)and continuous wide-pulse(WP)were used to stimulate the tibial nerve of SD rats.EMG signals in plantar muscle of hindpaw evoked by electrical stimulation were recorded by a signal acquisition system.We calculated the amplitude of the H-reflex response under all stimulation waveforms and stimulation intensities and established an H-reflex recruitment curve,which is increasing with the stimulation intensities.The effects of stimulation patterns and parameters on sensory fiber activation were quantified by extracting the eigenvalues of interest according to the normalized and fitted recruitment curves.Preliminary results suggested that mWPs waveform stimulation requires less charge to induce the same level of fiber activation and a greater H-reflex gain than WP.While,as the carrier pulse width of the uniformly modulated wide-pulse decreases,the amount of required charge increases and the recruitment gain decreases.Secondly,the response mode of the fiber is affected by the charge density distribution(modulated by carrier frequency),so the modulation of the carrier frequency may also affect the stimulation efficiency.In this part of experiments,modulation wide-pulse(mWP)and continuous wide-pulse(WP)stimulation modes with different carrier frequencies are set.Seven adult SD rats were used in experiments.Electrical stimulation stimulated the tibial nerve and EMG signals in plantar muscle of hindpaw were recorded.Preliminary results showed that the non-uniform modulation wide-pulse with different carrier frequencies requires less charge to activate the sensory fiber and obtain a larger H-reflex recruitment gain than the WP waveform.It has great application potential in optimizing the stimulation mode to enhance afferent input.For non-uniformly modulation wide-pulse,different charge density distributions have no significant effect on stimulation efficiency of fiber activation and recruitment gain.Finally,we verified the safety and stability of the experiment by means of Immunohistochemical analysis and electrophysiological characteristic.HE staining was performed on the NMES side and the unstimulated lateral tibial nerve in rats,and the tissue morphology was observed under electron microscope.The results showed that the long-term electrical stimulation in the study did not cause obvious direct damage to the nerve fibers,and the tissue structure was complete and ordered.During the experiment,the maximum H-reflex response was induced by WP mode before and after different stimulation waveforms,and the difference in response amplitude was analyzed to evaluate the stability of the rat state under long-term stimulation.The results showed that there was no significant difference in the maximum H-reflex evoked by electrical stimulation,which indicates that the animal status was stable during the long-term stimulation experiment.This study presented quantitative comparisons of uniform and non-uniform pulse-modulated wide-pulse waveforms against conventional continuous wide-pulse waveform in terms of charge efficiency and recruitment gain on the sensory fibers activation.And the safety and stability tests were investigated by histological analysis and electrophysiology recording.The results suggested that,compared with the conventional wide-pulse stimulus,pulse-modulated stimulus could improve the charge efficiency of fiber activation and increase the recruitment gain.Furthermore,in uniform pulse-modulated stimulus,the efficiency and recruitment gain decreased with the decreasing the pulse width,while in non-uniform pulse-modulated stimulus,there was no significant difference among different types of charge density distributions.Our results provide a new stimulation strategy to optimize the NMES stimulation parameters for the activation of the central pathway,which may improve the recruitment efficiency of afferent fiber activation and facilitate the clinic application of wide-pulse NMES.