As health care moves from the hospital to the home, opportunities are opening up for innovate semiconductor solutions. By Paul Errico.
Sophisticated semiconductor technology is enabling the development of increasingly smaller and more powerful medical devices for use in the home. For patients, this means easier access to care, fewer hospital visits, and reduced medical costs. But, to be effective in the home, medical devices must be easy to use, safe even under misuse conditions, and able to distinguish between correct results and those obtained by incorrect procedures. The need for home healthcare devices is expanding due to the aging population. According to the World Health Organisation, there were 650million persons aged 60 and older in 2006. This figure is expected to reach 1.2 billion by 2025. Much of today's semiconductor development is targeted at home and handheld consumer devices for entertainment and communication. This design expertise, and even some of the devices, can be useful in the implementation of the newest generation of home healthcare devices. When this is coupled with high performance instrumentation quality sensors and data acquisition devices, the resulting products can be built into medical grade systems that can be readily deployed at home. The precision side of semiconductor products is exemplified by reliable, high performance sensors, amplifiers and data converters that extract and digitise a precision signal, and embedded processors that can perform sophisticated analysis of the acquired signals. • Sensors. Today's diagnostic measurement systems are based on integrated solutions for monitoring specific target substances of clinical relevance. The measurement comprises a sensing layer that recognises the target substance and generates a physiochemical signal that is measured by a transducer. An example of this is blood glucose detection. Enzymes on glucose strips selectively convert glucose to a measurable product. In this process, electrons are generated proportional to glucose levels. These are measured with current based meters. Silicon transducers include capacitance to digital converters, impedance to digital converters, led based photonic systems, photodiodes, MEMS based motion sensors for acceleration, gravitational pull and inclination, and gyroscopic sensors for rotation sensing. • Data converters. Often used in combination with high accuracy amplifiers, this signal processing block can digitise and drive transducers. Products such as a/d converters enable low power, high accuracy systems. Successive approximation register (SAR) and sigma-delta converters are well suited for the resolution and measurement signal bandwidths required in these systems. • Embedded processing and wireless communications. 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 analyse the acquired signal to first verify the quality, turn it into medically useful information, then deliver the results to the patient in a useful format, while also controlling the device. The processor may also be called upon to manage wireless (or wired) connectivity for communicating patient data to the physician. It is easy to envision a wristwatch sized device that can monitor vital signs non intrusively. When developers seek more performance while keeping system cost and power consumption to a minimum, a converged dsp and microcontroller, such as ADI's Blackfin, is worth considering. Analog Devices recently introduced a radio SoC that combines data conversion, rf and 32bit processing to enable power efficient wireless connectivity. The ADuCRF101 (see fig 1) is suited to medical applications where data must be captured, measured and transmitted quickly in noisy environments without taxing battery life. For example, a wireless Holter or telemetry monitor worn by the patient needs to be small, to operate at low power for extended battery life and to offer the performance to sustain uninterrupted communication of the patient's vital signs. The ADuCRF101 enables these applications and allows patient monitoring to be undertaken outside of the hospital environment. Home healthcare devices in practice Examples of home healthcare devices include the Wholter, an overnight pulmonary monitor, and the Wheezometer, a personal asthmatic assessment device, both developed by Israeli company Karmelsonix. The Wholter and Wheezometer address the needs of more than 48m asthma sufferers worldwide to assess and manage their symptoms – a capability previously available only in a doctor's surgery or in hospital. Effective asthma assessment must be immediate and accurate for proper medical treatment to be administered. In the past, this level of reliability existed only in spirometer technology at hospitals or surgeries. In taking this ability from institution to the home, Karmelsonix used Analog Devices' Blackfin dsps and precision signal processing components to ensure that asthma suffers can obtain an accurate, reliable assessment of their 'wheeze rate', a significant asthmatic attack indicator. The Wheezometer uses a proprietary non invasive piezoelectric phonopneumography sensor array, whose signal is captured by a quad low noise AD8608 op amp and then digitised by the AD7656, a six channel simultaneous sampling 16bit a/d converter. This signal is then fed to an ADSP-BF524 for signature analysis. An ADM708 voltage monitor ensures the circuitry is running at the proper signal and supply levels. This signal chain, coupled with Karmelsonix' design expertise and software, delivers medically acceptable levels of performance at home or in transit. Many home health support devices are simpler, but just as critical for saving lives and preventing accidents. PocketCPR from ZOLL Medical, pictured, is placed under the hand of a person administering cardiopulmonary resuscitation (CPR) to a heart attack victim. The device measures the depth of the chest compressions, providing audible and visual feedback to the rescuer to adjust to the proper depth and to the correct rate. The PocketCPR employs the ADXL311 accelerometer, which makes precise measurements of the movement of the device under the rescuer's hand. Even simpler is the FallSaver patch, which can be attached to the patient's thigh for up to two weeks, provides continuous monitoring of their movements. The device uses ADXL323 and ADXL335 accelerometers, which provide motion information in digital format, allowing quick analysis of movement patterns. Growing demand for home use medical devices is making systems requirements progressively complex and demanding for medical equipment designers, who must reduce the size, improve ease of use, and increase the performance of next generation portable medical devices. These new system level demands mean analogue semiconductor manufacturers must rise to the challenge of developing building blocks for these next generation products. Paul Errico is a strategic marketing manager with Analog Devices' Healthcare Segment.