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Heart Activity Measurements

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Heart Activity Measurements

• Pulse rate
• ECG/EKG electrocardiogram
• Impedance cardiogram, IKG -- impedance
  cardiography
• EchoKG echocardiogram
• Magnetocardiography (MCG)

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Arterys pulsation
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Heart Activity Measurements

• Pulse rate
• ECG/EKG electrocardiogram
• Impedance cardiogram, IKG -- impedance
  cardiography
• EchoKG echocardiogram
• Magnetocardiography (MCG)

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EKG/ECG -- electrocardiogram
Williem Einthoven in 1924 Nobel prize
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ATRIUM
VENTRICLE
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The conduction system of the heart.
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Animation of a normal EKG wave
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Different waveforms for each of the specialized
cells found in the heart
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Information from EKG

• If the electric or muscular function of the heart
  is disturbed for some reason, it will affect how
  the electric signals spread through the heart
  muscle.

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• The heart's electrical axis refers to the general
  direction of the heart's depolarization wavefront
  (or mean electrical vector) in the frontal plane.

Lead I.
Lead II.
Lead III.
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EKG

• These three bipolar limb leads roughly form an
  equilateral triangle (with the heart at the
  center) that is called Einthoven's triangle in
  honor of Willem Einthoven who developed the
  electrocardiogram in 1901.

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Negative electrode on the right arm and the
positive electrode on the left arm
Different directions during the EKG measurement
Negative electrode on the right arm and the
positive electrode on the left leg.
Negative electrode on the left arm and the
positive electrode on the left leg.
Maximal positive deflection is obtained in lead
III when the depolarization wave travels
parallel to the axis between the left arm and
left leg.
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The realtively small P wave is produced by
electrical currents generated just before
contraction of the atria
EKG
Accoustic
QRS complex is caused by currents generated in
the ventricles during depolarization just prior
to venticular contraction. R is the most
prominent component of this wave complex.
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160 ms
300 ms
370 ms
830 ms
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positive deflection on the ECG
negative deflection on the ECG
equiphasic complex deflection on the ECG
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The ECG system
Instrumentation amplifier, which has a very high
CMRR (90dB) (common-mode rejection ratio) and
high gain (1000), with power supply 9V and -9V.
An opto-coupler to isolate the In-Amp and Output.
A transducer AgCl electrode, which convert ECG
into electrical voltage. The voltage is in the
range of 1 mV 5 mV
Bandpass filter of 0.04 Hz to 150 Hz filter.
Its implemented by cascading a low-pass filter
and a high pass filter
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Heart Activity Measurements

• Pulse rate
• ECG/EKG electrocardiogram
• Impedance cardiogram, IKG -- impedance
  cardiography
• EchoKG echocardiogram
• Magnetocardiography (MCG)

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Impedance cardiogram
Impedance changes
Differentiatior
Amplifier
dZ/dt
Z0 value is the total impedance between the two
inner leads
High-frequency 40-100 KHz Constant current
4 mA
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Impedance cardiogram
R-Z is the time interval from the R wave of the
ECG to maximum ejection as indicated by the
peak of dZ/dt
ventricular ejection time
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• Part of automated external defibrillator
• Investigate circulatory system problems valve
  defects, right-left shunting, congestive failure
• Impedance of the thorax can be considered to be
  divided into two parts
• the impedance of both tissue and fluids
• the amount and distribution of blood The amount
  of blood in the thorax changes as a function of
  the heart cycle. The changes in the distribution
  of blood in the thorax as a function of the heart
  cycle can be determined by measuring the
  impedance changes of the thorax.

Band electrodes
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Heart Activity Measurements

• Pulse rate
• ECG/EKG electrocardiogram
• Impedance cardiogram, IKG -- impedance
  cardiography
• EchoKG echocardiogram
• Magnetocardiography (MCG)

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EchoKG Echocardiogram
Ultrasound waves 2.518 MHz
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EchoKG -- Echocardiogram
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Transducer
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40 kHz Ultrasound receiver
A X100 transistor amplifier is followed by a zero
cross detector circuit, using a voltage
comparator. The output is a TTL logic signal,
corresponding to the received 40KHz signal.
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Medium Power 40KHz Ultrasound Transducer Driver

• This crystal controlled circuit drives a 40KHz
  piezoelectric transducer with a 30v peak to peak
  signal.

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Heart Activity Measurements

• Pulse rate
• ECG/EKG electrocardiogram
• Impedance cardiogram, IKG -- impedance
  cardiography
• EchoKG echocardiogram
• Magnetocardiography (MCG)

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dc SQUIDs

• Scanning electron micrograph of the SQUID ring
  with step-edge Josephson junctions.

• Magnetometers based on dc SQUIDs are currently
  the most sensitive sensors for magnetic fields,
  achieving a magnetic field resolution which is
  about a billion times below the earth's magnetic
  field.
• A dc SQUID basically consists of a
  superconducting ring interrupted by two weak
  links called Josephson junctions.
• SQUID can be viewed as a flux-to-voltage
  converter.

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Noise spectrum of the magnetic field
noise in an industrial environment, measured
with an unshielded multiloop magnetometer
The magnetometer's intrinsic noise level is
several orders of magnitude lower.
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dc SQUIDs

• A multiloop SQUID magnetometer. The diameter of
  this device is 8.5 mm.

• The SQUID ring itself is enlarged and it consists
  of several identical pickup loops, which are
  connected in parallel to reduce the inductance.
  The 16 loops are arranged to the cart-wheel like
  shape of the device. A multilayer technology is
  needed for the preparation.

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Block diagram of a SQUID magnetometer
transform the applied flux into a room
temperature voltage output
senses changes in the external magnetic field
and transforms them into an electrical current
acquiring, storing analyzing data
transforms the resulting current into a magnetic
flux in the SQUID sensor
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68-channel dc-SQUID system
SQUID maps the axial (BZ) component
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Real-time magnetocardiogram recorded with a
multiloop magnetometer.
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Magnetocardiography (MCG)

• Magnetic field x, y, z component
• Grid measurement
• Similar sensitivity to EKG
• Higher SNR than EKG

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magnode
Solenoid coil
Ir reciprocal current FLM reciprocal magnetic
scalar potential field HLM reciprocal magnetic
field BLM reciprocal magnetic induction field
ELM reciprocal electric field JLM lead
field   VLM voltage in the lead due to the
volume source i in the volume conductor  
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Measurement of the x-component of the magnetic
heart vector
The general construction of the measurement
system
Baule-McFee lead system
Measurement of the z-component of the magnetic
heart vector
Measurement of the y-component of the magnetic
heart vector
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Unipolar Bipolar measurement locations on the
anterior and posterior sides
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Schematic illustration of the generation of the x
component of the MCG signal.
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Advantages

• Insulating barriers such as the skull, varying
  layers of tissue, anatomical open spaces, do not
  attenuate or distort magnetic fields. The
  magnetic permeability of the tissue free space.
  Therefore the sensitivity of the MCG is not
  affected by the high electric resistivity of lung
  tissue.
• different sensitivity distribution with EKG
• the magnetic detector is not in contact with the
  subject
• SQUID magnetometer is readily capable of
  measuring DC signals. Such signals can be
  obtained electrically only with great difficulty.

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Disadvantages

• ECG is easier to use
• Technologically more complicated, requires
  complex and expensive equipment SQUID
  magnetometer, liquid helium, and a low-noise
  environment
• Because of the development of the SQUID
  technology, a shielded room is no longer needed
  in magnetocardiography.
• Future at the liquid nitrogen temperature which
  decreases the operational costs

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References

• MCG
• http//butler.cc.tut.fi/malmivuo/bem/bembook/20/2
  0.htm
• http//www.kreynet.de/asc/squids.html
• EchoKG
• http//www.heartsite.com/html/echocardiogram.html
  what_US
• http//www.discovercircuits.com/DJ-Circuits/ultra4
  0khzxtr1.htm
• EKG
• http//en.wikipedia.org/wiki/Electrocardiogram
• http//www.ecglibrary.com/
• http//www.americanheart.org/presenter.jhtml?ident
  ifier3005172
• http//www.medmovie.com/mmdatabase/MediaPlayer.asp
  x?ClientID68TopicID600
• John L. Andreassi Psychophysiology
• http//www.cisl.columbia.edu/kinget_group/student_
  projects/ECG20Report/E600120ECG20final20report
  .htm