Chronic nerve root entrapment: compression and degeneration

Electrode mounts are being developed to improve electrical stimulation and recording. Some are tight-fitting, or even re-shape the nervous structure they interact with, for a more selective, fascicular, access. If these are to be successfully used chronically with human nerve roots, we need to know more about the possible damage caused by the long-term entrapment and possible compression of the roots following electrode implantation. As there are, to date, no such data published, this paper presents a review of the relevant literature on alternative causes of nerve root compression, and a discussion of the degeneration mechanisms observed. A chronic compression below 40 mmHg would not compromise the functionality of the root as far as electrical stimulation and recording applications are concerned. Additionally, any temporary increase in pressure, due for example to post-operative swelling, should be limited to 20 mmHg below the patient's mean arterial pressure, with a maximum of 100 mmHg. Connective tissue growth may cause a slower, but sustained, pressure increase. Therefore, mounts large enough to accommodate the root initially without compressing it, or compliant, elastic, mounts, that may stretch to free a larger cross-sectional area in the weeks after implantation, are recommended

Corrosion of silicon integrated circuits and lifetime predictions in implantable electronic devices

Corrosion is a prime concern for active implantable devices. In this paper we review the principles underlying the concepts of hermetic packages and encapsulation, used to protect implanted electronics, some of which remain widely overlooked. We discuss how technological advances have created a need to update the way we evaluate the suitability of both protection methods. We demonstrate how lifetime predictability is lost for very small hermetic packages and introduce a single parameter to compare different packages, with an equation to calculate the minimum sensitivity required from a test method to guarantee a given lifetime. In the second part of this paper, we review the literature on the corrosion of encapsulated integrated circuits (ICs) and, following a new analysis of published data, we propose an equation for the pre-corrosion lifetime of implanted ICs, and discuss the influence of the temperature, relative humidity, encapsulation and field-strength. As any new protection will be tested under accelerated conditions, we demonstrate the sensitivity of acceleration factors to some inaccurately known parameters. These results are relevant for any application of electronics working in a moist environment. Our comparison of encapsulation and hermetic packages suggests that both concepts may be suitable for future implants

Unsafe Stimulation Correlates with Oxide Reduction Onset in Unbuffered Saline

Damage mechanisms in electrical stimulation must be better understood to address the demands of new electrode technologies. In this work, we studied the effect of pH on the charge injection mechanisms in a repeated pulsing experiment. We show that damage occurs when the electrode potential enters the oxide reduction region

CAPITEL: Design and Implementation of a wireless 6 channel EMG measurement system for permanent in vivo use: in vitro results

Introduction Surface Electromyography of partial limb amputees is used to control prostheses. Implantable EMG systems offer a higher Signal to Noise Ratio (SNR) as well as improved muscle specificity, and a more convenient daily use. Material and methods We present a design for an implantable device (“implant”) with 6 channels, each suitable for an electrode array with 3 electrodes. The implant uses an ADS1298 analog front end with ADG2188 multiplexers for versatile electrode array configuration. The analog input is filtered with a balanced analog bandpass filter with corner frequencies of 30 and 800 Hz. The ADC sample rate is 2 KHz per channel, with 9 bits resolution. The dimensions of the PCB implant are 17.2 x 14.1x2.15 mm. To measure the SNR a sinusoidal signal with a peak to peak amplitude of 7 mV and a frequency of 200 Hz was applied to each input. To simulate muscle impedance, an equivalent muscle impedance model (Figure 1) was placed between the generator and each channel of the implant [1]. We have implemented two data transmission methods: wired duplex communication and wireless inductive link. The wired link is used to transfer raw data, while only the 6 EMG envelopes, with an update rate of 20 Hz, are sent via the wireless link. Results Each analog input channel performed with a SNR better than 52 dB, both for wired and wireless operation. Wired data was received successfully at 115200 bps and wireless data at 1080 bps. Discussion Our design achieves a high SNR and data rate. These early results are promising and we are packaging the PCBs for in-vivo testing. Conclusion We have demonstrated a very compact design suitable for the monitoring of 6 EMG channels, with options for raw data or EMG envelope transmission. [1] Kalvoy, H, 2009, doi: 10.1088/0967-3334/30/2/002

An integrated circuit to enable electrodeposition and amperometric readout of sensing electrodes

This paper presents the design of an integrated circuit (IC) for (i) electrochemical deposition of sensor layers on the on-chip pad openings to form sensing electrodes, and (ii) amperometric readout of electrochemical sensors. The IC consists of two main circuit blocks: a Beta-multiplier based current reference for galvanostatic electrodeposition, and a switch-capacitor based amperometric readout circuit. The circuits are designed and simulated in a 180-nm CMOS process. The reference circuit generates a stable current of 99 nA with a temperature coefficient of 141 ppm/°C at best and 170 ppm/°C on average (across corners) over a supply voltage range of 1.2-2.4 V, and a line regulation of 0.7 %/V. The readout circuit measures current within pm 2 mu mathrmA with 99.9% linearity and a minimum integrated input-referred noise of 0.88 pA

Implantable electronic devices technology challenges for long-term human implantation

Purpose - The purpose of this paper is to discuss the requirements for long-term implantation of electronic devices with a focus on packaging and encapsulation.Design/methodology/approach - Owing to their intended long-term use in the human body, implants for electrical stimulation present specific challenges to the engineers. The respective roles of packaging and encapsulation must be clearly understood to make the most of new materials and modern machining technologies. This paper offers an introduction to the current situation and highlights challenges for future developments.Findings - The innovative application of modern technologies may be useful to tackle key issues of encapsulation and sealing of small electrical devices for long-term implantation.Originality/value - Two examples of innovative application of alternative package manufacture and sealing method are described

Triggering Postural Movements With Virtual Reality Technology in Healthy Young and Older Adults: A Cross-Sectional Validation Study for Early Dementia Screening

With the ultimate aim of early diagnosis of dementia, a new body balance assessment system with integrated head-mounted display-based virtual reality (VR) has been developed. We hypothesized that people would sway more in anterior-posterior (AP) direction when they were exposed to a VR environment where we intentionally provoked movements in forward and backward directions. A total of 14 healthy older adults (OA) (73.14±4.26 years) and 15 healthy young adults (YA) (24.93±1.49 years) were assessed for group differences in sway behavior. Body sway speed in 22 different conditions with and without VR environments was analyzed. Significant differences and large effect sizes were observed in AP sway under the VR environments (OA with P 0.61, YA with P 0.72) compared to the baseline condition without the VR environments. In addition, significant differences were found between the two groups in AP sway in all test conditions (P < 0.01). Our study shows that a VR environment can trigger body sway in an expected direction, which may indicate that it is possible to enhance the sensitivity of balance assessment by integrating immersive VR environments. The result of this study warrants a cross-sectional study in which OA diagnosed with and without dementia are compared on their sway behavior