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

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 $\sim 50\%$ activation with different waveforms, the burst-modulated waveform produced 11% less A fiber activation than the standard rectangular pulse waveform (rectangular: $50.8\pm1.5\%$ of maximal A response, mean $\pm $ standard error of the mean; burst-modulated: $39.8 \pm 1.3\%$), 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: $20.7 \pm 0.86~\mu{\rm C}$; burst-modulated: $11.3 \pm 0.41~\mu{\rm C}$ ). 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.