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Medical design engineers are using semiconductors as the foundation for devices as they move into home use.
Semiconductor technology is paving the way for development of increasingly smaller and more-powerful medical devices for use in the home. For patients, the benefits of smaller, portable devices translate into improved access to care, fewer hospital visits, and reduced medical costs. To be effective in the home environment, medical devices must be easy to use and safe even under misuse conditions.
The PocketCPR is one of many devices that have been aided by advances in semiconductor technology. Image courtesy of ZOLL MEDICAL.
The need for home healthcare devices is expanding due to the increasing number of aging baby boomers who require intensive home care. According to WHO, the number of people worldwide aged 60 and older was 650 million in 2006. This figure is expected to reach 1.2 billion by 2025. In the United States, people 65 and older now compose a greater share of the population than ever before, and this number is expected to steadily increase during the next century.
A significant number of modern semiconductor devices are targeted at home and handheld consumer devices for entertainment and communication. Much of this design expertise, and even some of the devices, are quite useful in the implementation of the newest generation of home healthcare devices. When these designs are coupled with high-performance sensors and data-acquisition devices, the resulting product combinations can be built into medical-grade systems that can be readily deployed in the home environment.
Semiconductor products have been a catalyst in this shift toward home healthcare devices. This is exemplified by reliable, high-performance sensors, amplifiers, and data convertors that extract and digitize a precision signal, as well as by embedded processors that can perform sophisticated analysis of the acquired signals. This article provides an overview of how recent advances in integrated circuit (IC) technologies, such as developments in sensors, data convertors, and embedded processing, are enabling effective home healthcare.
Today’s diagnostic measurement systems are based on integrated systems such as automated home test systems for glucose or even cholesterol for monitoring a specific target substance of clinical relevance. Clinical laboratory systems from Thermo Scientific, Bayer, and many others can perform multiple tests from a single blood sample. The measurement comprises a sensing layer that recognizes the target substance and generates a physiochemical signal that is measured by a transducer. An example of this measurement process is seen in blood glucose monitors. Glucose strips contain enzymes that selectively convert glucose to a measurable product. This conversion process generates electrons proportional to glucose levels, which are measured with current-based meters.
Silicon has traditionally provided the amplifier or data convertor interface to sensors but has now been extended to provide the actual sensing elements. Silicon transducers include microelectromechanical systems (MEMS)–based motion sensors for acceleration, gravitational pull, and inclination, as well as gyroscopic sensors for rotation sensing. Other products in this category include
• Capacitance-to-digital convertors.
• Impedance-to-digital convertors.
• Photonic systems using LEDs.
Often in combination with high-accuracy amplifiers, data convertors are a key signal-processing block between sensors and computing that can both digitize and drive transducers. Products such as analog-to-digital (AD) convertors enable low-power, high-accuracy systems. Successive approximation register and sigma-delta convertors are well suited for the resolution and measurement signal bandwidths required in these systems. One must consider power consumption, resolution, and speed in selecting the optimum convertor.
High-performance, low-power, low-cost, secure embedded processing will be necessary to enable compact, battery-powered medical diagnostics and monitoring for use outside clinical environments. Embedded processors control the entire device as well as perform on-the-spot sophisticated analysis of the acquired signal to first verify the quality, turn it into medically useful information, and then deliver the results to the patient in an understandable format. Processors may also be tasked with managing wireless (or wired) connectivity for communicating patient data to the physician. It is not a stretch to envision a device the size of a wristwatch that nonintrusively monitors vital signs key to a particular individual’s health status on an ongoing basis.
When developers seek more performance while keeping system costs and power consumption to a minimum, a converged digital signal processor (DSP) and multipoint control unit (MCU) may be beneficial. For example, the latest existing technology offers robust processing speed and power up to 750 MHz, and it also provides broad connectivity support for wired and wireless communication including USB, Ethernet, Wi-Fi, Bluetooth, and LCD. Additionally, some processors offer patented technology that enables increased intellectual property and code protection.
Complex Home Devices
Examples of home healthcare devices enabled by semiconductor technology include the Wholter, an overnight pulmonary monitor, and the Wheezometer, a personal asthmatic assessment device. Both were developed by KarmelSonix, a company that has been instrumental in the development of medical device technology for asthma management. The two aforementioned devices address the critical need of more than 48 million asthma sufferers worldwide to self-assess and manage their asthma symptoms—a capability that was previously only available at clinician’s offices or hospitals.
Results of an asthma assessment or a multivariable lung activity determination must be both immediate and accurate for proper medical treatment to be administered. In the past, this level of instrumentation reliability existed only in spirometer technology, which was typically located in hospitals or physicians’ offices, putting at-home or in-transit asthma patients at risk. To take this critical patient care from the institution to the home, Karmelsonix used high-speed DSPs and precision signal processing components in these products to ensure that asthma suffers can obtain an accurate, reliable assessment of their “wheeze rate,” a dynamic, but significant asthmatic attack indicator. Asthmatics can use these medical devices for early self-assessment of symptoms, which is essential for proper medication.
Continuing with the respiratory devices example, these products use a proprietary noninvasive piezoelectric phonopneumography sensor array. Its signal is captured by a quad low-noise op amp and then digitized by a six-channel simultaneous-sampling 16-bit AD convertor. This high-resolution signal can then be fed to a processor (such as the converged DSP and MCU previously described) for signature analysis. A voltage monitor ensures that all of the circuitry is running at the proper signal and supply levels. This signal chain, coupled with a device company’s design expertise and software, delivers a medically acceptable level of performance at home or in transit to facilitate proper self-treatment or diagnosis support.
Simple Home Devices
Many home-health support devices are much simpler in function but just as critical for saving lives and preventing accidents. For example, the PocketCPR from Zoll Medical is placed under the hand of a person administering CPR to a heart attack victim. The device measures the depth of the chest compressions, providing audible and visual feedback to the rescuer to allow adjustments to proper depth and to the correct rate. The device also gives spoken instructions, which can instill confidence in a relatively inexperienced rescuer or inform experienced caregivers about proper technique. It is enabled by an accelerometer that makes precise measurements of the movement of the device under the rescuer’s hand. Sudden cardiac arrest is a leading cause of death in the United States, and according to the Sudden Cardiac Arrest Association, claims nearly 300,000 lives each year. High-quality chest compressions can mean the difference between life and death.
Perhaps even simpler, the FallSaver developed by Motion Knowledge Systems is used on patients who should not move without help. Caregivers cannot be present at all times to monitor bedridden patients, who may move about because they suffer either from dementia or they choose not to bother the caregiver. This often leads to a debilitating fall, whether in a hospital, at home, or in a nursing home. The small FallSaver patch is attached to the thigh of the patient for up to two weeks and provides continuous monitoring of the movements of the patient, especially determining movements that indicate an attempt to stand and move about. The FallSaver unit then sounds an alarm and sends a radio signal to the nurse call station or radio carried by the caregiver. Ideally, the caregiver can to get to the bedside to aid with the intended movements before a fall occurs. This device is also enabled by accelerometers, which provide the motion information in a digital format, allowing quick algorithmic analysis of movement patterns. In addition to the previously mentioned accelerometers, next-generation three-axis accelerometers offer even higher levels of functionality at lower power and with smaller footprints. Examples include the ADXL345 and ADXL346 from Analog Devices.
Connectivity and Power
Two key aspects of future home healthcare devices are connectivity and power. In many situations, the ability to accurately communicate clinical readings from diagnostic devices to healthcare professionals is equally as vital as the ability for the patient to self-monitor, as in diabetes management. For example, a current ECG waveform can only be provided to a clinician as a printout or a signal transmitted through an electronic communication channel. Historically, to achieve this, the ECG instrument had to be connected directly to the computer, which then presents the potential of electrical hazards to the patient. A USB isolator, which is a recent technological advancement, can overcome this issue by providing full electrical isolation of the patient from the computer and network while still enabling a full-capability ECG and computer connectivity.
The measurement front end also requires a small amount of power to drive the amplifiers and data convertors used to acquire and digitize the ECG signals. Isolated power is provided by a dc-dc convertor, which eliminates the need for battery charging and replacement. Devices of this sort will also enable the design of many home health devices requiring direct electrical contact to the patient, and also the ability to connect directly to a computer through USB, thus providing a full capability for storage, analysis, and transmission of results. These technologies will also make it simpler for the medical designer to meet the requirements of the latest edition of IEC 60601.
By developing innovative ICs, semiconductor companies are improving the quality of healthcare for patients worldwide (see the sidebar on p. 33). Medical design engineers are using semiconductors as the foundation to develop the home healthcare systems aimed at disease management, health and wellness, and drug delivery. Much of the progress in semiconductor design for portable and home health products borrows from the strides made in other portable consumer products, such as cell phones and media players. This is especially true in areas such as power management, motion detection, and radio-frequency transmission. However, expertise in precision signal amplification, conversion, and processing is still essential to proper detection and analysis of low-level, complex clinical information.
The growing demand for home-use medical devices is making systems requirements progressively complex and demanding for medical equipment designers. These designers must reduce the size, improve ease of use, and increase the performance of next-generation portable medical devices. Such system-level demands mean that analog semiconductor manufacturers must rise to the challenge of developing breakthrough building-block ICs that enable the design of next-generation products. Developing future innovative capabilities for medical devices is increasingly dependent on the continuous and effective sharing of information between both system and analog IC designers. Such sharing enables semiconductor technology to become instrumental in the creation of products that change lives.
is a strategic marketing manager in the healthcare group at Analog Devices Inc. (Norwood, MA). He can be reached at email@example.com
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