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Lam DV, Chin J, Brucker-Hahn MK, Settell M, Romanauski B, Verma N, Upadhye A, Deshmukh A, Skubal A, Nishiyama Y, Hao J, Lujan JL, Zhang S, Knudsen B, Blanz S, Lempka SF, Ludwig KA, Shoffstall AJ, Park HJ, Ellison ER, Zhang M, Lavrov I. The role of spinal cord neuroanatomy and the variances of epidurally evoked spinal responses. Bioelectron Med 2024; 10:17. [PMID: 39020366 PMCID: PMC11253499 DOI: 10.1186/s42234-024-00149-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2024] [Accepted: 05/28/2024] [Indexed: 07/19/2024] Open
Abstract
BACKGROUND Spinal cord stimulation (SCS) has demonstrated multiple benefits in treating chronic pain and other clinical disorders related to sensorimotor dysfunctions. However, the underlying mechanisms are still not fully understood, including how electrode placement in relation to the spinal cord neuroanatomy influences epidural spinal recordings (ESRs). To characterize this relationship, this study utilized stimulation applied at various anatomical sections of the spinal column, including at levels of the intervertebral disc and regions correlating to the dorsal root entry zone. METHOD Two electrode arrays were surgically implanted into the dorsal epidural space of the swine. The stimulation leads were positioned such that the caudal-most electrode contact was at the level of a thoracic intervertebral segment. Intraoperative cone beam computed tomography (CBCT) images were utilized to precisely determine the location of the epidural leads relative to the spinal column. High-resolution microCT imaging and 3D-model reconstructions of the explanted spinal cord illustrated precise positioning and dimensions of the epidural leads in relation to the surrounding neuroanatomy, including the spinal rootlets of the dorsal and ventral columns of the spinal cord. In a separate swine cohort, implanted epidural leads were used for SCS and recording evoked ESRs. RESULTS Reconstructed 3D-models of the swine spinal cord with epidural lead implants demonstrated considerable distinctions in the dimensions of a single electrode contact on a standard industry epidural stimulation lead compared to dorsal rootlets at the dorsal root entry zone (DREZ). At the intervertebral segment, it was observed that a single electrode contact may cover 20-25% of the DREZ if positioned laterally. Electrode contacts were estimated to be ~0.75 mm from the margins of the DREZ when placed at the midline. Furthermore, ventral rootlets were observed to travel in proximity and parallel to dorsal rootlets at this level prior to separation into their respective sides of the spinal cord. Cathodic stimulation at the level of the intervertebral disc, compared to an 'off-disc' stimulation (7 mm rostral), demonstrated considerable variations in the features of recorded ESRs, such as amplitude and shape, and evoked unintended motor activation at lower stimulation thresholds. This substantial change may be due to the influence of nearby ventral roots. To further illustrate the influence of rootlet activation vs. dorsal column activation, the stimulation lead was displaced laterally at ~2.88 mm from the midline, resulting in variances in both evoked compound action potential (ECAP) components and electromyography (EMG) components in ESRs at lower stimulation thresholds. CONCLUSION The results of this study suggest that the ECAP and EMG components of recorded ESRs can vary depending on small differences in the location of the stimulating electrodes within the spinal anatomy, such as at the level of the intervertebral segment. Furthermore, the effects of sub-centimeter lateral displacement of the stimulation lead from the midline, leading to significant changes in electrophysiological metrics. The results of this pilot study reveal the importance of the small displacement of the electrodes that can cause significant changes to evoked responses SCS. These results may provide further valuable insights into the underlying mechanisms and assist in optimizing future SCS-related applications.
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Affiliation(s)
- Danny V Lam
- Neural Lab, Abbott Neuromodulation, Plano, TX, USA
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA
- Department of Veterans Affairs Medical Center, Advanced Platform Technology Center, Louis Stokes Cleveland, Cleveland, OH, USA
| | - Justin Chin
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA
| | - Meagan K Brucker-Hahn
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA
- Biointerfaces Institute, University of Michigan, Ann Arbor, MI, USA
| | - Megan Settell
- Wisconsin Institute for Translational Neuroengineering (WITNe), Madison, WI, USA
- Department of Neurosurgery, University of Wisconsin-Madison, Madison, WI, USA
| | - Ben Romanauski
- Department of Neurosurgery, Mayo Clinic, Rochester, MN, USA
| | | | - Aniruddha Upadhye
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA
| | - Ashlesha Deshmukh
- Department of Biomedical Engineering, University of Wisconsin Madison, Madison, USA
- Wisconsin Institute for Translational Neuroengineering (WITNe), Madison, WI, USA
| | - Aaron Skubal
- Department of Biomedical Engineering, University of Wisconsin Madison, Madison, USA
- Wisconsin Institute for Translational Neuroengineering (WITNe), Madison, WI, USA
| | | | - Jian Hao
- Department of Neurology, Mayo Clinic, Rochester, MN, USA
| | - J Luis Lujan
- Department of Neurosurgery, Mayo Clinic, Rochester, MN, USA
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN, USA
| | - Simeng Zhang
- Neural Lab, Abbott Neuromodulation, Plano, TX, USA
| | - Bruce Knudsen
- Department of Biomedical Engineering, University of Wisconsin Madison, Madison, USA
- Wisconsin Institute for Translational Neuroengineering (WITNe), Madison, WI, USA
| | - Stephan Blanz
- Department of Biomedical Engineering, University of Wisconsin Madison, Madison, USA
- Wisconsin Institute for Translational Neuroengineering (WITNe), Madison, WI, USA
- University of Wisconsin School of Medicine and Public Health, Madison, WI, USA
| | - Scott F Lempka
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA
- Biointerfaces Institute, University of Michigan, Ann Arbor, MI, USA
- Department of Anesthesiology, University of Michigan, Ann Arbor, MI, USA
| | - Kip A Ludwig
- Department of Biomedical Engineering, University of Wisconsin Madison, Madison, USA
- Wisconsin Institute for Translational Neuroengineering (WITNe), Madison, WI, USA
- Department of Neurosurgery, University of Wisconsin-Madison, Madison, WI, USA
| | - Andrew J Shoffstall
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA
- Department of Veterans Affairs Medical Center, Advanced Platform Technology Center, Louis Stokes Cleveland, Cleveland, OH, USA
| | | | | | | | - Igor Lavrov
- Department of Neurology, Mayo Clinic, Rochester, MN, USA.
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN, USA.
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North RB, Sung JH, Matthews LA, Zander HJ, Lempka SF. Postural Changes in Spinal Cord Stimulation Thresholds: Current and Voltage Sources. Neuromodulation 2024; 27:178-182. [PMID: 37804279 DOI: 10.1016/j.neurom.2023.08.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2023] [Revised: 07/27/2023] [Accepted: 08/04/2023] [Indexed: 10/09/2023]
Abstract
OBJECTIVE Spinal cord stimulation (SCS) thresholds are known to change with body position; however, these changes have not been fully characterized for both "constant-voltage" and "constant-current" pulse generators. This study aimed to evaluate and quantify changes in psychophysical thresholds resulting from postural changes that may affect both conventional paresthesia-based SCS and novel paresthesia-free SCS technologies. MATERIALS AND METHODS We measured perceptual, usage, and discomfort thresholds in four body positions (prone, supine, sitting, standing) in 149 consecutive patients, with temporary lower thoracic percutaneous epidural electrodes placed for treating persistent low back and leg pain. We trialed 119 patients with constant-voltage stimulators and 30 patients with constant-current stimulators. RESULTS Moving from supine to the sitting, standing, or prone positions caused all three thresholds (perceptual, usage, and discomfort) to increase by 22% to 34% for constant-voltage stimulators and by 44% to 82% for constant-current stimulators. Changing from a seated to a supine position caused stimulation to exceed discomfort threshold significantly more often for constant-current (87%) than for constant-voltage (63%) stimulators (p = 0.01). CONCLUSIONS Posture-induced changes in SCS thresholds occurred consistently as patients moved from lying (supine or prone) to upright (standing or sitting) positions. These changes were more pronounced for constant-current than for constant-voltage pulse generators and more often led to stimulation-evoked discomfort. These observations are consistent with postural changes in spinal cord position measured in imaging studies, and with computer model predictions of neural recruitment for these different spinal cord positions. These observations have implications for the design, implantation, and clinical application of spinal cord stimulators, not only for conventional paresthesia-based SCS but also for paresthesia-free SCS.
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Affiliation(s)
- Richard B North
- Neuromodulation Foundation, Inc, Baltimore, MD; Departments of Neurosurgery, Anesthesiology and Critical Care Medicine, The Johns Hopkins University School of Medicine, Baltimore, MD.
| | - Jung H Sung
- Department of Neurosurgery, The Johns Hopkins University School of Medicine, Baltimore, MD
| | - Liam A Matthews
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI; Biointerfaces Institute, University of Michigan, Ann Arbor, MI
| | - Hans J Zander
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI; Biointerfaces Institute, University of Michigan, Ann Arbor, MI
| | - Scott F Lempka
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI; Biointerfaces Institute, University of Michigan, Ann Arbor, MI; Department of Anesthesiology, University of Michigan, Ann Arbor, MI
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Sivanesan E, North RB, Russo MA, Levy RM, Linderoth B, Hayek SM, Eldabe S, Lempka SF. A Definition of Neuromodulation and Classification of Implantable Electrical Modulation for Chronic Pain. Neuromodulation 2024; 27:1-12. [PMID: 37952135 DOI: 10.1016/j.neurom.2023.10.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2023] [Revised: 09/24/2023] [Accepted: 10/09/2023] [Indexed: 11/14/2023]
Abstract
OBJECTIVES Neuromodulation therapies use a variety of treatment modalities (eg, electrical stimulation) to treat chronic pain. These therapies have experienced rapid growth that has coincided with escalating confusion regarding the nomenclature surrounding these neuromodulation technologies. Furthermore, studies are often published without a complete description of the effective stimulation dose, making it impossible to replicate the findings. To improve clinical care and facilitate dissemination among the public, payors, research groups, and regulatory bodies, there is a clear need for a standardization of terms. APPROACH We formed an international group of authors comprising basic scientists, anesthesiologists, neurosurgeons, and engineers with expertise in neuromodulation. Because the field of neuromodulation is extensive, we chose to focus on creating a taxonomy and standardized definitions for implantable electrical modulation of chronic pain. RESULTS We first present a consensus definition of neuromodulation. We then describe a classification scheme based on the 1) intended use (the site of modulation and its indications) and 2) physical properties (waveforms and dose) of a neuromodulation therapy. CONCLUSIONS This framework will help guide future high-quality studies of implantable neuromodulatory treatments and improve reporting of their findings. Standardization with this classification scheme and clear definitions will help physicians, researchers, payors, and patients better understand the applications of implantable electrical modulation for pain and guide informed treatment decisions.
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Affiliation(s)
- Eellan Sivanesan
- Department of Anesthesiology and Critical Care Medicine, School of Medicine, Johns Hopkins University, Baltimore, MD, USA.
| | - Richard B North
- Department of Anesthesiology and Critical Care Medicine, School of Medicine, Johns Hopkins University, Baltimore, MD, USA; Department of Neurosurgery, Johns Hopkins University, Baltimore, MD, USA
| | - Marc A Russo
- Hunter Pain Specialists, Broadmeadow, New South Wales, Australia
| | - Robert M Levy
- Neurosurgical Services, Clinical Research, Anesthesia Pain Care Consultants, Tamarac, FL, USA
| | - Bengt Linderoth
- Department of Clinical Neuroscience, Karolinska Institute, Stockholm, Sweden
| | - Salim M Hayek
- Division of Pain Medicine, University Hospitals, Cleveland Medical Center, Cleveland, OH, USA
| | - Sam Eldabe
- Department of Pain Medicine, The James Cook University Hospital, Middlesbrough, UK
| | - Scott F Lempka
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA; Department of Anesthesiology, University of Michigan, Ann Arbor, MI, USA; Biointerfaces Institute, University of Michigan, Ann Arbor, MI, USA
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Rogers ER, Mirzakhalili E, Lempka SF. Model-based analysis of subthreshold mechanisms of spinal cord stimulation for pain. J Neural Eng 2023; 20:066003. [PMID: 37906966 PMCID: PMC10632558 DOI: 10.1088/1741-2552/ad0858] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2023] [Revised: 10/11/2023] [Accepted: 10/31/2023] [Indexed: 11/02/2023]
Abstract
Objective.Spinal cord stimulation (SCS) is a common treatment for chronic pain. For decades, SCS maximized overlap between stimulation-induced paresthesias and the patient's painful areas. Recently developed SCS paradigms relieve pain at sub-perceptible amplitudes, yet little is known about the neural response to these new waveforms or their analgesic mechanisms of action. Therefore, in this study, we investigated the neural response to multiple forms of paresthesia-free SCS.Approach.We used computational modeling to investigate the neurophysiological effects and the plausibility of commonly proposed mechanisms of three paresthesia-free SCS paradigms: burst, 1 kHz, and 10 kHz SCS. Specifically, in C- and Aβ-fibers, we investigated the effects of different SCS waveforms on spike timing and activation thresholds, as well as how stochastic ion channel gating affects the response of dorsal column axons. Finally, we characterized membrane polarization of superficial dorsal horn neurons.Main results.We found that none of the SCS waveforms activate nor modulate spike timing in C-fibers. Spike timing was modulated in Aβ-fibers only at suprathreshold amplitudes. Ion channel stochasticity had little effect on Aβ-fiber activation thresholds but produced heterogeneous spike timings at suprathreshold amplitudes. Finally, local cells were preferentially polarized in their axon terminals, and the magnitude of this polarization was dependent on cellular morphology and position relative to the stimulation electrodes.Significance.Overall, the mechanisms of action of subparesthetic SCS remain unclear. Our results suggest that no SCS waveforms directly activate C-fibers, and modulation of spike timing is unlikely at subthreshold amplitudes. We conclude that potential subthreshold neuromodulatory effects of SCS on local cells are likely to be presynaptic in nature, as axons are preferentially depolarized during SCS.
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Affiliation(s)
- Evan R Rogers
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States of America
- Biointerfaces Institute, University of Michigan, Ann Arbor, MI, United States of America
| | - Ehsan Mirzakhalili
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States of America
- Biointerfaces Institute, University of Michigan, Ann Arbor, MI, United States of America
| | - Scott F Lempka
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States of America
- Biointerfaces Institute, University of Michigan, Ann Arbor, MI, United States of America
- Department of Anesthesiology, University of Michigan, Ann Arbor, MI, United States of America
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Rattay F, Tafvizi P. Blockage of pain by electrical spinal cord stimulation. Minerva Med 2023; 114:620-627. [PMID: 34269551 DOI: 10.23736/s0026-4806.21.07588-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
BACKGROUND Electrical spinal cord stimulation (SCS) is an alternative to conventional medication for chronic pain relief. Several hypotheses exist concerning the neurophysiological, vascular, and neurochemical mechanism behind SCS. METHODS The excitation and blockade effects of the three common SCS waveforms (tonic, burst, and high-frequency stimulation) on the nerve fibers bypassing the region of the electrodes are analyzed in a computational study. The simulations are based on the model of Hodgkin and Huxley which is fitted to spike durations of 1 ms. RESULTS SCS is a FDA approved technique for pain relief, but the mechanisms of action are still under investigation. The first element in the chain of mechanisms is the generation and the block of spikes in nerve fibers close to the stimulating electrode. For these "primary fibers" computer simulations showed that conventional SCS generates sharply synchronized spikes whereas the spread of the spiking times by burst stimulation is expected to cause the suppression of paresthesia. This rather uniform spread of spiking times (in comparison to tonic stimulation) is a consequence of more pulses (5 vs. 1), longer pulses, and increasing intensities within each train of 5 pulses. CONCLUSIONS High-frequency stimulation can block the conduction of spikes but the distance of the fiber to the lead is a critical factor.
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Affiliation(s)
- Frank Rattay
- Institute for Analysis and Scientific Computing, Technical University of Vienna, Vienna, Austria -
| | - Pegah Tafvizi
- Institute for Analysis and Scientific Computing, Technical University of Vienna, Vienna, Austria
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6
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Fisher LE, Lempka SF. Neurotechnology for Pain. Annu Rev Biomed Eng 2023; 25:387-412. [PMID: 37068766 DOI: 10.1146/annurev-bioeng-111022-121637] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/19/2023]
Abstract
Neurotechnologies for treating pain rely on electrical stimulation of the central or peripheral nervous system to disrupt or block pain signaling and have been commercialized to treat a variety of pain conditions. While their adoption is accelerating, neurotechnologies are still frequently viewed as a last resort, after many other treatment options have been explored. We review the pain conditions commonly treated with electrical stimulation, as well as the specific neurotechnologies used for treating those conditions. We identify barriers to adoption, including a limited understanding of mechanisms of action, inconsistent efficacy across patients, and challenges related to selectivity of stimulation and off-target side effects. We describe design improvements that have recently been implemented, as well as some cutting-edge technologies that may address the limitations of existing neurotechnologies. Addressing these challenges will accelerate adoption and change neurotechnologies from last-line to first-line treatments for people living with chronic pain.
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Affiliation(s)
- Lee E Fisher
- Rehab Neural Engineering Labs, Department of Physical Medicine and Rehabilitation, and Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA;
- Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, USA
| | - Scott F Lempka
- Department of Biomedical Engineering, Biointerfaces Institute, and Department of Anesthesiology, University of Michigan, Ann Arbor, Michigan, USA;
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Lubejko ST, Graham RD, Livrizzi G, Schaefer R, Banghart MR, Creed MC. The role of endogenous opioid neuropeptides in neurostimulation-driven analgesia. Front Syst Neurosci 2022; 16:1044686. [PMID: 36591324 PMCID: PMC9794630 DOI: 10.3389/fnsys.2022.1044686] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2022] [Accepted: 11/18/2022] [Indexed: 12/15/2022] Open
Abstract
Due to the prevalence of chronic pain worldwide, there is an urgent need to improve pain management strategies. While opioid drugs have long been used to treat chronic pain, their use is severely limited by adverse effects and abuse liability. Neurostimulation techniques have emerged as a promising option for chronic pain that is refractory to other treatments. While different neurostimulation strategies have been applied to many neural structures implicated in pain processing, there is variability in efficacy between patients, underscoring the need to optimize neurostimulation techniques for use in pain management. This optimization requires a deeper understanding of the mechanisms underlying neurostimulation-induced pain relief. Here, we discuss the most commonly used neurostimulation techniques for treating chronic pain. We present evidence that neurostimulation-induced analgesia is in part driven by the release of endogenous opioids and that this endogenous opioid release is a common endpoint between different methods of neurostimulation. Finally, we introduce technological and clinical innovations that are being explored to optimize neurostimulation techniques for the treatment of pain, including multidisciplinary efforts between neuroscience research and clinical treatment that may refine the efficacy of neurostimulation based on its underlying mechanisms.
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Affiliation(s)
- Susan T. Lubejko
- Department of Neurobiology, School of Biological Sciences, University of California, San Diego, La Jolla, CA, United States
| | - Robert D. Graham
- Department of Anesthesiology, Pain Center, School of Medicine, Washington University in St. Louis, St. Louis, MO, United States
| | - Giulia Livrizzi
- Department of Neurobiology, School of Biological Sciences, University of California, San Diego, La Jolla, CA, United States
| | - Robert Schaefer
- Department of Anesthesiology, Pain Center, School of Medicine, Washington University in St. Louis, St. Louis, MO, United States
| | - Matthew R. Banghart
- Department of Neurobiology, School of Biological Sciences, University of California, San Diego, La Jolla, CA, United States
- *Correspondence: Matthew R. Banghart,
| | - Meaghan C. Creed
- Department of Anesthesiology, Pain Center, School of Medicine, Washington University in St. Louis, St. Louis, MO, United States
- Department of Neuroscience, Washington University in St. Louis, St. Louis, MO, United States
- Department of Psychiatry, Washington University in St. Louis, St. Louis, MO, United States
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, United States
- Meaghan C. Creed,
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Graham RD, Bruns TM, Duan B, Lempka SF. The Effect of Clinically Controllable Factors on Neural Activation During Dorsal Root Ganglion Stimulation. Neuromodulation 2020; 24:655-671. [PMID: 32583523 DOI: 10.1111/ner.13211] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2020] [Revised: 05/08/2020] [Accepted: 05/10/2020] [Indexed: 12/15/2022]
Abstract
OBJECTIVE Dorsal root ganglion stimulation (DRGS) is an effective therapy for chronic pain, though its mechanisms of action are unknown. Currently, we do not understand how clinically controllable parameters (e.g., electrode position, stimulus pulse width) affect the direct neural response to DRGS. Therefore, the goal of this study was to utilize a computational modeling approach to characterize how varying clinically controllable parameters changed neural activation profiles during DRGS. MATERIALS AND METHODS We coupled a finite element model of a human L5 DRG to multicompartment models of primary sensory neurons (i.e., Aα-, Aβ-, Aδ-, and C-neurons). We calculated the stimulation amplitudes necessary to elicit one or more action potentials in each neuron, and examined how neural activation profiles were affected by varying clinically controllable parameters. RESULTS In general, DRGS predominantly activated large myelinated Aα- and Aβ-neurons. Shifting the electrode more than 2 mm away from the ganglion abolished most DRGS-induced neural activation. Increasing the stimulus pulse width to 500 μs or greater increased the number of activated Aδ-neurons, while shorter pulse widths typically only activated Aα- and Aβ-neurons. Placing a cathode near a nerve root, or an anode near the ganglion body, maximized Aβ-mechanoreceptor activation. Guarded active contact configurations did not activate more Aβ-mechanoreceptors than conventional bipolar configurations. CONCLUSIONS Our results suggest that DRGS applied with stimulation parameters within typical clinical ranges predominantly activates Aβ-mechanoreceptors. In general, varying clinically controllable parameters affects the number of Aβ-mechanoreceptors activated, although longer pulse widths can increase Aδ-neuron activation. Our data support several Neuromodulation Appropriateness Consensus Committee guidelines on the clinical implementation of DRGS.
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Affiliation(s)
- Robert D Graham
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA.,Biointerfaces Institute, University of Michigan, Ann Arbor, MI, USA
| | - Tim M Bruns
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA.,Biointerfaces Institute, University of Michigan, Ann Arbor, MI, USA
| | - Bo Duan
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, USA
| | - Scott F Lempka
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA.,Biointerfaces Institute, University of Michigan, Ann Arbor, MI, USA.,Department of Anesthesiology, University of Michigan, Ann Arbor, MI, USA
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9
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Zander HJ, Graham RD, Anaya CJ, Lempka SF. Anatomical and technical factors affecting the neural response to epidural spinal cord stimulation. J Neural Eng 2020; 17:036019. [PMID: 32365340 PMCID: PMC8351789 DOI: 10.1088/1741-2552/ab8fc4] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
OBJECTIVE Spinal cord stimulation (SCS) is a common neurostimulation therapy to treat chronic pain. Computational models represent a valuable tool to study the potential mechanisms of action of SCS and to optimize the design and implementation of SCS technologies. However, it is imperative that these computational models include the appropriate level of detail to accurately predict the neural response to SCS and to correlate model predictions with clinical outcomes. Therefore, the goal of this study was to investigate several anatomic and technical factors that may affect model-based predictions of neural activation during thoracic SCS. APPROACH We developed computational models that consisted of detailed finite element models of the lower thoracic spinal cord, surrounding tissues, and implanted SCS electrode arrays. We positioned multicompartment models of sensory axons within the spinal cord to calculate the activation threshold for each sensory axon. We then investigated how activation thresholds changed as a function of several anatomical variables (e.g. spine geometry, dorsal rootlet anatomy), stimulation type (i.e. voltage-controlled vs. current-controlled), electrode impedance, lead position, lead type, and electrical properties of surrounding tissues (e.g. dura conductivity, frequency-dependent conductivity). MAIN RESULTS Several anatomic and modeling factors produced significant percent differences or errors in activation thresholds. Rostrocaudal positioning of the cathode with respect to the vertebrae had a large effect (up to 32%) on activation thresholds. Variability in electrode impedance produced significant changes in activation thresholds for voltage-controlled stimulation (38% to 51%), but had little effect on activation thresholds for current-controlled stimulation (less than 13%). Changing the dura conductivity also produced significant differences in activation thresholds. SIGNIFICANCE This study demonstrates several anatomic and technical factors that can affect the neural response to SCS. These factors should be considered in clinical implementation and in future computational modeling studies of thoracic SCS.
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Affiliation(s)
- Hans J Zander
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States of America. Biointerfaces Institute, University of Michigan, Ann Arbor, MI, United States of America
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Idlett S, Halder M, Zhang T, Quevedo J, Brill N, Gu W, Moffitt M, Hochman S. Assessment of axonal recruitment using model-guided preclinical spinal cord stimulation in the ex vivo adult mouse spinal cord. J Neurophysiol 2019; 122:1406-1420. [PMID: 31339796 DOI: 10.1152/jn.00538.2018] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Spinal cord stimulation (SCS) is used clinically to limit chronic pain, but fundamental questions remain on the identity of axonal populations recruited. We developed an ex vivo adult mouse spinal cord preparation to assess recruitment following delivery of clinically analogous stimuli determined by downscaling a finite element model of clinical SCS. Analogous electric field distributions were generated with 300-µm × 300-µm electrodes positioned 200 µm above the dorsal column (DC) with stimulation between 50 and 200 µA. We compared axonal recruitment using electrodes of comparable size and stimulus amplitudes when contacting the caudal thoracic DC and at 200 or 600 μm above. Antidromic responses recorded distally from the DC, the adjacent Lissauer tract (LT), and in dorsal roots (DRs) were found to be amplitude and site dependent. Responses in the DC included a unique component not seen in DRs, having the lowest SCS recruitment amplitude and fastest conduction velocity. At 200 μm above, mean cathodic SCS recruitment threshold for axons in DRs and LT were 2.6 and 4.4 times higher, respectively, than DC threshold. SCS recruited primary afferents in all (up to 8) caudal segments sampled. Whereas A and C fibers could be recruited at nearby segments, only A fiber recruitment and synaptically mediated dorsal root reflexes were observed in more distant (lumbar) segments. In sum, clinically analogous SCS led to multisegmental recruitment of several somatosensory-encoding axonal populations. Most striking is the possibility that the lowest threshold recruitment of a nonprimary afferent population in the DC are postsynaptic dorsal column tract cells (PSDCs) projecting to gracile nuclei.NEW & NOTEWORTHY Spinal cord stimulation (SCS) is used clinically to control pain. To identify axonal populations recruited, finite element modeling identified scaling parameters to deliver clinically analogous SCS in an ex vivo adult mouse spinal cord preparation. Results showed that SCS first recruited an axonal population in the dorsal column at a threshold severalfold lower than primary afferents. These putative postsynaptic dorsal column tract cells may represent a previously unconsidered population responsible for SCS-induced paresthesias necessary for analgesia.
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Affiliation(s)
- Shaquia Idlett
- Wallace H Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, Georgia.,Department of Physiology, Emory University School of Medicine, Atlanta, Georgia
| | - Mallika Halder
- Department of Physiology, Emory University School of Medicine, Atlanta, Georgia
| | - Tianhe Zhang
- Boston Scientific Neuromodulation, Valencia, California
| | - Jorge Quevedo
- Departamento de Fisiología, Biofísica y Neurociencias, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Mexico City, Mexico
| | - Natalie Brill
- Boston Scientific Neuromodulation, Valencia, California
| | - Wendy Gu
- Boston Scientific Neuromodulation, Valencia, California
| | | | - Shawn Hochman
- Department of Physiology, Emory University School of Medicine, Atlanta, Georgia
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Kent AR, Min X, Rosenberg SP, Fayram TA. Computational modeling analysis of a spinal cord stimulation paddle lead reveals broad, gapless dermatomal coverage. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2015; 2014:6254-7. [PMID: 25571426 DOI: 10.1109/embc.2014.6945058] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Spinal cord stimulation (SCS) is an effective therapy for treating chronic pain. The St. Jude Medical PENTA(TM) paddle lead features a 4 × 5 contact array for achieving broad, selective coverage of dorsal column (DC) fibers. The objective of this work was to evaluate DC activation regions that correspond to dermatomal coverage with use of the PENTA lead in conjunction with a lateral sweep programming algorithm. We used a two-stage computational model, including a finite element method model of field potentials in the spinal cord during stimulation, coupled to a biophysical cable model of mammalian, myelinated nerve fibers to determine fiber activation within the DC. We found that across contact configurations used clinically in the sweep algorithm, the activation region shifted smoothly between left and right DC, and could achieve gapless medio-lateral coverage in dermatomal fiber tract zones. Increasing stimulation amplitude between the DC threshold and discomfort threshold led to a greater area of activation and number of dermatomal zones covered on the left and/or right DC, including L1-2 zones corresponding to dermatomes of the lower back. This work demonstrates that the flexibility in contact selection offered by the PENTA lead may enable patient-specific tailoring of SCS.
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Min X, Kent AR, Rosenberg SP, Fayram TA. Modeling dermatome selectivity of single-and multiple-current source spinal cord stimulation systems. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2015; 2014:6246-9. [PMID: 25571424 DOI: 10.1109/embc.2014.6945056] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
A recently published computational modeling study of spinal cord stimulation (SCS) predicted that a multiple current source (MCS) system could generate a greater number of central points of stimulation in the dorsal column (DC) than a single current source (1 CS) system. However, the clinical relevance of this finding has not been established. The objective of this work was to compare the dermatomal zone selectivity of MCS and 1 CS systems. A finite element method (FEM) model was built with a representation of the spinal cord anatomy and a 2 × 8 paddle electrode array. Using a contact configuration with two aligned tripoles, the FEM model was used to solve for DC field potentials across incremental changes in current between the two cathodes, modeling the MCS and 1 CS systems. The activation regions within the DC were determined by coupling the FEM output to a biophysical nerve fiber model, and coverage was mapped to dermatomal zones. Results showed marginal differences in activated dermatomal zones between 1 CS and MCS systems. This indicates that a MCS system may not provide incremental therapeutic benefit as suggested in prior analysis.
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Kramer J, Liem L, Russo M, Smet I, Van Buyten JP, Huygen F. Lack of Body Positional Effects on Paresthesias When Stimulating the Dorsal Root Ganglion (DRG) in the Treatment of Chronic Pain. Neuromodulation 2014; 18:50-7; discussion 57. [DOI: 10.1111/ner.12217] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2013] [Revised: 04/04/2014] [Accepted: 05/13/2014] [Indexed: 11/28/2022]
Affiliation(s)
- Jeffery Kramer
- Spinal Modulation, Inc.; Menlo Park CA USA
- University of Illinois College of Medicine; Peoria IL USA
| | - Liong Liem
- Sint Antonius; Nieuwegein The Netherlands
| | - Marc Russo
- Hunter Pain Clinic; Broadmeadow NSW Australia
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