Optimization of Interphase Intervals to Enhance the Evoked Muscular Responses of Transcutaneous Neuromuscular Electrical Stimulation

Abstract

Neuromuscular electrical stimulation (NMES) is a widely used technique for clinical diagnostic, treatment, and research. Normally, it applies charge-balanced biphasic pulses, which several publications have reported to be less efficient than monophasic pulses. A good alternative is the use of interphase intervals (IPI) on biphasic pulses that allows to achieve similar responses than those evoked by monophasic stimulation. This study analyzes the enhancing mechanism of the IPI and provides guidelines on how to optimize the IPI in order to reduce secondary effects such as the electrode corrosion. The tibial nerve was excited by NMES biphasic pulses with different IPI durations and polarities. Then, the elicited responses were recorded on the soleus muscle via electromyography. When cathodic-first pulses were applied, the responses increased proportionally to the IPI until the duration of 250 µs, where the increase saturated at 30% of the original amplitude. The responses evoked during anodic-first were 6% to 30% smaller than those evoked during cathodic-first pulses and continuously increased until the IPI duration of 2500 µs, where the responses reached an increase of around 30%. The results suggest that when a cathodic-first pulse is used, the IPI could be optimized (based on the setup geometry) to allow the action potentials to travel out of the hyperpolarization zone induced by the anodic phase. When anodic-first stimuli are applied, the IPI duration allows the fiber to recover from an apparent insensitive state induced by the anodic phase. The use of IPI is a viable option to improve the efficiency of actual stimulation systems, since only small modifications are required to significantly reduce the electrical charge required and boost the stimulation efficiency.

Burst‐modulated wide‐pulse neuromuscular electrical stimulation enhances H‐reflex recruitment in rats

“…Wide‐pulse NMES has been proposed as a better method of electrical stimulation due to its advantages of recruiting more sensory axons. Recently, researchers have tried to optimize the stimulation parameters to improve the rehabilitation effect, enhancing the efficiency by using interphase intervals, strengthening the intrinsic foot muscle and inducing neural responses in the sensorimotor area . Unlike other studies, we modulated the pulse waveform of the wide‐pulse NMES and explored its effect on the stimulus efficiency of sensory axon activation, and this may provide experimental evidence for optimizing parameters of burst‐modulated waveforms to enhance sensory fiber recruitment.…”

“…The brief burst of high‐frequency NMES increases the H‐reflex amplitude, and the resulting asynchronous activity of motor neurons resembles physiological activation. Furthermore, many experimental studies have proven that pulse‐modulated stimulation significantly augments central recruitment of motor neurons, increases isometric knee joint torque, promotes the selective activation of fibers, and enhances stimulation efficiency of peripheral nerves. Despite previous evaluations of motor nerve excitability, the mechanisms by which burst‐modulated waveforms adjust peripheral afferent pathways remain unknown.…”

Sub-threshold depolarizing pre-pulses can enhance the efficiency of biphasic stimuli in transcutaneous neuromuscular electrical stimulation

“…Therefore, the use of an additional compensatory phase, to establish appropriate charge-balance, would improve practicability and safety. The projection of earlier findings on DPPs effects on monophasic stimuli to biphasic pulses is not trivial since previous reports have shown that adding a second phase and changes in the polarity sequence can substantially modify the motor response [ 16 , 17 ]. On the one hand, these reports conclude that regardless the polarity sequence, the cathodic phase is always triggering the action potential.…”

“…On the one hand, these reports conclude that regardless the polarity sequence, the cathodic phase is always triggering the action potential. Moreover, the anodic phase could reduce the motor output either by blocking the action potential propagation (when applied at the end) or by pre-conditioning the fibers (when applied first) [ 17 ].…”

Artificial Organs 2017: A Year in Review

“…Luna et al of the Tecnológico de Monterrey, Monterrey, Mexico investigated the optimization of interphase intervals (IPIs) to enhance the evoked muscular responses of transcutaneous NMES. The tibial nerve was excited by NMES biphasic pulses with different IPI durations and polarities.…”