Transcript Progress Preentation

Enhancing the Capabilities
of a Wireless Holter Monitor
Senan Garry
4th ECE
Presentation Topics
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Background Holter Monitor and ECG waves
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Project Aims
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ECG Sensor
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Platform
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Progress
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Future Work
Holter Monitor
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The Holter monitor records electrical signals from the
heart via a series of electrodes attached to the chest.
Responsible for keeping a log of the heart's electrical
activity throughout the recording period (usually 24 or 48
hr period) with a sampling frequency of between 500Hz
and 1kHz
It is also useful in the fact that the patient can conduct
their normal activities while wearing the device.
ECG Waves
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The Electrocardiograph (ECG) signal is an electrical signal
generated by the heart’s beating, which can be used as a
diagnostic tool for examining some of the functions of the
heart.
The electrocardiogram or ECG is today used worldwide as
a relatively simple way of diagnosing heart conditions.
It has a principal measurement range of 0.5 to 4 mV and
signal frequency range of 0.01 to 250 Hz.
Uses for ECG
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assess your heart rhythm
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diagnose poor blood flow to the heart muscle (ischemia)
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diagnose a heart attack
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diagnose abnormalities of your heart, such as:
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heart chamber enlargement
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abnormal electrical conduction
Project Aims
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Integration of an LCD into the monitor to provide a display
of ECG and status of device
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Integration of GPRS functionality to provide an alternate
communication mechanism when out of WLAN coverage,
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Implementation of accurate ECG sampling at 500 Hz by
altering Linux kernel,
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Development of a voice recording mechanism onto the
monitor based on a button push with download of
recorded speech to system back-end.
Project Aims
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Development of analogue circuitry to implement ECG
sensor and amplification circuitry,
Basic ECG analysis software for back-end system
(e.g. determination of heart rate and associated statistics)
Enhanced ECG analysis software for ECG anomaly
detection
Design and implementation of ECG
sensor and amplification software
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E
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Amplify the ECG waves measured
Filter these to filter out undesirable low and high
frequency signals generated by noise and muscle
movement before sending onto ADC
AMP
FILTER
ADC
G
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Amplification
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An ECG signal can vary in magnitude from patient to patient
and can typically be in the range of 80-2OOOpV. This will
require the signal to be amplified several hundred times
before it is sampled.
The small voltage of the ECG also makes it vulnerable to
many types of noise.
Since the voltages and currents from the electrodes are small
in magnitude the amplifier input impedance must be very
high. This requires the use of instrumentation amplifiers
AD620
(low noise, low input bias current
and low power )
Filtering
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ECG signals may be corrupted by various kinds of noise
The typical heart beat signal is between 0.05Hz and 60Hz
therefore I decided I would keep it simple at first and filter
out signals:
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Less than 0.05 Hz and Greater than 60 Hz
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If need s be further filters can be added onto the circuit
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The OP97 is used in the right-leg common-mode feedback
circuit
applies an inverted version of the common-mode
interference to the subject’s right leg, with the
aim of canceling the interference.
ECG Sensor
Electrode placement:
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Eindhoven’s triangle (most commonly used electrode
placement scheme)
The differential potential is measured between: right
and left arm ,right arm and the left leg ,left arm and
left leg.
These part s of the body are used as they create the
least amount of movement when a patient is moving
GUMSTIX
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Decided on the Verdex XM4 as the platform to be used:
GPRS ( GPS expansion board + GPRS antenna),
LCD ready ( also GPRS ready),
Processor: Marvell® PXA270 with XScale™
Speed: 400MHz
Memory: 64MB RAM
16MB Flash
Features: USB host signals
CCD camera signals
Connections: 60-pin Hirose I/O connector
120-pin MOLEX connector
24-pin flex ribbon
Size: 80mm x 20mm
Progress To Date
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ECG Sensor built but having difficulty with the circuitry
(I think that the problem lie s in the filtering process as I
cannot seem to display a clear ECG wave.)
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Gained familiarization with the operation of the Gumstix
platform and the Linux Kernel through tutorials and by
compiling a new kernel and working my way through
directories etc.
Future Work
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Audio recording functionality
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Alteration of kernel to support 500 Hz sampling
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Basic LCD functionality + GPRS
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ECG analysis software for ECG anomaly detection
ANY QUESTIONS ?????