Constant Current Stimulation Research Articles

Wearable EMG Bridge—A Multiple-Gesture Reconstruction System Using Electrical Stimulation Controlled by the Volitional Surface Electromyogram of a Healthy Forearm

In this study, a wearable prototype system was developed for multiple-gesture rehabilitation using electrical stimulation controlled by a volitional surface electromyography (sEMG) scan of a healthy forearm. The purpose of the prototype system is to reconstruct multiple gestures of a paralysed limb and to simplify the positioning of sEMG detection sites on a healthy forearm. A self-designed eight-channel sEMG detection armband was used to detect the sEMG signal distributions of the muscle groups in healthy forearms. Linear discriminant analysis (LDA) was used to classify the sEMG signal distributions corresponding to different gestures, and then the classification results were mapped to corresponding stimulation channels. The sEMG signal with the maximum root mean square (RMS) was used as the source of stimulus coding for each gesture. Our proposed mean absolute value (MAV)/number of slope sign changes (NSS) dual-coding (MNDC) algorithm was used to encode the sEMG signal into an electrical stimulus with a dynamic pulse width and frequency. The constant-current stimulation armband electrically stimulated multiple muscles in the affected forearm by means of a circuit designed with a time-division multiplexed stimulation channel. An experiment involving 6 able-bodied volunteers showed that when the detection armband was located near the middle of the forearm, the gesture classification accuracy was greater than 90%, and each active sEMG signal was high. Gesture bridge experiments, including grasping, wrist flexion, wrist extension and finger extension, were carried out among six hemiplegic subjects and between one able-bodied volunteer acting as a controller and each of six stroke patients as the controllee. Both sets of results show that the proposed system can reconstruct these four gestures in the controlled subject with a delay of at most 360 ms and with a correlation coefficient of >0.72.

Muscle-evoked Potentials After Electrical Stimulation to the Brain in Patients Undergoing Spinal Surgery are Less Affected by Anesthetic Fade With Constant-voltage Stimulation Than With Constant-current Stimulation.

A prospective, within-subject study was conducted. We aimed to compare the influence of anesthetic fade under maximum stimulation conditions between constant-current and constant-voltage stimulation techniques. The monitoring of muscle-evoked potentials after electrical stimulation to the brain [Br(E)-MSEP)] is useful for assessing the integrity of spinal cord motor tracts during major spine surgery. Nonetheless, Br(E)-MSEP responses are known to deteriorate over the duration of surgeries performed under general anesthesia. This phenomenon is known as anesthetic fade. We recruited 117 patients undergoing various spinal surgeries from the cervical to the lumbar level. We excluded 29 cases with insufficient data. The decrease rate of the Br(E)-MSEP amplitude for each muscle was examined. Br(E)-MSEP monitoring with constant-current and constant-voltage stimulations at the C3 and C4 electrode positions was applied. Compound muscle action potentials (CMAPs) were bilaterally recorded from the abductor pollicis brevis, deltoid, abductor hallucis, tibialis anterior, gastrocnemius, and quadriceps muscles. We defined the decrease rate as follows: (initial CMAPs-final CMAPs)/initial CMAPs × 100. Differences in the decrease rate were evaluated between stimulators, limbs (upper vs. lower), and operative time group (lowest quartile vs. highest quartile). The overall decrease rate (across all muscles) increased as the operative time increased, and the rate was higher in the lower limbs than in the upper limbs. In addition, the overall decrease rate was lower with constant-voltage stimulation than with constant-current stimulation. Furthermore, the decrease rate for constant-current stimulation was significantly higher than that for constant-voltage stimulation, regardless of the operative time. The CMAP waveform with constant-voltage stimulation is less susceptible to anesthetic fade than that with constant-current stimulation, even during long surgeries. 3.

Improved Charge Pump Design and Ex Vivo Experimental Validation of CMOS 256-Pixel Photovoltaic-Powered Subretinal Prosthetic Chip.

An improved design of CMOS 256-pixel photovoltaic-powered implantable chip for subretinal prostheses is presented. In the proposed subretinal chip, a high-efficiency fully-integrated 4× charge pump is designed and integrated with on-chip photovoltaic (PV) cells and a 256-pixel array with active pixel sensors (APS) for image light sensing, biphasic constant current stimulators, and electrodes. Thus the PV voltage generated by infrared (IR) light can be boosted to above 1V so that the charge injection is increased. The proposed chip adopts the 32-phase divisional power supply scheme (DPSS) to reduce the required supply current and thus the required area of the PV cells. The proposed chip is designed and fabricated in 180-nm CMOS image sensor (CIS) technology and post-processed with biocompatible IrOx electrodes and silicone packaging. From the electrical measurement results, the measured stimulation frequency is 28.3 Hz under the equivalent electrode impedance load. The measured maximum output stimulation current is 7.1 μA and the amount of injected charges per pixel is 7.36 nC under image light intensity of 3200 lux and IR light intensity of 100 mW/cm2. The function of the proposed chip has been further validated successfully with the ex vivo experimental results by recording the electrophysiological responses of retinal ganglion cells (RGCs) of retinas from retinal degeneration (rd1) mice with a multi-electrode array (MEA). The measured average threshold injected charge is about 3.97 nC which is consistent with that obtained from the patch clamp recording on retinas from wild type (C57BL/6) mice with a single electrode pair.

High-charge-capacity sputtered iridium oxide neural stimulation electrodes deposited using water vapor as a reactive plasma constituent.

The deposition and properties of sputtered iridium oxide films (SIROFs) using water vapor as a reactive gas constituent are investigated for their potential as high-charge-capacity neural stimulation electrodes. Systematic investigation through a series of optical and electrochemical measurements reveals that the incorporation of water vapor as a reactive gas constituent, along with oxygen, alters the reduction-oxidation (redox) state of the plasma as well as its morphology and the electrochemical characteristics, including the cathodal charge-storage capacity (CSCc ) and charge-injection capacity (CIC), of the SIROF. An apparent optimal O2 :H2 O gas ratio of 1:3 produced SIROF with a CSCc of 182.0 mC cm-2 μm-1 (median, Q1 = 172.5, Q3 = 193.4, n = 15) and a CIC of 3.57 mC cm-2 (median, Q1 = 2.97, Q3 = 4.58, n = 12) for 300-nm-thick films. These values are higher than those obtained with SIROFs deposited using no water vapor by a factor of 2.3 and 1.7 for the CSCc and CIC, respectively. Additionally, the SIROF showed minimal changes in electrochemical characteristics over 109 pulses of constant current stimulation and showed no indication of cytotoxicity toward primary cortical neurons in a cell viability assay. These results warrant investigation of the chronic recording and stimulation capabilities of the SIROF for implantable microelectrode arrays.

Somatosensory Temporal Discrimination Threshold in Patients with Cognitive Disorders.

The temporal processing of sensory information can be evaluated by testing the somatosensory temporal discrimination threshold (STDT), which is defined as the shortest interstimulus interval needed to recognize two sequential sensory stimuli as separate in time. The STDT requires the functional integrity of the basal ganglia and of the somatosensory cortex (S1). Although there is evidence that time processing is impaired in patients with Alzheimer's disease (AD), no study has yet investigated STDT in patients with various degree of cognitive impairment. The aim of our study was to understand how cognition and attention deficits affect STDT values in patients with cognitive abnormalities. We enrolled 63 patients: 28 had mild-moderate AD, 16 had mild cognitive impairment (MCI), and the remaining 19 had subjective cognitive deficit (SCD). A group of 45 age-matched healthy subjects acted as controls. Paired tactile stimuli for STDT testing consisted of square-wave electrical pulses delivered with a constant current stimulator through surface electrodes over the distal phalanx of the index finger. STDT values were higher in AD and MCI patients than in SCD subjects or healthy controls. Changes in the STDT in AD and MCI were similar in both conditions and did not correlate with disease severity. STDT alterations in AD and MCI may reflect a dysfunction of the dopaminergic system, which signals salient events and includes the striatum and the mesocortical and mesolimbic circuits.

Triggered EMG (T-EMG) Values of Pedicle Screws with a Powered Screwdriver vs A Standard Probe in Adolescent Idiopathic Scoliosis Do Not Agree: A Prospective Validation Study

ABSTRACTTriggered electromyography (t-EMG) is a common technique used during spinal instrumentation in surgery for adolescent idiopathic scoliosis. This study tests the validity of t-EMG values obtained with a standard ball-tipped probe after completion of screw placement versus t-EMG values obtained during screw insertion with a powered screwdriver. t-EMG values were collected for screws spanning T7–L5 using both a standard probe and a powered screwdriver. A power analysis determined that a sample size of 300 screws would provide enough precision to estimate limits of agreement within ±2 mA. A monopolar constant current stimulation technique (0.2 ms duration and 3.11 Hz stimulation rate) was used at each level. EMG was acquired with placement of bipolar pairs of subdermal needle electrodes. A Bland-Altman plot was used to assess agreement between threshold readings from the two techniques. Twenty-nine patients were enrolled in this study with 305 screws. t-EMG values measured using a powered screwdriver were on average 1 mA lower than values from a standard probe. When readings less than or equal to 20 mA were considered, the limits of agreement were approximately 4 and 7 mA overall. In total, 28/305 (9%) screws were removed and reinserted, 9/305 (3%) screws were redirected, and 3/305 (1%) screws were aborted based on t-EMG readings. Despite a small overall difference in t-EMG value between the standard probe and screwdriver, there was still large variability in agreement between the two techniques. t-EMG values obtained with a powered screwdriver during screw insertion are not interchangeable with values measured by a probe.

An Ultra High-Frequency 8-Channel Neurostimulator Circuit With [Formula: see text] Peak Power Efficiency.

In order to recruit neurons in excitable tissue, constant current neural stimulators are commonly used. Recently, ultra high-frequency (UHF) stimulation has been proposed and proven to have the same efficacy as constant-current stimulation. UHF stimulation uses a fundamentally different way of activating the tissue: each stimulation phase is made of a burst of current pulses with adjustable amplitude injected into the tissue at a high (e.g., [Formula: see text]) frequency. This paper presents the design, integrated circuit (IC) implementation, and measurement results of a power efficient multichannel UHF neural stimulator. The core of the neurostimulator is based on our previously proposed architecture of an inductor-based buck-boost dc-dc converter without the external output capacitor. The ultimate goal of this work is to increase the power efficiency of the UHF stimulator for multiple-channel operation, while keeping the number of external components minimal. To this end, a number of novel approaches were employed in the integrated circuit design domain. More specifically, a novel zero-current detection scheme is proposed. It allows to remove the freewheel diode typically used in dc-dc converters to prevent current to flow back from the load to the inductor. Furthermore, a gate-driver circuit is implemented which allows the use of thin gate-oxide transistors as high-voltage switches. By doing so, and exploiting the fundamental working principle of the proposed current-controlled UHF stimulator, the need for a high-voltage supply is eliminated and the stimulator is powered up from a [Formula: see text] input voltage. Both the current detection technique and the gate driving circuit of the current implementation allow to boost the power efficiency up to [Formula: see text] when compared to previous UHF stimulator works. A peak power efficiency of [Formula: see text] is achieved, while 8 independent channels with 16 fully configurable electrodes are used. The circuit is implemented in a [Formula: see text] HV process, and the total chip area is [Formula: see text].

Arbitrary waveform constant current stimulator for long-term wearable applications

Subsensory electrical noise stimulation has been shown to improve sensory perception in humans. However, the majority of this work has been limited to the laboratory due to unavailability of portable body-worn stimulators. In this paper, we present a robust and reliable stimulator, engineered for wearable applications and designed to extend modulation of human sensory perception outside the physiology laboratory.The stimulator provides an arbitrary waveform constant current stimulation, offering continuous current stimulation up to ±5 mA with a voltage compliance of ±25 V (expandable up to 70 V). A graphical user interface allows setting of stimulus parameters within fixed ranges via a USB connected computer. The interface is very simple using a single power switch and a single multi-coloured LED for device feedback. The applied stimulus voltage and current are continually monitored and used to detect short circuit, high impedance conditions. These conditions, and other errors e.g. low battery state, put the device in a safe state with the user disconnected via a relay. All captured data, including accelerometer data, is logged to a removable SD card. Powered by an interchangeable, Li-Ion battery pack >4 h stimulation is achievable. The full circuit, system software and bench tests performed are presented.

Comparison of Intraoperative Motor Evoked Potentials Monitoring with Direct Cranial Stimulation by Peg-Screw and Transcranial Stimulation by Corkscrew for Supratentorial Surgery

Corkscrew (CS) electrodes are usually used for transcranial electrical stimulation (TES) in the intraoperative monitoring of motor evoked potentials (MEP). Direct cranial stimulation with peg-screw (PS) electrodes can elicit MEP. The present study investigated the difference in the initial threshold between PS and CS electrodes for intraoperative MEP monitoring. We retrospectively analyzed TES-MEP monitoring for supratentorial surgery in 72 patients. Of these 72 patients, 44 were monitored with PS and CS electrodes (PS/CS group) and 28 were monitored with CS and CS electrodes (CS/CS group). TES was used to deliver electrical stimulation by a train of 4-pulse anodal constant current stimulation. The initial threshold in each electrode was checked and analyzed. In the PS/CS group, the initial threshold with the PS electrode was 38.3 ± 15.1 mA (mean ± standard deviation) on the affected side, and the initial threshold with the CS electrode was 51.4 ± 13.9 mA on the unaffected side. The initial threshold with the PS electrode was significantly lower than that with the CS electrode (P=0.0001). In the CS/CS group, the initial threshold was 56.2 ± 16.5 mA on the affected side and 62.1 ± 18.6 mA on the unaffected side, with no statistically significant difference (P= 0.23). The initial threshold to elicit MEP was significantly lower with the PS electrode than with the CS electrode. A PS electrode can be used as a feasible stimulation electrode for TES-MEP.

Monophasic transcranial constant-current versus constant-voltage stimulation of motor-evoked potentials during spinal surgery

Constant-voltage and constant-current stimulators may be used for transcranial electrical stimulation of motor evoked potentials (TES-MEP). However, no previous report has determined whether the two monophasic stimulation methods lead to similar responses during intra-operative monitoring. We studied differences in the lateralities of compound muscle action potentials (CMAPs) during intra-operative spinal cord monitoring via TES-MEP using monophasic constant-current and constant-voltage stimulations. CMAPs were bilaterally recorded from the upper and lower limb muscles in 95 patients who underwent elective spine and spinal cord surgery. We used two monophasic stimulation patterns: pattern 1, right anode and left cathode; pattern 2, right cathode and left anode. There were no statistically significant differences between the right and left sides with respect to success rates, wave amplitudes, and efficiencies, with constant-voltage stimulation, however, there were statistically significant differences between the right and left sides with constant-current stimulation. In case of our stimulation condition, there were no statistically significant differences between the right and left sides with respect to CMAPs with constant-voltage stimulation; constant-current stimulation was influenced by the type of monophasic stimulation, which necessitates the switch the polarity of the stimulation to bilaterally record CMAPs.

The Bionode

Implantable closed-loop neuromodulation devices for use in long-term chronic studies in a lab or clinical trial are expensive to acquire and difficult to modify for specific use cases. This article documents the design and fabrication of a wireless implantable device using only commercially available off-the-shelf (COTS) components. This device, called the Bionode, can record and transmit up to four channels of biopotential data while simultaneously providing biphasic constant-current stimulation. The Bionode is a viable, low-cost, reusable, and easily modifiable research tool with clinical implications that has gained widespread use in various research projects at Purdue University.

Estimation of Intraoperative Stimulation Threshold of the Facial Nerve in Patients Undergoing Microvascular Decompression.

Introduction Facial weakness can result from surgical manipulation of the facial nerve. Intraoperative neuromonitoring reduces functional impairment but no clear guidelines exist regarding interpretation of intraoperative electrophysiological results. Most studies describe subjects with facial nerves encumbered by tumors or those with various grades of facial nerve weakness. We sought to obtain the neurophysiological parameters and stimulation threshold following intraoperative facial nerve triggered electromyography (t-EMG) stimulation during microvascular decompression for trigeminal neuralgia to characterize the response of normal facial nerves via t-EMG. Methods Facial nerve t-EMG stimulation was performed in seven patients undergoing microvascular decompression for trigeminal neuralgia. Using constant current stimulation, single stimulation pulses of 0.025 to 0.2 mA intensity were applied to the proximal facial nerve. Compound muscle action potentials, duration to onset, and termination of t-EMG responses were recorded for the orbicularis oculi and mentalis muscles. Patients were evaluated for facial weakness following the surgical procedure. Results Quantifiable t-EMG responses were generated in response to all tested stimulation currents of 0.025, 0.05, 0.1, and 0.2 mA in both muscles, indicating effective nerve conduction. No patients developed facial weakness postoperatively. Conclusions The presence of t-EMG amplitudes in response to 0.025 mA suggests that facial nerve conduction can take place at lower stimulation intensities than previously reported in patients with tumor burden. Proximal facial nerve stimulation that yields responses with thresholds less than 0.05 mA may be a preferred reference baseline for surgical procedures within the cerebellopontine angle to prevent iatrogenic injury.

Somatosensory temporal discrimination is impaired in fibromyalgia

ObjectiveFibromyalgia is the prototypical central sensitivity syndrome which is associated with increased sensitivity to pain and other stimuli. In this study, we aimed to evaluate whether somatosensory temporal discrimination ability, which provides information about central processing of sensory stimuli, was impaired in patients with fibromyalgia. MethodsFifteen patients with fibromyalgia and 15 healthy subjects participated in the study. Demographic characteristics of participants and severity for fatigue, sleep quality, cognitive symptoms, somatic symptoms and health-related quality of life in fibromyalgia patients were recorded. Somatosensory temporal discrimination thresholds were measured from the dorsum of the dominant hands of the participants by using a constant current stimulator (Medtronic, Keypoint). ResultsPatients with fibromyalgia had higher somatosensory temporal discrimination thresholds than healthy subjects (p < 0.001). There were significant correlations between STDTs and pain intensity, FIQ scores and symptom severity scale scores in fibromyalgia group (p = 0.006, r = 0.68; p = 0.037, r = 0.54; p = 0.017, r = 0.61 respectively). ConclusionSomatosensory temporal discrimination ability is impaired in fibromyalgia patients compared to healthy subjects. Disrupted somatosensory temporal discrimination ability correlates with increased widespread pain and severity of other symptoms including fatigue, sleep quality, cognitive symptoms, somatic symptoms and decreased functional status. The impaired somatosensory temporal discrimination ability indicates an alteration in higher cognitive sensory processing in fibromyalgia patients.

Transpalpebral Electrical Stimulation as a Novel Therapeutic Approach to Decrease Intraocular Pressure for Open-Angle Glaucoma: A Pilot Study.

Purpose To determine the effect on intraocular pressure of transpalpebral specific exogenous voltages in a cohort of open-angle glaucoma patients. Methods This is a prospective, comparative, and experimental pilot study. The electrical stimuli applied consisted of 10 Hz, biphasic, nonrectangular current pulses (100 μA) delivered from an isolated constant current stimulator. At intake, baseline IOP measurements were obtained from each eye. The measurement was repeated before and after microstimulation until the end of the treatment. Results Seventy-eight eyes of 46 patients diagnosed with POAG were studied: 58 eyes with maximum tolerated medical treatment and 20 eyes without treatment (naïve). The mean baseline IOP on the treated POAG group was 19.25 mmHg ± 4.71. Baseline IOP on the naïve group was 20.38 mmHg ± 3.28. At the four-month follow-up visit, the mean IOP value on the treatment group was 14.41 mmHg ± 2.06 (P < 0.0001). The obtained mean IOP measurement on the treatment-naïve group was 15.29 mmHg ± 2.28 (P < 0.0001). Conclusions The hypotensive response obtained using transpalpebral electrical stimulation on POAG patients, both on treatment-naïve patients and on patients receiving maximum tolerable treatment, was statistically significant when comparing basal IOP measurements to those obtained at the four-month follow-up visit.

Computational Simulation of Array-based Electroporation in the Cochlea.

We present a computational model for predicting electric field distributions following array-based closed-loop electroporation in the cochlea. The model geometry was reconstructed from magnetic resonance images of the guinea pig cochlea and an eight-channel electrode array embedded within this geometry. The model's electrode voltage output waveform was obtained from electric potential mapping conducted in physiological solution following constant-current stimulation using the electrode array. Our simulations predict that a tandem electrode configuration with four ganged cathodes and four ganged anodes produces a larger area in target tissue where the electric field is within the range for successful gene transfer compared to an alternate paired anode-cathode electrode configuration. These findings corroborate published in vivo evidence comparing the two configurations and support the utility of the developed model as a tool to optimize the efficacy of electroporation electrodes.

T97. A revisit of the clinically used methods for intraoperative nerve action potential recordings in nonhuman primate

Compound nerve action potential recordings are often used intraoperatively to assist the surgeon in decision making on surgical approaches during nerve repair surgeries. The methods used clinically are based on surgical recordings (Robert et al., 2009). Although these methods are of great simplicity as handheld electrodes are applied to a nerve dissected and isolated from surrounding tissues, implementation of the methods in the clinical setting remains challenging. Here, we report findings from an experiment where similar recordings were made in nonhuman primate in order to improve our understanding and the performance of the methods. Recordings were made from the median nerve at the upper arm of an adult female pigtail monkey under TIVA (pentobarbital) and full NMB (pancuronium). Core body temperature was maintained near 38 °C. Nerve action potentials were induced by constant current stimulation and recorded using laboratory equipment. IONM electrodes were used: triple and double hook electrodes (Cadwell) for stimulation and recording, respectively. Using the same recording configuration as in the clinical situation, we failed to record recognizable compound action potentials across a short conduction length of a nerve (3–4 cm) that was isolated and suspended from surrounding tissues as large stimulus artifacts obscured the neuronal signal. The stimulus artifacts were suppressed and the compound nerve action potential became unmasked after a saline-soaked gauze was placed underneath the nerve between the stimulating and recording electrodes to bridge the nerve and the surrounding tissues (i.e., ‘bridge grounding’). Furthermore, compound action potentials were of small amplitude when all prongs of the stimulation electrode were placed underneath the nerve. However, the potentials increased markedly in size with another modification, i.e. when the nerve was placed between the middle prong and the outer 2 prongs of the stimulation electrode (i.e., ‘sandwich stimulation’) after reshaping of the prongs. The recordings were made at room temperature (about 23 °C) without use of warm saline irrigation, at which the compound action potentials preserved good amplitudes but slowed in conduction, leading to a better separation of compound action potentials from stimulus artifacts. We reversely translated the clinical methods of nerve compound action potential recording to a laboratory setting in order to better understand the factors affecting performance. We observed that compound nerve action potentials could be reliably recorded with IONM electrodes when 2 modifications, the ‘bridge grounding’ and ‘sandwich stimulation’, were made. Confirmation and additional experiments are underway to revisit the clinically used recording techniques in the laboratory setting.

A power efficient, differential multichannel adiabatic electrode stimulator for deep brain stimulation

An energy efficient multichannel adiabatic switching based stimulator with high driving current capability (up to 10 mA) is presented in this paper. The high output current is needed especially for deep brain stimulation system. The stored energy in the electrode-tissue capacitor in the first phase of stimulation will be mostly recovered in the second phase. The proposed stimulator consists of a dynamic differential power supply which makes the biphasic stimulation possible without the need of H-bridge or midrail power supply in the output stage. The stimulation current is directly sensed and controlled by a current-controlled loop which makes the stimulation safe and flexible. In the proposed design, the simultaneous multichannel stimulation with independent electrode-tissue characteristics is possible by making use of the proposed simple digital control scheme. This feature is attained without the need of duplicating the inductors for each channel. A self-voltage-boosting bootstrap circuit is also introduced in order to drive the power MOSFETS of the power supply efficiently. The stimulator is simulated in a 0.18 µ, 32 V HV-CMOS technology for evaluating the effectiveness of the system. The simulation results show up to 1.5–2X efficiency improvement compared to the conventional constant current stimulators with adaptive power supply and around 5–10% efficiency improvement relative to the most recent state-of-the-art switching stimulators.

Electrical field stimulation‐induced vasorelaxation responses decreased in anterior and middle cerebral arteries of endotoxemic rats

IntroductionEndotoxic shock is characterized by vascular dysfunction, hypotension and multiple organ dysfunction. Loss of vascular tone is a key factor responsible for death in endotoxic shock. Perivascular innervation has an important role in the regulation of vascular tone. Neural control of the arteries is mediated by adrenergic and nitrergic neurons. The nitrergic component is dominant in brain arteries while adrenergic component is dominant in mesenteric arteries. Lipopolysaccharide (LPS) alters the electrical field stimulation (EFS) responses in mesenteric arteries in vitro. Our aim is to study the alterations of EFS responses of cerebral and mesenteric arteries in endotoxemia in rats.Material and MethodsLPS (10 mg/kg) were given intraperitoneally to rats to make an animal model os sepsis. Rats were anesthetized with gaseous carbon dioxide and decapitated 20 hours after injection, Basilar, anterior cerebral, middle cerebral and 3rd branch of mesenteric arteries were isolated and mounted in a wire myograph covered with platinum electrodes. After U46619 precontraction, frequency‐dependent EFS responses were obtained using a constant current stimulator.ResultsHigh K+ responses did not change in brain and peripheral arteries. EFS‐dependent vasorelaxation responses decreased in anterior and middle cerebral arteries in endotoxemic rats. EFS‐induced vasorelaxation responses of basilar artery and vasoconstriction responses of mesenteric arteries did not change in endotoxemic rats.ConclusionsIn this study we demonstrate for the first time that EFS‐induced vasorelaxation responses of some cerebral arteries decreased in endotoxemic rats. This EFS‐dependent alterations could be explained by degeneration of perivascular innervations or an imbalance between adrenergic and nitrergic neurons.Support or Funding InformationThis study was funded by Hacettepe University Scientific Research Projects Coordination Unit (TSA‐2017‐12848).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

A Neuromodulator Frontend With Reconfigurable Class-B Current and Voltage Controlled Stimulator

This letter presents a neuromodulator frontend that features a reconfigurable current and voltage mode stimulator for a bidirectional, neural interface. By implementing a capacitive high voltage (HV) to low voltage (LV) converter, a single-bit quantizer in the LV domain can be used to compare the difference between the electrode potential and the output of a 7-bit digital-to-analog converter. The digitized signal is integrated to generate a digital feedback signal, which controls a constant current stimulator in order to generate the desired output voltage by adjusting the output current. Thereby the stimulator can deliver up to ±10 mA of output current and ±6 V of stimulation voltage. The stimulation unit is connected over HV protection switches to a neural recorder that features a tunable high-pass cut-off frequency and impulse-based bioimpedance estimation, to form a bidirectional channel. The total consumed silicon area of the frontend is 0.45 mm2 for recording and stimulation. In standby mode the stimulator can be completely disconnected from its biasing, which leads to a power consumption of less than 1 ${\mu }\text{W}$ . The class-B operation during voltage stimulation yields an active power consumption, which is dominated by the stimulator output current in both voltage and current mode.

High-Throughput CMOS MEA System with Integrated Microfluidics for Cardiotoxicity Studies

High-Throughput CMOS MEA System with Integrated Microfluidics for Cardiotoxicity Studies