Electrical stimulation device

Electrical Stimulation Devices. Bioelectrodes that transmit electrical signals into the body are generally known as electrical stimulation devices, examples of which include cardiac pacemakers, transcutaneous electronic nerve stimulators (TENs) for pain suppression, and neural prostheses such as auditory stimulation systems for the deaf and phrenic nerve stimulators for artificial respiratory control. In these, and other similar devices, electrodes transmit current to appropriate areas of the body for direct control of, or indirect influence over, target cells. 

In the past 20 years bendable and disposable medical electrodes evolved. Instead of a rigid metal plate serving as electrode, a metal mesh, foil or carbon impregnated rubber or vinyl, ensuring more flexibility in the electrode structure, are used. A conductive adhesive layer, usually in the form of a gel, is disposed on the conductive side of the material to provide a good electrical conductive contact between the conductive material and the patient s skin. Connection between the conductive material and an electrical stimulation device is provided by means of an electrical wire. Instead of wires, pressure buttons on top of the conductive material may alternatively be used. The outside face of the conductive material is covered with a nonconductive material to prevent electrical contact. 

Nonpharmacologic methods improve venous blood flow by mechanical means and include early ambulation, electrical stimulation of calf muscles during prolonged surgery, graduated compression stockings, intermittent pneumatic compression devices, and inferior vena cava filters. 

Monitoring the effect of muscle relaxants during surgery (and recovery following the use of cholinesterase inhibitors) typically involves the use of a device that produces transdermal electrical stimulation of one of the peripheral nerves to the hand and recording of the evoked contractions (twitches Figure 27-6). The motor responses to different patterns of peripheral nerve stimulation are measured. The three most commonly used patterns of include (1) single-twitch stimulation, (2) train-of-four (TOF) stimulation, and (3) tetanic stimulation. Two newer modalities are also available to monitor neuromuscular transmission double-burst stimulation and posttetanic count. 

Another surgical intervention, widely used in Europe for more than a decade gained United States Food and Drug Administration in 2002. The procedure involves implanting a pacemaker-hke device to provide electrical stimulation to areas of the brain deprived of dopamine. Still more research... 

The only way to obtain all necessary parameters is to apply model-based measurement techniques and electrical stimulation during wafer-level tests for each single device or by using test structures designed especially to obtain in-process measurement data (see [28, 29] and Section 5.10). This requires that the sensor s behavior is well understood and the dependencies of the various parameters can be expressed analytically according to Eq. 4.3. 

Heart Valves and Pacemakers. Pacemakers, which regulate the heart beat by electrical stimulation, have been used on humans since 1952, and implantable models have been used since 1958. The wires and electrodes are usually plastic coated for purposes of insulation, and the entire device is usually embedded in a plastic for protection from the body fluids. Over 60,000 of these pacemakers are placed in people each year. 

Other biomedical applications of polymers include sustained and controlled drug delivery formulations for implantation, transdermal and trans-cornealuses, intrauterine devices, etc. (6, 7). Major developments have been reported recently on the use of biomaterials for skin replacement (8), reconstruction of vocal cords (9), ophthalmic applications such as therapeutic contact lenses, artificial corneas, intraocular lenses, and vitreous implants (10), craniofacial, maxillofacial, and related replacements in reconstructive surgery (I), and neurostimulating and other electrical-stimulating electrodes (I). Orthopedic applications include artificial tendons (II), prostheses, long bone repair, and articular cartilage replacement (I). Finally, dental materials and implants (12,13) are also often considered as biomaterials. 

An Implantable Bionic Network of Injectable Neural Prosthetic Devices The Future Platform for Functional Electrical Stimulation and Sensing to Restore Movement and Sensation... 

The fundamental properties of excitation of CNS neurons were presented with a focus on what neural elements around the electrode are activated under different conditions. During CNS stimulation action potentials are initiated in the axons of local cells, even for electrodes positioned over the cell body. The threshold difference between cathodic and anodic stimuli arises due to differences in the mode of activation. Anodic stimuli cause depolarization of the axon and excitation via a virtual cathode, while cathodic stimuli cause hyperpolarization at the site of excitation and the action potential is initiated during repolarization. The threshold for activation of presynaptic terminals projecting into the region of stimulation is often less than or equal to the threshold for direct excitation of local cells, and indirect effects mediated by synaptic transmission may alter the direct effects of stimulation on the postsynaptic cell. The fundamental understanding provided by this analysis enables rational design and interpretation of studies and devices employing electrical stimulation of the brain or spinal cord. 

Schuhnan, J., Mobley, R, Wolfe, J., Voelkel, A., Davis, R., and Arcos, I. An implantable bionic network of injectable neural prosthetic devices the future platform for functional electrical stimulation and sensing to restore movement and sensation. In Biomedical Engineering Fundamentals, Walker, C.F. and DiLorenzo, D.J. (eds). CRC Press, Boca Raton, FL, 2006, Chapter 34, pp. 34-1-34-18. 

Type of end use — this may deal with transmission of information (biopotentials, temperature, pressure, blood flow rate), energy (electrical stimulation, power for heart-assist devices), transfer of matter (cannula for blood), and load (attachment of a prosthesis) ... 

Absolute qualitative identification can be assured only if samples are removed and analyzed. Two examples of such a procedure have been reported. The first was an attempt to determine if direct electrical stimulation of the caudate nucleus resulted in the release of dopamine as well as ascorbic acid from that tissue. Micro voltammetric and stimulating electrodes were micromanipulated into excised caudate tissue which was flushed with warmed, oxygenated buffer. Reference and auxiliary electrodes were nearby. Quantitative information was taken, stored, manipulated, and displayed by a minicomputer. Simultaneously a push-pull cannula device sampled the caudate and delivered the perfusate to an iced vial. Changes in the electrochemical signal that followed stimulation were correlated with changes in the dopamine and ascorbic acid content of the perfusate as determined via HPLC with electrochemical detection. It was found that little if any ascorbic acid was released as a result of electrical stimulation in these experiments. Although there is some question concerning the stability of ascorbate in an iced vial, the above example does illustrate this coincident analytical technique. 

Increasingly, biopotentials have to be measured within implanted devices and need to be transmitted to an external monitor or controller. Such applications include cardiac pacemakers transmitting the intracardiac ECG and functional electrical stimulation where, for example, action potentials measured at one eyelid serve to stimulate the other lid to restore the physiological function of a damaged lid at least to some degree. In these applications, the power consumption of the implanted biopotential amplifier hmits the life span of the implanted device. The usual solution to this problem is an inductive transmission of power into the implanted device that serves to recharge an implanted battery. In applications where the size of the implant is of concern, it is desirable to eliminate the need for the battery and the related circuitry by using a quasi-passive biopotential amplifier, that is, an amplifier that does not need a power supply. 

Scoliosis treatment—Progressive lateral curvature of the adolescent vertebral column with simultaneous rotation is known as idiopathic scoliosis. Electrical stimulation applied to the convex side of the curvature has been used to stop or reduce its progression. Initially rf powered stimulators have been replaced by battery powered totally implanted devices (Bobechko et al., 1979 Herbert and Bobechko, 1989). Stimulation is applied intermittently, stimulation amplitudes are under 10.5 V (510 Q), and frequency and pulsewidth are within usual FES parameter values. 

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