Biomedical subjects

Jan Holsheimer

Publications and source records attributed to Jan Holsheimer.

6 recordsLinked to original sources

PubMed2006

Anodal vs cathodal stimulation of motor cortex: a modeling study.

OBJECTIVE: To explore the effects of electrical stimulation performed by an anode, a cathode or a bipole positioned over the motor cortex for chronic pain management. METHODS: A realistic 3D volume conductor model of the human precentral gyrus (motor cortex) was used to calculate the stimulus-induced electrical field. The subsequent response of neural elements in the precentral gyrus and in the anterior wall and lip of the central sulcus was simulated using compartmental neuron models including the axon, soma and dendritic trunk. RESULTS: While neural elements perpendicular to the electrode surface are preferentially excited by anodal stimulation, cathodal stimulation excites those with a direction component parallel to its surface. When stimulating bipolarly, the excitation of neural elements parallel to the bipole axis is additionally facilitated. The polarity of the contact over the precentral gyrus determines the predominant response. Inclusion of the soma-dendritic model generally reduces the excitation threshold as compared to simple axon model. CONCLUSIONS: Electrode polarity and electrode position over the precentral gyrus and central sulcus have a large and distinct influence on the response of cortical neural elements to stimuli. SIGNIFICANCE: Modeling studies like this can help to identify the effects of electrical stimulation on cortical neural tissue, elucidate mechanisms of action and ultimately to optimize the therapy.

Axons↗

PubMed2006

A reproducibility study of corpus cavernosum electromyography in young healthy volunteers under controlled conditions.

INTRODUCTION: Although the corpus cavernosum electromyography (CC-EMG) has been studied already for 16 years, doubts regarding its reproducibility have remained. AIM: To assess the reproducibility of CC-EMG under controlled conditions and the influence of confounding factors. METHODS: Three CC-EMG recording sessions were performed in 13 healthy young men under the same conditions. Furthermore, the effects of potentially confounding factors, such as intake of caffeine, alcohol and smoking, and sexual activity, were investigated in the same population. Using auto- and cross-correlation techniques, CC-potentials were characterized with parameters amplitude (A), duration (D), dominant frequency (DF), maximum cross-correlation coefficient of longitudinal and bilateral CC-potential pairs (Rmax-lon. and Rmax-bi.), and propagation velocity (PV ). MAIN OUTCOME MEASURES: Comparison of CC-EMG parameters A, D, DF, Rmax-lon., and Rmax-bi. between three recording sessions and assessment of the impact of confounding factors on these parameters. RESULTS: DF, D, A, and Rmax-lon. showed significant correlations among three sessions; PV showed significant correlations between two sessions performed within the same day but not between those performed on different days; Rmax-bi. did not show significant correlations between any two sessions. Intake of caffeine, alcohol, and smoking did not affect CC-potentials, while the recordings shortly after ejaculation showed more irregular oscillations and less CC-potentials with smaller A. CONCLUSIONS: CC-potential parameters DF, D, A, and Rmax-lon. have been demonstrated to be reproducible. The results provide a basis for the clinical and scientific application of CC-EMG. CC-potentials are not sensitive to confounding factors such as intake of caffeine, alcohol, and smoking, while measurements shortly after ejaculation should be avoided.

Adult↗

PubMed2005

Three-dimensional topography of the motor endplates of the rat gastrocnemius muscle.

Spatial distribution of motor endplates affects the shape of the electrical activity recorded from muscle. In order to provide information for realistic models of action potential propagation within muscles, we assembled three-dimensional maps of the motor endplates of the rat medial gastrocnemius (MGM) and lateral gastrocnemius (MGL) muscles. The maps were assembled from histological cross sections stained for acetylcholinesterase activity. Within MGL, the motor endplates formed three columns along its longitudinal axis. Within MGM, the motor endplates were arranged in a leaf-like body that shifted obliquely from proximal to distal. As inferred from the proximo-distal distribution of the cross-sectional projection area, the majority of the motor endplates were concentrated in the middle of MGL and in the distal third of MGM. Regions of maximal motor endplate concentration are considered most suitable for injections of neuroactive substances, such as neuronal tracers. The assembled maps of the gastrocnemius muscles can be used as guides for such injections within the motor endplate zones.

Acetylcholine↗

PubMed2002

An implantable two channel drop foot stimulator: initial clinical results.

This article reports preliminary results of pilot studies of a new implantable two channel drop foot stimulator. The stimulator consists of an externally worn transmitter inductively coupled to an implanted receiver unit located in the lower leg, lateral and distal to the knee. The receiver is connected to electrodes located under the epineurium of the deep and the superficial peroneal nerves. Stimulation is triggered by detection of heel lift and terminated at heel strike in a manner similar to surface mounted systems. The location of the electrodes allows for a degree of selectivity over the resultant moment about the ankle joint that is not possible with surface stimulation of the common peroneal nerve. The two subjects used the stimulator on a regular basis and showed increases in walking speed of between 10% and 44% when compared to their baseline measurements. Isometric tests have demonstrated that the stimulator allows selective and repeatable stimulation of ankle joint muscles.

Electric Stimulation Therapy↗

PubMed2002

New trends in neuromodulation for the management of neuropathic pain.

Since its first application in 1967, the methodology and technology of spinal cord stimulation for the management of chronic, intractable pain have evolved continuously. Despite these developments and improved knowledge of the effects of spinal anatomy and epidural contact configuration on paresthesia coverage, the clinical results of spinal cord stimulation-particularly the long-term effects-are still unsatisfactory in many patients. This dissatisfaction has come primarily from the failure of single-electrode configurations to provide consistent paresthesia coverage of the entire painful area. Therefore, new approaches were developed during the late 1990s that attempted to selectively cover one or more dermatomes with paresthesia as well as to provide sequential stimulation of different anatomic sites. These approaches have been applied both intraspinally and extraspinally by stimulating either the spinal nerves or the dorsal columns. To target parts of the latter, different methods have been developed and tested using either two-dimensional contact configurations or electronic field steering. These developments hold promise for improving long-term outcomes as well as increasing the number of pain conditions that can be treated with neuromodulation therapy. In this review, the history, theoretical basis, and evolution of these methodologies, as well as the ways in which they represent new trends in neuromodulation, are discussed.

Electric Stimulation Therapy↗

PubMed1994

Perception threshold and electrode position for spinal cord stimulation.

The perception threshold for epidural spinal cord stimulation in chronic pain management was analyzed on 3,923 testing data obtained from 136 implanted patients. The initial areas of paresthesiae due to stimulation were recorded and reported as the stimulation map according to the location of electrodes. Measurement of dorsal thickness of the cerebrospinal fluid (CSF) layer was obtained from 26 subjects using magnetic resonance imaging (MRI). The results indicate that the perception threshold is a function of the spinal level of the implanted electrodes, of the mediolateral position in the spinal canal and the contact separation of electrode. Differences in perception threshold at various vertebral levels are mainly due to varying depths of the dorsal CSF layer. The medially placed electrodes caudal to the mid-cervical levels have a higher perception threshold than more laterally placed ones. The electrodes at high and mid-cervical levels, however, have a smaller perception threshold if placed medially. The information obtained from this investigation has important implications for the design of a new-generation stimulation system and clinical application to maximize the longevity of the power source.

Adult↗