Extramuscular Recording of Spontaneous EMG Activity and Transcranial Electrical Elicited Motor Potentials in Horses:Characteristics of Different Subcutaneous and Surface Electrode Types and Practical Guidelines

Introduction: Adhesive surface electrodes are worthwhile to explore in detail as alternative to subcutaneous needle electrodes to assess myogenic evoked potentials (MEP) in human and horses. Extramuscular characteristics of both electrode types and different brands are compared in simultaneous recordings by also considering electrode impedances and background noise under not mechanically secured (not taped) and taped conditions. Methods: In five ataxic and one non-ataxic horses, transcranial electrical MEPs, myographic activity, and noise were simultaneously recorded from subcutaneous needle (three brands) together with pre-gelled surface electrodes (five brands) on four extremities. In three horses, the impedances of four adjacent-placed surface-electrode pairs of different brands were measured and compared. The similarity between needle and surface EMGs was assessed by cross-correlation functions, pairwise comparison of motor latency times (MLT), and amplitudes. The influence of electrode noise and impedance on the signal quality was assessed by a failure rate (FR) function. Geometric means and impedance ranges under not taped and taped conditions were derived for each brand. Results: High coherencies between EMGs of needle-surface pairs degraded to 0.7 at moderate and disappeared at strong noise. MLTs showed sub-millisecond simultaneous differences while sequential variations were several milliseconds. Subcutaneous MEP amplitudes were somewhat lower than epidermal. The impedances of subcutaneous needle electrodes were below 900 Ω and FR = 0. For four brands, the FR for surface electrodes was between 0 and 80% and declined to below 25% after taping. A remaining brand (27G DSN2260 Medtronic) revealed impedances over 100 kΩ and FR = 100% under not taped and taped conditions. Conclusion: Subcutaneous needle and surface electrodes yield highly coherent EMGs and TES-MEP signals. When taped and allowing sufficient settling time, adhesive surface-electrode signals may approach the signal quality of subcutaneous needle electrodes but still depend on unpredictable conditions of the skin. The study provides a new valuable practical guidance for selection of extramuscular EMG electrodes. This study on horses shares common principles for the choice of adhesive surface or sc needle electrodes in human applications such as in intraoperative neurophysiological monitoring of motor functions of the brain and spinal cord

Multipulse transcranial electrical stimulation (TES):Normative data for motor evoked potentials in healthy horses

Background: There are indications that transcranial electrical stimulation (TES) assesses the motor function of the spinal cord in horses in a more sensitive and reproducible fashion than transcranial magnetic stimulation (TMS). However, no normative data of TES evoked motor potentials (MEP) is available. In this prospective study normative data of TES induced MEP wave characteristics (motor latency times (MLT); amplitude and waveform) was obtained from the extensor carpi radialis (ECR) and tibial cranialis (TC) muscles in a group of healthy horses to create a reference frame for functional diagnostic purposes. For the 12 horses involved in the study 95% confidence intervals for MLTs were 16.1-22.6 ms and 31.9-41.1 ms for ECR and TC muscles respectively. Intraindividual coefficients of variation (CV) and mean of MLTs were: ECR: 2.2-8,2% and 4.5% and TC: 1.4-6.3% and 3.5% respectively. Inter-individual CVs for MLTs were higher, though below 10% on all occasions. The mean +/- sd of MEP amplitudes was respectively 3.61 +/- 2.55 mV (ECR muscle left) and 4.53 +/- 3.1 mV (right) and 2.66 +/- 2.22 mV (TC muscle left) and 2.55 +/- 1.85 mV (right). MLTs showed no significant left versus right differences. All MLTs showed significant (p < 0.05) voltage dependent decreases with slope coefficients of linear regression for ECR: 0.049; - 0.061 ms/V and TC: - 0.082; - 0.089 ms/V (left; right). There was a positive correlation found between height at withers and MLTs in all 4 muscle groups. Finally, reliable assessment of MEP characteristics was for all muscle groups restricted to a transcranial time window of approximately 15-19 ms. Conclusions: TES is a novel and sensitive technique to assess spinal motor function in horses. It is easy applicable and highly reproducible. This study provides normative data in healthy horses on TES induced MEPs in the extensor carpi radialis and tibialis cranialis muscles bilaterally. No significant differences between MLTs of the left and right side could be demonstrated. A significant effect of stimulation voltage on MLTs was found. No significant effect of height at the withers could be found based upon the results of the current study. A study in which both TMS and TES are applied on the same group of horses is needed

Detection of tremor bursts by a running second order moment function and analysis using interburst histograms

Introduction: Conventional linear signal processing techniques are not always suitable for the detection of tremor bursts in clinical practice due to inevitable noise from electromyographic (EMG) bursts. This study introduces (1) a non-linear analysis technique based on a running second order moment function (SOMF) and (2) auto- and cross-interburst interval histograms (IBIH) showing distributions of interburst interval EMG bursts of pathological tremors illustrating an application of the SOME Materials and methods: EMG recordings from extensors and flexors of two patients with Parkinson's disease with a rest tremor and from a healthy subject during sustained muscular contraction were preliminary analyzed in a pilot study. The SOMF was obtained by repeated second order moment calculations within a window of fixed width W (time scale parameter) plotted as a function of time. Minimum SOMF values indicate local "moments of inertia" of each EMG burst. Bursts were detected and located when minimum SOMF values were below level L (decision parameter). Optimal settings of parameters W and L were calculated empirically for pathological tremor EMGs. Auto- and cross-IBIHs were obtained from minimum SOMF values of detected bursts. Results: Tremor frequency and phase relation between EMG bursts from auto- and cross-IBIHs agreed with those derived from spectral analysis. Burst detection by SOMF has a high sensitivity and selectivity even with noisy background. Conclusion: The SOMF is appropriate for detection of individual EMG bursts of pathological tremors. The technique is sensitive to non-stationary changes of tremor bursts regardless of their amplitude. IBIHs provide a measure of tremor frequency and phase difference between EMG bursts. (c) 2007 IPEM. Published by Elsevier Ltd. All rights reserved

Experimental Study of the Course of Threshold Current, Voltage and Electrode Impedance During Stepwise Stimulation From the Skin Surface to the Human Cortex

<p>Background: Transcranial electric stimulation as used during intraoperative neurostimulation is dependent on electrode and skull impedances.</p><p>Objective: Threshold currents, voltages and electrode impedances were evaluated with electrical stimulation at 8 successive layers between the skin and the cerebral cortex.</p><p>Patients and Methods: Data of 10 patients (6f, 53 +/- 11 years) were analyzed. Motor evoked potentials were elicited by constant current stimulation with corkscrew type electrodes (CS) at C3 and C4 in line with standard transcranial electric stimulation. A monopolar anodal ball tip shaped probe was used for all other measurements being performed at the level of the skin, dura and cortex, as well as within the skull by stepwise performed burr holes close to C3 resp. C4.</p><p>Results: Average stimulation intensity, corresponding voltage and impedance for muscle MEPs at current motor threshold (CMT) were recorded: CS 54 +/- 23 mA (mean +/- SD), 38 +/- 21 V. 686 +/- 146 Omega; with the monopolar probe on skin 55 +/- 28 mA, 100 +/- 44 V. 1911 +/- 683 Omega and scalp 59 +/- 32 mA, 56 +/- 28 V. 1010 +/- 402 Omega; within the skull bone: outer compact layer 33 23 mA, 91 +/- 53 V. 3734 +/- 2793 Omega; spongiform layer 33 +/- 23 mA, 70 +/- 44 V.2347 +/- 1327 Omega; inner compact layer (ICL) 28 +/- 19 mA, 48 +/- 23 V. 2103 +/- 14980; on dura 25 +/- 12 mA, 17 +/- 12 V.643 +/- 244 Omega and cortex 14 +/- 6 mA, 11 +/- 5 V.859 +/- 300 Omega. CMTs were only significantly different for CS (P = 0.02) and for the monopolar probe between the cortex and ICL (P = 0.03), scalp (P = 0.01) or skin (P = 0.01) and between ICL and CS (P</p><p>Conclusion: The mean stimulation current of the CMT along the extracranial to intracranial anodal trajectory followed a stepwise reduction. VMT was strongly dependent on electrode impedance. CMT within the skull layers was noted to have relative strong shunting currents in scalp layers. (C) 2013 Elsevier Inc. All rights reserved.</p>