SEMICONDUCTORS
The pressure to change—nowhere is that felt more acutely than in the health care industry. Institutions and services are pushed to cut costs, but the trick is to do so while continuing to improve patient quality of life. Reducing staff, equipment costs and power consumption, as well as limiting patient hospital stays can all help reduce health care costs, but at what cost to the patient? This is a significant challenge, and health care providers are counting on technology to help them successfully meet the challenge of better care at a reasonable cost.
Semiconductor technology is having a profound effect on health care systems. Patient monitoring, drug dispensing and many other applications can enhance the capabilities of scarce manpower resources by capturing information on patients, rapidly processing the data and then distributing critical information through an in-hospital network to those who need it. monitoring systems can stream data to, and from, almost anywhere in the world. This not only provides pin-point distribution without additional human resources, but allows many applications to move into any home with an Internet connection. In some cases, a similar system can control treatment options, such as dispensing drugs based on a pre-determined schedule.
This kind of remote monitoring and data processing starts with a simple platform that has sensing, control and communication capabilities that can include a radio frequency (RF) transceiver to improve portability and simplify operation.
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Figure 1. An example of a chip set that provides sensing, control, and Zigbee RF capabilities for healthcare applications.
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A simple chip set of off-the-shelf components can provide all the functionality needed to sense, process and transmit information at a reasonable cost. Figure 1 illustrates the interaction among the three chip set components. The microcontroller (in this example a member the MC9S08GT* Family) is needed to process the information received from the sensor, which is then sent to the low-power transceivers. This can be one of any number of general purpose 8-bit microcontrollers on the market today with an analog-to-digital converter (ADC), and the required embedded memory dictated by the networking standard featured on the wireless transceiver (simple, proprietary wireless protocols, IEEE 802.15.4 or ZigBee™, for instance).
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Figure 2. A SIP featuring a MC1319× compatible tranceiver and an 8-bit HCS08 microcontroller core.
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Furthermore, the microcontroller and transceiver can be combined into a single package to create more compact and efficient solutions. Figure 2 illustrates a system-in-a-package (SIP) that features an IEEE 802.15.4 compliant wireless transceiver and an HCS08 microcontroller core.
Sensor Technology
Sensors are the contact points for monitoring a patient’s condition. Both pressure sensors and acceleration sensors can be employed in a broad range of health care monitoring applications. In the chip set example in Figure 1, all the other components are used to process and disseminate the information the sensors gather.
A typical piezoresistive transducer (a commonly used pressure sensor) consists of an etched silicon diaphragm upon which a piezoresistive element is implanted. Piezoresistive materials change their resistance under physical pressure, such as increased air pressure. A silicon piezoresistive pressure sensor provides a highly accurate and linear voltage output that is directly proportional to the applied pressure.
Acceleration sensors also present changes in motion through varying voltage output levels. An advanced acceleration sensor, such as a dual-axis (X and Z) low-g device, is significantly more complex than a pressure sensor. It consists of two surface micromachined capacitive sensing cells (g-cells) and a signal conditioning ASIC contained in a single integrated circuit package. The sensing elements are sealed hermetically at the wafer level using a bulk micromachined cap wafer.
The g-cell is a mechanical structure formed using semiconductor processes, and it can be modeled as a set of beams attached to a central mass that moves between the beams. The g-cell beams form two back-to-back capacitors. As the center beam moves with acceleration, the distance between the beams changes and each capacitor’s value will change. The ASIC uses switched capacitor techniques to measure the g-cell capacitors and extract the acceleration data from the difference between the two capacitors. The ASIC also signal conditions and filters the signal, providing a high-level output voltage that is ratiometric and proportional to acceleration.
The g-cell architecture can be used to develop a number of varying acceleration sensors. One company developed a 3-axis low g acceleration sensor, which measure motion along the X, Y and Z axes. To demonstrate the capabilities of acceleration sensors, In the past few years, acceleration sensors have changed dramatically, with increased sensitivity, reduced power consumption and reduced package size. Tools, such as STAR, help developers learn how to best employ the new technology advances.
Sensors and Microcontrollers in Application
The sensors described above provide 3-volt or 5-volt analog output that must be processed before it can be transmitted and stored for health care personnel to analyze. An inexpensive, general purpose 8-bit microcontroller with an ADC is sufficient to do the job. Essentially, the sensor generates analog signals and inputs to the ADC, which then processes them into digital signals to be used by computers or monitors through a communication interface, such as an RF transceiver or a direct Universal Serial Bus (USB) connection. A more accurate ADC (10-bit vs. 8-bit, for example) will ensure cleaner input and output signals.
8-bit processing speeds are generally sufficient for handling the data rates and algorithmic compression and decompression functions, but the amount of Flash memory required is largely determined by the communications protocol used by the transceiver. For instance, processing ZigBee compliant data requires more memory than that for simple point-to-point wireless connectivity. The combination of sensor and 8-bit controller is a compact, cost-effective solution that consumes little power yet gathers and processes large amounts of useful data. This data can be transmitted to a remote location through an associated RF device or can be used to initiate on-the-spot treatment. Some sensors and microcontrollers are so inexpensive that they can be used in disposable systems that may operate for only a few days before they are discarded and replaced.
An interesting application of such technology is the OmniPod™ Insulin Management System from Insulet Corporation. The OmniPod is designed to replace conventional insulin pumps that require people with diabetes to learn about and carry a number of cumbersome components, such as insulin reservoirs, infusion sets, insertion devices and blood glucose meters. The system includes two fully integrated wireless components—a small, self-adhesive, disposable OmniPod insulin reservoir and delivery system with a wireless receiver and the Personal Diabetes Manager (PDM), a PDA-sized handheld device with a microcontroller and RF transmitter that the patient uses to program the OmniPod with customized insulin delivery instructions. It also monitors the OmniPod’s operation, contains an integrated blood glucose meter and automatically stores patient records. The system delivers insulin according to the patient’s pre-programmed personal basal rates and bolus dosages.
The PDM is compact enough to be carried in a pocket or purse, and the semiconductor and shape memory alloy wire activation (for insulin delivery) components in the OmniPod are so inexpensive that the entire unit is completely disposable after a few days use. Such applications have made it possible for patients to manage their conditions in a cost effective, more comfortable setting, such as their own home. What’s more, it’s possible to expand the wireless capabilities of a similar controller unit to connect directly to an Internet gateway to communicate test results and dosage information directly to a health care provider.
Another example uses sensor technology to not only monitor patient symptoms but also determine the conditions under which the symptoms appear. For instance, for patients suffering from incontinence, a wearable device that includes pressure sensors, a microcontroller and RF transceiver can detect even minute leakage and transmit time and volume data to be stored and analyzed at a later time. If the system also included acceleration sensors, the patient’s activity—lying down, standing, walking, running, etc.—could also be recorded, helping care givers determine if there are specific physical activity triggers that precipitate leaking, which can lead to more effective countermeasures.
The Wireless Connection
Wireless communications technology is what makes a portable sensing and processing device even more convenient for both the patients and the care givers. It also gives devices the ability to seamlessly transfer data to other networks, such as hospital Ethernet or CAN systems or the Internet for worldwide accessibility. In Figure 1, a family of low power, 2.4 GHz ISM band transceivers provide a cost effective solution for short-range data links and networks. A four wire serial peripheral interface (SPI) connection allows direct communication with a wide variety of microcontrollers. The software and processor can be scaled to fit applications ranging from simple point-to-point systems, through complete ZigBee networking.
A simple proprietary wireless connection requires only a physical layer (PHY) and simple media access controller software (SMAC) for point-to-point and STAR networks applications. Requiring less than 2.5K memory, the simple wireless connection is useful for very cost-effective applications that have extremely low power requirements, such as portable, disposable health care monitoring devices.
In 2003 the IEEE® released its 802.15.4 standards-based simple packet data protocol for lightweight wireless networks. The robust communication and time-critical protocol consists of 802.15.4 PHY and media access controller (MAC). 802.15.4 works well for applications requiring long battery life and selectable latency for controllers, sensors and remote monitoring. 802.15.4 provides a greater level of security over a simple wireless connection and can be used in mesh and clustertree network applications.
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Figure 3. This diagram compares the needs for three wireless communication solutions suitable for healthcare monitoring applications, using microcontroller cores and wireless transceivers.
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The capabilities of the IEEE 802.15.4 protocol standard can also provide the base for a fully embedded ZigBee compliant platform. The ZigBee stack includes network and security layers, the application framework and application profiles that can be loaded onto an 802.15.4 compliant transceiver. Figure 3 compares simple wireless connection, 802.15.4 compliant and ZigBee platforms, including microcontroller memory requirements and wireless transceiver examples (MC1319x family of devices).
ZigBee has several attractive features that make it a strong alternative for health care monitoring applications. Many applications only operate periodically and for short periods of time. To minimize power consumption, greatly extending battery life, ZigBee and Bluetooth ® can “sleep” for extended periods of time, waking up and communicating only when necessary. Wi-Fi ® cannot efficiently operate in a sleep-wake-sleep mode so it must be on all the time, making it unsuitable for many applications.
Both ZigBee and Bluetooth can operate at very low duty cycles (a one percent duty cycle would mean the application is active only one percent of the time), but latency issues work in ZigBee’s favor. It may take several seconds for a Bluetooth device to wake, synchronize with the network and begin communicating. ZigBee, however, does not need to synchronize before communicating, which cuts the wake-to-communicate latency to about 27 milliseconds. This allows for more precise scheduling and just a little more battery life for each wake cycle.
ZigBee can also be scaled from simple point-to-point applications to large mesh network environments by adding memory and the appropriate software.
Extending the Communications
Hospitals and other health care facilities are relying more on network communications to move massive amounts of data and make it more accessible for those who need it. A Controller Area Network (CAN), originally developed for automotive applications, can connect a cluster of instruments and monitors that rely on shared information. The CAN, in turn, can port to an Ethernet backbone for facility-wide distribution. But most of the equipment used is portable in one way or another, usually stationed on a cart or rolling stand. Short-range wireless communication allows a permanent connection to the facility backbone, even while a cart is being rolled from one room to another.
In the same respect, home health care monitoring devices can connect to the Internet through cable or DSL via a Wi-Fi access point or home networking gateway. Once on the Internet, critical patient monitoring information can be accessed through dedicated Web sites that can also provide health care personnel quick access to the patient’s medical records. It’s all a matter of managing the flow of information from multiple sources so that it can be analyzed efficiently for a faster and more accurate doctor-to-patient response.
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Figure 4. A healthcare monitoring gateway block diagram using an embedded processor.
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Health Care Monitoring Gateways
Health care personnel today have a wider variety of patient information sources than ever before, yet the multitude of information can be an impediment if the data is not interconnected, analyzed, recorded and responded to in the event of an emergency. One of the key emerging applications consists of health care monitoring gateways that allow health care personnel to monitor and interface with equipment both locally and from a central base station. Equipment such as respirators, heart monitors and medicine dosage controllers from different hospital rooms can be securely and remotely monitored from a central base station. The local bedside health care-related equipment may be connected to a microprocessor-based local health care monitoring gateway via Ethernet or, in the case of legacy health care-related devices, via a serial RS-232 port. The gateway in each room is normally wired to a central router that is in turn connected to the central base station.
Microprocessors used in medical gateways must offer connectivity, security and product lifetime longevity. The latest generation of microprocessors designed specifically for this application offers connectivity options such as multiple 10/100 Fast Ethernet controllers, USB and queued serial peripheral interfaces. The latest generation of microprocessors help to provide secure point-to-point communication across an insecure Ethernet network without sacrificing system performance. The microprocessor encrypts the data received from the bedside equipment before it is transmitted by Ethernet to the central base station, where the data is decrypted and interpreted.
In addition to the ability to monitor bedside health care-related equipment in a given room from the remote central base station, health care personnel may prefer to access the same data while in the patient’s room using a USB interface. For instance, the system could be accessed through the Gateway’s USB-to-Ethernet adapter port using a PDA with a USB On-The-Go (OTG) port. USB-OTG is a new supplement to the USB 2.0 specification that augments the capabilities of existing mobile devices and USB peripherals by adding host functionality for connection to USB peripherals. With this additional USB feature, a health care provider can keep track of his or her patients’ condition upon every visit.
The Personal Touch
Often there is no substitute for vocal communications. An interesting application of a technology that is spreading throughout the consumer and business communities and shows great potential in the health care industry is voice over Internet Protocol (VoIP), which provides the additional service of voice communications. VoIP can be built right into a hospital bed, for instance, for wireless communication to a nurse station and beyond. Since information is traveling as packets over the Internet, it can be routed almost anywhere—to a central handling area that may serve a number of hospitals or to an individual’s cell phone, accommodating an extended doctor/patient relationship. Also, using VoIP text and voice data could be stored directly into a database, accommodating rapid retrieval and avoiding bulky tape storage systems.
Conclusion
Recording, processing, transmitting and storing massive amounts of data more efficiently than ever before while still cutting costs is a tall order. Semiconductor technology is helping the health care industry do just that, in hospitals and clinics around the world.
In addition, providing the tools that allow patients to spend more time at home and less time in hospitals and other health care facilities helps patients get on with their lives. What’s more, through advanced network communication, if doctors can reach inside the home and make virtual house calls, the benefits to health care providers is timely, accurate information that can be used to more efficiently administer treatment. Extending the doctor/patient relationship into the home and back out again, to any part of the world, is technology well placed for patients and care givers alike.
*The HC08 products incorporate SuperFlash® technology licensed from SST.
