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 ∼ 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.