Stimulation Amplitude Research Articles

The Effect of Clinically Controllable Factors on Neural Activation During Dorsal Root Ganglion Stimulation

ObjectiveDorsal root ganglion stimulation (DRGS) is an effective therapy for chronic pain, though its mechanisms of action are unknown. Currently, we do not understand how clinically controllable parameters (e.g., electrode position, stimulus pulse width) affect the direct neural response to DRGS. Therefore, the goal of this study was to utilize a computational modeling approach to characterize how varying clinically controllable parameters changed neural activation profiles during DRGS. Materials and MethodsWe coupled a finite element model of a human L5 DRG to multicompartment models of primary sensory neurons (i.e., Aα-, Aβ-, Aδ-, and C-neurons). We calculated the stimulation amplitudes necessary to elicit one or more action potentials in each neuron, and examined how neural activation profiles were affected by varying clinically controllable parameters. ResultsIn general, DRGS predominantly activated large myelinated Aα- and Aβ-neurons. Shifting the electrode more than 2 mm away from the ganglion abolished most DRGS-induced neural activation. Increasing the stimulus pulse width to 500 μs or greater increased the number of activated Aδ-neurons, while shorter pulse widths typically only activated Aα- and Aβ-neurons. Placing a cathode near a nerve root, or an anode near the ganglion body, maximized Aβ-mechanoreceptor activation. Guarded active contact configurations did not activate more Aβ-mechanoreceptors than conventional bipolar configurations. ConclusionsOur results suggest that DRGS applied with stimulation parameters within typical clinical ranges predominantly activates Aβ-mechanoreceptors. In general, varying clinically controllable parameters affects the number of Aβ-mechanoreceptors activated, although longer pulse widths can increase Aδ-neuron activation. Our data support several Neuromodulation Appropriateness Consensus Committee guidelines on the clinical implementation of DRGS.

Direct Electrical Stimulation of the Human Brain Has Inverse Effects on the Theta and Gamma Neural Activities.

Our goal was to analyze the electrophysiological response to direct electrical stimulation (DES) systematically applied at a wide range of parameters and anatomical sites, with particular focus on neural activities associated with memory and cognition. We used a large set of intracranial EEG (iEEG) recordings with DES from 45 subjects with electrodes implanted both subdurally on the cortical surface and subcortically into the brain parenchyma. Subjects were stimulated in blocks of alternating frequency and amplitude parameters during quiet wakefulness. Stimulating at different frequencies and amplitudes of electric current revealed a persistent pattern of response in the slow and the fast neural activities. In particular, amplification of the theta (4-7 Hz) and attenuation of the gamma (29-52 Hz) power-in-band was observed with increasing the stimulation parameters. This opposite effect on the low and high frequency bands was found across a network of selected local and distal sites proportionally to the proximity and magnitude of the electric current. Power increase in the theta and decrease in the gamma band was driven by the total electric charge delivered with either increasing the frequency or amplitude of the stimulation current. This inverse effect on the theta and gamma activities was consistently observed in response to different stimulation frequencies and amplitudes. Our results suggest a uniform DES effect of amplifying theta and suppressing gamma neural activities in the human brain. These findings reveal the utility of simple power-in-band features for understanding and optimizing the effects of electrical stimulation on brain functions.

Does hemispheric vascular regulation differ significantly in glaucoma patients with altitudinal visual field asymmetry? A single-center, prospective study

PurposeVascular risk factors and ocular perfusion are heatedly discussed in the pathogenesis of glaucoma. The retinal vessel analyzer (RVA, IMEDOS Systems, Germany) allows noninvasive measurement of retinal vessel regulation. Significant differences especially in the veins between healthy subjects and patients suffering from glaucoma were previously reported. In this pilot-study we investigated if localized vascular regulation is altered in glaucoma patients with altitudinal visual field defect asymmetry.Methods15 eyes of 12 glaucoma patients with advanced altitudinal visual field defect asymmetry were included. The mean defect was calculated for each hemisphere separately (−20.99 ± 10.49 profound hemispheric visual field defect vs −7.36 ± 3.97 dB less profound hemisphere). After pupil dilation, RVA measurements of retinal arteries and veins were conducted using the standard protocol. The superior and inferior retinal vessel reactivity were measured consecutively in each eye.ResultsSignificant differences were recorded in venous vessel constriction after flicker light stimulation and overall amplitude of the reaction (p < 0.04 and p < 0.02 respectively) in-between the hemispheres. Vessel reaction was higher in the hemisphere corresponding to the more advanced visual field defect. Arterial diameters reacted similarly, failing to reach statistical significance.ConclusionLocalized retinal vessel regulation is significantly altered in glaucoma patients with asymmetric altitudinal visual field defects. Veins supplying the hemisphere concordant to a less profound visual field defect show diminished diameter changes. Vascular dysregulation might be particularly important in early glaucoma stages prior to a significant visual field defect.

Acute effect of spinal cord stimulation on autonomic nervous system function in patients with heart failure.

To test the hypothesis that spinal cord stimulation (SCS) acutely improves heart rate variability (HRV) and baroreceptor sensitivity (BRS) in patients with heart failure (HF). SCS (15 minutes) was delivered in four different settings: 90% of maximal tolerated stimulation amplitude (MTA) targeting the T1-T4 spinal cord segments (SCS90T1-4), 60% of MTA (SCS60T1-4), 90% of MTA with cranial (SCS90CR) and caudal (SCS90CA) electrode configuration. HRV and BRS were recorded continuously and stimulation was compared to device off. Fifteen HF patients were included. SCS90T1-4 did not change the standard deviation of intervals between normal beats (SDNN, p = 0.90), BRS (p = 0.55) or other HRV parameters. In patients with baseline SDNN <50 ms, SCS90T1-4 significantly increased SDNN (p = 0.004). Acute SCS at 60-90% of MTA targeting upper thoracic spinal cord segments does not improve autonomic balance or baroreceptor sensitivity in unselected patients with heart failure but may improve HRV in patients with low SDNN.

Ramp Rate Evaluation and Configuration for Safe and Tolerable Closed-Loop Deep Brain Stimulation.

Closed-loop deep brain stimulation is a novel form of therapy that has shown benefit in preliminary studies and may be clinically available in the near future. Initial closed-loop studies have primarily focused on responding to sensed biomarkers with adjustments to stimulation amplitude, which is often perceptible to study participants depending on the slew or "ramp" rate of the amplitude changes. These subjective responses to stimulation ramping can result in transient side effects, illustrating that ramp rate is a unique safety parameter for closed-loop neural systems. This presents a challenge to the future of closed-loop neuromodulation systems: depending on the goal of the control policy, clinicians will need to balance ramp rates to avoid side effects and keep the stimulation therapeutic by responding in time to affect neural dynamics. In this paper, we demonstrate the results of an initial investigation into methodology for finding safe and tolerable ramp rates in four people with Parkinson's disease (PD). Results suggest that optimal ramp rates were found more accurately during varying stimulation when compared to simply toggling between maximal and minimal intensity levels. Additionally, switching frequency instantaneously was tolerable at therapeutic levels of stimulation. Future work should focus on including optimization techniques to find ramp rates.

268 Smart polymer implants as an emerging technology for treating airway collapse in OSA: a proof of concept study

Abstract Introduction Implantable 3D printed ‘smart’ polymers are an emerging technology with potential applications in treating collapse in adult obstructive sleep apnea through mechanical airway manipulation. There is a paucity of devices that are commercially available or in research and development stage. Limited studies have investigated the use of implantable smart polymers in reversing the collapsibility of the pharyngeal airway by creating counter forces during sleep. This paper describes an application of implantable magnetic polymer technology in an in-vivo porcine model. Study Objectives: To assess the use of a novel magnetic polymer implant in reversing airway collapse and identifying potential anatomical targets for airway implant surgery in an in-vivo porcine model. Methods Target sites of airway collapse were genioglossus muscle, hyoid bone and middle constrictor. Magnetic polymer implants were sutured to these sites and external magnetic forces, through magnets with pull forces rated at 102kg and 294kg, were applied at the skin. The resultant airway movement was assessed via nasendoscopy. Pharyngeal plexus branches to the middle constrictor muscle were stimulated at 0.5mA, 1.0mA and 2.0mA and airway movement assessed via nasendoscopy. Results At the genioglossus muscles large magnetic forces were required to produce airway movement. At the hyoid bone, anterior movement of the airway was noted when using a 294kg rated magnet. At the middle constrictor muscle, an anterolateral (or rotatory) pattern of airway movement was noted when using the same magnet. Stimulation of pharyngeal plexus branches to the middle constrictor revealed contraction and increasing rigidity of the lateral walls of the airway as stimulation amplitude increased. The resultant effect was prevention of collapse, a previously unidentified pattern of airway movement. Conclusion Surgically implanted smart polymers are an emerging technology showing promise in the treatment of airway collapse in obstructive sleep apnea. Future research should investigate their biomechanical role as an adjunct to treatment of airway collapse through nerve stimulation. Support (if any) Garnett-Passe and Rodney Williams Memorial Foundation, Conjoint Grant, 2016-18.

Pulse Shaping Strategies for Electroceuticals: A Comprehensive Survey of the Use of Interphase Gaps in Miniature Stimulation Systems.

Interphase gaps (IPGs) are among the most commonly suggested pulse shape variations to try to enhance neural stimulation efficiency by reducing the action potential (AP) suppressing effect of an early anodic hyperpolarization. The majority of published literature on the effect of IPGs is based on investigations of monopolar stimulation configurations. However, many contemporary neuromodulation applications including the emerging field of electroceutical devices operate in a bipolar electrode configuration. We investigated the effect of IPGs and asymmetric biphasic current controlled pulses with reduced anodic amplitude on neural activation in both principal electrode configurations in a rodent in-vivo nerve muscle preparation. In the monopolar electrode configuration, our findings of 10.9 ± 1.5% decreased stimulation amplitude with 200 μs IPGs in biphasic pulses of 40 μs phase width are in agreement with published literature in this configuration. Surprisingly, using the bipolar configuration, opposite effects of IPGs were observed and neural activation required up to 18.6 ± 3.1% (phase width 100 μs, IPG = 1000 μs) higher amplitudes. Electroneurogram recordings of the stimulated nerve revealed temporal differences in AP generation between the monopolar and bipolar configuration. In the bipolar configuration excitation first occurred in response to the middle field transition of biphasic pulses. This is the first study to report consistently increased amplitude requirements with IPGs in bipolar stimulation configurations. Our findings must be taken into consideration when designing stimulation waveforms for neuromodulation devices that operate in a bipolar mode to avoid increased amplitude requirements that result in increased energy consumption.

Layer-specific parameters of intracortical microstimulation of the somatosensory cortex

Objective. Intracortical microstimulation of the primary somatosensory cortex (S1) has shown great progress in restoring touch sensations to patients with paralysis. Stimulation parameters such as amplitude, phase duration, and frequency can influence the quality of the evoked percept as well as the amount of charge necessary to elicit a response. Previous studies in V1 and auditory cortices have shown that the behavioral responses to stimulation amplitude and phase duration change across cortical depth. However, this depth-dependent response has yet to be investigated in S1. Similarly, to our knowledge, the response to microstimulation frequency across cortical depth remains unexplored. Approach. To assess these questions, we implanted rats in S1 with a microelectrode with electrode-sites spanning all layers of the cortex. A conditioned avoidance behavioral paradigm was used to measure detection thresholds and responses to phase duration and frequency across cortical depth. Main results. Analogous to other cortical areas, the sensitivity to charge and strength–duration chronaxies in S1 varied across cortical layers. Likewise, the sensitivity to microstimulation frequency was layer dependent. Significance. These findings suggest that cortical depth can play an important role in the fine-tuning of stimulation parameters and in the design of intracortical neuroprostheses for clinical applications.

Clinical Study of the IOPTx™ System - an Electroceutical Wearable to Lower Intraocular Pressure

ABSTRACT Purpose: To investigate the safety and efficacy of the IOPTx™ system – a novel wearable, electroceutical treatment to lower intraocular pressure. Methods: Patients wear the customized contact lens and spectacles of the IOPTx™ system and undergo three 15-minute randomized stimulation trials at different stimulus amplitudes with 15 minutes of rest in between. The parameters for the stimulation trials include a frequency of 50 Hz, a pulse width of 100 µs, and current amplitudes between 90–150 µA. The optometrist measures the intraocular pressure (IOP) before, immediately after, and 15 minutes after the trial, and performs topography, a slit eye examination, and specular microscopy before and after the entire study to check the health of the eye and confirm the safety of the system. Results: The IOPTx™ system successfully modulates a patient’s IOP. By testing various currents, we create individual tuning curves examining the effect of the stimulation amplitude on the change in IOP. Each patient may have an optimal dose-response curve and by normalizing to this value, the IOPTx™ system decreased IOP by an average of 17.7% with fifteen minutes of therapy. No Adverse Events or Adverse Device Effects occurred.Conclusions: The results of this clinical case series provide preliminary evidence of efficacy and safety of the IOPTx™ system and its potential usefulness to lower IOP in glaucoma and ocular hypertension.

Investigation of Magnetoelectric Sensor Requirements for Deep Brain Stimulation Electrode Localization and Rotational Orientation Detection.

Correct position and orientation of a directional deep brain stimulation (DBS) electrode in the patient’s brain must be known to fully exploit its benefit in guiding stimulation programming. Magnetoelectric (ME) sensors can play a critical role here. The aim of this study was to determine the minimum required limit of detection (LOD) of a ME sensor that can be used for this application by measuring the magnetic field induced by DBS. For this experiment, a commercial DBS system was integrated into a head phantom and placed inside of a state-of-the-art Superconducting Quantum Interference Device (SQUID)-based magnetoencephalography system. Measurements were performed and analyzed with digital signal processing. Investigations have shown that the minimum required detection limit depends on various factors such as: measurement distance to electrode, bandwidth of magnetic sensor, stimulation amplitude, stimulation pulse width, and measurement duration. For a sensor that detects only a single DBS frequency (stimulation frequency or its harmonics), a LOD of at least 0.04 pT/Hz is required for 3 mA stimulation amplitude and 60 s pulse width. This LOD value increases by an order of magnitude to 0.4 pT/Hz for a 1 kHz, and by approximately two orders to 3 pT/Hz for a 10 kHz sensor bandwidth. By averaging, the LOD can be reduced by at least another 2 orders of magnitude with a measurement duration of a few minutes.

Potential Therapeutic Effect of Low Amplitude Burst Spinal Cord Stimulation on Pain

The SUNBURST Study, a USA-based controlled cross-over trial demonstrated that burst spinal cord stimulation was superior compared to tonic stimulation in suppressing chronic intractable pain. However, when on burst stimulation, participants preferred lower to higher amplitudes. This led to the hypothesis that lower burst amplitudes will correlate with lower pain scores while higher amplitudes will be associated with higher pain scores. To investigate correlations between burst amplitude and self-reported pain and different psychosocial measures. One hundred participants in the SUNBURST study were randomized to receive burst or tonic stimulation, each for 12 weeks in a cross-over manner. Complete data of 99 participants were used in this secondary analysis. Pearson correlations were conducted at 6-, 12-, 18-, and 24-weeks postactivation to determine the strength of linear relationships between burst amplitude and (1) the average seven-day daily pain Visual Analogue Scale (VAS), (2) the different domains of the Pain Catastrophizing Scale (PCS), (3) the different domains of the SF-36v2 (Quality Metric Incorporated, Lincoln, RI) Health Survey. In addition, correlations between tonic stimulation amplitude and the above-mentioned outcome measures were examined. Significant positive correlations were identified between burst amplitude and total, "worst," and "trunk" pain for VAS; all domains for PCS; and "Role-Physical," "Bodily Pain," and "General Health" for SF-36v2™ after 12-weeks of burst stimulation. In burst spinal cord stimulation, in contrast to tonic stimulation, lower amplitudes are more effective in suppressing pain than high amplitudes.

The Effect of Amplitude, Event, and Duration of Electrical Stimulation on the Evacuation Velocity of Rodents: An Evacuation Experiment

The Effect of Amplitude, Event, and Duration of Electrical Stimulation on the Evacuation Velocity of Rodents: An Evacuation Experiment

Subthalamic beta band suppression reflects effective neuromodulation in chronic recordings

Biomarkers for future adaptive deep brain stimulation still need evaluation in clinical routine. Here, we aimed to assess stimulation-induced modulation of beta-band activity and clinical symptoms in a Parkinson's disease patient during chronic neuronal sensing using a novel implantable pulse generator. Subthalamic activity was recorded OFF and ON medication during a stepwise increase of stimulation amplitude. Off-line fast fourier transfom -based analysis of beta-band activity was correlated with motor performance rated from blinded videos. The stepwise increase of stimulation amplitude resulted in decreased beta oscillatory activity and improvement of bradykinesia. Mean low beta-band (13-20Hz) activity correlated significantly with bradykinesia (ρ= 0.662, p<0.01). Motor improvement is reflected in reduced subthalamic beta-band activity in Parkinson's disease, supporting beta activity as a reliable biomarker. The novel PERCEPT neurostimulator enables chronic neuronal sensing in clinical routine. Our findings pave the way for a personalized precision-medicine approach to neurostimulation.

A task-relevant experimental pain model to target motor adaptation.

Motor adaptation is thought to be a strategy to avoid pain. Current experimental pain models do not allow for consistent modulation of pain perception depending on movement. We showed that low-frequency sinusoidal stimuli delivered at painful intensity result in minimal habituation of pain perception (over 60s) and minimal stimulation artefacts on electromyographic signals. When the amplitude of the low-frequency sinusoidal stimuli was modulated based on the vertical force participants applied to the ground with their right leg while standing upright, we demonstrated a strong association between perceived pain and motor adaptation. By enabling task-relevant modulation of perceived pain intensity and the recording electromyographic signals during electrical painful stimulation, our novel pain model will permit direct experimental testing of the relationship between pain and motor adaptation. Contemporary pain adaptation theories predict that motor adaptation occurs to limit pain. Current experimental pain models, however, do not allow for pain intensity modulation according to one's posture or movements. We developed a task-relevant experimental pain model using low-frequency sinusoidal electrical stimuli applied over the infrapatellar fat pad. In fourteen participants, we compared perceived pain habituation and stimulation-induced artefacts in vastus medialis electromyographic recordings elicited by sinusoidal (4, 10, 20 and 50Hz) and square electrical waveforms delivered at constant peak stimulation amplitude. Next, we simulated a clinical condition where perceived knee pain intensity is proportional to the load applied on the leg by controlling sinusoidal current amplitude (4Hz) according to the vertical force the participants applied with their right leg to the ground while standing upright. Pain ratings habituated over a 60s period for 50Hz sinusoidal and square waveforms but not for low-frequency sinusoidal stimuli (P<0.001). EMG filters removed most stimulation artefacts for low-frequency sinusoidal stimuli (4Hz). While balancing upright, participants' pain ratings were correlated with the force applied by the right leg (R2 =0.65), demonstrating task-relevant changes in perceived pain intensity. Low-frequency sinusoidal stimuli can induce knee pain of constant intensity for 60s with minimal EMG artefacts while enabling task-relevant pain modulation when controlling current amplitude. By enabling task-dependent modulation of perceived pain intensity, our novel experimental model replicates key temporal aspects of clinical musculoskeletal pain while allowing quantification of neuromuscular activation during painful electrical stimulation. This approach will enable researchers to test the predicted relationship between movement strategies and pain.

Multivariate analysis of the systemic response to auditory stimulation: An integrative approach.

What is the central question of this study? Auditory stimulation produces a response in different physiological systems: cardiac, peripheral blood flow, electrodermal, cortical and peripheral haemodynamic responses and auditory event-related potentials. Do all these subsystems covary when responding to auditory stimulation, suggesting a unified locus of control, or do they not covary, suggesting independent loci of control for these physiological responses? What is the main finding and its importance? Auditory sensory gating reached a fixed level of neural activity independently of the intensity of auditory stimulation. The use of multivariate techniques revealed the presence of different regulatory mechanisms for the different physiologically recorded signals. We studied the effects of an increasing amplitude of auditory stimulation on a variety of autonomic and CNS responses and their possible interdependence. The subjects were stimulated with an increasing amplitude of auditory tones while the auditory event-related potentials (ERPs), the cortical and extracerebral functional near-infrared spectroscopy (fNIRS) signal of standard and short separation channel recordings, the peripheral pulse measured by photoplethysmography, heart rate and electrodermal responses were recorded. Trials with eight tones of equal amplitude were presented. The results showed a parallel increase of activity in ERPs, fNIRS and peripheral responses with the increase in intensity of auditory stimulation. The ERPs, measured as peak-to-peak N1-P2, showed an increase in amplitude with auditory stimulation and a high attenuation from the first presentation with respect to the second to eighth presentations. Peripheral signals and standard and short channel fNIRS responses showed a decrease in amplitude in the high-intensity auditory stimulation conditions. Principal components analysis showed independent sources of variance for the recorded signals, suggesting independent control of the recorded physiological responses. The present results suggest a complex response associated to the increase of auditory stimulation with a fixed amplitude for ERPs, and a decrease in the peripheral and cortical haemodynamic response, possibly mediated by activation of the sympathetic nervous system, constituting a defensive reflex to excessive auditory stimulation.

Influence of Virchow-Robin spaces on the electric field distribution in subthalamic nucleus deep brain stimulation

Patient MRI from DBS implantations in the subthalamic nucleus (STN) were reviewed and it was found that around 10% had Virchow-Robin spaces (VRS). Patient-specific models were developed to evaluate changes in the electric field (EF) around DBS leads. The patients (n = 7) were implanted bilaterally either with the standard voltage-controlled lead 3389 or with the directional current-controlled lead 6180. The EF distribution was evaluated by comparing simulations using patient-specific models with homogeneous models without VRS. The EF, depicted with an isocontour of 0.2 V/mm, showed a deformation in the presence of the VRS around the DBS lead. For patient-specific models, the radial extension of the EF isocontours was enlarged regardless of the operating mode or the DBS lead used. The location of the VRS in relation to the active contact and the stimulation amplitude, determined the changes in the shape and extension of the EF. It is concluded that it is important to take the patients' brain anatomy into account as the high conductivity in VRS will alter the electric field if close to the DBS lead. This can be a cause of unexpected side effects.

Speech Function Following Deep Brain Stimulation of the Caudal Zona Incerta: Effects of Habitual and High-Amplitude Stimulation

Purpose Deep brain stimulation (DBS) is often successful in alleviating motor symptoms of essential tremor (ET); however, DBS may also induce adverse speech effects. The caudal zona incerta (cZi) is a promising DBS target for tremor, but less is known about the consequences of cZi DBS for speech. This preliminary study examined how habitual cZi DBS and cZi stimulation at high amplitudes may affect speech function in persons with ET. Method Fourteen participants with ET were evaluated: off stimulation, on habitual cZi DBS, and with unilateral cZi stimulation at increasing stimulation amplitudes. At each stimulation condition, the participants read three 16-word sentences. Two speech-language pathologists made audio-perceptual consensus ratings of overall speech function, articulation, and voice using a visual sort and rate method. Rated functions when off stimulation, on habitual cZi DBS, and at maximal-amplitude stimulation were compared using Friedman nonparametric tests. For participants with bilateral habitual DBS (n = 5), the effects of bilateral and unilateral stimulation were described in qualitative terms. Results Habitual cZi DBS had no significant group-level effect on any of the investigated speech parameters. Maximal-amplitude stimulation had a small but significant negative effect on articulation. Participants with reduced articulatory precision (n = 9) had more medially placed electrodes than the nonaffected group (n = 5). Bilateral and unilateral left stimulation had comparable effects on speech. Conclusions Findings from this preliminary study of cZi DBS indicate that speech is generally not affected by stimulation at habitual levels. High-amplitude cZi stimulation may, however, induce adverse effects, particularly on articulation. Instances of decreased articulatory function were associated with stimulation of more medial electrode contacts, which could suggest cerebello-rubrospinal involvement.

Electrophysiological mapping and assessment of facial nerve functioning during acoustic neuroma operations.

BackgroundElectrophysiological monitoring is used routinely to protect the facial nerve during acoustic neuroma surgery. This study aimed to clarify the relationship between the facial nerve’s electrophysiological monitoring parameters and its function after surgery.MethodsFifty-two patients with acoustic neuroma who underwent surgery were included. After localizing the facial nerve, its monitoring results during surgeries performed at our center were analyzed. Postoperative nerve functioning was correlated with the stimulation threshold of the facial nerve’s proximal segment, proximal-to-distal amplitude ratio of the facial nerve, and proximal stimulation amplitude. Receiver-operating characteristic curves of the three parameters were calculated.ResultsElectrical stimulation accurately described the facial nerve’s anatomic distribution after the depth of anesthesia was assessed via accessory nerve stimulation. The data recorded after resection showed that a higher proximal-to-distal amplitude ratio was associated with better facial nerve functioning (P=0.037). A lower stimulation threshold of the proximal segment correlated with better facial nerve functioning (P=0.038).ConclusionsThe most sensitive index to predict postoperative nerve functioning is the facial nerve’s proximal-to-distal amplitude ratio. Accessory nerve stimulation can determine the appropriate depth of anesthesia, Electromyography (EMG) monitoring of the facial nerve during acoustic neuroma surgery can protect it effectively.

Model-based analysis of implanted hypoglossal nerve stimulation for the treatment of obstructive sleep apnea

Individuals with obstructive sleep apnea (OSA), characterized by frequent sleep disruptions from tongue muscle relaxation and airway blockage, are known to benefit from on-demand electrical stimulation of the hypoglossal nerve. Hypoglossal nerve stimulation (HNS) therapy, which activates the protrusor muscles of the tongue during inspiration, has been established in multiple clinical studies as safe and effective, but the mechanistic understanding for why some stimulation parameters work better than others has not been thoroughly investigated. In this study, we developed a detailed biophysical model that can predict the spatial recruitment of hypoglossal nerve fascicles and axons within these fascicles during stimulation through nerve cuff electrodes. Using this model, three HNS programming scenarios were investigated including grouped cathode (---), single cathode (o-o), and guarded cathode bipolar (+-+) electrode configurations. Regardless of electrode configuration, nearly all hypoglossal nerve axons circumscribed by the nerve cuff were recruited for stimulation amplitudes <3 V. Within this range, monopolar configurations required lower stimulation amplitudes than the guarded bipolar configuration to elicit action potentials within hypoglossal nerve axons. Further, the spatial distribution of the activated axons was more uniform for monopolar versus guarded bipolar configurations. The computational models predicted that monopolar HNS provided the lowest threshold and the least sensitivity to rotational angle of the nerve cuff around the hypoglossal nerve; however, this setting also increased the likelihood for current leakage outside the nerve cuff, which could potentially activate axons in unintended branches of the hypoglossal nerve. NCT01161420.

An Instrumented Cochlea Model for the Evaluation of Cochlear Implant Electrical Stimulus Spread.

Cochlear implants use electrical stimulation of the auditory nerve to restore the sensation of hearing to deaf people. Unfortunately, the stimulation current spreads extensively within the cochlea, resulting in “blurring” of the signal, and hearing that is far from normal. Current spread can be indirectly measured using the implant electrodes for both stimulating and sensing, but this provides incomplete information near the stimulating electrode due to electrode-electrolyte interface effects. Here, we present a 3D-printed “unwrapped” physical cochlea model with integrated sensing wires. We integrate resistors into the walls of the model to simulate current spread through the cochlear bony wall, and “tune” these resistances by calibration with an in-vivo electrical measurement from a cochlear implant patient. We then use this model to compare electrical current spread under different stimulation modes including monopolar, bipolar and tripolar configurations. Importantly, a trade-off is observed between stimulation amplitude and current focusing among different stimulation modes. By combining different stimulation modes and changing intracochlear current sinking configurations in the model, we explore this trade-off between stimulation amplitude and focusing further. These results will inform clinical strategies for use in delivering speech signals to cochlear implant patients.