Burst-Modulated Waveforms Optimize Electrical Stimuli for Charge Efficiency and Fiber Selectivity

Abstract

We demonstrate an alternative method of designing electrical stimuli-termed burst modulation--for producing different patterns of nerve fiber recruitment. By delivering electrical charge in bursts of "pulsons"--miniature pulses-instead of as long continuous pulses, our method can optimize the waveform for stimulation efficiency and fiber selectivity. In our in vivo validation experiments, while maintaining C fibers of the rat vagus nerve at ∼ 50% activation with different waveforms, the burst-modulated waveform produced 11% less A fiber activation than the standard rectangular pulse waveform (rectangular: 50.8±1.5% of maximal A response, mean ± standard error of the mean; burst-modulated: 39.8 ±1.3%), which equates to a 20% reduction in A fiber response magnitude. In addition, the burst-modulated waveform required 45% less stimulus charge per phase to maintain 50% C fiber activation (rectangular: 20.7 ±0.86 μC; burst-modulated: 11.3 ±0.41 μC ). Burst-modulated waveforms produced consistent patterns of fiber recruitment within and across animals, which indicate that our methods of stimulus design and response analysis provide a reliable way to study neurostimulation and deliver therapy.

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

“…The stimulus charge ( Q ) was calculated by: where I is the stimulation current and D is the pulse duration for the WP waveform or the effective pulse duration for the mWP waveform. By definition, the effective pulse duration for the mWP waveform is half of the WP waveform, due to a 50% duty cycle . The H‐reflex recruitment curve (HRC) and M‐wave recruitment curve (MRC) were then obtained (see Figure S3B online).…”

“…The H‐reflex recruitment curve (HRC) and M‐wave recruitment curve (MRC) were then obtained (see Figure S3B online). The interpolated response magnitude of the H‐reflex corresponding to different stimulus charges was calculated by fitting the ascending limb of each individual recruitment curve with a three‐parameter sigmoid function, as in Equation : where Hmax is the upper limit of the recruitment curve that corresponds to the maximum H‐reflex response, m is a constant that represents the slope of the function, Q 50 is determined as the required charge to achieve 50% of the Hmax. Similarly, the response amplitude of the M‐wave can be interpolated through the fitting characteristics of its recruitment curve.…”

“…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.…”

Effects of chronic abdominal vagal stimulation of small-diameter neurons on brain metabolism and food intake

“…Recently, Qing et al (17) proposed to chop rectangular based waveforms into shorter rectangular waves lasting between 40 to 80 µsec, called pulsons. While individual pulsons were unable to trigger an action potential, they appear collectively to be effective in anaesthetized rats for stimulating C fibres at the cervical level.…”

Towards closed-loop neuromodulation: a wireless miniaturized neural implant SoC

“…Devastating damage to the electrode or biological tissue can be avoided if the bio-impedance at the electrode-electrolyte interface can be monitored to not only ensure the robustness of the electrode but also help define the safe stimulation parameters to ensure the electrode overpotential is well within its water window. A stimulator with versatile programmability to generate flexible waveform is also preferred to facilitate the selective stimulation 7-9 . The capability of performing selective and focal stimulation to specific nerves would greatly ameliorate the treatment efficacy.…”