Constant Current Stimulation Research Articles

Bone fracture during electrical stimulation of the quadriceps in a spinal cord injured subject

We report a fracture through the lateral femoral condyle of a paraplegic subject caused by electrical stimulation (ES). The subject was a 50-year-old man who 4 years earlier had sustained a complete spinal cord injury (SCI) at level T6. The fracture occurred during ES-induced measurement of maximal isometric torque of the quadriceps with the knee flexed at an angle of 90°. ES was delivered through surface electrodes with biphasic square wave pulses from a constant current stimulator. The torque was calculated to be 93Nm, corresponding to 20.8kg at the ankle. The regional bone mineral density of the entire lower extremities was .83g/cm 2, corresponding to 60% of sex- and age-matched able-bodied reference values. Several factors are suspected to have contributed to the fracture: maximal ES in combination with a muscle spasm, servere osteoporosis, increased muscular strength induced by regular ES cycling (twice a week), and testing position with the knee locked in 90° flexion. The risk of fracture as well as various precautions are discussed and should be taken into consideration in future studies.

Signal averaged laser Doppler measurements of activation–flow coupling in the rat forepaw somatosensory cortex

Regional alterations in cerebral blood flow (CBF) are widely used as a surrogate for neuronal function based on an intact coupling between changes in regional CBF and metabolism, activation–flow coupling (AFC). To further investigate parameters affecting AFC, we have implemented a rat model with electrical forepaw stimulation under α-chloralose anesthesia using laser Doppler (LD) measurements of flow parameters through thinned skull over contralateral somatosensory cortex. Signal averaging of the LD response was used to improve reproducibility. A characteristic flow response to electrical forepaw stimulation was reliably recorded from the somatosensory cortex using signal averaging. Stimulation at 5 Hz maximized the LD response, and constant current stimulation up to 1 mA did not induce changes in systemic blood pressure. The shape of the flow response consisted of an initial peak followed by a steady state plateau phase which was observed for stimulation durations longer than 4 s. When individual LD parameters of velocity, red blood cell concentration (CRBC), and cerebral blood flow (CBF) were compared, changes in LD CBF were primarily attributable to changes in LD velocity rather than LD CRBC. This finding was also observed during hypercapnia. Characterization of AFC in the model provides a background for future studies of the effects of pharmacological manipulation or pathophysiological states.

Adding Sodium Bicarbonate to Lidocaine Enhances the Depth of Epidural Blockade

Adding Sodium Bicarbonate to Lidocaine Enhances the Depth of Epidural Blockade

Transcranial electrical stimulator producing high amplitude pulses and pulse trains

Transcranial electrical stimulation can be used for clinical investigations of the central nervous system and for monitoring of motor nerve tracts during surgical operations. We wished to reduce the pain involved with the transcranial electrical stimulation and to improve the usefulness of the method for monitoring during surgical operations. A dedicated trans-cranial electrical stimulator was designed having special features to reduce the pain sensation and the nerve blocking effect of anaesthetics. It provides constant current and constant voltage stimulation pulses with very short duration and high amplitude. The pulse length is adjustable in the range of 15 to 125 μs, while the maximum amplitude is 1000 V and 1 A for voltage and current stimulation modes, respectively. Special features included high-repetition-rate pulse trains (50–2000 pulses s−1) and a three-electrode stimulation configuration. We suggest that the electrical transcranial stimulation has the potential to be a relatively painless method for routine clinical investigations and a reliable method for monitoring during surgery.

Neuropathy as an Extrahepatic Manifestation of Chronic Liver Diseases

Gastrointestinal motor disturbances and various cardiovascular symptoms are the characteristic features of autonomic neuropathy. Autonomic and sensory neuropathy has been described in chronic alcoholic liver diseases. Cardiovascular autonomic reflex tests as the gold standard for autonomic neuropathy and measuring of thresholds for constant current electric sine wave stimulation by neurometer were used for measuring sensory neuropathy in patients with chronic liver diseases of different etiology. Autonomic and sensory neuropathy was also observed in non-alcoholic liver diseases. We proved that there is a correlation between autonomic neuropathy and prolongation of corrected QT interval in chronic liver diseases. We claim that autonomic neuropathy may have a role to play in the development of hyperdynamic circulation and portal hypertension in chronic liver diseases.

Referred pain is dependent on sensory input from the periphery: a psychophysical study

Muscle pain can be characterized by local pain and pain referred to distant somatic structures with concomitant cutaneous and deep somatosensory changes. The mechanisms responsible for referred muscle pain are poorly understood. The aim of this study was to study the origin of experimentally-induced referred muscle pain by anaesthetizing the skin overlying the referred pain area and to quantify deep somatosensory changes in the area. Fourteen healthy subjects (mean age = 25.1 years, range 22–34 years) were included in a placebo controlled study consisting of two sessions separated by 1 week. Two stimulation needles were inserted into the right anterior tibial muscle. Electrical stimuli (1Q Hz) were delivered by a computer-controlled constant current stimulator. The intensity required to generate referred pain was determined and the circumference of the referred pain area was marked. At the centre of the area, pressure pain threshold and pinprick perception threshold were determined. Either an anaesthetic cream (EMLA®, Astra AB, Sweden) or a placebo cream (Astra AB, Sweden) covered by an occlusive dressing was applied to the marked referred pain area for 90 min. Afterwards, a 600-s stimulation at 150% of the referred pain threshold was induced while the VAS score of referred pain was recorded continuously. Pressure pain threshold and pinprick perception threshold were determined before, during and 5 min after the prolonged stimulation. A significantly lower referred pain visual analogue scale (VAS) score was recorded during the interval from 50 to 150s ( p=0.04). The area under the referred pain VAS score vs time curve tended to be lower (22.7%) with the application of skin anaesthetic ( p=0.07). The mean referred pain threshold and the mean referred pain area did not differ significantly between the two sessions ( p>0.6). No difference was found in pressure pain threshold between the two treatments or between the four recordings during each session ( p>0.8). Pinprick perception threshold increased significantly after EML® application ( p<0.04). Decreased referred pain intensity with application of anaesthetic cream at the referred pain site indicates that referred muscle pain depends on input from the periphery (skin) in humans.

A battery-powered constant current stimulator for motor end-point detection

The device described was developed as an external electrical stimulator to assist in the accurate location of motor end-points prior to the injection of nerve blocking agents in the treatment of spasticity. Monophasic pulses are produced with a duration of 10–100 μs and a current from 0 to 10 mA. The current is maintained over a wide range of electrode impedance and is independent of battery voltage.

Recent Advances in Intraoperative Neuromonitoring of Spinal Cord Function: Pedicle Screw Stimulation Techniques

ABSTRACT.The evolution of internal spinal instrumentation is grounded in the therapeutic constructs and spinal biomechanics associated with spinal deformities. Newer instrumentation methods for spinal fusion, which involve placing screws into the vertebral pedicles to hold the rods, have evolved for the treatment of degenerative spinal disease and traumatic insult to the lumbosacral spine. Two significant advantages of spinal instrumentation using segmental, transpedicular, screw fixation are enhanced rigidity and stability of the spine, and greater flexibility for the surgeon to accommodate a patient's individual anatomy. Despite these advances in instrumentation design, neurological deficits from improper screw placement may occur. The determination of screw placement using traditional methods like anatomical identification of bony landmarks and radiographic techniques have significant limitations. An alternative method for monitoring pedicle screw placement involves an electrophysiological approach called pedicle screw stimulation technique. Evoked electromyographic activity is recorded from muscle groups innervated by the spinal nerve roots at risk. Either constant current or voltage stimulation applied through the hardware used to form the pedicle holes, inside the pedicle holes, and through the implanted screws is performed to determine the stimulation threshold needed to produce a compound muscle action potential. These threshold values for evoked EMG are then used for evaluating the success or failure of screw placement. A relatively high EMG threshold suggests proper pedicle screw placement with an intact pedicle wall surrounding the screw; a relatively low threshold indicates a malposed screw resulting in a possible cracked or breached pedicle.

歯髄の電気刺激に応答するネコ三叉神経中脳路核一次ニューロンの性質

The existence of primary afferent neurons innervating the tooth pulp (TP) has been demonstrated by the HRP tracing method in the mesencephalic trigeminal nucleus (MTN) of the cat, dog and monkey by Amano et al. (1987) and Yoshino et al. (1989), (1993). The intention of the present study was to confirm electrophysiologically that the neurons in the feline MTN that respond to electrical stimulation of the TP are cell bodies of primary afferent fibers and to examine their functional properties. Adult cats of either sex were anesthetized with urethane-chloralose and mounted on a stereotaxic apparatus. For electrical stimulation and whole nerve recordings, the right inferior alveolar nerve (IAN) was exposed and a pair of Ag-AgCl wire electrodes were placed in contact with the intact nerve. For bipolar EMG recording, a pair of copper wire electrodes were sutured into the ipsilateral anterior digastric muscle (DIG). The right maxillary and mandibular canine teeth were used for electrical stimulation of the TP. To activate as many pulpal afferent fibers as possible with constant low current stimulation, two Ag-AgCl wire electrodes were implanted into deep dentin cavities prepared in the canine root portions corresponding to the apical one- and two-fourths. Single-unit recordings were made with glass-coated elgiloy microelectrodes in the region of P2.5 and L2.5, corresponding to the caudal part of the MTN. During recordings in the MTN, unitary spindle and periodontal activities were detected with occasional manual force to the mandible or to the canine teeth. The only unitary activity related to the electrical TP stimulation was investigated. The recording sites were histologically verified with the aid of electrode tip marking. A total of 25 single neurons were recorded from the MTN of 20 cats. These neurons followed faithfully double pulse stimuli separated by 2 msec (i.e., 500 Hz) delivered to the canine TP, responded with a consistent short latency ranging 1.2-2.0 msec (1.6±0.2 msec, mean±SD) and were histologically confirmed to locate in the MTN. Their conduction velocities were 38.0-63.3 m/sec (48.9±6.4 m/sec, mean±SD) and agreed well with the aβ range of 35-70 m/sec. Prior to paralyzation, recordings were carried out simultaneously from an ipsilateral MTN primary pulpal neuron, whole IAN and DIG. The responses to gradually increasing intensity of single pulse stimuli (20 μsec duration) to the mandibular canine TP were graded and the thresholds were carefully determined. The fastest component of the IAN compound action potential due to the largest pulpal afferent fibers apperared at 2.7 mA. Stimulus intensity had to be increased to 1.4 times threshold to cause firing of the MTN pulpal neuron and short-latency digastric reflex activity (7.0 msec latency). This MTN pulpal neuron with the same threshold for the digastric reflex was histologically confirmed to locate in the mesencephalic trigeminal tract a little away from other primary afferent neurons with relatively large soma aggregating in clusters. The main finding of the present study is that the feline MTN primary neurons supply the TP with Aβ afferent fibers. These MTN pulpal neurons might play a role of mechanoreception, as indicated by Dong et al. (1985) in the feline intradental afferents with soma in the TG.

Otoacoustic emissions evoked by electrical stimulation

Otoacoustic emissions evoked by electrical stimulation of the cochlea were measured in guinea pigs. Alternating current with acoustic frequencies was delivered directly to the scala tympani and the vestibuli of the basal turn by using a constant current stimulator made in our laboratory. The amplitude of the electrically evoked otoacoustic emmisson (EEOAE), which was 21.0 dB SPL in response to 2 kHz electrical stimuli of 120 microArms, was decreased gradually with anoxia of the animal and was reduced to below the noise level by extirpation of the ossiculum. The EEOAEs rose with a delay of 100 microseconds from the beginning of the stimulus, and reached maximum amplitude within three cycles. The output of EEOAE was magnified in a linear manner as the stimulus current increased from 10 to 200 microArms. The averages and standard deviations of the EEOAE output at the stimulus level of 170 microArms in six animals were 20.5 +/- 4.1 dB SPL for 1 kHz, 23.3 +/- 4.8 dB SPL for 2 kHz, 10.5 +/- 6.0 dB SPL for 3 kHz, 17.1 +/- 4.7 dB SPL for 4 kHz, 13.6 +/- 4.4 dB for 5 kHz and 18.3 +/- 4.8 dB SPL for 6 kHz. Measurement of EEOAE, in which stable responses could be obtained with simple and easy preparation, was considered a potential procedure for assessing the electromotility of the cochlear outer hair cells in vivo.

Comparison in Young Healthy Volunteers of 3 Different Parameters of Constant Current Stimulation Used to Determine Sensory Thresholds in the Lower Urinary Tract

Comparison in Young Healthy Volunteers of 3 Different Parameters of Constant Current Stimulation Used to Determine Sensory Thresholds in the Lower Urinary Tract

Comparison in Young Healthy Volunteers of 3 Different Parameters of Constant Current Stimulation Used to Determine Sensory Thresholds in the Lower Urinary Tract

Purpose We compared different parameters of constant current stimulation used for evaluation of sensation in the lower urinary tract. Materials and Methods In 24 healthy male and 9 healthy female volunteers (mean age 24 years) sensory thresholds were determined at the same site on the bladder, urethra and skin with 3 different parameters of constant current stimulation (2.5, 20 and 95 Hz. at pulses 1, 1 and 0.5 msec., respectively) given at random. Results Thresholds were highly reproducible at all sites and with the 3 currents. Thresholds obtained with 2.5 Hz. were significantly greater than those obtained with 20 Hz. at all sites or 95 Hz. at the bladder and male urethra. No significant difference was found between thresholds in the bladder or urethra with 20 and 95 Hz. In 2 volunteers no bladder sensation was elicited with 2.5 Hz. even at 33 mA. A reproducible elevated threshold was found with 20 and 95 Hz. No intravesical pressure increase occurred during stimulation. Conclusions Absolute values of sensory thresholds vary in relation to the site of stimulus and stimulation parameters in healthy young subjects. Low frequency current (2.5 Hz.) is less easily perceived and, therefore, would seem less suitable for evaluation of electrical sensation in the lower urinary tract. Thresholds obtained with frequences of 20 and 95 Hz. were not statistically different.

Current perception thresholds in toe-to-digit transplantation and digit-to-digit replantation.

Recovery of digital nerve function in toe-to-digit transplantation and digit-to-digit replantation was evaluated by transcutaneous constant current sine wave stimulation at 5-, 250-, and 2000-Hz frequencies to determine the current perception thresholds (CPT). For toe transplantation and digit replantation, the mean interval between injury and surgery was 9 months and 7 h, respectively, while the mean interval between surgery and CPT study was 52 months and 20 months, respectively. Control CPTs evoked by three frequency stimuli were obtained from contralateral corresponding normal finger and normal toe. Normal finger had significantly lower 250- and 2000-Hz CPTs than normal toe, but the 5-Hz CPT was not different between them. Replanted digit achieved nearly complete recovery of these three frequency CPTs when compared to normal finger. In toe transplantation, 2000-Hz CPT was comparable to normal finger, while 5- and 250-Hz CPTs were comparable to normal toe. The present findings suggest that the transplanted toe was intermediate between normal finger and normal toe, but more like normal toe than normal finger with regard to detection thresholds of the current-evoked sensation.

Variation between centers in electrophysiologic techniques used in lumbosacral selective dorsal rhizotomy for spastic cerebral palsy.

The extent of variation between centers in the electrophysiologic techniques used in lumbosacral selective dorsal rhizotomy (SDR) for spastic cerebral palsy was studied using a questionnaire survey. Nineteen centers completed the questionnaire, and the responses were analyzed for those 16 centers in which the extent of dorsal root section was guided by intraoperative electrophysiologic responses. Consistent techniques included: use of unipolar stimulating electrodes (11 of 15 responses); stimulation < 4 cm from the root exit foramen (14 of 16); separation of dorsal roots into three to eight rootlets each (14 of 16); tetanic stimulation frequency of 50 Hz (11 of 16); tetanic stimulation at 100% of threshold (13 of 16); recording from multiple lower limb muscles simultaneously (16 of 16), and using contralateral spread of the response as a major criterion of electrophysiologic abnormality (13 of 16). There was more variation (< 11 of 16 concurrence) with respect to the use of a constant current versus constant voltage stimulator; the location of the cathode of the stimulating electrode relative to the anode; the definition of the threshold for a response; whether threshold was determined from stimulation of a dorsal root, or individual rootlets; the type of recording electrodes (needle versus surface), and the relative importance of electrophysiologic versus clinical findings in determining how much of each dorsal root to cut. In 10 centers, SDR would proceed without the benefit of electrophysiologic guidance if the equipment should fail intraoperatively (only if quadriplegic in 4), and this had happened in 6. The results indicate significant variation in many aspects of electrophysiologically guided SDR.

A comparison of the effects of noxious and innocuous counterstimuli on experimentally induced itch and pain

We have studied experimentally induced itch (using histamine iontophoresis) and pain (using topical mustard oil) in healthy human volunteers, measured using visual analogue scale (VAS) ratings. The effects of the following counterstimuli were evaluated: innocuous vibration; innocuous transcutaneous electrical nerve stimulation (TENS); innocuous warming of skin; noxious heating of skin; noxious chemical skin stimulation (using mustard oil); mildly noxious constant current transdermal electrical stimulation. Inncuous stimuli applied 2 min after histamine or mustard oil challenge produced a moded reduction of itch and pain ratings (20–30%), which did not persist for more than 20 sec when the counterstimuli were removed. These changes may well be due to distraction. The same stimuli (in some cases applied for periods of up to 1 h) given prior to the histamine or mustard oil, produced no significant reduction in evoked itch or pain. Noxious stimuli of all types applied 2 after histamine or mustard oil challenge produced a consistent and significant inhibition of itch (22.8–52.7%) which outlasted the period of counterstimulation application. In contrast, these stimuli had no significant effects on chemically induced pain. The anti-pruritic state produced by brief noxious stimuli were effective for periods of more than 30 min. The differential effects of noxious counterstimuli on itch and pain do not support the suggestion that itch is a subliminal form of pain. Noxious counterstimuli are likely to act via a central rather than peripheral mechanism. The novel finding that a persistent anti-pruritic state can be induced by transdermal constant current may be useful in conditions of clinical itch.

A robust transcutaneous electro-muscle stimulator (RTES): a multi-modality tool

This paper introduces a transcutaneous electro-muscle stimulator design that has a wide range of output capabilities. Because of this, the unit is referred to as a robust transcutaneous electro-muscle stimulator (RTES). The RTES is a constant current stimulator that is designed to be capable of generating significant tetanic contractions from large muscle groups, such as the quadriceps. It is capable of generating complex current pulse profiles and has been tested at pulse frequencies greater than 7500 Hz. It is routinely used to generate rectangular, bi-phasic pulses in muscle-modelling studies in ranges of widths from 3 to 1000 μs, amplitudes from −50 to +50 mA and frequencies from 10 to 60 Hz. The design extrema on pulse width and amplitude, are 1000 μs and ±100 mA respectively. Because of the stimulator's robust output characteristics, it is suitable for many types of electro-stimulation studies including pain management, edema reduction and more.

Electrically evoked basilar membrane motion

Electrically induced outer hair cell (OHC) motility, demonstrated by a number of investigators in isolated OHC preparations, has been considered to be a key mechanism in the active process which brings about the excellent sensitivity and frequency selectivity of the mammalian cochlea. In this study, electrical-to-mechanical transduction in the gerbil cochlea was demonstrated in vivo by direct measurement of basilar membrane motion evoked by sinusoidal electrical current injected into the scala media. The characteristic frequency (CF) of the measurement place was approximately 40 kHz as determined by the basilar membrane (BM) responses to acoustic stimulation. The results showed that basilar membrane motion could be evoked by electrical current of frequencies from below 10 Hz to exceeding 40 kHz. The magnitude and phase of the BM velocity response to constant current stimulation, from 100 Hz to 10,000 Hz, were similar to the acoustically driven BM velocity for constant umbo velocity. For frequencies in this range, the BM motion evoked by a current of 50 microA was comparable to the BM motion evoked by a 60 dB SPL acoustic stimulus. The phase of the electrically evoked BM motion indicates that positive current injected into the scala media caused the BM to move toward scala vestibuli for frequencies between 100 and 10 kHz. This result is consistent with the hypothesis that the electrically evoked BM motion is due to electrically evoked OHC length changes.

Electrical oscillation in lipid-impregnated porous membrane filter and its modulation by a light-driven proton pump, bacteriorhodopsin

A lipid-impregnated porous membrane filter (placed between two chambers) was able to display reproducibly an electrical oscillation under constant current stimulation when alamethicin (a channel-forming polypeptide) and protamine (a basic protein) were added to the chamber whose salt concentration was higher than that of the other and the membrane was left for 12 h. In addition, bacteriorhodopsin, which is a light-driven proton pump, was found to control the oscillation. The oscillatory phenomenon is considered to be driven by the alternating change in the ion selectivity of the membrane between cation and anion.

Electrochemical Reactions During Constant DC Current Stimulation: AnIn VitroExperiment with Cultured Rat Calvarial Cells

While various electrode materials, methods of insertion, and levels of current and voltage have been used in animal experiments and clinical situations, the mechanism for constant direct current (DC) stimulation is still unknown. Little information has been provided on the behavior of active metallic electrodes in the complex biochemical environment. The findings of this study are the following: (1) Electrochemical reactions in culture medium (DMEM + 10% FBS) were recorded at a current density of 85 μA/cm2. Current density higher than 212 μA/cm2 leads to acute reactions including liberation of H2. (2) O2 plays an important role in the electrochemical reaction. (3) The resistance of the culture medium increased exponentially during electrical stimulation. (4) pH increased in the region around the cathode as a function of current density and time. (5) The initial response of osteoblastic cells to a DC current of 100 μA/ cm2 is proliferation and alignment parallel to field lines. Studies on mechanisms and techniques of DC stimulation may lead to revolutionary changes in general clinical practice.

Oscillatory phenomena in model membrane: electrical oscillation in lipid-impregnated membrane filter induced by alamethicin and controlled by bacteriorhodopsin

A lipid-impregnated membrane filter was able to show reproducibly of an electrical oscillation under constant current stimulation when alamethicin and protamine were present in the chamber whose salt concentration was higher than the other and the membrane was left for about 12 h. In addition, bacteriorhodopsin, which is a light-activated proton pump, was found to control the oscillation. The oscillatory phenomenon was considered to be driven by the alternating change in the ion-selectivity of the membrane between cation and anion. Impedance measurement indicated the existence of lipid rearrangement which might prepare an environment for both alamethicin and protamine to cause the oscillation.