DESIGN AND DEVELOPMENT OF MEDICAL ELECTRONIC ...

9. Control of Parkinsonian tremor. Electrical stimulation of neuron clusters deep insidethe brain [also known as deep brain stimulation (DBS)] is now used to inactivate the subthalamicnucleus, which is overactive in Parkinson’s disease. A multielectrode lead isimplanted into the ventrointermediate nucleus of the thalamus. The lead is connected to apulse generator that is surgically implanted under the skin in the upper chest. When thepatient passes a magnet over the pulse generator, the device delivers high-frequency pulsetrains to the subthalamic nucleus to block the tremor.10. Gastric “pacing.” Electrical stimulation of the stomach is currently being used toreduce symptoms of nausea and vomiting for patients suffering from gastroparesis (a stomachdisorder in which food moves through the stomach more slowly than normal).11. Restoration of lost sight. Electrical stimulation of the retina, the optical nerve, andthe visual cortex is now developed to the point at which implants for functionally restoringsights to blind patients will soon be available commercially. Functional sight may begiven to patients blinded by retinitis pigmentosa by using integrated circuits embedded incontact with the retina. The ICs contain an array of photovoltaic cells that directly poweran array of microstimulators and electrodes to convert the image into a directly mappedelectrical image, bypassing degenerated photoreceptors and directly stimulating theremaining nerve cells in the retina. For patients with blindness caused farther down theoptical nerve, the possibility exists of stimulating the visual cortex directly using microelectrodearrays to generate coherent images from phosphenes (sensation of a spot of light)elicited by the electrical stimulation.12. Restoration of lost hearing. Cochlear implants stimulate spinal ganglion cells of theauditory nerves, bypassing nonfunctional hair cells to restore limited hearing in some typesof deafness. The cochlear implant system really consists of an implanted stimulator connectedto an electrode array inserted in the cochlea and an external speech processor thatcodes the speech into stimulation patterns that can be translated back into sounds by thebrain. The external speech processor also powers the implant via an inductive energy transferlink. Cochlear implants are now common and provide substantial benefits to many profoundlydeafened children and adults. Benefits vary by person and range from increasedperception of environmental sounds to the ability to use a telephone.13. Restoration of lost or impaired neuromuscular function. Functional electrical stimulation(FES), also known as functional neuromuscular stimulation (FNS), is a rehabilitationstrategy that applies electrical currents to the nerves that control paralyzed muscles inorder to stimulate functional movements such as standing or stepping. FNS systems includeeither skin-surface or implanted electrodes, a control unit which often also receives motioninformation back from sensors, and a stimulus generator. A number of FNS units are noweither available commercially or under clinical investigation. Typical applications of FNSinclude controlling foot drop, enabling lower-limb paraplegics to stand or sit, and restoringhand function to the paralyzed upper limb.14. Maintenance or increase in range of movement. Electrical muscle stimulation(EMS) is used to strengthen muscle and facilitate voluntary motor function. AlthoughEMS devices are often advertised for muscle toning and weight reduction, they are authorizedby the FDA only as prescription devices for maintaining or increasing range ofmotion, relaxation of muscle spasm, prevention or retardation of disuse atrophy, musclereeducation, increasing local blood circulation, and postsurgical stimulation of calf musclesto prevent the formation of blood clots.15. Electroconvulsive therapy (ECT). This is a relatively painless procedure that iseffective in treating major depression. A short, controlled set of electrical pulses isgiven for about a minute through scalp electrodes to produce generalized seizures.Biological changes that result from the seizure are believed to result in a change inbrain chemistry which is believed to be the key to restoring normal function. Becausepatients are under anesthesia and have taken muscle relaxants, they neither convulsenor feel the current.CLINICAL USES OF ELECTRICAL STIMULATION 313