Electrode geometry and preferential stimulation of spinal nerve fibers having different orientations: a modeling study

In a computer modeling study of epidural spinal cord stimulation using a longitudinal array of electrode contacts, the effect of contact geometry and contact combination on the threshold voltages for stimulation of dorsal column (DC) fibers and dorsal root (DR) fibers was investigated. It was concluded that DC-fiber stimulation will be favoured when a tripolar combination and small contact length and spacing are used, while DR-fiber stimulation will be favoured when unipolar stimulation and large contact length are used

Effects of electrode configuration and geometry on fiber preference in spinal cord stimulation

In contrast to the widespread assumption that dorsal column fibers are the primary targets of spinal cord stimulation by a dorsal epidural electrode, it appears that dorsal root fibers are recruited as well, and even preferentially under various conditions. This will, however, limit the coverage of the painful body areas with paresthesia, a prerequisite for the management of chronic pain. In order to favor the preferential stimulation of dorsal column fibers, advantage was taken of the different positions and orientations of fibers in the dorsal columns and dorsal roots. Using an SCS computer model, electrode configurations have been designed for the selective stimulation of the human dorsal column

Recruitment characteristics of nerve fascicles stimulated by a multi-groove electrode

The recruitment characteristics of fascicle-selective nerve stimulation by a multigroove electrode have been investigated both theoretically and in acute experiments. A three-dimensional (3-D) volume conductor model of fascicles in a multigroove device and a model of myelinated nerve fiber stimulation were used to calculate threshold stimuli of nerve fibers in these fascicles. After their exposition, fascicles from rat sciatic nerve were positioned in different grooves of appropriate sizes and stimulated separately. The device appeared to be suitable for fascicle-selective stimulation, because both computer simulations and acute animal experiments showed that crosstalk between neighboring fascicles is not a problem, even when monopolar stimulation was used. The threshold stimulus was lower for a small fascicle than for a large one. When the amount of (conducting) medium between contact and perineurium or its conductivity was reduced, threshold stimuli were lower. Moreover, simulations predict that the slopes of recruitment curves are smaller and inverse recruitment order is less pronounced. Simulations also showed that a small contact is preferable to a large one, because a small contact gives a slightly smaller slope of the recruitment curve. Both experimentally and theoretically a significantly smaller slope of recruitment curves was obtained by stimulation with a cathode and an anode at opposite sides of the fascicle, driven by two current sources giving simultaneous pulses with different, but linearly dependent amplitude

Perception threshold and electrode position for spinal cord stimulation

The perception threshold for epidural spinal cord stimulation in chronic pain management was analyzed on 3923 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

Simulation of activation and propagation delay during tripolar neural stimulation

Computer simulations were perfonned to investigate the influence of stimulus amplitude on cathodal activation delay, propagation delay and blocking during stimulation with a bipolar cuff electrode. Activation and propagation delays were combined in a total delay term which was minimized between the excitation and blocking thresholds

Paresthesia thresholds in spinal cord stimulation: a comparison of theoretical results with clinical data

The potential distributions produced in the spinal cord and surrounding tissues by dorsal epidural stimulation at the midcervical, midthoracic, and low thoracic levels were calculated with the use of a volume conductor model. Stimulus thresholds of myelinated dorsal column fibers and dorsal root fibers were calculated at each level in models in which the thickness of the dorsal cerebrospinal fluid (CSF) layer was varied. Calculated stimulus thresholds were compared with paresthesia thresholds obtained from measurements at the corresponding spinal levels in patients. The influences of the CSF layer thickness, the contact separation in bipolar stimulation and the laterality of the electrodes on the calculated thresholds were in general agreement with the clinical dat

Calculation of the potential field in nerve stimulation using a multigrid method

This paper deals with the first step in the modeling of newe stimulation: the calculation of the potential field in a 3D volume conductor model of the nerve. surroundings and electrodes. Because of its time efficiency, a multigrid method was used to calculate the field. Compared to a Gauss-Seidel relaxation (overrelaxation factor = 1.7), a calculation time reduction of a factor 20 was obtaine

Definition of Fiducial Points in the Normal Seismocardiogram

Abstract The purpose of this work is to define fiducial points in the seismocardiogram (SCG) and to correlate them with physiological events identified in ultrasound images. For 45 healthy subjects the SCG and the electrocardiogram (ECG) were recorded simultaneously at rest. Immediately following the SCG and ECG recordings ultrasound images of the heart were also obtained at rest. For all subjects a mean SCG signal was calculated and all fiducial points (peaks and valleys) were identified and labeled in the same way across all signals. Eight physiologic events, including the valve openings and closings, were annotated from ultrasound as well and the fiducial points were correlated with those physiologic events. A total of 42 SCG signals were used in the data analysis. The smallest mean differences (±SD) between the eight events found in the ultrasound images and the fiducial points, together with their correlation coefficients (r) were: atrial systolic onset: −2 (±16) ms, r = 0.75 (p < 0.001); peak atrial inflow: 13 (±19) ms, r = 0.63 (p < 0.001); mitral valve closure: 4 (±11) ms, r = 0.71 (p < 0.01); aortic valve opening: −3 (±11) ms, r = 0.60 (p < 0.001); peak systolic inflow: 13 (±23) ms, r = 0.42 (p < 0.01); aortic valve closure: −5 (±12) ms, r = 0.94 (p < 0.001); mitral valve opening: −7 (±19) ms, r = 0.87 (p < 0.001) and peak early ventricular filling: −18 (±28 ms), r = 0.79 (p < 0.001). In conclusion eight physiologic events characterizeing the cardiac cycle, are associated with reproducible, well-defined fiducial points in the SCG