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In JoVE (1)
Other Publications (6)
- Neuromodulation : Journal of the International Neuromodulation Society
- Neuromodulation : Journal of the International Neuromodulation Society
- Neuromodulation : Journal of the International Neuromodulation Society
- Neuromodulation : Journal of the International Neuromodulation Society
- Pain Physician
- Medical & Biological Engineering & Computing
Articles by Kerry Bradley in JoVE
JoVE Clinical and Translational Medicine
Dorsal Column Steerability with Dual Parallel Leads using Dedicated Power Sources: A Computational Model
Boston Scientific , Neuromodulation
Using a mathematical model of spinal cord stimulation, we found that a multi-source system with independent power sources for each contact can target more central points of stimulation on the dorsal column (100 vs 3) and has 50-fold more field steering resolution (0.02mm vs 1mm) than a single-source system.
Other articles by Kerry Bradley on PubMed
Real-Time Paresthesia Steering Using ContinuousElectric Field Adjustment. Part I: IntraoperativePerformance
We present data collected from a multicenter study using a new neurostimulation system. This new system uses a current-shifting programming technique for spinal cord stimulation. The system maintains a continuous, suprathreshold stimulation field while adjusting the distribution of anodic and cathodic current among contacts along a multi-contact array. The changing distribution of current shifts the electric field along the spinal cord, resulting in real-time, dynamic paresthesia steering. This process of adjusting the stimulation field has been termed continuous electric field adjustment (CEFA). This technique has been used to assess paresthesia coverage for patients undergoing implantation of stimulation contact arrays for chronic pain. This multicenter study evaluated the performance of the CEFA technique. The results of the study showed that paresthesia coverage could be shifted in real-time to different regions on the patient's body in a comfortable fashion, with the patient always feeling paresthesia during the adjustment process. The results of the study also show that the process was time-efficient: intraoperatively, the median time to assess 71 combinations on a single 8-contact lead across 18 patients was 4.1 (3.6-5.0) minutes.
A Preliminary Feasibility Study of Different Implantable Pulse Generators Technologies for Diaphragm Pacing System
Diaphragm pacing stimulation (DPS) for ventilator-dependent patients provides several advantages over conventional techniques such as phrenic nerve pacing or mechanical ventilator support. To date, the only existing system for DPS uses lead electrodes, percutaneously attached to an external pulse generator (PG). However, for a widespread use of this technique it would be more appropriate to eliminate the need for percutaneous wire and use a totally implantable system. The aim of this study was to determine if it were feasible to replace the external PG by an implantable system. We present here the results of a preliminary study of two different PG, currently used in other electrical stimulation (ES) clinical applications, which could be used as implantable DPS systems. One radio-frequency-powered PG, one rechargeable battery-powered PG, and the current external PG were tested. Each was attached to the externalized part of the wires, connected to the diaphragm and tidal volume (TV) was measured in one ventilator-dependent patient who has been using the current percutaneous stimulator for 3 years. Results indicated that both implantable PGs could achieve equivalent ventilatory requirements to the current external stimulator. No significant differences were observed between the three PG systems when stimulating the electrodes as used in the patient's own chronically attached PG system. We found that TV increased with increases in charge and frequency as expected when stimulating the patient's electrodes individually and in combination with each PG system. These results are a significant step toward developing a totally implantable DPS system for the ventilator-dependant patients. Further clinical tests to demonstrate the safety and efficacy of a fully implanted DPS system are warranted.
Factors Affecting Impedance of Percutaneous Leads in Spinal Cord Stimulation
Objectives. Although the load impedance of a pulse generator has a significant effect on battery life, the electrical impedance of contact arrays in spinal cord stimulation (SCS) has not been extensively studied. We sought to characterize the typical impedance values measured from common quadripolar percutaneous SCS contact arrays. Methods. In 36 patients undergoing percutaneous trial stimulation for various chronic pain conditions, bipolar impedance between adjacent contacts of 64 leads with 9 mm center-to-center spacing was measured in two different vertebral level regions, cervical (C3-C7) and lower-thoracic (T7-T12). Multiple linear regression was applied to analyze the contribution of six variables to the biological tissue portion of the impedance (excluding the resistance of the lead wires). Results. The median impedance in the cervical region (351 ± 90 Ω) was significantly lower (36%, p < 0.001) than in the lower-thoracic region (547 ± 151 Ω). In addition, time since implant had a weaker but still significant effect on tissue impedance. Conclusions. Results from finite-difference mathematical modeling of SCS suggest that the difference in tissue impedance related to vertebral level may be due to the dorsoventral position of the lead in the epidural space. The presence of a larger space between the triangularly shaped dorsal part of the vertebral arch and the round shape of the dural sac in the lower-thoracic region increases the likelihood that the stimulating lead will not make dural contact, and thus "see" an increased impedance from the surrounding epidural fat. This implies that the energy requirements for stimulation in the thoracic region will be higher than in the cervical region, at least during the acute phase of implant.
Theoretical Investigation into Longitudinal Cathodal Field Steering in Spinal Cord Stimulation
Objective. When using spinal cord stimulation (SCS) for chronic pain management, precise longitudinal positioning of the cathode is crucial to generate an electrical field capable of targeting the neural elements involved in pain relief. Presently used methods have a poor spatial resolution and lack postoperative flexibility needed for fine tuning and reprogramming the stimulation field after lead displacement or changes in pain pattern. We describe in this article a new method, "electrical field steering," to control paresthesia in SCS. The method takes advantage of newer stimulator design and a programming technique allowing for "continuous" adjustment of contact combination while controlling stimulation current for each contact separately. Method. Using computer modeling we examined how stimulation of dorsal column (DC) and dorsal root (DR) fibers was influenced by changing the current ratio of the cathodes of a dual (--) and a guarded dual cathode (+--+) configuration programmed on a percutaneous lead with 9 and 4 mm center-to-center contact spacing. Results. A cathodal current ratio could be found for which DC or DR fiber recruitment and thus, most likely, paresthesia coverage was maximized. The DR threshold profiles shifted longitudinally, thus following the shift in the electrical field during steering. The profiles had a constant shape when the contact spacing was small and a varying shape for wider contact separation. Generally, the wider contact separation provided less DC and more DR fiber recruitment. Conclusions. By means of cathodal steering on a longitudinal contact array, the group of excited DC and DR fibers, and thus paresthesia coverage, can be controlled when using SCS. With widely spaced contacts, superposition of the electrical field from each steering contact is limited. To precisely control segmental paresthesia (DR stimulation), a small contact spacing is necessary.
Pulse Width Programming in Spinal Cord Stimulation: a Clinical Study
With advances in spinal cord stimulation (SCS) technology, particularly rechargeable implantable, patients are now being offered a wider range of parameters to treat their pain. In particular, pulse width (PW) programming ranges of rechargeable implantable pulse generators now match that of radiofrequency systems (with programmability up to 1000 microseconds. The intent of the present study was to investigate the effects of varying PW in SCS.
Predicted Effects of Pulse Width Programming in Spinal Cord Stimulation: a Mathematical Modeling Study
To understand the theoretical effects of pulse width (PW) programming in spinal cord stimulation (SCS), we implemented a mathematical model of electrical fields and neural activation in SCS to gain insight into the effects of PW programming. The computational model was composed of a finite element model for structure and electrical properties, coupled with a nonlinear double-cable axon model to predict nerve excitation for different myelinated fiber sizes. Mathematical modeling suggested that mediolateral lead position may affect chronaxie and rheobase values, as well as predict greater activation of medial dorsal column fibers with increased PW. These modeling results were validated by a companion clinical study. Thus, variable PW programming in SCS appears to have theoretical value, demonstrated by the ability to increase and even 'steer' spatial selectivity of dorsal column fiber recruitment. It is concluded that the computational SCS model is a valuable tool to understand basic mechanisms of nerve fiber excitation modulated by stimulation parameters such as PW and electric fields.
