Publications by authors named "David Dinsmoor"

5 Publications

  • Page 1 of 1

The Evoked Compound Action Potential as a Predictor for Perception in Chronic Pain Patients: Tools for Automatic Spinal Cord Stimulator Programming and Control.

Front Neurosci 2021 12;15:673998. Epub 2021 Jul 12.

Medtronic PLC, Minneapolis, MN, United States.

Objectives: Spinal cord stimulation (SCS) is a drug free treatment for chronic pain. Recent technological advances have enabled sensing of the evoked compound action potential (ECAP), a biopotential that represents neural activity elicited from SCS. The amplitudes of many SCS paradigms - both sub- and supra-threshold - are programmed relative to the patient's perception of SCS. The objective of this study, then, is to elucidate relationships between the ECAP and perception thresholds across posture and SCS pulse width. These relationships may be used for the automatic control and perceptually referenced programming of SCS systems.

Methods: ECAPs were acquired from 14 subjects across a range of postures and pulse widths with swept amplitude stimulation. Perception (PT) and discomfort (DT) thresholds were recorded. A stimulation artifact reduction scheme was employed, and growth curves were constructed from the sweeps. An estimate of the ECAP threshold (ET), was calculated from the growth curves using a novel approach. Relationships between ET, PT, and DT were assessed.

Results: ETs were estimated from 112 separate growth curves. For the postures and pulse widths assessed, the ET tightly correlated with both PT ( = 0.93; < 0.0001) and DT ( = 0.93; < 0.0001). The median accuracy of ET as a predictor for PT across both posture and pulse width was 0.5 dB. Intra-subject, ECAP amplitudes at DT varied up to threefold across posture.

Conclusion: We provide evidence that the ET varies across both different positions and varying pulse widths and suggest that this variance may be the result of postural dependence of the recording electrode-tissue spacing. ET-informed SCS holds promise as a tool for SCS parameter configuration and may offer more accuracy over alternative approaches for neural and perceptual control in closed loop SCS systems.
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http://dx.doi.org/10.3389/fnins.2021.673998DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8320888PMC
July 2021

A Clinical Feasibility Study of Spinal Evoked Compound Action Potential Estimation Methods.

Neuromodulation 2021 Jul 22. Epub 2021 Jul 22.

Medtronic plc, Minneapolis, MN, USA.

Objectives: Spinal cord stimulation (SCS) is a treatment for chronic neuropathic pain. Recently, SCS has been enhanced further with evoked compound action potential (ECAP) sensing. Characteristics of the ECAP, if appropriately isolated from concurrent stimulation artifact (SA), may be used to control, and aid in the programming of, SCS systems. Here, we characterize the sensitivity of the ECAP growth curve slope (S) to both neural response (|S |) and SA contamination (|S |) for four spinal ECAP estimation methods with a novel performance measure (|S /S |).

Materials And Methods: We collected a library of 112 ECAP and associated artifact recordings with swept stimulation amplitudes from 14 human subjects. We processed the signals to reduce SA from these recordings by applying one of three schemes: a simple high pass (HP) filter, subtracting an artifact model (AM) consisting of decaying exponential and linear components, or applying a template correlation method consisting of a triangularly weighted sinusoid. We compared these against each other and to P2-N1, a standard method of measuring ECAP amplitude. We then fit the ECAP estimates from each method with a function representing the growth curve; we then calculated the S and S parameters following the fit.

Results: Any SA reduction scheme selected may result in under- or overestimation of neural activation, or misclassification of SA as ECAP. In these experiments, the ratio of neural signal preservation to SA misclassification (|S /S |) on the ECAP estimate was superior (p < 0.05) with the HP and AM schemes relative to the others.

Conclusions: This work represents the first comprehensive assessment of spinal ECAP estimation schemes. Understanding the clinically relevant sensitivities of these schemes is increasingly important, particularly with closed-loop SCS systems using ECAP as a feedback control variable where misclassification of artifact as neural signal may lead to suboptimal therapy adjustments.
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http://dx.doi.org/10.1111/ner.13510DOI Listing
July 2021

Sensing Evoked Compound Action Potentials from the Spinal Cord: Novel Preclinical and Clinical Considerations for the Pain Management Researcher and Clinician.

J Pain Res 2020 4;13:3269-3279. Epub 2020 Dec 4.

Neuromodulation, Medtronic Plc, Minneapolis, MN, USA.

Purpose: Spinal cord stimulation (SCS) is a drug-free treatment for chronic neuropathic pain. Recent SCS technology can record evoked compound action potentials (ECAPs) in the spinal cord during therapy and utilize features of the sensed ECAP to optimize the SCS. The purpose of this work is to characterize the relevant parameters that govern the integrity and morphology of acquired ECAPs, and the implications for pain management clinicians and researchers working with ECAPs.

Materials And Methods: Eight-contact percutaneous SCS leads were implanted into sheep, and a prototype ECAP-sensing system was used to record spinal cord activity across a range of electrode configurations, pulse widths, and stimulus amplitudes. Similar iterative testing was then completed in human subjects who were undergoing trials of commercial SCS systems.

Results: Longer pulse width stimulation results in a progressive increase in ECAP latency, a neurophysiologic effect that enables ECAP sensing with longer pulses despite more encroachment by stimulation artifact. ECAPs may manifest a polyphasic morphology-an effect not seen in all subjects studied-with longer pulse width stimulation; these later phases may be used to assess ECAP amplitude when earlier features are effaced by artifact. Triphasic stimulation limits artifact from spinal cord ECAPs at the expense of potentially higher activation thresholds. If applied, alternating polarity stimulation must account for the ECAP latency differences resulting from alternating sites of neural activation.

Conclusion: Together, this information can allow the ECAP to be readily distinguished from the stimulation artifact, although movement may continue to be a confounder; caution is inculcated for ECAP signal processing techniques that rely on the stability of the artifact to avoid clinically misleading results. The promise of closed-loop, ECAP-servoed neuromodulation relies on accurate and proper sensing of the ECAP, while clearly elucidating the clinically relevant trade-offs and design choices made to enable these novel features.
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http://dx.doi.org/10.2147/JPR.S289098DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7733896PMC
December 2020

Comparison of Active Stimulating Electrodes of Sacral Neuromodulation.

Neuromodulation 2017 Dec 24;20(8):799-806. Epub 2017 Oct 24.

Medtronic, Inc., Restorative Therapies Group, Research & Core Technology, Minneapolis, MN, USA.

Objective: The goal of this study was to compare the motor response to sacral neuromodulation (SNM) with different pairs of stimulating electrodes in anesthetized and awake sheep.

Materials And Methods: Similar to SNM clinical use in humans, the InterStim quadripolar tined lead was implanted adjacent to the S3 nerve root in sheep and bipolar stimulation was configured with one electrode negative and one electrode positive on the four contacts (0 most distal to device, 1, 2, and 3 most proximal).

Results: Electrode 3-cathode and electrode 0-anode (3-/0+) stimulation had the lowest visual response threshold (0.46 ± 0.14V, anesthetized, 0.56 ± 0.21V, conscious), representing the most sensitive stimulation. Stimulation on electrode 0 (0-/1+) had the highest response threshold among tested electrodes (2.70 ± 0.23V, anesthetized, 3.38 ± 0.96V, conscious). The order according to response threshold from low to high was 3 < 2 < 1 < 0. The triggered response by 3-/0+ stimulation solely occurred in the perineum, tail, or bellows. In contrast, the 0-/1+ stimulation frequently evoked response in gluteal and thigh regions. The electromyographic activities from the anus were sensitive to low intensities of stimulation on electrode 3 (e.g., 3-/0+, 3-/2+).

Conclusions: Objective motor responses to SNM as a functional indicator for optimal lead placement may be used to demonstrate that the contact which is most proximal to the foramen (electrode 3) is an optimal electrode to trigger an "on-target" response to lower intensity stimulation. Data from this preclinical work suggest that there are several principles that may be referenced to simplify and expedite the programming process in clinical practice.
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http://dx.doi.org/10.1111/ner.12710DOI Listing
December 2017

Evaluation of Pulse-Width of Spinal Nerve Stimulation in a Rat Model of Bladder Micturition Reflex.

Neuromodulation 2017 Dec 8;20(8):793-798. Epub 2017 Sep 8.

Restorative Therapies Group, Research & Core Technology, Medtronic, Inc., Minneapolis, MN, USA.

Objectives: The spinal nerve stimulation (SNS) evoked motor threshold (T ) response across different pulse-widths (PWs) was first explored and a subset of selected stimulation PWs were further assessed with respect to bladder reflex contraction (BRC).

Materials And Methods: In anesthetized female rats, wire electrodes were placed under each of the L6 spinal nerves to produce bilateral SNS. The relationship of T response with PW was analyzed using a monoexponential nonlinear regression. A cannula was placed into the bladder via the urethra to ensure an isovolumetric bladder. Saline infusion induced BRC.

Results: The chronaxie of the T -PW curve was 0.04 ms. The stimulation charges/energies (current × PW) associated with shorter PWs of 0.02, 0.03, and 0.06 ms were significantly lower than those with longer PW (e.g., >0.15 ms). SNS (T , 10 Hz) at selected PWs from 0.03 to 0.21 ms inhibited the frequency of BRCs. There were no significantly different attenuations among tested PWs. SNS of PWs of 0.03, 0.06, and 0.09 ms decreased bladder contraction frequency from 103 ± 3%, 100 ± 4%, and 103 ± 4% of controls, to 52 ± 16% (n = 8, p = 0.02, paired t-test), 56 ± 15% (n = 11, p = 0.02) and 40 ± 19% (n = 10, p = 0.01), respectively.

Conclusions: Effective PWs to produce bladder inhibitory effects in the rat appear much shorter than 0.21 ms typically used with sacral neuromodulation in practice. Potential battery savings manifested by shorter PW while maintaining equivalent efficacy would provide more efficient therapy delivery and increased longevity of the stimulator.
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http://dx.doi.org/10.1111/ner.12650DOI Listing
December 2017
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