A model for transcutaneous current stimulation: simulations and experiments

Complex nerve models have been developed for describing the generation of action potentials in humans. Such nerve models have primarily been used to model implantable electrical stimulation systems, where the stimulation electrodes are close to the nerve (near-field). To address if these nerve models can also be used to model transcutaneous electrical stimulation (TES) (far-field), we have developed a TES model that comprises a volume conductor and different previously published non-linear nerve models. The volume conductor models the resistive and capacitive properties of electrodes, electrode-skin interface, skin, fat, muscle, and bone. The non-linear nerve models were used to conclude from the potential field within the volume conductor on nerve activation. A comparison of simulated and experimentally measured chronaxie values (a measure for the excitability of nerves) and muscle twitch forces on human volunteers allowed us to conclude that some of the published nerve models can be used in TES models. The presented TES model provides a first step to more extensive model implementations for TES in which e.g., multi-array electrode configurations can be teste

Non-rectangular neurostimulation waveforms elicit varied sensation quality and perceptive fields on the hand

Electrical stimulation of the nerves is known to elicit distinct sensations perceived in distal parts of the body. The stimulation is typically modulated in current with charge-balanced rectangular shapes that, although easily generated by stimulators available on the market, are not able to cover the entire range of somatosensory experiences from daily life. In this regard, we have investigated the effect of electrical neurostimulation with four non-rectangular waveforms in an experiment involving 11 healthy able-bodied subjects. Weiss curves were estimated and rheobase and chronaxie values were obtained showing increases in stimulation time required to elicit sensations for some waveforms. The localization of the sensations reported in the hand also appeared to differ between waveforms, although the total area did not vary significantly. Finally, the possibility of distinguishing different charge- and amplitude-matched stimuli was demonstrated through a two-alternative-forced-choice (2AFC) match-to-sample task, showing the ability of participants to successfully distinguish between waveforms with similar electrical characteristics but different shapes and charge transfer rates. This study provides evidence that, by using different waveforms to stimulate nerves, it is possible to affect not only the required charge to elicit sensations but also the sensation\ua0quality and its localization

Ultrasound-Guided Percutaneous Neuromodulation in Patients with Chronic Lateral Epicondylalgia : A Pilot Randomized Clinical Trial

Objective: The aim was to analyze effects of a percutaneous neuromodulation (PNM) treatment on the radial nerve, regarding pain, functionality, electrophysiologic excitability, and morphology, in patients with chronic lateral epicondylalgia (LE). Methods: Twenty-four patients with chronic unilateral elbow pain were recruited for this preliminary study and were divided into two groups: control (n = 12) and PNM group (n = 12). The subjects in the PNM group received percutaneous peripheral neurostimulation with an acupuncture needle that was located next to the nerve with ultrasound guidance. Pain using a numerical rating scale (NRS), functional ability using patient-rated tennis elbow evaluation (PRTEE), radial nerve cross-sectional area measured by ultrasound, and chronaxie and accommodation index (AI) measured by the strength-duration curve were evaluated. Results: Both groups showed no differences in the baseline measurements (all p = 0.001). However, at the end of the treatment, there were significant differences between groups since only the PNM group significantly improved their values compared to their baseline values: level of pain and cross-sectional area (CSA) values showed a significant decrease while the PRTEE scores showed a significant improvement. Then, regarding AI, the PNM group showed significant improvement for the electrophysiologic nerve excitability pattern, reporting normal function in all radial nerves after treatment (p = 0.001). However, chronaxie values always reported similar values with no differences between groups (p >0.05); Conclusion: Ultrasound-PNM technique may be an interesting therapeutic tool for the treatment of chronic LE due to the improvement in the level of pain, functionality, nerve morphology, and excitability in this population

The electrical diagnosis of peripheral nerve injury, and some applications of electronics to physiology and clinical medicine

In the summer of 1941 the Scottish E. M. S. Hospitals organization established a special Unit for the reception and treatment of patients suffering from peripheral nerve injury at Gogarburn Hospital on the outskirts of Edinburgh. In connection with this specialized type of injury, relatively rare in peacetime but assuming considerable importance in War, invitations were issued to various Persons sroecializing in ancillary branches of Medicine and Surgery to attend the clinical meetings of the Peripheral Nerve Unit, to consider applications of their work to this particular problem, and to have access to the patient for the assessment of their methods.Peripheral nerve injury diagnosis and treatment involves a considerable field of application for methods which have been primarily developed as physiological techniques, particularly in the use of modern electrical apparatus, and the Director of the Unit, Professor J. R. Learmonth, invited me to attend the clinical meetings, and to make a study on the patients of modern methods of electrical diagnosis, and this opportunity, gladly accepted, has furnished me with a wealth of problems and of material ever since.This thesis accordingly presents such of these problems as have at present been worked out to the extent of being of clinical or laboratory use

Patient-specific computational modeling for spinal cord stimulation therapy optimization

[EN] Chronic pain disease has 35-50% of prevalence worldwide. When drugs stop working, spinal cord stimulation (SCS) therapy is a non-drug alternative treatment for several conditions of chronic pain, such as neuropathic pain. In the last 40 years, SCS computational modeling has been the key tool to analyze and understand the effect of the stimulation parameters on neural response. However, the lack of realistic models limits the model-based predictions accuracy for SCS therapy optimization concerning the stimulation parameters management and the development of clinical applications. This thesis presents three improvements in SCS modeling from cellular to organic levels: · Cellular level: a human A -beta sensory myelinated nerve fiber model is shown. The model simulates the action potential creation and propagation of human sensory fibers produced by electrical stimulation. Moreover, to consider the current losses produced at the internodal compartments, a realistic myelin model is included. · Organic level: two spinal cord volume conductor models are presented. The first one is a generalized SCS model, which is based on in vivo 3T high-resolution magnetic resonance images from the human spinal cord, solving then one of the main limitations of previous SCS models, which is the inclusion of cadaveric measurements. The second one is a 3D patient-specific SCS model, which includes the entire spinal cord geometry variation of three different vertebral levels (T8, T9, and T10) from patients undergoing SCS treatment. This novel approach is validated clinically, showing that patient-specific modeling improves model-based predictions accuracy compared to generalized SCS models. In addition to this, this thesis presents three studies related to SCS therapy by using the three computational models developed previously: - Role of stimulation frequency: it is performed using the human A-beta sensory myelinated nerve fiber model. The outcome of this study showed that frequency could have a significant influence on the reduction or increase of the neuron activity, participating thus in the selection of the targeted neural elements in SCS therapy, in tonic stimulation. - Effect of electrode polarity: using the 3D generalized SCS model, the effect of the most used and known polarities (bipolar, guarded cathode, and dual-guarded cathode) is shown. The results showed that, unlike guarded cathode, dual-guarded cathode maximized the activating area and depth in dorsal columns, also increasing the probability of activating dorsal roots fibers. - Clinical applications: the pre-implantation selection of the electrode polarity was performed with the 3D patient-specific model. The findings showed that this clinical application could determine the electrode configurations that best overlapped paresthesia coverage to the painful dermatomes of the patient before the SCS device implant. On the other hand, the effect of offset electrodes was also investigated. In this case, the results revealed that staggered offset placement canceled the left- or right-activation displacement in the dorsal columns, suggesting that offset electrodes placement should be avoided in tonic stimulation.[ES] El dolor crónico es una enfermedad que tiene una prevalencia de entre el 35% y el 50% de la población mundial. Cuando los fármacos dejan de hacer efecto, la terapia de estimulación de médula espinal (EME) es una alternativa no farmacológica que se usa para el tratamiento de diversas condiciones de dolor crónico, como el dolor neuropático. En los últimos 40 años, el modelado computacional de la EME ha sido la herramienta clave para analizar y entender el efecto de los parámetros de estimulación eléctrica en la respuesta neuronal. Sin embargo, la falta de modelos realistas limita la precisión de las predicciones de los modelos para la optimización de la terapia de EME, en referencia a la programación de los parámetros de estimulación y el desarrollo de aplicaciones clínicas. Esta tesis presenta tres mejoras en el modelado computacional de la terapia de EME, desde el nivel celular hasta el nivel orgánico: · Nivel celular: se presenta un modelo de fibra mielínica A-beta sensitiva humana. El modelo simula la creación y propagación del potencial de acción de fibras humanas sensitivas que se produce bajo el efecto de un estímulo eléctrico. Además, con el fin de considerar las pérdidas de corriente producidas en los compartimentos internodales, la mielina se modeliza de forma realista. · Nivel orgánico: se presentan dos modelos de conductor volumétrico de médula espinal. El primero se trata de un modelo de EME generalizado, el cual está basado en imágenes de resonancia magnética de 3T de alta resolución de médula espinal humana obtenidas in vivo. Esta propuesta resuelve una de las principales limitaciones presente en modelos de EME anteriores, que es la inclusión de medidas geométricas obtenidas de cadáveres. El segundo modelo es un modelo tridimensional personalizado al paciente, el cual incluye la variación de la geometría de la médula espinal en tres niveles vertebrales diferentes (T8, T9 y T10) a partir de pacientes sometidos al tratamiento de EME. Esta novedosa propuesta es validada clínicamente, mostrando además que el modelado computacional personalizado mejora la precisión de las predicciones del modelo en comparación a un modelo generalizado. Además, esta tesis presenta tres estudios relacionados con la terapia de EME usando los tres modelos desarrollados previamente: - El papel de la frecuencia de estimulación: se realiza mediante el uso del modelo de fibra mielínica A -beta sensitiva humana. Los resultados de este estudio muestran que la frecuencia podría tener una influencia significante en la reducción o aumento de la actividad de la neurona, participando de este modo en la selección de los elementos neurales objetivo en la terapia de EME, en estimulación tónica. - Efecto de la polaridad del electrodo: usando el modelo 3D generalizado de EME, se muestra el efecto de las polaridades más conocidas y usadas: bipolar, cátodo guardado y doble-cátodo guardado. Los resultados muestran que, a diferencia del cátodo guardado, la polaridad de doble-cátodo guardado maximiza el área y profundidad de activación en los cordones posteriores, aumentando también la probabilidad de activar las fibras de las raíces dorsales. - Aplicaciones clínicas: usando el modelo 3D personalizado al paciente, se ha realizado la selección pre-implante de la polaridad del electrodo. Los resultados muestran que esta aplicación clínica podría determinar las configuraciones de electrodos que mejor solapan la cobertura de parestesia con los dermatomas dolorosos del paciente antes del implante del dispositivo de EME. Por otro lado, también se ha estudiado el efecto de la posición escalonada de los electrodos en el paciente. En este caso, los resultados revelan que el posicionamiento escalonado cancela el desplazamiento izquierdo o derecho de la activación neuronal en los cordones posteriores, sugiriendo así que el posicionamiento escalonado debería evitarse cuando se aplica la estimu[CAT] El dolor crònic es una enfermetat amb una prevalència d'entre el 35% i el 50% de la població mundial. Quan els fàrmacs deixen de fer efecte, la teràpia d'estimulació de mèdul·la espinal (EME) és una alternativa no farmacològica que s'usa per al tractament de diverses condicions de dolor crònic, com el dolor neuropàtic. En els últims 40 anys, el modelatge computacional de l'EME ha sigut la ferramenta clau per a analitzar i entendre l'efecte dels paràmetres d'estimulació elèctrica en la resposta neuronal. No obstant això, la falta de models realistes limita la precisió de les prediccions dels models per a l'optimizació de la teràpia d'EME, en referència a la programació dels paràmetres d'estimulació i el desenvolupament d'aplicacions clíniques. Esta tesi presenta tres millores en el modelatge computacional de la teràpia d'EME, des del nivell cel·lular fins al nivell orgànic: · Nivell cel·lular: es presenta un model de fibra mielínica A-beta sensitiva humana. El model simula la creació i propagació del potencial d'acció de fibres humanes sensitives que es produeix baix l'efecte d'un estímul elèctric. A més a més, amb la finalitat de considerar les pèrdues de corrent produïdes als compartiments internodals, la mielina es modela de forma realista. · Nivell orgànic: es presenten dos models de conductor volumètric de mèdul·la espinal. El primer es tracta d'un model d'EME generalitzat, el qual es basa en imatges de ressonància magnètica de 3T d'alta resolució de mèdul·la espinal humana obtingudes in vivo. Esta proposta resol una de les principals limitacions present en models d'EME anteriors, que és la inclusió de mesures geomètriques obtingudes de cadàvers. El segon model és un model tridimensional personalitzat al pacient, el qual inclou la variació de la geometria de la mèdul·la espinal en tres nivells vertebrals diferentes (T8, T9 i T10) a partir de pacients sotmesos al tractament d'EME. Aquesta innovadora proposta és validada clínicament, demostrant també que el modelatge computacional personalitzat millora la precisió de les prediccions del model en comparació a un model generalitzat. A més, esta tesi presenta tres estudis relacionats amb la teràpia d'EME utilitzant els tres models desenvolupats prèviament: - El paper de la freqüència d'estimulació: es realitza mitjançant l'ús del model de fibra mielínica A-beta sensitiva humana. Els resultats d'este estudi mostren que la freqüència podria tindre una influència significant en la reducció o augment de l'activitat de la neurona, participant així en la selecció dels elements neurals objectiu en la teràpia d'EME, en estimulació tònica. - Efecte de la polaritat de l'elèctrode: usant el model 3D generalitzat d'EME, es mostra l'efecte de les polaritats més conegudes i utilitzades: bipolar, càtode guardat i doble-càtode guardat. Els resultats mostren que, a diferència del càtode guardat, la polaritat de doble-càtode guardat maximitza l'àrea i profunditat d'activació en els cordons posteriors, augmentant també la probabilitat d'activar les fibres de les arrels dorsals. - Aplicacions clíniques: usant el model 3D personalitzat al pacient, s'ha realitzat la selecció pre-implant de la polaritat de l'elèctrode. Els resultats mostren que esta aplicació clínica podria determinar les configuracions d'elèctrodes que millor solapen la cobertura de parestèsia amb els dermatomes dolorosos del pacient abans de l'implant del dispositiu d'EME. D'altra banda, també s'ha estudiat l'efecte de la posició esglaonada dels elèctrodes en el pacient. En este cas, els resultats revelen que el posicionament esglaonat cancel·la el desplaçament esquerre o dret de l'activació neuronal en els cordons posteriors, sugerint així que el posicionament esglaonat deuria evitar-se quan s'aplica l'estimulació tònica.Solanes Galbis, C. (2021). Patient-specific computational modeling for spinal cord stimulation therapy optimization [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/176007TESI

Optimisation of a neuromuscular electrical stimulation paradigm for targeted strengthening of an intrinsic foot muscle

The intrinsic foot muscles stabilise and stiffen the foot during posture and locomotion. Since they are placed under continued load, these muscles merit training to meet the weight-bearing demands of everyday activities. Their strengthening is however a largely neglected area and furthermore, the occurrence of common foot-related pathologies is associated with their dysfunction. Indeed, atrophy and dysfunction of the strongest intrinsic foot muscle, abductor hallucis (AbH), is symptomatic to pes planus and Hallux Valgus. AbH’s oblique mechanical action along with an inability for its voluntary activation in many individuals limits the strengthening capacity of existing training modalities. Due to the superficial location of AbH, neuromuscular electrical stimulation (NMES) offers a solution to this problem; however, its efficacy for muscle strength gains relies on high stimulation-intensity protocols, which are uncomfortable and limit participant adherence. Therefore, the purpose of this thesis was to develop an optimised NMES paradigm that is tolerable and efficacious for a targeted strengthening intervention of AbH. The studies reported in this thesis were undertaken with the overarching aim to systematically establish a tolerable and low stimulation-intensity NMES paradigm to train AbH. With this motivation in mind, four sequential experimental studies were designed to identify the optimal mode of NMES application (muscle vs nerve) and stimulation pulse duration (Chapter 3), pulse frequency and train duration (Chapter 4), training stimulus intensity (Chapter 5), and duty-cycle (Chapter 6), respectively. A major finding from the work undertaken in this thesis was the prevalent inability to voluntary activate AbH that exists in healthy participants. Since this inability also limits the measurement of voluntary force generation following an intervention, this thesis also developed a methodological approach that overcomes this limitation. Collectively, the studies in this thesis demonstrated that NMES successfully evokes contractions from AbH irrespective of ability for its voluntary activation and can therefore be used as a training modality. The optimised NMES paradigm presented in this thesis targets the motor point of AbH using 22s-trains of 1ms pulses at 20-100-20Hz with an intensity of 200% motor threshold and a 1:4 duty-cycle. This wide-pulse, high-frequency, low-intensity paradigm promotes adherence and has the potential to depolarise sensory axons due to their lower rheobase, and evoke contractions with a contribution of the central nervous system. When delivered using long trains and an alternating frequency pattern, it can take advantage of post-tetanic potentiation to produce force, which is then preserved across trains using a duty-cycle with long rest periods. This thesis intended to bind the aforementioned experimental chapters together with a final chapter investigating the effectiveness of the developed NMES paradigm instrengthening AbH following long-term exposure. However, the implementation of this study was not possible in light of the COVID-19 pandemic and is therefore not reportedin this thesis. Nevertheless, future work in this area can benefit from the extensive methodological work undertaken in this thesis and implement a longitudinal study to better understand the clinical implications for targeted AbH strengthening via NMES

Strength–duration relationship for intra- versus 3 extracellular stimulation with microelectrodes

Abstract—Chronaxie, a historically introduced excitability time parameter for electrical stimulation, has been assumed to be closely related to the time constant of the cell membrane. Therefore, it is perplexing that significantly larger chronaxies have been found for intracellular than for extracellular stimulation. Using compartmental model analysis, this controversy is explained on the basis that extracellular stimulation also generates hyperpolarized regions of the cell membrane hindering a steady excitation as seen in the intracellular case. The largest inside/outside chronaxie ratio for microelectrode stimulation is found in close vicinity of the cell. In the case of monophasic cathodic stimulation, the length of the primarily excited zone which is situated between the hyperpolarized regions increases with electrode–cell distance. For distant electrodes this results in an excitation process comparable to the temporal behavior of intracellular stimulation. Chronaxie also varies along the neural axis, being small for electrode positions at the nodes of Ranvier and axon initial segment and larger at the soma and dendrites. As spike initiation site can change for short and long pulses, in some cases strength–duration curves have a bimodal shape, and thus, they deviate from a classical monotonic curve as described by the formulas of Lapicque or Weis

Magneettistimulaatio liikkuvilla kestomagneeteilla

Transcranial magnetic stimulation (TMS) is a noninvasive method used to stimulate small regions of the brain. It has clinical applications for both therapeutic and diagnostic purposes. Traditionally TMS is conducted with an electromagnetic coil. The changing electric current gives rise to a changing magnetic field, which induces an electric field in the brain. In this study, we employ moving permanent magnets to induce an electric field. Using permanent magnets for TMS could potentially remove two disadvantages of the electromagnet-based systems: acoustic noise, and heating of the coil. The electric field from moving magnets was calculated using the spherical head model. The calculations were verified experimentally by measuring the induced electric field with a triangular detector loop. In those experiments, the magnets were dropped past the detector loop. A prototype was built with 32 magnets (20 × 20 × 20 mm, grade N52), that were rotated on a circular track at the radius of 40 cm. The rotation rate was 507 revolutions per minute. The magnets were placed on a disk in such a pattern that the rate of change of the magnetic field would be maximal at the center point. The closest point of measurement was at 16.3 mm distance from the magnets’ surface, and the peak of the induced electric field was 2.17 ± 0.10 V/m. At 20.0 mm distance, the peak of the induced electric field was 1.72 ± 0.08 V/m. These fields are not yet strong enough to trigger action potentials in the nerve cells, but they may have some applications nevertheless. For future research, we propose some improvements with which the field strength could be increased.Transkraniaalinen magneettistimulaatio (TMS) on ei-invasiivinen menetelmä, jolla voidaan stimuloida pieniä aivoalueita. Sitä voidaan käyttää kliinisesti sekä diagnosointiin että terapiaan. Perinteisesti TMS:ään käytetään sähkömagneettista kelaa. Muuttuva sähkövirta synnyttää muuttuvan magneettikentän, joka indusoi aivoihin sähkökentän. Tässä tutkimuksessa käytämme liikkuvia kestomagneetteja indusoimaan sähkökentän. Kestomagneeteilla tehtävällä aivostimulaatiolla voitaisiin mahdollisesti päästä eroon kahdesta sähkömagneetteihin perustuvan TMS:n ongelmasta: häiritsevästä äänestä ja kelan kuumenemisesta. Liikkuvien magneettien tuottama sähkökenttä laskettiin käyttäen pallomallia. Laskennan tulokset tarkistettiin kokeellisesti, mittaamalla indusoitunut sähkökenttä kolmion muotoisella virtasilmukalla. Näissä kokeissa magneetti pudotettiin virtasilmukan ohitse. Tutkimuksen seuraavassa vaiheessa rakennettiin prototyyppi, jossa käytettiin 32 magneettia (20 × 20 × 20 mm, luokka N52), joita pyöritettiin ympyräradalla 40 cm:n säteellä. Kierrosnopeus oli 507 kierrosta minuutissa. Magneetit aseteltiin levylle siten, että magneettikentän muutosnopeus olisi mahdollisimman suuri levyn keskipisteessä. Lähin mittauspiste oli 16.3 mm etäisyydellä magneettien pinnasta, ja indusoituneen sähkökentän huippuarvo oli 2.17 ± 0.10 V/m. Mentäessä 20.0 mm etäisyydelle, huipun suuruus oli 1.72 ± 0.08 V/m. Nämä kentät eivät ole vielä tarpeeksi suuria aiheuttaakseen aktiopotentiaaleja hermosoluissa. Niillä saattaa siitä huolimatta olla joitakin sovelluksia. Myöhempää tutkimusta varten ehdotamme parannuksia, joilla kentän suuruutta voitaisiin kasvattaa