- The document discusses biomedical instrumentation and focuses on cardiac pacemakers and defibrillators. - It describes how pacemakers use electrical impulses to regulate abnormal heart rhythms by contracting heart muscles. Pacemakers can be temporary or permanent depending on the cardiac condition. - Defibrillators deliver electric shocks to the heart in ventricular fibrillation which can be fatal if not corrected. The document discusses different types of defibrillators and how they function to reestablish normal heart rhythm.

1. Biomedical Instrumentation
Course Code:EE372
MODULE IV
1
Dr.LINSS T ALEX
ASSOCIATE PROFESSOR
DEPARTMENT OF EEE
MET’S SCHOOL OF ENGINEERING,MALA

3. Cardiac Pacemakers

4. • A pacemaker is a medical device which uses electrical
impulses, delivered by electrodes contracting the
heart muscles, to regulate the beating of the heart.
• In the past few years electronic pacemaker systems
have become extremely important in saving and
sustaining the lives of cardiac patients whose normalsustaining the lives of cardiac patients whose normal
pacing functions have become impaired.
• Depending on the exact nature of a cardiac
dysfunction, a patient may require temporary
artificial pacing during the course of treatment or
permanent pacing in order to lead an active,
productive life after treatment.

5. • The rhythmic action of the heart is initiated by
regularly recurring action potentials
(electrochemical impulses) originating at the
natural cardiac pacemaker, located at the sinoatrial
(SA) node.
• Each pacing impulse is propagated throughout the
myocardium, spreading over the surface of themyocardium, spreading over the surface of the
atria to the atrioventricular (AV) node—which is
located within the septum, adjacent to the
atrioventricular valves—and depolarizing the atria.
• After a brief delay at the AV node, the impulse is
rapidly conducted to the ventricles to depolarize
the ventricular musculature.

6. • A normal sinus rhythm (NSR) depends on the
continuous, periodic performance of the pacemaker
and the integrity of the neuronal conducting pathways.
• Any change in the NSR is called an arrhythmia
(abnormal rhythm).
• Should the SA node temporarily or permanently fail
because of disease (SA node disease) or a congenitalbecause of disease (SA node disease) or a congenital
defect, the pacing function may be taken over by
pacemaker-like cells located near the AV node.
• However, under certain conditions, cells in the
conduction system may pace the ventricles instead.
• Similarly, an area in the excitable ventricular
musculature may try to control the heartbeat.

7. • Unfortunately, under these conditions the heart is
paced at a much slower rate than normal, ranging
between 30 and 50 beats per minute (BPM).
• The result is a condition called bradycardia (slow
heart), in which the heart cannot provide
sufficient blood circulation to meet the body's
physical demands.physical demands.
• During the transition period from an NSR to a
slow rhythm, dizziness and loss of consciousness
(syncope) may occur because of diminished
cardiac output.

8. • Heart block occurs whenever the conduction
system fails to transmit the pacing impulses from
the atria to the ventricles properly.
• In first-degree block an excessive impulse delay at
the AV junction occurs that causes the P-R interval
to exceed 0.2 second for normal adults.
• Second-degree block results in the complete but• Second-degree block results in the complete but
intermittent inhibition of the pacing impulse, which
may also occur at the AV node.
• Total and continuous impulse blockage is called
third-degree block. It may occur either at the AV
node or elsewhere in the conduction system.

9. • In this case, the ventricles usually continue to contract but
at a sharply reduced rate (40 BPM) because of the
establishment of an idioventricular escape rhythm or
because of impulses that only periodically originate from
the atria.
• In all these conditions, an artificial method of pacing is
generally required to ensure that the heart beats at a rate
that is sufficient to maintain proper circulation.that is sufficient to maintain proper circulation.

10. Pacemaker Systems
• A device capable of generating artificial pacing
impulses and delivering them to the heart is known
as a pacemaker system (commonly called a
pacemaker) and consists of a pulse generator and
appropriate electrodes.
• Pacemakers are available in a variety of forms.
Internal pacemakers may be permanently implantedInternal pacemakers may be permanently implanted
in patients whose SA nodes have failed to function
properly or who suffer from permanent heart block
because of a heart attack.
• An internal pacemaker is defined as one in which the
entire system is inside the body.
• In contrast, an external pacemaker usually consists of
an externally worn pulse generator connected to
electrodes located on or within the myocardium.

11. • External pacemakers are used on patients with
temporary heart irregularities, such as those
encountered in the coronary patient, including
heart blocks.
• They are also used for temporary management of
certain arrhythmias that may occur in patients
during critical postoperative periods and in patientsduring critical postoperative periods and in patients
during cardiac surgery, especially if the surgery
involves the valves or septum.

12. • Internal pacemaker systems are implanted with the
pulse generator placed in a surgically formed pocket
below the right or left clavicle, in the left subcostal
area, or, in women, beneath the left or right major
pectoralis muscle.
• Internal leads connect to electrodes that directly
contact the inside of the right ventricle or thecontact the inside of the right ventricle or the
surface of the myocardium .
• The exact location of the pulse generator depends
primarily on the type of electrode used, the nature
of the cardiac dysfunction, and the method (mode)
of pacing that may be prescribed

13. • Since there are no external connections for applying
power, the pulse generator must be completely self-
contained, with a power source capable of
continuously operating the unit for a period of
years.
• External pacemakers, which include all types of
pulse generators located outside the body, arepulse generators located outside the body, are
normally connected through wires introduced into
the right ventricle via a cardiac catheter.
• The pulse generator may be strapped to the lower
arm of a patient who is confined to bed, or worn at
the midsection of an ambulatory patient.

14. • Several pacing techniques are possible with both
internal and external pacemakers.
• They can be classed as either competitive and
noncompetitive pacing modes.
• The noncompetitive method, which uses pulse
generators that are either ventricular programmedgenerators that are either ventricular programmed
by the atria, is more popular.
• Ventricular-programmed pacemakers are designed
to operate either in a demand (R-wave-inhibited)
or standby (R-wave-triggered) mode, whereas
atrial-programmed pacers are always synchronized
with the P wave of the ECG.

20. • The type of power source used for a pulse
generator depends on whether the unit is an
external or an implantable type.
• Today most of the manufactured external pulse
generators are battery-powered, although earlier
units that receive power from the ac power line are
still in use.still in use.
• Because of the need to electrically isolate patients
with direct-wire connections to their hearts from
any possible source of power-line leakage current
and for portability, battery-powered units are
preferred.

21. • Implantable pulse generators commonly use
mercury batteries whose life span ranges between
2 and 3 years, after which a new pulse generator
must be installed.
• Recognizing the need to develop longer-lasting
batteries for pacing use, the industry has
developed the lithium-iodine battery, which hasdeveloped the lithium-iodine battery, which has
an estimated life expectancy of 5 years.
• A pulse generator with rechargeable batteries
whose life span is estimated at 10 years is now
available.

22. DEFIBRILLATORSDEFIBRILLATORS

23. • The heart is able to perform its important pumping
function only through precisely synchronized action
of the heart muscle fibers.
• The rapid spread of action potentials over the
surface of the atria causes these two chambers of
the heart to contract together and pump blood
through the two atrioventricular valves into the
ventricles.
through the two atrioventricular valves into the
ventricles.
• After a critical time delay, the powerful ventricular
muscles are synchronously activated to pump blood
through the pulmonary and systemic circulatory
systems.
• A condition in which this necessary synchronism is
lost is known as fibrillation.

24. • During fibrillation the normal rhythmic contractions
of either the atria or the ventricles are replaced by
rapid irregular twitching of the muscular wall.
• Fibrillation of atrial muscles is called atrial
fibrillation; fibrillation of the ventricles is known as
ventricular fibrillation.
• Under conditions of atrial fibrillation, the ventricles
can still function normally, but they respond with ancan still function normally, but they respond with an
irregular rhythm to the non synchronized
bombardment of electrical stimulation from the
fibrillating atria.
• Since most of the blood flow into the ventricles
occurs before atrial contraction, there is still blood
for the ventricles to pump.

25. • Thus, even with atrial fibrillation circulation is still
maintained, although not as efficiently.
• The sensation produced, however, by the fibrillating
atria and irregular ventricular action can be quite
traumatic for the patient.
• Ventricular fibrillation is far more dangerous, for under
this condition the ventricles are unable to pump
blood; and if the fibrillation is not corrected, death willblood; and if the fibrillation is not corrected, death will
usually occur within a few minutes.
• Unfortunately, fibrillation, once begun, is not self-
correcting.
• Hence, a patient susceptible to ventricular fibrillation
must be watched continuously so that the medical
staff can respond immediately if an emergency occurs.

26. • Defibrillation is a treatment for life threatening cardiac
dysrhythmias, specifically ventricular fibrillation (VF)
and non - perfusing ventricular tachycardia (VT).
• A defibrillator delivers a dose of electric current (often
called a counter shock) to the heart.
This depolarizes a large amount of the heart muscle,• This depolarizes a large amount of the heart muscle,
ending the dysrhythmia.

27. Arrhythmias: SA Block
P QRS T

28. Defibrillators
• The defibrillator is a device that delivers electric shock to
the heart muscle undergoing a fatal arrhythmia.
• Electric shock can be used to reestablish normal activity
• Four basic types of Defibrillators
– AC Defibrillator– AC Defibrillator
– DC Defibrillator

29. • Before 1960 were AC model
• This machine applied 5 to 6 A of 60 Hz across the
patient’s chest for 250 to 1000 ms.
• The success rate for AC defibrillator was rather low
• Since 1960, several different dc defibrillators have
been devised.been devised.
• This machines store a dc charge that can be
delivered to the patient.
• The different between dc types in the wave shape
of the charge delivered to the patient

30. DC types
• 1- lown
• 2- monopulse
• 2- tapered (dc) delay
• 3- trapezoidal wave.• 3- trapezoidal wave.

31. Lown
- The current will rise very rapidly to about 20 A under the
influence of slightly less than 3 kV .
- The waveform then decays back to zero within 5 ms and then
produces a smaller negative pulse also about 5 ms.

32. Lown wave form defibrillator

33. • That is, the capacitor stores energy, WA,
which develops a voltage, V, across its metal
plates.
– The amount of energy in units of joules is given
by
2
V
• where C is the value of the capacitance measured in
units of farads and V is the voltage across the
capacitor.
2
2
V
CWA =

34. • The energy stored in the capacitor is
proportional to the square of the voltage
between its plates.
– The amount of energy typically stored in the
capacitor of a defibrillator, so that it can be later
delivered to the patient, ranges from 50 to 400
joules.joules.
• All of this energy does not get into the patient.
– Some is lost in the internal resistance of the
defibrillator circuit, RD and some is wasted in the
paddle—skin resistance, RE .

35. • To calculate how much of
this energy gets to the
patient, resistance RT,
consider the equivalent
circuit.
– The four resistors in this
circuit are in series.

36. • Therefore, the current in each of them is the
same.
– And the energy absorbed by any one resistor is
proportional to the total available energy,proportional to the total available energy,
according to the voltage division principle.
• The formula for the energy absorbed by the thorax, WT
is
D
TED
T
T W
RRR
R
W
++
=
2

37. EXAMPLE
• A defibrillator has an available energy, WA,
of 200 joules (J).
– If the thorax resistance is 40 ohms (Ω), the– If the thorax resistance is 40 ohms (Ω), the
electrode—skin resistance of a paddle with
sufficient electrode gel is 30 ohms and the
internal resistance of the defibrillator is 10
ohms.
• Calculate the energy delivered to the thorax of the
patient.

38. Solution
• In this case, RT = 40 ohms, RE =30 ohms, and RD = 10
ohms. The equation for the amount energy delivered
yields
R
D
TED
T
T W
RRR
R
W
++
=
2
200
4030210
40
+×+
=TW
JoulesWT 7.72=

39. - Monopulse is a modified lown waveform and
commonly found in certain portable defibrillator.
- It is created by the same circuit of lown but without
inductor L.
- Tapered delay wave form , a lower amplitude 1.2- Tapered delay wave form , a lower amplitude 1.2
kV and longer duration 15 ms to a chive the energy
level
- It is created by placing two L–C sections
- Trapeziodal low voltage / long duration ( 800 V :
500 V & 20 ms

40. Defibrillator: Electrodes
• Excellent contact with the body is essential
– Serious burns can occur if proper contact is not
maintained during discharge
• Sufficient insulation is required• Sufficient insulation is required
– Prevents discharge into the physician
• Three types are used:
– Internal – used for direct cardiac stimulation
– External – used for transthoracic stimulation
– Disposable – used externally

41. Defibrillator: Electrodes

42. Cardioverters
• Special defibrillator constructed to have synchronizing circuitry so
that the output occurs immediately following an R wave
– In patients with atrial arrhythmia, this prevents possible discharge during a
T wave, which could cause ventricular fibrillation
• The design is a combination of a cardiac monitor and a
defibrillatordefibrillator
ECG
Electrodes
Analog
Switch
Trigger
Circuit
Defibrillator
Defibrillation
Electrodes
Cardioscope
30ms
Delay
Threshold
Detector
Filter
Operator-controlled
Switch
ECG AMP
AND
Gate

44. ELECTROENCEPHALOGRAM(EEG)ELECTROENCEPHALOGRAM(EEG)

45. • The electroencephalogram (EEG) is a recording of
the electrical activity of the brain from the scalp.
• The first recordings were made by Hans Berger in
1929
• EEG is the record of electrical activity of brain(
superficial layer i.e. the dendrites of pyramidal cells)
by placing the electrodes on the scalp.by placing the electrodes on the scalp.

46. History
• 1912-First animal EEG was performed by Adolf
Beck
• 1924-First human EEG was recorded
• 1936-First EEG lab was opened at Mass• 1936-First EEG lab was opened at Mass
General

47. History
1929: Hans Berger developed
electroencephalography, the
graphic representation of the
difference in voltage between
two different cerebral locations
plotted over time
He described the human alpha
and beta rhythms

48. Objectives of EEG practical
• Familiarize with the principles of techniques
involved
• Count frequencies and measure the amplitudes
of the record obtained.
• Categories the records into appropriate rhythms
– α, β, θ,and δ.– α, β, θ,and δ.
• Identify and describe changes produced by
provocation tests.
e.g. eye opening & closing, intermittent photic
stimulation (IPS) clapping sound, induce
thinking & hyperventilation.

49. EEG

50. EEG
Many neurons need to sum their activity in order to be detected by EEG electrodes.
The timing of their activity is crucial. Synchronized neural activity produces larger
signals.

51. EEG Waves
• Alpha wave -- 8 – 13 Hz.
• Beta wave -- >13 Hz. (14 – 30 Hz.)
• Theta wave -- 4 – 7.5 Hz.
• Delta waves – 1 – 3.5 Hz.Delta waves – 1 – 3.5 Hz.
Different types of brain waves in normal EEG

52. EEG Recording From Normal Adult Male

53. EEG
EEG potentials are good indicators of global brain state. They
often display rhythmic patterns at characteristic frequencies

54. Alpha wave
• rhythmic, 8-13 Hz
• mostly on occipital lobe
• 20-200 μ V
• normal,• normal,
• relaxed awake rhythm with eyes closed

55. Beta wave
• irregular, 14-30 Hz
• mostly on temporal and frontal lobe
• mental activity
• excitement• excitement

56. Theta wave
• rhythmic, 4-7 Hz
• Drowsy, sleep

57. Delta wave
• slow, < 3.5 Hz
• in adults
• normal sleep rhythm

59. Different types of brain waves in normal EEG
Rhythm Frequency
(Hz)
Amplitude
(uV)
Recording
& Location
Alpha(α) 8 – 13 50 – 100 Adults, rest, eyes closed.
Occipital region
Beta(β) 14 - 30 20 Adult, mental activityBeta(β) 14 - 30 20 Adult, mental activity
Frontal region
Theta(θ) 5 – 7 Above 50 Children, drowsy adult,
emotional distress
Occipital
Delta(δ) 2 – 4 Above 50 Children in sleep
D T A B

60. Requirements
• EEG machine (8/16 channels).
• Silver cup electrodes/metallic bridge
electrodes.
• Electrode jelly.• Electrode jelly.
• Rubber cap.
• Quiet dark comfortable room.
• Skin pencil & measuring tape.

61. EEG Electrodes
Sliver Electrodes Electrodes Cap

62. Procedure of EEG recording
• A standard EEG makes use of 21 electrodes
linked in various ways (Montage).
• Apply electrode according to 10/20% system.
• Check the impedance of the electrodes.• Check the impedance of the electrodes.

63. 10 /20 % system of EEG electrode placement

64. EEG Electrodes
• Each electrode site is labeled with a letter and a number.
• The letter refers to the area of brain underlying the electrode
e.g. F - Frontal lobe and T - Temporal lobe.
• Even numbers denote the right side of the head and
• Odd numbers the left side of the head.• Odd numbers the left side of the head.

65. Two types of recording
• Bipolar – both the electrodes are at active site
– Bipolar montage are parasagital montage.
• Unipolar – one electrode is active and the
other is indifferent kept at ear lobe.other is indifferent kept at ear lobe.
• Always watch for any abnormal muscle activity.
• Ask the subject to open eyes for 10 sec. then ask them
to close the eyes.

66. Analysis
• Electrical activity from the brain consist of
primarily of rhythms.
• They are named according to their frequencies
(Hz) and amplitude in micro volt (μv).(Hz) and amplitude in micro volt (μv).
• Different rhythms at different ages and
different conditions (level of consciousness)
• Usually one dominant frequency
(background rhythm)

67. Factor influencing EEG
• Age
– Infant – theta, delta wave
– Child – alpha formation.
– Adult – all four waves.
• Level of consciousness (sleep)• Level of consciousness (sleep)
• Hypocapnia(hyperventilation) slow & high amplitude
waves.
• Hypoglycemia
• Hypothermia
• Low glucocorticoids Slow waves

68. Use of EEG
• Epilepsy
» Generalized (grandmal) seizures.
» Absence (petitmal) seizures.
• Localize brain tumors.
• Sleep disorders (Polysomnography)
» Narcolepsy» Narcolepsy
» Sleep apnea syndrome
» Insomnia and parasomnia
• Helpful in knowing the cortical activity, toxicity, hypoxia and
encephalopathy &
• Determination of brain death.
– Flat EEG(absence of electrical activity) on two records run 24 hrs
apart.

69. Sleep studies
• The EEG is frequently used in the investigation of sleep
disorders especially sleep apnoea.
• Polysomnography : EEG activity together with
– heart rate,
– airflow,
respiration,– respiration,
– oxygen saturation and
– limb movement

70. Limitations
• Cost: Anywhere from $200-3000 without insurance
• Accuracy: Can be affected by inconsistencies in the
testing procedure

71. Electroencephalography
Pros Cons
• Good time resolution
• Portable and affordable
• More tolerant to subject movement
• Low spatial resolution
• Artifacts / Noise
• More tolerant to subject movement
• EEG is silent and so useful for studying
auditory processing
• Can be combined with fMRI or TMS

72. Neuronal Communication
• Neurons are among the special group of cells that
are capable of being excited and that, when excited,
generate action potentials.
• In neurons, these action potentials are of very short
duration and are often called neuronal spikes orduration and are often called neuronal spikes or
spike discharges.
• Information is usually transmitted in the form of
spike discharge patterns.

73. • These patterns, which are simply the sequences of
spikes that are transmitted down a particular
neuronal pathway, are shown in Figures.
• The form of a given neuronal pattern depends on
the firing patterns of other neurons that
communicate with the neuron generating the
pattern and the refractory period of that neuron .pattern and the refractory period of that neuron .
• When an action potential is initiated in the neuron,
usually at the cell body or axon hillock, it is
propagated down the axon to the axon terminals
where it can be transmitted to other neurons.

76. • Given sufficient excitation energy, most neurons can be
triggered at almost any point along the dendrites, cell
body, or axon and generate action potentials that can
move in both directions from the point of initiation.
• The process does not normally happen, however,
because in their natural function, neurons synapse only
in a certain way; that is, the axon of one neuron excites
the dendrites or cell body of another.
• The result is a one-way communication path only.• The result is a one-way communication path only.
• If an action potential should somehow be artificially
generated in the axon and caused to travel up the
neuron to the dendrites, the spike cannot be
transmitted the wrong way across the gap to the axon
of another neuron.
• Thus, the one-way transmission between neurons
determines the direction of communication.

77. • It was believed for many years that transmission
through a synapse was electrical and that an action
potential was generated at the input of a neuron
due to ionic currents or fields set up by the action
potentials in the adjacent axons of other neurons.
• More recent research, however, has disclosed that
in mammals, and in most synapses of otherin mammals, and in most synapses of other
organisms, the transmission times across synapses
are too slow for electrical transmission.
• This has led to the presently accepted chemical
theory, which states that the arrival of an action
potential at an axon terminal releases a chemical —

78. • Probably acetylcholine in most cases—that excites
the adjacent membrane of the receiving neuron.
• Because of the close proximity of the transmitting
axon terminal to the receiving membrane, the time
of transmission is still quite short.
• The possibility that some of the chemical may still
be present after the refractory period is eliminated
by the presence of acetylcholine esterase, another
be present after the refractory period is eliminated
by the presence of acetylcholine esterase, another
chemical that breaks down the acetylcholine as
soon as it is produced, but not before it has been
able to initiate its intended action potential in the
nearby membrane.
• This chemical theory of transmission is diagrammed
in Figure 10.6.

80. • Actually, the situation is not quite as simple as has
been described.
• There are really two kinds of communication
across a synapse, excitatory and inhibitory.
• The same chemical appears to be used in both. In
general, several axons from different neurons are
in communication with the * input'* of any givenin communication with the * input'* of any given
neuron.
• Some act to excite the membrane of the receiver,
while others tend to prevent it from being excited.
• Whether the neuron fires or not depends on the
net effect of all the axons interacting with it.

81. • The effects of the various neurons acting on a receiving
neuron are reflected in changes in the graded
potentials of the receiving neuron.
• Graded potentials are variations around the average
value of the resting potential.
• When this graded potential reaches a certain threshold,
the neuron fires and an action potential develops.the neuron fires and an action potential develops.
• Regardless of the graded potential before firing, the
action potentials of a given neuron are always the same
and always travel at the same rate.
• An excitatory graded potential is called an excitatory
postsynaptic potential (EPSP), and an inhibitory graded
potential is called an inhibitory postsynaptic potential
(IPSP).

82. • There are several theories as to how inhibitory action
takes place.
• One possibility is that the inhibitory axon somehow
causes a graded potential (IPSP) in the receiving neuron
which is more negative than the normal resting
potential, thus requiring a greater amount of excitation
to cause it to fire.
• Another possibility is that the inhibiting axon acts, not• Another possibility is that the inhibiting axon acts, not
on the receiving neuron but on the excitatory
transmitting axon.
• In this case, the inhibiting axon might set up a
premature action potential in the transmitting axon, so
that the necessary combination of chemical discharges
cannot occur in synchronism as it would without the
inhibition.

83. • Whatever method is actually used, the end result is
that certain action potentials which would
otherwise be transmitted through the synapse are
prevented from doing so when inhibitory signals are
present.
• Synapses, then, behave much like multiple input
AND and NOR logic gates and, by their widely varied
patterns of excitatory and inhibitory
AND and NOR logic gates and, by their widely varied
patterns of excitatory and inhibitory
**connections," provide a means of switching and
interconnecting parts of the nervous system with a
complexity far greater than anything yet conceived
by man.

84. Electroencephalograph
• Electroencephalograph is an instrument for
recording the electrical activity of the brain, by
suitably placing surface electrodes on the scalp.
• EEG, describing the general function of the brain• EEG, describing the general function of the brain
activity, is the superimposed wave of neuron
potentials operating in a non-synchronized manner
in the physical sense.

85. • Monitoring the electroencephalogram has proven to
be an effective method of diagnosing many
neurological illnesses and diseases, such as epilepsy,
tumour, cerebrovascular lesions, ischemia and
problems associated with trauma.
• It is also effectively used in the operating room to
facilitate anaesthetics and to establish the integrityfacilitate anaesthetics and to establish the integrity
of the anaesthetized patient’s nervous system.
• This has become possible with the advent of small,
computer-based EEG analyzers.
• Several types of electrodes may be used to record
EEG. These include: Peel and Stick electrodes, Silver
plated cup electrodes and Needle electrodes.

86. • EEG electrodes are smaller in size than ECG
electrodes. They may be applied separately to the
scalp or may be mounted in special bands, which
can be placed on the patient’s head.
• In either case, electrode jelly or paste is used to
improve the electrical contact.
• If the electrodes are intended to be used under the• If the electrodes are intended to be used under the
skin of the scalp, needle electrodes are used.
• They offer the advantage of reducing movement
artifacts.

87. • EEG electrodes give high skin contact impedance as
compared to ECG electrodes.
• Good electrode impedance should be generally
below 5 kilohms.
• Impedance between a pair of electrodes must also
be balanced or the difference between them should
be less than 2 kilohms.be less than 2 kilohms.
• EEG preamplifiers are generally designed to have a
very high value of input impedance to take care of
high electrode impedance.

88. • EEG may be recorded by picking up the voltage
difference between an active electrode on the
scalp with respect to a reference electrode on
the ear lobe or any other part of the body.
• This type of recording is called ‘monopolar’
recording.recording.
• However, ‘bipolar’ recording is more popular
wherein the voltage difference between two
scalp electrodes is recorded.
• Such recordings are done with multi-channel
electroencephalographs.

89. • EEG signals picked up by the surface electrodes
are usually small as compared with the ECG
signals.
• They may be several hundred microvolts, but 50
microvolts peak-to-peak is the most typical.
• The brain waves, unlike the electrical activity of• The brain waves, unlike the electrical activity of
the heart, do not represent the same pattern over
and over again.
• Therefore, brain recordings are made over a much
longer interval of time in order to be able to
detect any kind of abnormalities.

90. Block diagram

91. • Montages: A pattern of electrodes on the head and
the channels they are connected to is called a
montage. Montages are always symmetrical.
• Electrode Montage Selector: EEG signals are
transmitted from the electrodes to the head box,
which is labeled according to the 10–20 system, and
then to the montage selector.
The montage selector on analog EEG machine is a large• The montage selector on analog EEG machine is a large
panel containing switches that allow the user to select
which electrode pair will have signals subtracted from
each other to create an array of channels of output
called a montage.
• Each channel is created in the form of the input from
one electrode minus the input from a second electrode.

92. • Montages are either bipolar (made by the subtraction of
signals from adjacent electrode pairs) or referential (made
by subtracting the potential of a common reference
electrode from each electrode on the head).
• In order to minimize noise, a separate reference is often
chosen for each side of the head e.g. the ipsilateral ear.
• Bipolar and referential montages contain the same basic
information that is transformable into either format by
simple substration as long as all the electrodes, includingsimple substration as long as all the electrodes, including
reference, are included in both montages and linked to one
common reference.
• Many modern digital EEG machines record information
referentially, allowing easy conversion to several different
bipolar montages.
• The advantage of recording EEG in several montages is that
each montage displays different spatial characteristics of
the same data.

93. • Preamplifier: Every channel has an individual, multistage,
ac coupled, very sensitive amplifier with differential input
and adjustable gain in a wide range.
• Its frequency response can be selected by single-stage
passive filters.
• A calibrating signal is used for controlling and documenting
the sensitivity of the amplifier channels.
• This supplies a voltage step of adequate amplitude to the
input of the channels.
A typical value of the calibration signal is 50 µV/cm.• A typical value of the calibration signal is 50 µV/cm.
• The preamplifier used in electroencephalographs must have
high gain and low noise characteristics because the EEG
potentials are small in amplitude.
• In addition, the amplifier must have very high common-
mode rejection to minimize stray interference signals from
power lines

94. • Sensitivity Control: The overall sensitivity of an EEG
machine is the gain of the amplifier multiplied by the
sensitivity of the writer.
• Thus, if the writer sensitivity is 1 cm/V, the amplifier
must have an overall gain of 20,000 for a 50 mV signal.
• The various stages are capacitor coupled.
• An EEG machine has two types of gain controls.• An EEG machine has two types of gain controls.
• One is continuously variable and it is used to equalize
the sensitivities of all channels.
• The other control operates in steps and is meant to
increase or reduce the sensitivity of a channel by
known amounts. This control is usually calibrated in
decibels.

95. • The gain of amplifiers is normally set so that signals of
about 200 mV deflect the pens over their full linear
range.
• Artefacts, several times greater than this, can cause
excessive deflections of the pen by charging the coupling
capacitors to large voltages.
• This will make the system unusable over a period• This will make the system unusable over a period
depending upon the value of the coupling capacitors.
• To overcome this problem, most modern EEG machines
have de-blocking circuits similar to those used in ECG
machines.

96. • Filters: Just like in an ECG when recorded by surface
electrodes, an EEG may also contain muscle artefacts due
to contraction of the scalp and neck muscles, which overlie
the brain and skull.
• The artefacts are large and sharp, in contrast to the ECG,
causing great difficulty in both clinical and automated EEG
interpretation.
• The most effective way to eliminate muscle artefact is to• The most effective way to eliminate muscle artefact is to
advise the subject to relax, but it is not always successful.
• These artefacts are generally removed using lowpass filters.
• This filter on an EEG machine has several selectable
positions, which are usually labelled in terms of a time
constant.

97. • Noise: EEG amplifiers are selected for minimum noise
level, which is expressed in terms of an equivalent
input voltage.
• Two microvolts is often stated as the acceptable figure
for EEG recording.
• Noise contains components at all frequencies and
because of this, the recorded noise increases with thebecause of this, the recorded noise increases with the
bandwidth of the system.
• It is therefore important to restrict the bandwidth to
that required for faithful reproduction of the signal.
• Noise level should be specified as peak-to-peak value as
it is seen on the record rather than rms value, which
could be misleading.

98. • Writing Part: The writing part of an EEG machine is
usually of the ink type direct writing recorder.
• The best types of pen motors used in EEG machines
have a frequency response of about 90 Hz.
• Most of the machines have a response lower than
this, and some of them have it even as low as 45 Hz.
• The ink jet recording system, which gives a response
up to 1000 Hz, is useful for some special
applications.

99. • Paper Drive: This is provided by a synchronous motor.
An accurate and stable paper drive mechanism is
necessary and it is normal practice to have several
paper speeds available for selection.
• Speeds of 15, 30 and 60 mm/s are essential. Some
machines also provide speed values outside this range.
• A time scale is usually registered on the record by one• A time scale is usually registered on the record by one
or two time marker pens, which make a mark once per
second.
• Timing pulses are preferably generated independently
of the paper drive mechanism in order to avoid
difference in timing marks due to changes in paper
speed.

100. • Channels: An electroencephalogram is recorded
simultaneously from an array of many electrodes.
• The record can be made from bipolar or monopolar
leads.
• The electrodes are connected to separate amplifiers
and writing systems.
• Commercial EEG machines have up to 32 channels,
although 8 or 16 channels are more common.although 8 or 16 channels are more common.
• Microprocessors are now employed in most of the
commercially available EEG machines.
• These machines permit customer programmable
montage selection; for example, up to eight electrode
combinations can be selected with a keyboard switch.
• In fact, any desired combination of electrodes can be
selected with push buttons and can be memorized.

101. • These machines also include a video monitor
screen to display the selected pattern (montage)
as well as the position of scalp sites with
electrode-to-skin contact.
• Individual channel control settings for gain and
filter positions can be displayed on the video
monitor for immediate review.monitor for immediate review.
• Therefore, a setting can be changed by a simple
push button operation while looking at the
display.

102. • Modern EEG machines are mostly PC based,
with a pentium processor, 16-MB RAM, atleast
a 2 GB hard disk, cache memory and a 4 GB
DAT tape drive.
• The system can store up to 40 hours of EEG.
• The EEG is displayed on a 43 cm colour• The EEG is displayed on a 43 cm colour
monitor with a resolution of 1280 1024
pixels.
• The user interface is through an ASCII
keyboard and the output is available in the
hard copy form through a laser printer.

103. ELECTROMYOGRAM(EMG)

104. INTRODUCTION
• Electromyogram (EMG) is a technique for
evaluating and recording the activation signal of
muscles.
• EMG is performed by an electromyograph,• EMG is performed by an electromyograph,
which records an electromyogram.
• Electromyograph detects the electrical potential
generated by muscle cells when these cells
contract and relax.

105. EMG Apparatus Muscle Structure/EMG

106. ELECTRICAL CHARACTERITICS
• The electrical source is the muscle membrane
potential of about -70mV.
• Measured EMG potentials range between
< 50 µV up to 20 to 30 mV, depending on the muscle
under observation.under observation.
• Typical repetition rate of muscle unit firing is about 7-
20 Hz.
• Damage to motor units can be expected at ranges
between 450 and 780 mV

107. EMG Electrodes
Fine wire
Surface
Electrodes
Needle
electrode

108. Typical EMG recording
Amplitude(mv)
Time axis (msec)
Amplitude(mv)
Average amplitude over a time interval = 0

109. Factors Influencing Signal Measured
• Geometrical & Anatomical Factors
– Electrode size
– Electrode shape
– Electrode separation distance with respect to muscle
tendon junctions
– Thickness of skin and subcutaneous fat– Thickness of skin and subcutaneous fat
– Misalignment between electrodes and fiber alignment
• Physiological Factors
– Blood flow and temperature
– Type and level of contraction
– Muscle fiber conduction velocity
– Number of motor units (MU)
– Degree of MU synchronization

110. EMG PROCEDURE
• Clean the site of application
of electrode;
• Insert needle/place surface• Insert needle/place surface
electrodes at muscle belly;
• Record muscle activity at rest;
• Record muscle activity upon
voluntary contraction of the
muscle.

111. EMG Contd.EMG Contd.
• Muscle Signals are
Analog in nature.
• EMG signals are also
collected over a
specific period of
time.
Analog Signal

112. EMG Contd.EMG Contd.
EMG processing:
Amplification
& Filtering
Signal pick up
& Filtering
Conversion of Analog
signals to Digital signals
Computer

113. APPLICATION OF EMG
• EMG can be used for diagnosis of Neurogenic
or Myogenic Diseases.

114. SAMPLE EMG DATA

115. Block Diagram of EMGBlock Diagram of EMG

116. • Electromyograph is an instrument used for recording
the electrical activity of the muscles to determine
whether the muscle is contracting or not; or for
displaying on the CRO and loudspeaker the action
potentials spontaneously present in a muscle or
those induced by voluntary contractions as a means
of detecting the nature and location of motor unitof detecting the nature and location of motor unit
lesions; or for recording the electrical activity evoked
in a muscle by the stimulation of its nerve.
• The instrument is useful for making a study of
several aspects of neuromuscular function,
neuromuscular condition, extent of nerve lesion,
reflex responses, etc.

117. • EMG measurements are also important for the
myoelectric control of prosthetic devices (artificial
limbs).
• This use involves picking up EMG signals from the
muscles at the terminated nerve endings of the
remaining limb and using the signals to activate a
mechanical arm.mechanical arm.
• This is the most demanding requirement from an
EMG since on it depends the working of the
prosthetic device.

118. • EMG is usually recorded by using surface electrodes
or more often by using needle electrodes, which are
inserted directly into the muscle.
• The surface electrodes may be disposable, adhesive
types or the ones which can be used repeatedly.
• A ground electrode is necessary for providing a
common reference for measurement.
• These electrodes pick up the potentials produced• These electrodes pick up the potentials produced
by the contracting muscle fibres.
• The signal can then be amplified and displayed on
the screen of a cathode ray tube.
• It is also applied to an audio amplifier connected to
a loudspeaker.

119. • A trained EMG interpreter can diagnose various
muscular disorders by listening to the sounds
produced when the muscle potentials are fed to the
loudspeaker.
• The block diagram shows a typical set-up for EMG
recordings.
• The oscilloscope displays EMG waveforms.
• The tape recorder is included in the system to
facilitate playback and study of the EMG sound
waveforms at a later convenient time.
• The waveform can also be photographed from the
CRT screen by using a synchronized camera.

120. • The amplitude of the EMG signals depends upon
various factors, e.g. the type and placement of
electrodes used and the degree of muscular exertions.
• The needle electrode in contact with a single muscle
fibre will pick up spike type voltages whereas a surface
electrode picks up many overlapping spikes and
therefore produces an average voltage effect.therefore produces an average voltage effect.
• A typical EMG signal ranges from 0.1 to 0.5 mV.
• They may contain frequency components extending up
to 10 kHz.
• Such high frequency signals cannot be recorded on the
conventional pen recorders and therefore, they are
usually displayed on the CRT screen.

121. • Modern EMG machines are PC based (Fig. 5.16)
available both in console as well as laptop models.
• They provide full colour waveform display,
automatic cursors for marking and making
measurements and a keyboard for access to
convenient and important test controls.
• The system usually incorporates facilities for• The system usually incorporates facilities for
recording of the EMG and evoked potentials.
• The stimulators are software controlled.
• For report generation in the hard copy form,
popular laser printers can be used.

123. • Preamplifier: The preamplifiers used for EMG are
generally of differential type with a good
bandwidth.
• Low Frequency and High Frequency Filters: These
are used to select the pass band of the incoming
signal and to modify the progressive reduction in
voltage output which occurs at either end of thevoltage output which occurs at either end of the
frequency spectrum roll-off.

124. • Signal Delay and Trigger Unit: Sometimes, it is
necessary to examine the signals from individual
fibres of muscle tissue.
• For this purpose, special needles are available with
a 25 micron diameter electrode surface and up to
14 pick-up surfaces down the side of one needle.
• These 14 points are scanned sequentially to• These 14 points are scanned sequentially to
determine which point is acquiring the largest
signal.
• This point is then considered as the reference and
its signal is used to trigger the sweep

125. • Integrator: The integrator is used for quantifying
the activity of a muscle.
• Stimulators: The stimulators incorporated in the
EMG machines are used for providing a single or
double pulse or a train of pulses

126. • The measurement of conduction velocity in motor
nerves is used to indicate the location and type of nerve
lesion.
• Here the nerve function is examine directly at the
various segments of the nerve by means of stimulating it
Determination of conduction
velocities in motor nerves
various segments of the nerve by means of stimulating it
with a brief electric shock having a pulse duration of 0.2
-0.5 ms and measuring the latencies, we can calculate
the conduction velocity in that peripheral nerve.
• Latency is defined as the elapsed time between the
stimulating impulse and muscles action potential

127. • The EMG electrode and the stimulating electrode
are placed at two points on the skin,seperated by a
known distance l1.
• A brief electrical pulse is applied through the
stimulating electrode
• When excitation reaches the muscle, this contracts
with a short twitch.with a short twitch.
• Since all the nerve fibers are stimulated at the same
time and conduction velocity is normally the same
in all nerve fibres,there is synchronous activation of
the muscle fiber.

128. • This action potential of the muscle is picked up
by the EMG electrode and is displayed on the
oscilloscope along with the stimulating impulse.
• The elapsed time t1 between the stimulating
impulse and muscle’s action potential is
measured.measured.
• Now the two electrodes are repositioned with
the distance of separation as l2 meters.
• Among the distance l1 and l2,l2<l1.
• The latency is now measured as t2 seconds

129. Determination of conduction velocity in a motor nerve

130. • The conduction velocity in peripheral nerves is normally
50m/s.
• When we have it below 40m/s, there is some disorder in
that nerve conductionthat nerve conduction

131. SPIROMETRYSPIROMETRY
• The instrument used to measure lung capacity and
volume is called a spirometer.
• Basically, the record obtained from this device is
called a spirogram.
• Spirometers are calibrated containers that collect• Spirometers are calibrated containers that collect
gas and make measurements of lung volume or
capacity that can be expired.
• By adding a time base, flow–dependent quantities
can be measured.
• The addition of gas analyzers makes the spirometer
a complete pulmonary function testing laboratory.

132. Basic spirometerBasic spirometer
• Most of the respiratory measurements can be
adequately carried out by the classic water-sealed
spirometer
• This consists of an upright, water filled cylinder
containing an inverted counter weighted bell.
• Breathing into the bell changes the volume of gases• Breathing into the bell changes the volume of gases
trapped inside, and the change in volume is
translated into vertical motion, which is recorded
on the moving drum of a Kymograph.
• The excursion of the bell will be proportional to the
tidal volume. For most purposes, the bell has a
capacity of the order of 6–8 l.

133. • Unless a special light weight bell is provided, the
normal spirometer is only capable of responding
fully to slow respiratory rates and not to rapid
breathing, sometimes encountered after
anesthesia.
• Also, the frequency response of a spirometer must
be adequate for the measurement of the forcedbe adequate for the measurement of the forced
expiratory volume.
• The instrument should have no hysteresis, i.e. the
same volume should be reached whether the
spirometer is being filled or being emptied to that
volume.

135. • As the water-sealed spirometer includes moving
masses in the form of the bell and counterweights, this
leads to the usual problems of inertia and possible
oscillation of the bell.
• This can lead to an over-estimation of the expiratory
volume.
• A suggested compensation is by the use of a spirometer
bell having a large diameter and which fits closely over
the central core of the spirometer, so that the area ofthe central core of the spirometer, so that the area of
water covered by the bell is small in relation to that of
the water tank.
• If the spirometer is used for time-dependent
parameters, then it must also have a fast response
time, with a flat frequency response up to 12 Hz.
• This requirement applies not only to the spirometer,
but also to the recorder used in conjunction with the
recording device.

136. • The spirometer is a mechanical integrator, since the
input is air flow and the output is volume displacement.
• An electrical signal proportional to volume
displacement can be obtained by using a linear
potentiometer connected to the pulley portion of the
spirometer.
• The spirometer is a heavily damped device so that
small changes in inspired and expired air volumes are
not recorded.not recorded.
• The spirometers can be fitted with a linear motion
potentiometer, which directly converts spirometer
volume changes into an electrical signal.
• The signal may be used to feed a flow-volume
differentiator for the evaluation and recording of data.
• The response usually is ― Tests made using the
spirometer are not analytical.

137. • Also, they are not completely objective because the
results are dependent on the cooperation of the
patient and the coaching efforts of a good
respiratory technician.
• There have been efforts to develop electronic
spirometers which could provide greater
information- delivering and time-saving capabilities.
Also, there have been efforts to obtain more• Also, there have been efforts to obtain more
definitive diagnostic information than spirometry
alone can provide.
• Calculating results manually from the graph of the
mechanical volume spirometer requires
considerable time.

138. • Transducers have been designed to transform the
movement of the bell, bellows or piston of volume
spirometers into electrical signals.
• These are then used to compute the numerical
results electronically.
• The popularity and low cost of personal computers
have made them an attractive method ofhave made them an attractive method of
automating both volume and flow spirometers.
• An accurate spirometer connected to a personal
computer with a good software programme has the
potential of allowing untrained personnel to obtain
accurate result.

139. Wedge spirometer
• A wedge spirometer consists of two square pans,
parallel to each other and hinged along one edge.
• The first pan is permanently attached to the wedge
casting stand and contains a pair of 5 cm inlet tubes.
• The other pan swings freely along its hinge with respect
to the fixed pan.
• A space existing between the two pans is sealed airtight
with vinyl bellows.with vinyl bellows.
• The bellows is extremely flexible in the direction of pan
motion but it offers high resistance to ‘ballooning’ or
inward and outward expansion from the spirometer.
• As a result, when a pressure gradient exists between
the interior of the wedge and the atmosphere, there
will only be a negligible distortion of the bellows.

141. Ultrasonic spirometer
• Ultrasonic spirometers depend, for their action on
transmitting ultrasound between a pair of transducers
and measuring changes in transit time caused by the
velocity of the intervening fluid medium (McShane,
1974).
• They employ piezo-electric transducers and are
operated at their characteristic resonant frequency foroperated at their characteristic resonant frequency for
their highest efficiency.
• Gas flowmeters generally operate in the range from
about 40 to 200 kHz.
• At frequencies higher than 200 kHz, absorption losses
in the gas are very high whereas sounds below 40 kHz
are audible and can be irritating.

142. • Ultrasonic spirometers utilize a pair of ultrasonic
transducers mounted on opposite sides of a flow
tube .
• The transducers are capable of both transmitting
and receiving ultrasonic pulses.

143. PNEUMOGRAPHPNEUMOGRAPH
• A pneumograph, also known as a pneumatograph
or spirograph, is a device for recording velocity and
force of chest movements during respiration.

144. Impedance PneumographyImpedance Pneumography
• This is an indirect technique for the measurement of
respiration rate.
• Using externally applied electrodes on the thorax, the
impedance pneumograph measures rate through the
relationship between respiratory depth and thoracic
impedance change.
• The technique avoids encumbering the subject with• The technique avoids encumbering the subject with
masks, tubes, flow meters or spirometers, does not
impede respiration and has minimal effect on the
psychological state of the subject.
• Impedance method for measuring respiration rate
consists in passing a high frequency current through
the appropriately placed electrodes on the surface of
the body and detecting the modulated signal.

145. • The signal is modulated by changes in the body
impedance, accompanying the respiratory cycle.
• The electrode used for impedance pneumograph
are of the self-adhesive type.
• Contact with the skin is made through the
electrode cream layer for minimizing motion
artefacts.artefacts.
• The electrodes, when the skin is properly
prepared, offer an impedance of 150 to 200 W.
• The change in impedance corresponding to each
respiratory cycle is of the order of 1% of the base
impedance.

146. • The two electrode impedance pneumograph is
convenient for use with quiet subjects.
• Movement artefacts are produced due to changes
in the electrode contact impedance, in case the
subject is moving.
• These artefacts can be significantly reduced by using
a four electrode impedance pneumograph.
• In this case, the output from the oscillator is applied• In this case, the output from the oscillator is applied
to the two outer electrodes.
• By doing so, the main oscillator current does not
flow through the contact impedance of the
measuring electrodes.
• This system is useful for monitoring restless subjects
such as babies.

147. • To avoid the stimulation of sensory receptors,
nerves and muscle, currents higher in frequency
than 5 kHz must be used for the measurement of
physiological events by impedance.
• Frequencies lower than 5 kHz are particularly
hazardous since ventricular fibrillation may be
produced with substantial current flow.produced with substantial current flow.
• The use of higher frequencies not only provides
the protection sought in the avoidance of tissue
stimulation, but also provides the safe use of
currents of magnitude, which could be lethal if
the frequencies were lower.

149. • Electrical impedance changes associated with
physiological activity have been studied extensively.
• Some of the physiological quantities which have
been measured and recorded by the impedance
method include respiration, blood flow, stroke
volume, autonomic nervous system activity, muscle
contraction, eye movement, endocrine activity and
activity of the brain cells.
contraction, eye movement, endocrine activity and
activity of the brain cells.
• The impedance-based method of measuring
respiration rate is commonly employed in patient
monitoring systems.
• The electrodes used for this purpose are the same
as those used for ECG measurement.

150. • The dynamic measuring range of the amplifier is 0.1
to 3.0 W with a frequency response of 0.2 to 3.0 Hz
corresponding to respiratory rate of 12 to 180 per
minute.
• The amplifier operates within an impedance
window established by the static impedance level
(approx. 3 k ohms) and its output produces a(approx. 3 k ohms) and its output produces a
respiratory waveform from which respiratory rate is
derived.