Enhancing the Capabilities of a Wireless Holter Monitor

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Enhancing the Capabilities of a Wireless Holter
Monitor

• Senan Garry
• 4th ECE

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Presentation Topics

• Background Holter Monitor and ECG waves
• Project Aims
• ECG Sensor
• Platform
• Progress
• Future Work

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Holter Monitor

• 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.

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ECG Waves

• The Electrocardiograph (ECG) signal is an
  electrical signal generated by the hearts
  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.

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Uses for ECG

• assess your heart rhythm
• diagnose poor blood flow to the heart muscle
  (ischemia)
• diagnose a heart attack
• diagnose abnormalities of your heart, such as
• heart chamber enlargement
• abnormal electrical conduction

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Project Aims

• Integration of an LCD into the monitor to provide
  a display of ECG and status of device
• Integration of GPRS functionality to provide an
  alternate communication mechanism when out of
  WLAN coverage,
• Implementation of accurate ECG sampling at 500 Hz
  by altering Linux kernel,
• Development of a voice recording mechanism onto
  the monitor based on a button push with download
  of recorded speech to system back-end.

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Project Aims

• 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

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Design and implementation of ECG sensor and
amplification software

• 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

ELECTRODES
GUMSTIX
AMP
ADC
FILTER
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Amplification

• 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 )

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Filtering

• 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
• Less than 0.05 Hz and Greater than 60 Hz
• If need s be further filters can be added onto
  the circuit
• The OP97 is used in the right-leg common-mode
  feedback circuit
• applies an inverted version of the common-mode
• interference to the subjects right leg, with
  the
• aim of canceling the interference.

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ECG Sensor
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Electrode placement

• Eindhovens 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

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GUMSTIX

• 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

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Progress To Date

• 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.)
• 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.

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Future Work

• Audio recording functionality
• Alteration of kernel to support 500 Hz sampling
• Basic LCD functionality GPRS
• ECG analysis software for ECG anomaly detection

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ANY QUESTIONS ?????