Processing power creates portability
01 October 2007
As new technology is increasingly applied to medical applications, one of the most interesting opportunities is to provide patients with portable monitors. Home monitoring can improve the patient’s quality of life, reduce the risk of potentially life-threatening problems by early detection, and lead to cost savings for the patient and medical care provider
One condition that can benefit from such home monitoring is atrial fibrillation (AF). This is a relatively common complaint, with about one person in 20 over the age of 20 developing AF. Normally, the human heart beats at a steady rate between about 60 and 100 beat/minute (BPM). During atrial fibrillation, random electrical impulses in the heart override the normal regular rhythm, and cause the upper chambers (atria) to ‘fibrillate’: beating very rapidly at up to 400 times/minute, but only partially contracting.
This then causes the lower chambers (ventricles) of the heart to beat irregularly, usually between 140 and 180 times/ minute, with the force of each beat possibly also of different intensities. Because of this fibrillation, the blood can pool in the atria in the heart and form clots. It is possible that a clot can break free and travel through the bloodstream to the brain, which may cause a stroke. People with AF are five times more likely than the general population to suffer from a stroke. Early detection and treatment of AF can significantly reduce the risk of heart attack or stroke. Some people do not know they are in AF, while others can experience palpitations, exhaustion, shortness of breath, dizziness, or other symptoms. Daily monitoring of the heart rhythm enables patients to notify their doctor immediately if AF occurs.
Portable AF monitoring
Lechnologies Research, Inc. (www.afibalert.com) has developed a portable AF monitor called AfibAlert. Currently, this is the only long-term home monitor for the detection of AF. It is designed for daily use in the home to record and analyse heart rhythm data, and indicates via a red or green light the likelihood AF is occurring and if the patient should contact their physician. To analyse the data, which takes around 45 seconds, the patient either presses their thumbs to electrodes on the device, or uses the supplied cable and wrist electrodes.
The monitor has been designed to be straightforward to use. It does not require the patient to analyse complicated data, but simply indicates with a red light when they should transmit the data captured to their doctor for interpretation. A proprietary algorithm is used to analyse the ECG data and determine if further medical intervention is required After taking a test, the patient can upload the data using a PC (connecting the AfibAlert via a USB cable) to a secure storage area on the AfibAlert website and then contact their doctor to let them know data is ready, or they can simply transmit it over a standard phone line to a doctor or specialised receiving centre by holding the monitor to the phone handset and pushing a transmit button. The ECG strip recorded by the AfibAlert can be reviewed by the patient, as well as their doctor.
The USB connection can also be used to update the AfibAlert with new versions of software from the website, allowing it to update the algorithm used to analyse the heart rhythm data. There are four lights that indicate different functions on the AfibAlert. The green light means that data has been successfully stored and there is a low probability that AF is present. The red light indicates a high probability of AF and the data should be sent to the patient’s doctor. The yellow light signifies when there is poor contact with the electrodes and the test should be repeated.
The blue light signifies when the recorder is acquiring and analysing data. It also indicates when data is being transmitted. The device’s LCD also shows the patient’s heart rate. The AfibAlert has thirty memory slots in its flash memory, one to store a baseline, plus a system that cycles up to thirty tests through its memory system, replacing the oldest recording when a new set of data is captured. Up to thirty recordings can be uploaded to the web site, or up to five can be sent by telephone.
Embedded processing
With size and portability important factors in customer acceptance, it was important for Lechnologies to build their product around an efficient processor which maximised battery life while using compact cells. The AfibAlert uses a Blackfin BF533 processor, which operates the AfibAlert’s LCD controller, LED outputs, audio generation, flash storage and high-quality ADC. The Blackfin also acts as a signal processor, receiving data from the microcontroller peripherals and applying digital filtering and mathematical and statistical analysis to provide feedback to the patient. The Blackfin is a 16/32bit embedded processor that provides excellent performance and power efficiency. It includes both DSP functionality as well as control functions in a single processor core, so can be used in applications that would previously have required a separate DSP and microcontroller. The AfibAlert uses only two AAA batteries.
Tim Lohman, Lechnologies president and CEO, said, ‘The Blackfin’s ability to operate at extremely low power levels also means patients can depend on their AfibAlert for up to six months between battery changes. ‘Building the AfibAlert on a Blackfin processor made it possible for Lechnologies to offer heart patients a sophisticated diagnostic tool that is also small, lightweight, and easy to use,’ concluded Lohman.
Hi-tech home healthcare
Telehealth monitoring devices have been designed to help people with long-term conditions, such as heart disease or diabetes, to monitor and manage their condition in the comfort of their own homes. Patients can, for example, test their blood glucose levels or blood pressure on a small machine at ome. Healthcare professionals can then monitor the results remotely and can alert the patient if they see anything in the data that they receive back that gives them cause for concern.
Technology is also being adopted to enable elderly people to remain in their own homes for longer. Telecare devices that consist of sensors in the home can carry out simple tasks like switching lights on or raising an alarm if an old person does not return to bed in the middle of the night. These systems can be closely monitored to ensure that assistance is sent as soon as it is needed.
ANDERS FREDERIKSEN is marketing manager for industrial and embedded processing, Analog Devices
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