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A Physical Action Potential Generator: Design, Implementation and Evaluation
Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, Faculty of Science & Engineering. (MINT)
Department of Systems and Computer Engineering, Carleton University, Ottawa, Ontario, Canada.
Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, Faculty of Science & Engineering. (MINT)ORCID iD: 0000-0002-0012-7867
2015 (English)In: Frontiers in Neuroscience, ISSN 1662-4548, E-ISSN 1662-453X, Vol. 9, 1-11 p., 371Article in journal (Refereed) Published
Abstract [en]

The objective was to develop a physical action potential generator (Paxon) with the ability to generate a stable, repeatable, programmable, and physiological-like action potential. The Paxon has an equivalent of 40 nodes of Ranvier that were mimicked using resin embedded gold wires (Ø = 20 μm). These nodes were software controlled and the action potentials were initiated by a start trigger. Clinically used Ag-AgCl electrodes were coupled to the Paxon for functional testing. The Paxon’s action potential parameters were tunable using a second order mathematical equation to generate physiologically relevant output, which was accomplished by varying the number of nodes involved (1 to 40 in incremental steps of 1) and the node drive potential (0 to 2.8V in 0.7 mV steps), while keeping a fixed inter-nodal timing and test electrode configuration. A system noise floor of 0.07 ± 0.01 μV was calculated over 50 runs. A differential test electrode recorded a peak positive amplitude of 1.5 ± 0.05 mV (gain of 40x) at time 196.4 ± 0.06 ms, including a post trigger delay. The Paxon’s programmable action potential like signal has the possibility to be used as a validation test platform for medical surface electrodes and their attached systems.

Place, publisher, year, edition, pages
Frontiers Research Foundation , 2015. Vol. 9, 1-11 p., 371
Keyword [en]
Action potential, biomedical electrode, electronic nerve model, nodes of Ranvier, ulnar nerve
National Category
Medical Engineering
Identifiers
URN: urn:nbn:se:liu:diva-121086DOI: 10.3389/fnins.2015.00371OAI: oai:DiVA.org:liu-121086DiVA: diva2:851636
Note

Funding agencies| Linköping University; the Swedish Research Council (Grant No. 621-2013-6078)

At the time for thesis presentation publication was in status: Manuscript

Available from: 2015-09-07 Created: 2015-09-07 Last updated: 2017-06-19Bibliographically approved
In thesis
1. Action Potential Generator and Electrode Testing
Open this publication in new window or tab >>Action Potential Generator and Electrode Testing
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Design, validation and application of a test platform for electrode characterization and comparison is a problem today. Development of target specific electrodes is increasing, for example surface cloth electrodes, non-contact electrodes, and deep brain stimulation electrodes. Whenever these new designs are implemented, there is always a need for testing. How these tests should be performed to verify the function of the electrode in an environment like the one they are designed for is still not solved.

In this thesis, a physical axon, the Paxon, is suggested as a possibility to overcome this issue. The intent of the Paxon was to generate an electric field that is similar to the external field created by a live axonal process when an action potential is propagating along its length, and to do this in a stable, repeatable manner. In order to meet these specifications, the Paxon was designed with a microcontroller to drive the sequence of events and control the output parameters. A chamber with gold wire nodes entering through the bottom was manufactured as a dimensional mimic to a myelinated 20 μm diameter nerve axon segment. The chamber was flooded with normal saline solution mimicking the intervening tissues and to allow ionic coupling of electrodes to the electrical field produced in the chamber.

The initial validation tests demonstrated that the timing is stable (196.4 ± 0.06 ms between trigger to action potential), as is the output “detected” amplitude (1.5 ± 0.05 mV with a gain of 40).

Once the Paxon test platform was verified as functional for its intended application of testing electrodes for comparison, it was then used to compare a set of six electrodes (used as a set of three differential pairs) from a single manufacturer lot and batch number.

With this approach, better assessment of the stability of the  manufactured electrode, as well as longer term stability, can be attained. As more electrodes of similar and differing types are tested, the data can be used for inter-electrode comparisons and eventually verification of newelectrode designed.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. 44 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1725
National Category
Medical Engineering
Identifiers
urn:nbn:se:liu:diva-121088 (URN)978-91-7685-974-2 (ISBN)
Presentation
2015-09-25, IMT 1, Campus US, Linköpings universitet, Linköping, 13:00 (Swedish)
Opponent
Supervisors
Note

The Series name Linköping Studies in Science and Technology Licentiate Thesis in the thesis is incorrect. The correct series name is Linköping Studies in Science and Technology. Thesis.

Available from: 2015-09-07 Created: 2015-09-07 Last updated: 2017-02-13Bibliographically approved
2. The Physical Axon: Modeling, Simulation and Electrode Evaluation
Open this publication in new window or tab >>The Physical Axon: Modeling, Simulation and Electrode Evaluation
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Electrodes are used in medicine for detection of biological signals and for stimulating tissue, e.g. in deep brain stimulation (DBS). For both applications, an understanding of the functioning of the electrode, and its interface and interaction with the target tissue involved is necessary. To date, there is no standardized method for medical electrode evaluation that allows transferability of acquired data. In this thesis, a physical axon (Paxon) potential generator was developed as a device to facilitate standardized comparisons of different electrodes. The Paxon generates repeatable, tuneable and physiological-like action potentials from a peripheral nerve. It consists of a testbed comprising 40 software controlled 20 μm gold wires embedded in resin, each wire mimicking a node of Ranvier. ECG surface Ag-AgCl electrodes were systematically tested with the Paxon. The results showed small variations in orientation (rotation) and position (relative to axon position) which directly impact the acquired signal. Other electrode types including DBS electrodes can also be evaluated with the Paxon.

A theoretical comparison of a single cable neuronal model with an alternative established double cable neuron model was completed. The output with regards to DBS was implemented to comparing the models. These models were configured to investigate electrode stimulation activity, and in turn to assess the activation distance by DBS for changes in axon diameter (1.5-10 μm), pulse shape (rectangular biphasic and rectangular, triangular and sinus monophasic) and drive strength (1-5 V or mA). As both models present similar activation distances, sensitivity to input shape and computational time, the neuron model selection for DBS could be based on model complexity and axon diameter flexibility. An application of the in-house neuron model for multiple DBS lead designs, in a patient-specific simulation study, was completed. Assessments based on the electric field along multiple sample planes of axons support previous findings that a fixed electric field isolevel is sufficient for assessments of tissue activation distances for a predefined axon diameter and pulse width in DBS.

Abstract [sv]

Elektroder används inom sjukvården, både för att mäta biologiska signaler, t.ex. hjärtats aktivitet med EKG, eller för att stimulera vävnad, t.ex. vid djup hjärnstimulering (DBS). För båda användningsområdena är det viktigt med en grundläggande förståelse av elektrodens interaktion med vävnaden. Det finns ingen standardiserad metod för att utvärdera medicinsk elektroders dataöverföringsfunktion. I den här avhandlingen presenteras en metod för att underlätta elektrodtestning. En hårdvarumodell av ett axon (Paxon) har utvecklats. Paxon kan programmeras för att efterlikna repeterbara aktionspotentialer från en perifer nerv. Längs axonet finns 40 noder, vilka var och en består av en tunn (20 μm) guldtråd inbäddad i harts och därefter kopplad till elektronik. Denna testbädd har använts för att undersöka EKG elektroders egenskaper. EKG elektroderna visade på variationer i orientering och position i relation till Paxon. Detta har en direkt inverkan på den registrerade signalen. Även andra elektrotyper kan testas i Paxon, t.ex. DBS elektroder.

En teoretisk jämförelse mellan två neuronmodeller med olika komplexitet, anpassade för användning vid DBS studier, har utförts. Modellerna konfigurerades för att studera inverkan på aktiveringsavstånd från olika axondiametrar, stimulationspuls och stimulationsstyrka. Då båda modellerna visade likvärdiga aktiveringsavstånd och beräkningstid så förordas den enklare neuronmodellen för DBS simuleringar. En enklare modell kan lättare introduceras i klinisk verksamhet. Simuleringarna stöder tidigare resultat som visat att det elektriska fältet är en bra parameter för presentation av resultat vid simulering av DBS. Metoden exemplifieras vid simulering av aktiveringsavstånd och elektriska fältets utbredning för olika typer av DBS elektroder i en patient-specifik studie.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2017. 75 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1847
National Category
Medical Laboratory and Measurements Technologies Other Medical Engineering Biomedical Laboratory Science/Technology Computer Systems
Identifiers
urn:nbn:se:liu:diva-138587 (URN)10.3384/diss.diva-138587 (DOI)9789176855294 (ISBN)
Public defence
2017-08-25, Campus US, Linköpings universitet, Linköping, 09:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 621-2013-6078Swedish Research Council, 2016-03564Linköpings universitetSwedish Foundation for Strategic Research , BD15-0032
Available from: 2017-06-19 Created: 2017-06-19 Last updated: 2017-08-21Bibliographically approved

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