unit i

MEDICAL ELECTRONICS
Prepared by,
A.Johny Renoald M.E., (Ph.d.,)

• Biomedical engineering is the application of
engineering principles and techniques to the
medical field.
• This field seeks to close the gap between
engineering and medicine:
• It combines the design and problem solving
skills of engineering with medical and biological
sciences to improve healthcare diagnosis,
monitoring and therapy.

• Much of the work in biomedical
engineering consists of
research and development, spanning a
broad array of subfields.

• Prominent biomedical engineering applications
include the development of biocompatible
prostheses,
• various diagnostic and therapeutic
medical devices ranging from clinical equipment
to micro-implants,
• common imaging equipment such as MRIs and
EEGs,
• biotechnologies such as regenerative tissue
growth, and pharmaceutical drugs and
biopharmaceuticals.

• A medical device is intended for use in:
• the diagnosis of disease or other
conditions, or
• in the cure, mitigation, treatment, or
prevention of disease,

• Some examples include pacemakers,
infusion pumps, the heart-lung machine,
dialysis machines, artificial organs,
implants, artificial limbs, corrective lenses,
cochlear implants, ocular prosthetics,
facial prosthetics, somato prosthetics, and
dental implants

UNIT I
RECORDING AND
MONITORING SYSTEMS

BIO ELECTRIC SIGNALS
• Biosignal is a summarizing term for all kinds of
signals that can be (continually) measured and
from biological beings.
• The term biosignal is often used to mean bio-
electrical signal but in fact, biosignal refers to
both electrical and non-electrical signals.
• Electrical biosignals ("bio-electrical" signals) are
usually taken to be (changes in) electric currents
produced by the sum of electrical potential
differences across a specialized tissue, organ or
cell system like the nervous system.

• Electrical currents and changes in
electrical resistances across tissues can
also be measured from plants.
• Bio-signals may also refer to any non-
electrical signal that is capable of being
monitored from biological beings,
• such as mechanical signals (e.g. the
mechanomyogram or MMG),
• acoustic signals (e.g. phonetic and non-
phonetic utterances, breathing),
• chemical signals (e.g. pH, oxygenation) and
optical signals (e.g. movements).

• As a consequence of the chemical activity
in the nerves and muscles of the body,
variety of electrical signals are generated.
• Bio electric potentials are generated at a
cellular level.
• Each cell is a minute voltage generator.

• Because positive and negative ions tend
to concentrate unequally inside and
outside the cell wall, a potential difference
is established and the cell becomes a tiny
biological battery.

• Thus, among the best-known bio-electrical
signals are the
• Electroencephalogram (EEG)
• Magnetoencephalogram (MEG)
• Galvanic skin response (GSR)
• Electrocardiogram (ECG)
• Electromyogram (EMG)
• Heart Rate Variability (HRV)

ORIGIN
• ECG - Heart muscles
• EEG – Neuronal activity of the brain
• EMG – Skin muscles
• EGG ( Electro Gastro gram) – Movements
of the gastrointestinal tract
• ERG ( Electro Retino Gram) – Retina of
the eye
• EOG ( Electro Oculo Gram) – Retinal
potential variations

• An electrode is an electrical conductor
used to make contact with a nonmetallic
part of a circuit (e.g. a semiconductor, an
electrolyte or a vacuum).

• An electrode in an electrochemical cell is
referred to as either an anode or a
cathode.
• The anode is now defined as the electrode
at which electrons leave the cell and
oxidation occurs, and the cathode as the
electrode at which electrons enter the cell
and reduction occurs.

• Each electrode may become either the
anode or the cathode depending on the
direction of current through the cell.
• A bipolar electrode is an electrode that
functions as the anode of one cell and the
cathode of another cell.

• Electrodes are employed to pick up the
electrical signals of the body.
• The electrode, electrode paste and body
fluids can produce a battery like action
causing ions to accumulate on the
electrodes.
• The polarization effect can be reduced by
coating the electrodes with some
electrolytes.

Corneal Electrodes in EOG , ERG

ECG
• Electrocardiography (ECG, or EKG
[from the German Elektrokardiogramm]) is
a transthoracic interpretation of the
electrical activity of the heart over time
captured and externally recorded by skin
electrodes.
• It is a noninvasive recording produced by
an electrocardiographic device.

• The ECG works mostly by detecting and
amplifying the tiny electrical changes on the skin
that are caused when the heart muscle
"depolarises" during each heart beat.
• At rest, each heart muscle cell has a charge
across its outer wall, or cell membrane.
• Reducing this charge towards zero is called de-
polarisation, which activates the mechanisms in
the cell that cause it to contract.

• During each heartbeat a healthy heart will
have an orderly progression of a wave of
depolarisation that is triggered by the cells
in the sinoatrial node, spreads out through
the atrium, passes through "intrinsic
conduction pathways" and then spreads
all over the ventricles.

• This is detected as tiny rises and falls in
the voltage between two electrodes placed
either side of the heart which is displayed
as a wavy line either on a screen or on
paper.
• This display indicates the overall rhythm of
the heart and weaknesses in different
parts of the heart muscle.

• Usually more than 2 electrodes are used
and they can be combined into a number
of pairs (For example: Left arm (LA), right
arm (RA) and left leg (LL) electrodes form
the pairs: LA+RA, LA+LL, RA+LL).
• The output from each pair is known as a
lead.
• Each lead is said to look at the heart from
a different angle.

• Different types of ECGs can be referred to
by the number of leads that are recorded,
for example 3-lead, 5-lead or 12-lead
ECGs (sometimes simply "a 12-lead").

• A 12-lead ECG is one in which 12 different
electrical signals are recorded at
approximately the same time and will often
be used as a one-off recording of an ECG,
typically printed out as a paper copy.

• 3- and 5-lead ECGs tend to be monitored
continuously and viewed only on the
screen of an appropriate monitoring
device, for example during an operation or
whilst being transported in an ambulance.
• There may, or may not be any permanent
record of a 3- or 5-lead ECG depending
on the equipment used.

• It is the best way to measure and
diagnose abnormal rhythms of the heart,
particularly abnormal rhythms caused by
damage to the conductive tissue that
carries electrical signals, or abnormal
rhythms caused by electrolyte imbalances.

• In a myocardial infarction (MI), the ECG can
identify if the heart muscle has been damaged in
specific areas, though not all areas of the heart
are covered.
• The ECG cannot reliably measure the pumping
ability of the heart, for which ultrasound-based (
echocardiography) or nuclear medicine tests are
used.
• It is possible to be in cardiac arrest with a
normal ECG signal (a condition known as
pulseless electrical activity).

ECG PAPER GRAPH
• The output of an ECG recorder is a graph (or sometimes
several graphs, representing each of the leads) with time
represented on the x-axis and voltage represented on
the y-axis.
• A dedicated ECG machine would usually print onto
graph paper which has a background pattern of 1mm
squares (often in red or green), with bold divisions every
5mm in both vertical and horizontal directions.
• It is possible to change the output of most ECG devices
but it is standard to represent each mV on the y axis as
1 cm and each second as 25mm on the x-axis (that is a
paper speed of 25mm/s).

• Faster paper speeds can be used - for
example to resolve finer detail in the ECG.
• At a paper speed of 25 mm/s, one small
block of ECG paper translates into 40 ms.
• Five small blocks make up one large
block, which translates into 200 ms.
• Hence, there are five large blocks per
second.

• A calibration signal may be included with a
record.
• A standard signal of 1 mV must move the
stylus vertically 1 cm, that is two large
squares on ECG paper.

Leads
• The term "lead" in electrocardiography causes
much confusion because it is used to refer to
two different things.
• In accordance with common parlance the word
lead may be used to refer to the electrical cable
attaching the electrodes to the ECG recorder.
• As such it may be acceptable to refer to the "left
arm lead" as the electrode (and its cable) that
should be attached at or near the left arm.
• There are usually ten of these electrodes in a
standard "12-lead" ECG.

• Alternatively the word lead may refer to
the tracing of the voltage difference
between two of the electrodes and is what
is actually produced by the ECG recorder.
• "Lead I" (lead one) is the voltage between
the right arm electrode and the left arm
electrode, whereas "Lead II" (lead two) is
the voltage between the right limb and the
feet.

• Twelve of this type of lead form a "12-
lead" ECG
• To cause additional confusion the term
"limb leads" usually refers to the tracings
from leads I, II and III rather than the
electrodes attached to the limbs.

Placement of electrodes
• Ten electrodes are used for a 12-lead
ECG.
• The electrodes usually consist of a
conducting gel, embedded in the middle of
a self-adhesive pad onto which cables
clip.
• Sometimes the gel also forms the
adhesive.

• They are labeled and placed on the
patient's body as follows:
• RA - On the right arm, avoiding bony
prominences.
• LA - In the same location that RA was
placed, but on the left arm this time.
• RL - On the right leg, avoiding bony
prominences.

• LL - In the same location that RL was
placed, but on the left leg this time.

WAVES AND INTERVALS
• A typical ECG tracing of the cardiac cycle
(heartbeat) consists of a P wave, a QRS
complex, a T wave, and a U wave which is
normally visible in 50 to 75% of ECGs.
• The baseline voltage of the electrocardiogram is
known as the isoelectric line.
• Typically the isoelectric line is measured as the
portion of the tracing following the T wave and
preceding the next P wave.

• RR interval The interval between an R wave and
the next R wave is the inverse of the heart rate.
• Normal resting heart rate is between 50 and 100
bpm. Duration - 0.6 to 1.2s
• P wave During normal atrial depolarization, the
main electrical vector is directed from the SA
node towards the AV node, and spreads from
the right atrium to the left atrium.
• This turns into the P wave on the ECG.
• Duration - 80ms

• PR interval The PR interval is measured from
the beginning of the P wave to the beginning of
the QRS complex.
• The PR interval reflects the time the electrical
impulse takes to travel from the sinus node
through the AV node and entering the ventricles.
• The PR interval is therefore a good estimate of
AV node function. Duration - 120 to 200ms

• PR segment The PR segment connects the P
wave and the QRS complex.
• This coincides with the electrical conduction
from the AV node to the bundle of His to the
bundle branches and then to the Purkinje Fibers.
• This electrical activity does not produce a
contraction directly and is merely traveling down
towards the ventricles and this shows up flat on
the ECG.
• The PR interval is more clinically relevant.
Duration - 50 to 120ms

• QRS complex The QRS complex reflects the
rapid depolarization of the right and left
ventricles.
• They have a large muscle mass compared to
the atria and so the QRS complex usually has a
much larger amplitude than the P-wave.80 to
120ms
• J-point The point at which the QRS complex
finishes and the ST segment begins.
• Used to measure the degree of ST elevation or
depression present.N/A

• J-point - The point at which the QRS complex
finishes and the ST segment begins.
• Used to measure the degree of ST elevation or
depression present.
• ST segment - The ST segment connects the
QRS complex and the T wave.
• The ST segment represents the period when the
ventricles are depolarized.
• It is iso electric. Duration - 80 to 120ms

• T wave - The T wave represents the
repolarization (or recovery) of the ventricles.
• The interval from the beginning of the QRS
complex to the apex of the T wave is referred to
as the absolute refractory period.
• The last half of the T wave is referred to as the
relative refractory period (or vulnerable period).
Duration - 160ms

• ST interval - The ST interval is measured from
the J point to the end of the T wave.
• Duration 320ms
• QT interval - The QT interval is measured from
the beginning of the QRS complex to the end of
the T wave.
• A prolonged QT interval is a risk factor for
ventricular tachyarrhythmias and sudden death.
• It varies with heart rate and for clinical relevance
requires a correction for this, giving the QTc.
• Duration - 300 to 430ms

• U wave - The U wave is not always seen.
It is typically low amplitude, and, by
definition, follows the T wave.
• The J wave, elevated J-Point or Osborn
Wave appears as a late delta wave
following the QRS or as a small secondary
R wave .
• It is considered pathognomic of
hypothermia or hypocalcemia.

MEDICAL DISPLAY
SYSTEMS
Compared to standard commercial
displays, dedicated medical display
systems offer significant advantages
for diagnostic imaging.

1 DISPLAY RESOLUTION AND
ORIENTATION
• Standard computer displays offer limited
resolution with a form-fit factor (landscape)
that is not optimized for diagnostic
imaging.
• Medical grade displays, on the other hand,
offer resolutions up to 2048 x 2560 (5
megapixel) in portrait or landscape that
corresponds better with the image format
of the medical images.

• Higher resolution allows the radiologist to
see much more detail without panning or
zooming the image.
• As a result, image quality is higher and
productivity is increased.

2 LUMINANCE RANGE
• Consumer grade displays typically offer a
maximum luminance of 250 – 300 cd/m2.
• State-of-the-art medical displays by contrast
achieve luminance levels of more than 1000
cd/m2, much closer to conventional film.
• According to DICOM 3.14, a larger luminance
range results in a broader spectrum of
grayscales that can be discerned by the human
eye.

• As a result, it will be easier to detect on a
medical display and radiologists can reach
a diagnosis faster.
• To conclude: the higher luminance offered
by medical displays results in higher
image quality and increases productivity
during diagnostic reading.

3 CONTRAST
• Luminance is not the only important
parameter for diagnostic reading.
• For many applications, contrast is even
more important than luminance.
• Medical displays offer a contrast (up to
1000:1) that is substantially better than
most consumer displays, which have on
average a contrast ratio of only 300:1.

4 VIEWING ANGLE
• We have all experienced that the
perception of an image on a flat panel
display substantially changes depending
on the viewing angle.
• Flat panel displays all use different LCD
technologies with viewing angle
characteristics that can vary substantially.

• Medical grade displays use a technology with
state-of-the-art viewing angle characteristics.
• As medical workstations combine multiple
heads, viewing inevitably happens from different
viewing angles.
• Because of this, viewing angle characteristics
are much more important than with consumer
displays, where the viewer usually sits in front of
the display and always looks at the image from a
perpendicular angle.

5 GRAYSCALE RANGE
• The number of available shades of gray
on most consumer displays is limited to
256 (8 bit).
• Medical displays have a much wider
grayscale range, enabling them to render
every grayscale
• The new Coronis grayscale display family,
for instance, offers up to 4096 shades of
gray (12 bit).

• Such an extensive range is necessary to
comply with the guidelines set forward by
the latest medical guidelines.
• Displays with a grayscale resolution of 8
bit will fail to meet this requirement.

• 6 IMAGE CONSISTENCY
• 7 LUMINANCE UNIFORMITY
• 8 CALIBRATION
• 9 MEDICAL APPROVALS
• 10 CONFIGURATION AND QUALITY
CONTROL

• A medical monitor or physiological
monitor or display, is an electronic
medical device that measures a patient's
vital signs and displays the data so
obtained, which may or may not be
transmitted on a monitoring network.

• Physiological data are displayed
continuously on a CRT or LCD screen as
data channels along the time axis,
• They may be accompanied by of
computed parameters on the original data,
such as maximum, minimum and average
values, pulse and respiratory frequencies,
and so on.

• In critical care units of hospitals, bedside units
allow continuous monitoring of a patient, with
medical staff being continuously informed of the
changes in general condition of a patient.
• Some monitors can even warn of pending fatal
cardiac conditions before visible signs are
noticeable to clinical staff, such as
atrial fibrillation or
premature ventricular contraction (PVC).

Medical monitor as used in
anesthesia

A monitor/defibrillator from an
Austrian EMS service.

A close up view of the screen
of the PIC 50.

Analog monitoring
• Old analog patient monitors were based
on oscilloscopes, and had one channel
only, usually reserved for
electrocardiographic monitoring (ECG).
• So, medical monitors tended to be highly
specialized.
• One monitor would track a patient's
blood pressure, while another would
measure pulse oximetry, another the
ECG.

• Later analog models had a second or third
channel displayed in the same screen, usually to
monitor respiration movements and
blood pressure.
• These machines were widely used and saved
many lives, but they had several restrictions,
including sensitivity to electrical interference,
base level fluctuations, and absence of numeric
readouts and alarms.

• In addition, although wireless monitoring
telemetry was in principle possible (the
technology was developed by NASA in the
late 1950s for manned spaceflight, it was
expensive and cumbersome.

Digital monitoring
• With the development of
digital signal processing (DSP) technology,
however, medical monitors evolved enormously,
and all current models are digital, which also has
the advantages of miniaturization and portability.
• Today the trend is toward multiparameter
monitors that can track many different vital signs
at once.
• The parameters (or measurements) now consist
of pulse oximetry (measurement of the saturated
percentage of oxygen in the blood, referred to as
SpO2, and measured by an infrared finger cuff),

• ECG (electrocardiograph of the QRS
waves of the heart with or without an
accompanying external heart pacemaker),
blood pressure (either invasively through
an inserted blood pressure transducer
assembly, or non-invasively with an
inflatable blood pressure cuff), and body
temperature through an containing a
thermoelectric transducer.

• In some situations, other parameters can
be measured and displayed, such as
cardiac output, capnography (CO2
measurements, referred to as or end-tidal
carbon dioxide concentration), respiration
(through a thoracic transducer belt, an
ECG channel)

• Besides the tracings of physiological
parameters along time (X axis), digital
medical monitors have automated of the
peak and/or average parameters
displayed on the screen, and high/low
alarm levels can be set, which alert the
staff when some parameter exceeds of
falls the level limits, using audible signals.

• Several models of multiparameter monitors are
networkable, i.e., they can send their output to a
central ICU monitoring station,
• where a single staff member can observe and
respond to several bedside monitors
simultaneously.
• can also be achieved by portable, battery-
operated models which are carried by the patient
and which transmit their data via a wireless data
connection.

Special applications
• There are special patient monitors for several
applications, such as anesthesia monitoring,
which incorporate the monitoring of brain waves
(EEG), gas anesthetic concentrations, bispectral
index (BIS), etc.
• They are usually incorporated into anesthesia
machines.
• In neurosurgery intensive care units, brain EEG
monitors have a larger multichannel capability
and can monitor other physiological events, as
well.

• Portable heart monitors are now very common
too, and they exist in several configurations,
ranging from single-channel models for domestic
use,
• which are capable of storing or transmitting the
signals for appraisal by a physician, to 12-lead
complete, portable ECG machines which can
store for 24 hours or more.
• There are also portable monitors for blood
pressure and EEG.

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