2、Visual prosthese[edit]

  Fig 5 The Visual Cortical Implant

Theoretical and experimental clinical evidences suggest that direct electrical stimulation of the retina might be able to provide some vision to subjects who have lost the photoreceptive   elements   of   their retina。[19]  Therefore, visual   prosthesesare   developed  to

restore vision for the blind by using the stimulation。 Depending upon which visual pathway location is targeted for neural stimulation, different approaches have been considered。 Visual pathway consists mainly of  the eye, optic  nerve, lateral  geniculate  nucleus (LGN), and visual cortex。 Therefore retinal, optic nerve and visual cortex stimulation are the three different methods used in visual prostheses。[20] Retinal degenerative diseases, such as retinitis pigmentosa (RP) and age-related macular degeneration (AMD), are two likely candidate diseases in which retinal stimulation may be helpful。 Three approaches called intraocular epiretinal, subretinal and extraocular transretinal stimulation are pursued in retinal devices

that stimulate remaining retinal neural cells to bypass lost photoreceptors and allow the visual signal to reach the brain via the normal visual pathway。 In epiretinal approach, electrodes are placed on the top side of the retina nearganglion cells,[21] whereas the electrodes are placed under the retina in subretinal approaches。[22] Finally, the posterior scleral surface of the eye is the place in which extraocular approach electrodes are positioned。 Second Sight and the毕业论文

Humayun group at USC are the most active groups in the design of intraocular retinal prostheses。 The ArgusTM 16 retinal implant is an intraocular retinal prosthesis utilizing video processing technologies。  Regarding to the visual cortex  stimulation, Brindley, and    Dobelle

were the first ones who did the experiments and demonstrated that by stimulating the visual cortex most of the electrodes can produce visual percept。[6]LGN, which is located in the midbrain to relay signals from the retina to the visual cortex, is another potential area that can be used for stimulation。 But this area has limited access due to surgical difficulty。 The recent success of deep brain stimulation techniques targeting the midbrain has encouraged  research to pursue the approach of LGN stimulation for a visual prosthesis。[23]

3、Cardiac electrostimulation devices[edit]

  Fig 6 A pacemaker, scale in centimeters

Implantable pacemakers were proposed for the first time in 1959 and became more sophisticated since then。 The therapeutic application of pacemakers consists of numerous rhythm disturbances including some forms of tachycardia (too fast a heart beat), heart failure, and even stroke。 Early implantable pacemakers worked only a short time and needed periodic recharging by an inductive link。 These implantable pacemakers needed a pulse generator to

stimulate heart muscles with a certain rate in addition to electrodes。[24]  Today, modern    pulse

generators are programmed non-invasively by sophisticated computerized machines using RF, obtaining information about the patient's and device's status by telemetry。 Also they use a single hermetically sealed lithium iodide (LiI) cell as the battery。 The pacemaker circuitry includes sense amplifiers to detect the heart's intrinsic electrical signals, which are used to track heart activity, rate adaptive circuitry, which determine the need for increased or reduced pacing rate, a microprocessor, memory to store the parameters, telemetry control for communication protocol and power supplies to provide regulated voltage。[25]