Clinical application of electrically evoked compound action potentials

ECAPs are the summary of multiple neurons’ spikes which could be recorded by a bidirectional stimulation-recording system via the cochlear implant,with the artifact elimination paradigms of forward-masking subtraction paradigm or alternating polarity paradigm.Three kinds of FDA approved cochlear implants support ECAP testing.This article is to summarize the clinical application of ECAP lest.ECAP test after insertion of electrode during implant operation has been widely used during cochlear implant surgery.In recent years.ECAP thresholds are also used to estimate the T levels and C levels helping programming.However,correlation between ECAP thresholds and psychophysical thresholds is affected by many factors.So far,ECAPs cannot yet be a good indicator of post-operative hearing and speech performance.

A Study of Compound Action Potentials in Current-Coupled Tracts: the General Case

In this paper, the authors investigate compound action potentials formed when the underlying tract's axons have current-mediated coupling amongst themselves, and no field-mediated coupling. The key finding of the paper is that, for the case of biophysically inhomogeneous axon tracts, the compound action potential is governed by a Hodgkin-Huxley like equation itself in certain cases. The paper extends an earlier result for the identical axon case.

The optimal distance between two electrode tips during recording of compound nerve action potentials in the rat median nerve

The distance between the two electrode tips can greatly influence the parameters used for record- ing compound nerve action potentials. To investigate the optimal parameters for these recordings in the rat median nerve, we dissociated the nerve using different methods and compound nerve action potentials were orthodromically or antidromically recorded with different electrode spac- ings. Compound nerve action potentials could be consistently recorded using a method in which the middle part of the median nerve was intact, with both ends dissociated from the surrounding fascia and a ground wire inserted into the muscle close to the intact part. When the distance be- tween two stimulating electrode tips was increased, the threshold and supramaximal stimulating intensity of compound nerve action potentials were gradually decreased, but the amplitude was not changed significantly. When the distance between two recording electrode tips was increased, the amplitude was gradually increased, but the threshold and supramaximal stimulating intensity exhibited no significant change. Different distances between recording and stimulating sites did not produce significant effects on the aforementioned parameters. A distance of 5 mm between recording and stimulating electrodes and a distance of 10 mm between recording and stimulating sites were found to be optimal for compound nerve action potential recording in the rat median nerve. In addition, the orthodromic compound action potential, with a biphasic waveform that was more stable and displayed less interference （however also required a higher threshold and higher supramaximal stimulus）, was found to be superior to the antidromic compound action potential.

Promising application of a new ulnar nerve compound muscle action potential measurement montage in amyotrophic lateral sclerosis:a prospective cross-sectional study

Previous studies have shown that ulnar nerve compound muscle action potential recorded by the conventional“belly-tendon”montage does not accurately and completely reflect the action potential of the ulnar nerve dominating the abductor digiti minimi muscle due to the effects of far-field potentials of intrinsic hand muscles.A new method of ulnar nerve compound muscle action potential measurement was developed in 2020,which adjusts the E2 electrode from the distal tendon of the abductor digitorum to the middle of the back of the proximal wrist.This new method may reduce the influence of the reference electrode and better reflect the actual ulnar nerve compound muscle action potential.In this prospective cross-sectional study,we included 64 patients with amyotrophic lateral sclerosis and 64 age-and sex-matched controls who underwent conventional and novel ulnar nerve compound muscle action potential measurement between April 2020 and May 2021 in Peking University Third Hospital.The compound muscle action potential waveforms recorded by the new montage were unimodal and more uniform than those recorded by traditional montage.In the controls,no significant difference in the compound muscle action potential waveforms was found between the traditional montage and new montage recordings.In amyotrophic lateral sclerosis patients presenting with abductor digiti minimi spontaneous activity and muscular atrophy,the amplitude of compound muscle action potential-pE2 was significantly lower than that of compound muscle action potential-dE2(P<0.01).Using the new method,damaged axons were more likely to exhibit more severe amplitude decreases than those measured with the traditional method,in particular for patients in early stage amyotrophic lateral sclerosis.In addition,the decline in compound muscle action potential amplitude measured by the new method was correlated with a decrease in Revised Amyotrophic Lateral Sclerosis Functional Rating Scale scores.These findings suggest that the new ulnar nerve compound muscle action potential measurement montage reduces the effects of the reference electrode through altering the E2 electrode position,and that this method is more suitable for monitoring disease progression than the traditional montage.This method may be useful as a biomarker for longitudinal follow-up and clinical trials in amyotrophic lateral sclerosis.

Effects of dexmedetomidine and dexketoprofen on the conduction block of rat sciatic nerve

Dexmedetomidine is a selective α2-adrenoceptor agonist that is used because of its sedative,anxiolytic,and analgesic effects.Dexketoprofen,which is used as an analgesic,is a nonselective nonsteroidal anti-inflammatory drug (NSAID).The use of dexmedetomidine and dexketoprofen as adjuvants to local anesthetics for the peripheral nerve is gradually increasing.In this study,we aimed to investigate the effects of different doses of dexmedetomidine and dexketoprofen on conduction block of rat sciatic nerve.The isolated sciatic nerve from adult rats was transferred to a nerve chamber.The compound action potentials (CAPs) were recorded from stimulated nerve with electrophysiological methods.Dexmedetomidine (n = 8) and dexketoprofen (n = 8) were administered in the chamber with cumulative concentrations of 10–9 to 10–5 M,and the CAPs were recorded for 5 and 10 minutes.The CAP parameters were calculated.Both dexmedetomidine and dexketoprofen significantly depressed all CAP parameters in a dose-dependent manner compared with the control group,i.e.,the group in which rats did not receive treatment.CAP parameters showed there was no significant difference in nerve conduction inhibition between dexmedetomidine and dexketoprofen.Higher doses of dexmedetomidine suppressed the conduction in the fast-conducting fibers;however,dexketoprofen was found to suppress the conduction in the slow-conducting fibers in a time-dependent manner and suppress the conduction in the medium- and slow-conducting fibers in a dose-dependent manner.These findings suggest that dexmedetomidine and dexketoprofen exhibit better anesthetic effects on peripheral nerve through different ways of action.The experimental procedures were approved by the Necmettin Erbakan University on January 30,2013 (approval No.2013-024).

In vivo auditory nerve stimulation with visible light

Background:Infrared laser stimulation has been proposed as an innovative method to elicit an auditory nerve response.Most studies have focused on usi ng long-wavelength infrared(>980 nm)pulsod lasers with high water absoption cofficients.This paper sought to assts8 whether a short-wavelength laser(465 nm)with an absorption cofficient as low as 103 cm^(-1) would activate the auditory nerve and studied its potential mechanism.Method:Optical compound action potentials(OCAPs)were recorded when synchronous triger laser pulses st imulate the cochlea before and after deafening,varying the pulse durations(from 8001us to 36001us)and the amount of radiant enengy(fom 18.05 mJ/cm^(2) to 107.91 mJ/cm^(2)).A thermal infrared imager was applied to monitor the tempenature change of the guinea pig cochlea.Results:The results showed that pulsed laser stimulation at 465 nm could invoke OCAPs and had a similar waveform compared to the acoustical compound action potentials.The amplitude of OCAPs had a poaitive correlation with the in-creasi ng laser peak power,while the latency of OCAPs showed a negative correlation.The imager data showed that the temperature in thecochlea rose quickly by about 0.3℃ right after stimulating the cochlea and decreased quickly back to the initial temperature as the stimulation ended.Con-clusions:This paper demonstrates that 465-nm laser st imulation can successfully induce OCAPs outside the cochlea,and that the amplitude and latency of the invoked OCAPs are highly affected by laser peak power.This paper proposes that a photothermal efect might be the main mechanism for the auditory nerve response induced by short-wavelength laser stimulation.

Stimulating effect of thyroid hormones in peripheral nerve regeneration:research history and future direction toward clinical therapy

Injury to peripheral nerves is often observed in the clinic and severe injuries may cause loss of motor and sensory functions.Despite extensive investigation,testing various surgical repair techniques and neurotrophic molecules,at present,a satisfactory method to ensuring successful recovery does not exist.For successful molecular therapy in nerve regeneration,it is essential to improve the intrinsic ability of neurons to survive and to increase the speed of axonal outgrowth.Also to induce Schwann cell phenotypical changes to prepare the local environment favorable for axonal regeneration and myelination.Therefore,any molecule that regulates gene expression of both neurons and Schwann cells could play a crucial role in peripheral nerve regeneration.Clinical and experimental studies have reported that thyroid hormones are essential for the normal development and function of the nervous system,so they could be candidates for nervous system regeneration.This review provides an overview of studies devoted to testing the effect of thyroid hormones on peripheral nerve regeneration.Also it emphasizes the importance of combining biodegradable tubes with local administration of triiodothyronine for future clinical therapy of human severe injured nerves.We highlight that the local and single administration of triiodothyronine within biodegradable nerve guide improves significantly the regeneration of severed peripheral nerves,and accelerates functional recovering.This technique provides a serious step towards future clinical application of triiodothyronine in human severe injured nerves.The possible regulatory mechanism by which triiodothyronine stimulates peripheral nerve regeneration is a rapid action on both axotomized neurons and Schwann cells.

Electrically evoked auditory nerve responses in the cochlea with normal outer hair cells

As hybrid cochlear implant devices are increasingly used for restoring hearing in patients with residual hearing, it is important to understand electrically evoked responses in cochleae having functional hair cells. To test the hypothesis that extracochlear electrical stimulation (EES) from sinusoidal current can provoke an auditory nerve response with normal frequency selectivity, the EES-evoked compound action potential(ECAP) was investigated in this study. Brief sinusoidal electrical currents, delivered via a round window electrode, were used to evoke ECAP. The ECAP waveform was observed to be the same as the acoustically evoked CAP(ACAP), except for a shorter latency. The input/output and intensity/latency functions of ACAPs and ECAPs were also similar. The maximum acoustic masking for both ACAP and ECAP occurred near probe frequencies. Since the masked tuning curve of a CAP reflects the frequency selectivity of neural excitation, these data demonstrate a highly specific activation of the auditory nerve, which would result in high degree of frequency selectivity. This frequency selectivity likely results from the cochlear traveling wave caused by electrically stimulated outer hair cells.

Repairing whole facial nerve defects with xenogeneic acellular nerve grafts in rhesus monkeys

Acellular nerve allografts conducted via chemical extraction have achieved satisfactory results in bridging whole facial nerve defects clinically,both in terms of branching a single trunk and in connecting multiple branches of an extratemporal segment.However,in the clinical treatment of facial nerve defects,allogeneic donors are limited.In this experiment,we exposed the left trunk and multiple branches of the extratemporal segment in six rhesus monkeys and dissected a gap of 25 mm to construct a monkey model of a whole left nerve defect.Six monkeys were randomly assigned to an autograft group or a xenogeneic acellular nerve graft group.In the autograft group,the 25-mm whole facial nerve defect was immediately bridged using an autogenous ipsilateral great auricular nerve,and in the xenogeneic acellular nerve graft group,this was done using a xenogeneic acellular nerve graft with trunk-branches.Examinations of facial symmetry,nerve-muscle electrophysiology,retrograde transport of labeled neuronal tracers,and morphology of the regenerated nerve and target muscle at 8 months postoperatively showed that the faces of the monkey appeared to be symmetrical in the static state and slightly asymmetrical during facial movement,and that they could actively close their eyelids completely.The degree of recovery from facial paralysis reached House-Brackmann grade II in both groups.Compound muscle action potentials were recorded and orbicularis oris muscles responded to electro-stimuli on the surgical side in each monkey.Fluoro Gold-labeled neurons could be detected in the facial nuclei on the injured side.Immunohistochemical staining showed abundant neurofilament-200-positive axons and soluble protein-100-positive Schwann cells in the regenerated nerves.A large number of mid-graft myelinated axons were observed via methylene blue staining and a transmission electron microscope.Taken together,our data indicate that xenogeneic acellular nerve grafts from minipigs are safe and effective for repairing whole facial nerve defects in rhesus monkeys,with an effect similar to that of autologous nerve transplantation.Thus,a xenogeneic acellular nerve graft may be a suitable choice for bridging a whole facial nerve defect if no other method is available.The study was approved by the Laboratory Animal Management Committee and the Ethics Review Committee of the Affiliated Wuxi No.2 People's Hospital of Nanjing Medical University,China(approval No.2018-D-1)on March 15,2018.

Compound muscle action potential(CMAP)scan examination of paretic and contralateral muscles reveals motor unit alterations after stroke

This study presents a novel compound muscle action potential(CMAP)examination of motor unit changes in paretic muscle post stroke.CMAP scan of the first dorsal interosseous(FDI)muscle was performed bilaterally in 16 chronic stroke subjects.Various parameters were derived from the CMAP scan to examine paretic muscle changes,including CMAP amplitude,D50,step index(STEPIX)and amplitude index(AMPIX).A significant decrease in CMAP amplitude and STEPIX was observed in paretic muscles compared with contralateral muscles(CMAP amplitude:paretic(9.0±0.5)mV,contralateral(11.3±0.9)mV,P=0.024;STEPIX:paretic 101.2±7.6,contralateral 121.9±6.5,P=0.020).No significant difference in D50 and AMPIX was observed between the paretic and contralateral sides(P>0.05).The findings revealed complex paretic muscle changes including motor unit degeneration,muscle fiber denervation,reinnervation and atrophy,providing useful insights to help understand neuromuscular mechanisms associated with weakness and other functional deterioration post stroke.The CMAP scan experimental protocols and the applied processing methods are noninvasive,convenient,and automated,offering practical benefits for clinical application.

Photoacoustic effect invokes auditory response in infrared neuron stimulation

Infrared neuron stimulation is regarded as an innovative approach for stimulating cochleae in animals while the exact mechanism still remains unknown.In this paper,we studied compound action potentials of guinea pig cochleae with chronic or acute deafness.We recorded optical compound action potentials and analyzed stretched cochlear preparations by fiuorescence microscopy.Photoacoustic signals were measured by hydrophone and microphone,respectively.In our experiment,we observed a switch response effect in vitro and in vivo experiments.Therefore,we proposed photoacoustic effect could invoke auditory response in infrared neuron stimulation.

Prophylactic effect of Ca^(2+)-deficient artificial perilymph perfusion on noise-induced hearing loss

Objective To investigate the prophylactic effect of low calcium concentration perilymph on noise-induced hearing loss. Methods Forty guinea pigs with normal hearing weighing 250-350 g were assigned to five groups (8 in each group): (1) Ca2+-deficient perilymph perfusion (CDP) for 2 h; (2) white noise (120 dB SPL) exposure (WNE) only for 1 h, (3) combination of calcium-deficient perilymph perfusion and white noise (120 dB SPL) exposure (WNE+CDP); (4) normal artificial perilymph (NAP) perfusion for 2 h; and (5) white noise exposure + normal artificial perilymph perfusion (WNE+NAP) for 2 h. Compound action potentials (CAP) evoked by click was recorded from round window every 15 min. The cochleae from 5 animals in each group were examined with scanning electron microscope. Results The CAP for group 1 experienced a threshold shift (TS) of 15-26 dB, while group 2 yielded a 46-59 dB TS and group 3 a 37-45 dB TS; no threshold shift occurred in group 4. The CAP TS in group 5 was 33-64 dB. The CAP TS of group 3 was less than that of group 2. After one hour of noise exposure, the CAP TS of group 3 were 45.92±2.90 dB and 59.30±3.95dB in group 2. There were significant differences (P<0.05) between groups 3 and 2. The CAP TS of group 3 was less than that of group 5 at the points of 1, 1.5 and 2 h after noise exposure. There was a significant difference between groups 3 and 5 (P<0.01). Stereocilia of 89 OHC3 were in disarray in five cochleae after noise exposure in group 2. The cuticular plates of 8 OHC2,3 sank and the stereocilia became fused in only one animal cochlea after noise exposure in group 3 combined with low calcium perilymph perfusion. Conclusions Low calcium concentration appears to participate in preventing noise-induced hearing loss and the rising of calcium concentrations in inner hair cells after noise exposure, which may have been due to the opening of calcium channels in inner hair cells during noise exposure. The mechanism of the prophylactic effect might be caused by a lower calcium concentration in inner hair cells in the cochlea attenuating the influence of noise exposure on hearing loss; calcium deficient perilymph perfusion prevented calcium accumulation in inner hair cells of the cochlea. The motility of the OHCs might be partially inhibited by low calcium concentration that reduced noise-induced hearing loss in turn.

Effects of Head-down Tilt on Nerve Conduction in Rhesus Monkeys

Background： Few studies have focused on peripheral nerve conduction during exposure to microgravity. The -6° head-down tilt （HDT） comprises an experimental model used to simulate the space flight environment. This study investigated nerve conduction characteristics of rhesus monkeys before and alter prolonged exposure to H DT. Methods： Six rhesus monkeys （3-4 years old） were tilted backward 6° from the horizontal. Nerve conduction studies （NCSs） were performed on the median, ulnar, tibial, and fibular motor nerves. Analysis of variance with a randomized block design was conducted to compare the differences in the NCS belbre and 7, 2 l, and 42 days alter the 6° HDT. Results： The proximal amplitude of the CMAP of the median nerve was significantly decreased at 21 and 42 days of HDT compared with the amplitude before HDT （4.38 ± 2.83 vs. 8.40 ±2.66 mV, F = 4.85, P = 0.013 and 3.30± 2.70 vs. 8.40± 2.66 mV, F = 5.93, P = 0.004, respectively）. The distal amplitude of the CMAP of the median nerve was significantly decreased at 7, 21, and 42 days of HDT compared with the amplitude before HDT （7.28 ± 1.27 vs. 10.25 ± 3.40 mV, F= 4.03, P = 0.039; 5.05 ± 2.01 vs. 10.25 ± 3.40 mV, F = 6.25, P = 0.04; and 3.95 ± 2.79 vs. 10.25 ± 3.40 mV, F = 7.35, F=- 0.01; respectively）. The proximal amplitude of the CMAP of the tibial nerve was significantly decreased at 42 days of HDT compared with the amplitude betbre HDT （6.14± 1.94 vs. 11.87± 3.19 mV, F = 5.02, P = 0.039）. Conclusions： This study demonstrates that the compound muscle action potential amplitudes of nerves are decreased under simulated microgravity in rhesus monkeys. Moreover, rhesus monkeys exposed to HDT might be served as an experimental model for the study of NCS under microgravity.