PHYSICAL & LIFE SCIENCE TECHNOLOGIES
Biomedical engineering
Wearing your heart condition on your sleeve
New signal processing scheme allows long-term cardiac monitoring
Xin Liu and co-workers from the A*STAR Institute of Micro- electronics1
which opens the way to long-term monitoring of heart condi- tions using a wearable silicon chip. Electrocardiography (ECG) is currently the most straightfor-
ward method of recording and measuring the heart’s electrical acitivity over time. It employs non-invasive external electrodes on the chest or limbs to record the contractile activity of the heart. This can then be used to assist diagnosis of many heart conditions. The signals produced by ECG are periodic wave- forms accompanied by occasional heart-beat spikes so often seen in medical programs on television. To interpret them accurately, however, the ECG signals must
be cleaned up or processed. This is because an ECG signal suffers from both short-term noise—generally interference from nearby contractions of other muscles—and from longer-term baseline drift, which can be caused by the effect of perspiration on the electrodes or increased body movement. The researchers used a mathematical technique known as
Wavelet transform to break the complex ECG wave signals into their components of different cyclic frequency. The signals can be adjusted for the shorter and longer term form of interference. In fact, the processing scheme they have developed allows them not only to remove baseline-drift and suppress noise, but also to detect the wave form typical of heart-beat, to analyze and classify it, and predict future heart activity all at the same time. When tested with data simulating typical ECG output signals of known heart conditions, this comprehensive analysis provided accurate results. The processing required for all of the critical functions of the
scheme can be implemented on one silicon chip as application- specific integrated circuits. This chip can then be fitted with a wireless transceiver, which allows it to transmit details of the ECG waveform together with information extracted from it. To save power, this transmission needs to be performed only if the analysis shows a deviation from the norm. The result is a low-power, wearable chip highly suitable as a long-term heart monitor. “Our research team currently is focusing on
50 have developed a new signal processing scheme
developing a multi-functional signal processing system on a chip for multiple biomedical signals,” says Liu. “Various innovative designs are under development to achieve high performance, ultra-low power consumption and miniaturization.” The researchers envision that the resulting ‘system on a chip’
can also be modified and adapted for other purposes, such as automotive or multimedia applications.
1. Liu, X., Zheng, Y., Phyu, M. W., Zhao, B., Je, M. & Yuan, X. Multiple functional ECG signal processing for wearable applications of long-term cardiac monitoring. IEEE Transactions on Biomedical Engineering 58, 380–389 (2011).
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A*STAR RESEARCH OCTOBER 2011– MARCH 2012
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