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Electronics gears for health care innovation

Posted: 01 Feb 2007 ?? ?Print Version ?Bookmark and Share

Keywords:portable medical devices? biomedical research and semiconductors? miniaturization in medical devices? medical and electronics technology? medical device connectivity?

Biomedical research is making huge strides in unlocking the secrets of human physiology and identifying potential new therapeutic and diagnostic instruments. At the same time, advances in electronics are enabling those new devices to be realized. As a result, medical applications make up one of the fastest-growing segments for ICs. The growing convergence of electronics and medicine can also be seen in trends that are common to both disciplines. While it may seem that the two fields have little in common, they actually share several technological frontiers: Both are driven by the need for small physical size, low power and advanced connectivity.

Some medical devices require the maximum possible processing power. Radiological and magnetic imaging systems consume all the gigaflops they can get, and size is not the main concern. In other applications, however, computing requirements are more modest, and there's no room for large components. The enabling factor in these devices is getting enough processing power into a given space.

Size matters
The space allowed for a medical device can be subject to some interesting constraints. Diabetics use glucose meters to monitor their blood sugar. Typically, these portable electronic medical devices are about the size and shape of a PDA, where the user inserts a test strip with a drop of blood. Using an electrochemical or optical sensor, these meters determine the concentration of glucose in the blood. One company has created a meter small enough to be integrated into the cap of the pill bottle-size canister that holds the test strips. The sensor, MCU, LCD and battery all fit into a finished product roughly the size of a ladies' wristwatch. Small size has also yielded low cost, as the meter is disposableafter the 50 strips are used, the container is thrown away, meter and all.

In the case of implanted devices, size is also important in determining where they can be placed. Consider an aortic aneurysm, which occurs when the heart's main artery, the aorta, develops a weak spot and bulges from blood pressure. A common surgical treatment is to run an artificial liner, called a stent graft, through the weakened aorta. It's now possible to place a tiny pressure sensor inside the aorta at the same time. The sensor uses a MEMS pressure element to monitor the long-term success of the surgery.

The MEMS sensor is made using the same processing technologies as ICs. To read the pressure in the aorta, the surgeon uses a radio-controlled interrogator to activate the device, which transmits via RF. If the stent graft fails, a follow-up exam will show increased pressure, indicating the need for further intervention. Some other implanted devices that benefit from smaller size are cardiac pacemakers, neurostimulators for treating central nervous system disorders, and hearing aids, including cochlear implants.

One of the most fascinating applications to exploit the mutual shrinking of medical devices and electronics is the sensor that's designed to be swallowed like a pill. Using RF, these minute instruments travel the full length of the digestive system during their operating lifetimes. The first such sensor transmitted body temperature, and has been used by astronauts and athletes. Newer versions can report pH levels in the esophagus to diagnose acid reflux disease and other conditions.

With innovation in electronics and medicine aligning around miniaturization, low power and connectivity, the development of new electronic medical devices is expected to accelerate.

The very latest devices transmit still images, which can be assembled into video, allowing a doctor to examine the small intestine. The "camera pills" use a minute CMOS imager coupled to an ASIC transmitter. White LEDs surrounding the lens provide illumination. Early work is being done on next-generation ingestible devices, incorporating navigation control and self-propulsion to allow more detailed imaging of a particular site.

Portability, power
Along with miniaturization is the trend toward lower power. In an implanted device, the benefit of minimal current consumption and the resulting impact on battery life are obvious. While some implants can be recharged through the skin with inductive coupling, less battery drain is always a desirable objective.

External devices are also sensitive to power consumption. As electronic components get smaller, medical devices that were once stationary are becoming portable. Defibrillators were once used only in hospitals by trained professionals. Automatic external defibrillators are now commonplace in airports, shopping malls, schools and even on airliners. Portable oxygen concentrators extract oxygen from the air for patients on oxygen therapy and can be carried over the shoulder like a handbag. All of these devices are enabled by low power, in addition to small size. Their tight power budgets are met by various means.

Ironically, reducing the size of electronic components can actually work against power reduction. As transistors get smaller to allow greater density, effective channel lengths get shorter and leakage current increases. Other mechanisms such as gate tunneling have a similar adverse impact on power as geometries shrink. With each geometric reduction, chipmakers have countered these negative effects by optimizing silicon-processing parameters. In addition, the designers of both digital and analog chips spend time minimizing the power consumption of their circuits. Reducing supply voltage, managing capacitance, clock gating and other techniques are used to eliminate unnecessary current.

Chip designers also incorporate features into their parts to allow medical device designers control over power consumption. For example, the dsPIC33F family from Microchip Technology has idle, sleep and doze modes, each with multiple options, giving designers the flexibility to scale power consumption. In many medical devices, an MCU spends most of its time doing nothing.

The inputs to vital sign monitors, infusion pumps, data recorders and many diagnostic instruments are fairly slow-moving temperatures, pressures and bioelectrical signals. Processors in such devices can remain in a low-power state most of the time, waking up every few milliseconds to execute instructions. In this way, the total average current is a fraction of the processor's normal run current.

Further progress in the area of power conservation will enable the development of new classes of devices. Piezoelectric or thermoelectric power sources may someday replace batteries in some implants. Already, a microsensor has been built into a hip implant to monitor the integration of the implant into the healing bone tissue. The device is kinetically powered, using the patient's movement as its energy source.

Connectivity trend
The third trend shared by electronics and medical devices is connectivity. In both fields, wireless is the leading technology. In 1999, the FCC allotted a bandwidth of 402-405MHz to the Medical Implant Communication Service. This band is used to communicate with implanted devices such as a pacemaker.

Other external devices use Bluetooth, IR, the Zigbee protocol, Wi-Fi or proprietary protocols to communicate. Home health-care networks connect weight scales, blood pressure cuffs, thermometers, spirometers and other diagnostic instruments to telemedicine terminals. These networks allow effective disease-management care without frequent trips to a doctor's office.

The dsPIC33F family from Microchip Technology has idle, sleep and doze modes, each with multiple options, giving designers the flexibility to scale power consumption.

Of course, not all medical networks are wireless. Some devices are complex enough to make use of their own internal networks. For example, a dialysis machine may contain a dozen or more MCUs. Wired and wireless LANs are getting busier in hospitals as well. Electronic patient records, prescription ordering and delivery, and imaging data can all be made available online or at the patient's bedside.

With innovation in electronics and medicine aligning around miniaturization, low power and connectivity, the development of new electronic medical devices is expected to accelerate. At the same time, it's appropriate to be mindful of the challenges presented by differences between the two fields. The rate of change in ICs is far more rapid than in medical devices. Component suppliers naturally prefer to offer their newest products, built on their newest processes. On the other hand, the designer of a medical device typically prefers to design in a component after it has been on the market for a while and established a track record. Similarly, by the time a medical device has passed the review and been released to production, the manufacturer is generally reluctant to accept changes to components.

In the end, an ongoing convergence of medical and electronics technology is inevitable. Biomedical research is continuing to identify new treatments for disease. Electronics research is likely to continue to enable the development of devices to apply those treatments. Greater cooperation between engineers in the two fields will advance health care in ways barely imaginable today.

- Steve Kennelly
Manager, Medical Products Group
Microchip Technology Inc.

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