Mapping the current flow in sacral nerve stimulation using computational modelling

• Main Authors: Nada Yousif, Carolynne J. Vaizey, Yasuko Maeda
• Format: Article
• Language: English
• Published: Wiley 2018-09-01
• Series: Healthcare Technology Letters
• Subjects: biomedical electrodes; prosthetics; patient treatment; neurophysiology; neuromuscular stimulation; bioelectric potentials; physiological models; biological tissues; finite element analysis; biomechanics; bioelectric phenomena; current flow; sacral nerve stimulation; computational modelling; established treatment; quadripolar electrode; sacral foramen; electrical stimulus; sacral nerve root; induced spread; electric current; SNS electrode; adjacent tissues; finite element model; biophysical models; nerve fibres; electrode model choice; contact configuration; electrode contacts; neural fibre stimulation; monopolar stimulation; bipolar stimulation; similar effect; therapeutic stimulation effects; adverse stimulation effects; stimulation parameters
• Online Access: https://digital-library.theiet.org/content/journals/10.1049/htl.2018.5030

Sacral nerve stimulation (SNS) is an established treatment for faecal incontinence involving the implantation of a quadripolar electrode into a sacral foramen, through which an electrical stimulus is applied. Little is known about the induced spread of electric current around the SNS electrode and its effect on adjacent tissues, which limits optimisation of this treatment. The authors constructed a 3-dimensional imaging based finite element model in order to calculate and visualise the stimulation induced current and coupled this to biophysical models of nerve fibres. They investigated the impact of tissue inhomogeneity, electrode model choice and contact configuration and found a number of effects. (i) The presence of anatomical detail changes the estimate of stimulation effects in size and shape. (ii) The difference between the two models of electrodes is minimal for electrode contacts of the same length. (iii) Surprisingly, in this arrangement of electrode and neural fibre, monopolar and bipolar stimulation induce a similar effect. (iv) Interestingly when the active contact is larger, the volume of tissue activated reduces. This work establishes a protocol to better understand both therapeutic and adverse stimulation effects and in the future will enable patient-specific adjustments of stimulation parameters.