ASCENT (Automated Simulations to Characterize Electrical Nerve Thresholds): A pipeline for sample-specific computational modeling of electrical stimulation of peripheral nerves
Fig 5
Using ASCENT to replicate previously published computational models and to model an in vivo experiment.
(A) Recruitment curve for each fascicle in a model of the rabbit sciatic nerve for two rotations of a bipolar cuff electrode [11]. Fiber thresholds are in response to a 100 μs per phase biphasic rectangular pulse (i.e., BIPHASIC_PULSE_TRAIN). We simulated mammalian myelinated fibers at 0.5 μm diameter increments from 2 to 16 μm (i.e., MRG_INTERPOLATION) with 10 fibers of each diameter at consistent locations in each fascicle (i.e., UNIFORM_COUNT). We generated fiber recruitment curves by defining a population of fiber diameters from a normal distribution (8.85 ± 3.1 μm, 100 fibers per fascicle) and rounded each fiber diameter to the nearest 0.5 μm to draw from our modeled activation thresholds randomly. Configuration and input files used to replicate the results are provided in examples/results/bucksot_2019/. (B) Using ASCENT to model electrophysiology study of dog vagus stimulation [40]. We used Photoshop (Adobe Inc., San Jose, CA) to segment a micrograph from one of the animals in the original publication. We placed the nerve in a 2 mm diameter LivaNova helical cuff electrode delivering a 300 μs monophasic rectangular pulse (i.e., MONOPHASIC_PULSE_TRAIN), as used experimentally. We computed activation thresholds for myelinated (i.e., MRG_INTERPOLATION: 2.1, 3.6, and 7.8 μm diameter) and unmyelinated (i.e., TIGERHOLM: 1.0 μm diameter) fiber models, corresponding to the fiber types reported in the original study. We report the modeled threshold of a single fiber of each type at the centroid of the fascicle (i.e., CENTROID) (red dot) overlaid on the in vivo ENG thresholds (blue bars with black error bars: mean ± SD) of both myelinated (n = 5 dogs) and unmyelinated (n = 4 dogs) vagus nerve fibers. Our prior modeling studies show that fibers of a consistent diameter placed in the same fascicle have nearly identical thresholds [10]. Configuration and input files used to model the experiment are provided in examples/results/yoo_2013/.