Implantable medical electronics theory and design of power supply

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Implantable medical devices can be divided into two kinds of passive and active.

Most passive implantable medical device is a non-electronic products, such as contact lenses, cardiac stents, artificial heart valves, artificial joints and other organizational structures. Active implantation-equipment such as implantable cardiac subject quite and cardiac pacemakers and other incentive system, requires energy supply to replace or enhance the functionality of an organ, or treatment of a disease. Currently, implantable cardiac, except quite and pacemakers such device maintains the lives of millions of patients with heart disease. Other incentive system is also being used for the treatment of various types of problems as incontinence and diseases such as chronic pain, deep brain stimulation device is also used for the treatment of pain such as epilepsy, spastic-quite and diseases such as Parkinson's syndrome. Although these products are now the size of the application is not a big place, but certainly will in the near future for wider use. Table 1 lists some implanted electronic devices and their indications.

　　

Implantable medical electronic devices typically consists of two parts, namely, implanted part and part of in vitro measurement and control.

External part of the task in the body is the measurement and control of information in order to complete the diagnosis and treatment of disease. The entire unit including information acquisition, processing, archiving, control, command, display and record function. In vitro section and general medical instruments are the same, the system's features are mainly concentrated in the implantation of the section, as well as in vivo and in the exchange of information and energy. Implantable medical electrical equipment requires energy supply in order to work, its energy supply are implanted battery and an external power supply. This article combines specific implantable medical electronic devices in detail both the characteristics of the energy supply.

1, implanted battery

The use of implanted battery of important reason is because of its high reliability.

Unlike many consumer electronic products, for implantable medical device battery is not easily replaced. In implantable medical electronic devices before the battery is sealed securely in its interior. From this, in implantable medical electronic devices side on the stage, the storage phase and after the implantation of the human body, implanted battery has power for the device. Usually, we can determine the battery life. Then, as implantable medical electronic equipment part of implantable electric he qualified the implantable medical electronic equipment service life. Generally, implanted battery to work (5 ~ 10) years. During this period, implanted battery to have very small output voltage drop, without any adverse side effects. If medical technical progress allows the implantable medical electronic equipment replacement easier, you no longer need to consider the cell's own usage, this is only an ideal situation.

Doctors and patients want implantable medical electronic devices in volume as small as possible.

An implantable cardiac pacemaker volume about 20ml, implantable defibrillator volume about pacemaker mentioned (3 ~ 4) times. Either an implant type medical and electronic equipment, almost half of the volume occupied by internal battery. Therefore, volume energy density (energy volume ratio) or quality quality] [energy energy density than) implanted battery design choices are important to consider the parameters.

In order to avoid sharp edges and corners may damage the surrounding tissue or penetrate the skin, the majority of implantable medical electronic equipment shape is a circle or oval ring-shaped, implanted battery general design into a circle shape.

The shape of the battery can only be determined after the implantable medical device geometry.

1.1 early development of low-power or rarely high power usage of implantable medical devices, typically you can use the internal battery.

For example, implantation of cardiac pacemakers, battery power for cardiac stimulation in half, while the other half power to complete monitoring, data logging, the energy consumption is low. The implantable cardiac pacemaker of power, for example, the implantable cardiac pacemaker was originally used as a power rechargeable, through Inductive charging for energy delivery. There is a single battery voltage, capacity 190mAh 125v, the main problem is the battery life is short, the charging of reliability depends on the patient himself. Currently rechargeable power implantable cardiac pacemaker is no longer for sale.

In the 1960s, zinc and mercury batteries are widely used in implantable cardiac pacemaker.

This type of battery has a high charge volume density and stability of voltage, 3-6, zinc and mercury batteries in series provides voltage 4V ' SV. But this type of battery can not be done completely sealed and easy to make liquid permeability person caused a short circuit and the pacemaker. In addition, zinc and mercury batteries in the battery drain during voltage change is very small, so it is difficult to estimate the battery usage. There is no longer using the battery as the implantable cardiac pacemaker.

Radionuclide battery has also been used as the implantable cardiac pacemaker.

Radioactive element polonium has a half-life of 87 years, this element made of radionuclide battery in 10 years the output voltage drops only 1%. Radionuclide battery has a long service life, but bulky, poisonous, radioactive, and many other problems between limits its application.

1.2 lithium battery

In the mid-1970s successfully developed a lithium battery, the battery has a high energy density, high reliability, low self discharge as well as the application of solid electrolyte, sealed, override the zinc and mercury battery, the implantable pacemaker to extend the life span (5 ~ 10) years.

New titanium shell used to encapsulate the internal battery and circuit, from epoxy resin and silicone rubber padding. New titanium shell as well as special shielding from well protected internal objects, and reduce external electromagnetic interference. Install this new type of pacemaker patients can safely use microwave ovens and other household or Office within a common electrical appliances.

Currently, lithium-iodine batteries widely become implanted medical electronics energy choices.

Lithium-iodine battery is a solid state ion battery, the battery negative terminal anode is made of lithium, cathode that battery cathode consists of iodine and polymers such as polyethylene a 2 a vinyl compound adjoins the rebelsBetween the two levels is the solid electrolyte. Solid electrolyte for lithium iodide low conductivity will current limit in µA levels, but has enough drive cardiac pacemakers. Lithium iodide diaphragm can automatically healing, this makes lithium-iodine battery very safe and reliable is the implantable cardiac pacemaker-powered energy. Batteries and the control circuit engineering progress allows implanted battery only half the size of a previously. Since 1972, with approximately 50 million lithium-iodine batteries successfully applied to the implantable cardiac pacemaker. 1.3 internal rechargeable battery

Widely used in implantable medical electronic devices of rechargeable batteries have a nickel-cadmium batteries, nickel hydrogen batteries and lithium ion rechargeable battery (Li-ion battery).

Three battery part performance indicators refer to table 2.

Lithium ion rechargeable battery with its high voltage, high cycle life and high energy density, and other outstanding performance and attracts worldwide attention, is believed to be the current comprehensive performance best battery system.

Secondary lithium battery is a lithium metal (anode) to the cathode, to fit to the lithium lithium ion migration as electrolyte solution in order to have the channel structure of lithium-ion can easily be embedded, prolapse, prolapse, embedded in the structure of small material is the positive electrode (cathode) new battery system.

Currently. lithium secondary battery cathode materials have lithium cobalt oxide, lithium and nickel oxide and lithium lithium vanadium oxide, iron oxide, manganese oxide and lithium, different as-level materials secondary lithium batteries of different volume energy density, see table 3 below.

　　

Lithium cobalt oxide is this stage commercialization lithium-ion batteries in most successful cathode materials.

Currently, compared to other cathode materials, reversibility, LiCoO2 in discharge capacity, charging efficiency and voltage stability, best performance, but the price of lithium cobalt oxide is dearer, and pollution to the environment. Lithium nickel oxides of lithium cobalt compounds performance is similar, but because of its low price, it helps a lot. Lithium manganese oxide inexpensive, nontoxic and contamination of small, small impact on the environment. Lithium vanadium oxide with high capacity, particularly in recent years and developed the V2O3 gel, its energy density is far more than other materials, in substantial increase lithium-ion battery for use at the same time, due to its low cost, and no pollution to the environment, for a lot of promotion.

In short, different types of implantable medical electronic devices on battery requirements differ considerably, select implanted battery to be considered.

Such as implantable defibrillator, it can provide amplitude is greater than the pacemaker pulse amplitude 6 orders of magnitude of electrical impulses, but this situation is not frequent. Because the battery is not possible to produce electrical pulses, the sudden power prior to the release of the heart, the battery to the internal capacitor charging 20 seconds, the energy stored in the internal capacitor. During the charge, need 1A ~ ZA current. Lithium-iodine batteries can not provide large current, thus the implantable defibrillator generally use lithium batteries silver vanadium oxides. Some devices such as drug pumps it using electrochemical reactor to produce high pressure pump Chamber, which will inject the drug from storage room. Pump into the drug action is not continuous, regular actions or triggers by patients.

When the pump is opened several Ma current.

In this case, you can choose to have a low internal resistance of the battery, such as regulating thionyl chloride batteries, lithium fluoride carbon batteries, lithium, silver vanadium oxide battery, etc. 2 external power supply some implantable medical electronic devices can also be used portable external power supply, either through direct electrical connection or through a wireless RF connection. The article describes how wireless RF, wireless RF power diagram shown in Figure 1.

This power supply is an external battery-powered radio frequency oscillator

　　

Output after via RF power amplifiers to in vitro junior RF Induction coil, coil attached to the skin surface, implantation system of small parallel secondary Induction coil is placed under the surface coil and induction out r.f. voltage.

The RF voltage with rectifier, filter, regulator after stable DC voltage, or to the body charging the battery, or work directly supply the body electronic circuits.

In order to guarantee the implantable medical electronic devices of high reliability, use the external power supply are generally has a backup battery.

External device maintenance costs increased, because the wireless radio frequency interference and caused local tissue heating effect is not to be ignored. Nevertheless, for some implantable medical electronic devices, use the external power supply are still is the best choice.

Some implantable device volume very small to hold the battery.

As cochlear, it is the need for surgical implant replacement inner ear hair cells play a role of an electronic device. It's implanted part including implant and implant electrode, in vitro section includes a microphone, language processor, transmission cables, sensing coil, two parts. Power and data through emitting radio frequency range of electromagnetic waves.

Other implant device such as a left ventricular assist device LVAD) is a heart surgery machinery circulation devices, its main role is to lighten the load, lower left ventricular myocardial oxygen consumption, improving the diastolic pressure improve coronary perfusion, and increased cardiac output.

At present, the LVAD is clinically focused on helping cardiac surgery patients out of extracorporeal circulation and cardiac transplantation as transitional. LVAD by power, control system and pump components, control system and power is external, the pump can be built-in or external. Left ventricular assist device for electrical and pneumatic. Some electric implanted LVAD is equipped with a rechargeable battery, the external power supply to its charging. Generally the pneumatic LVAD of size is very small, the use of external rechargeable battery produce compressed air.

Use the external power supply mode for implantable medical electronic devices with high power continuously; use wireless RF connections, not only can achieve energy delivery, but also on implantable medical electronic devices for control and enquiries

Sought; in addition, implantable medical electronic equipment life and shelf life are no longer affected by the battery.

3 prospect

About implantable medical electronic devices of the energy supply continued to have exciting new breakthroughs and advances.

Rechargeable battery technology progress promoted by the body charging battery-powered by planting in the development of medical electronics devices; high energy density of lithium polymer battery and thin film cell has the potential to become future implanted battery preferred; use of other energy transformation in the body for energy supply (such as bio-fuel cells, the body temperature battery, use the organism itself mechanical energy as well as directly from Ann extraction power, and so on) have also been reported. In short, to a more secure, long-term supply of energy, without external radiation intensity energy (wave or near-infrared) of energy supply, will be implanted medical electronic devices development direction of the power supply.