gtu topic 6_cardiovascular measurement

TOPIC NO.6

Compiled By: Prof. G B Rathod

ET department-BVM College,

Email: [email protected]

CARDIOVASCULAR

MEASUREMENT

TOPIC OUTLINES…

ELECTROCARDIOGRAPHY

MEASUREMENT OF BLOOD PRESSURE

MEASUREMENT OF BLOOD FLOW AND

CARDIAC OUTPUT

PLETHYSMOGRAPHY

MEASUREMENT OF HEART SOUND

OUTCOMES

REFERENCES

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ELECTROCARDIOGRAPHY

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Electrocardiography(ECG or EKG) is a graphic recording

or display of the time-variant voltage produced by the

myocardium during the cardiac cycle.

The ECG is used clinically in diagnosing various diseases

and conditions associated with the heart.

Here only measurement related concepts will be discussed.

For analysis, the cardiologist looks critically at the various

time intervals, polarities and amplitudes of ECG.

The EGC waveforms and its intervals of time and

amplitudes values are in upcoming slides.

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Fig.6.1: ECG waveform with amplitude value

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As mentioned in earlier topics, an instrument used to

obtain and record the electrocardiogram is called an

electrocardiograph.

The string galvanometer, which was introduced to

electrocardiography by Einthoven in 1903 and it was

used until 1920. After that the signal amplifier are used

to design the new instruments.

Day by day improvements done in various ECG

measuring instruments and accuracy is also achieved

up to certain marks.

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WAVE AMPLITUDE

P 0.25 mV

R 1.6 mV

Q 25% of R wave

T 0.1 to 0.5 mV

INTERVAL TIME

P-R 0.12 to 0.20 sec

Q-T 0.35 to 0.44 sec

S-T 0.05 to 0.15

P 0.11 sec

QRS 0.09 sec

Table.6.1: Amplitude of various waves in ECG

Table.6.2: Time interval of various

Segments in ECG

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Normal heart rate is lies between 60 to 100 beats per

minute.

A slow rate than this is called BRADYCARDIA (SLOW

HEART) and a higher rate, TACHYCARDIA (FAST

HEART).

If the heart cycles are not evenly spaced, an arrhythamia

may be indicated.

If the P-R interval is greater than 0.2 second, it can suggest

blockage of the AV node.

If one or more of the basic features of the ECG should be

missing, a heart block of some sort might be indicated.

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When we use electronic amplifiers to measure bioelectricpotentials, interference problem occur due to groundthrough their power supply.

To reduce this, differential amplifier are used.

A differential amplifier can be considered as two amplifierswith separate inputs but with common output terminal,which deceivers the sum of the two amplifier outputvoltages.

The ratio of the differential gain to the common mode gainis called the common-mode rejection ratio of thedifferential amplifier, which in modern amplifiers can be ashigh as 1000000:1.

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Fig.6.2.1: Differential amplifier with common out put

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Fig.6.2.2:Differential amplifier used to amplify the bioelectric signals

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Electrodes and Leads:

To record an electrocardiogram, a number of electrodes,

usually five, are affixed to the body of the patient. The

electrodes are connected to the ECG machine by the same

number of electrical wires known as leads.

The electrode applied to the right leg of the patient, for

example, is called RL lead.

To avoid ambiguity between electrodes and the measuring

techniques, we use lead term for the particular group of

electrodes taken for the measurements.

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For individual lead wire, as well as the physical connection

to the body of the patient, the term electrode will be used.

When ECG recorded by using certain placement of the

electrode, may be some aspects of the waveform missed.

To avoid this problem, usually 12 different leads techniques

are used so that no important detail of the waveform is

missed.

Placement of electrodes and names and configurations of

the leads have become standardized and are used the same

way throughout the world.

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Electrodes: The placement of the electrodes, as well as

the color code use to identify each electrode, is shown

in Figure 6.3.

Mr. Einthoven had found better results using the

electrodes placements at specific locations.

As a ground reference, we can use right leg.(It can be

anywhere but it became convention to use right leg).

Chest or precordial electrodes will be introduced later.

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Leads: The placement of the electrodes as shown in

figure 6.3.

Because the input of the ECG recorder has only two

terminals, a selection must be made among the

available active electrodes.

The 12 standard leads used most frequently are shown

in upcoming figure 6.4.

The three bipolar limp lead selections first introduced

by Einthoven.

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LEAD CONNECTIONS

LEAD-I Left Arm(LA) and Right Arm (RA)

LEAD-II Left Leg (LL) and Right Arm (RA)

LEAD-III Left leg (LL) and Left Arm (LA)

• These three leads are called bipolar because for

each lead the ECG is recorded from two electrodes

and third electrode is not connected.

•In each of these lead positions, the QRS of a

normal heart is such that the R wave is positive.

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Figure.6.4.1. Three lead techniques for measurement of ECG

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Figure.6.4.2: Limbleads

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Einthoven made few assumption related to the cardiacactivity and ECG.

He said that at any given instant of the cardiac cycle,the frontal plane representation of the electrical axis ofthe heart is two dimensional vector.

The ECG measured from any three limb leadtechniques is time variant single dimensionalcomponent of that vector.

He also said that the heart is near the center of anequilateral triangle, the apexes of which are the rightand left shoulders and the crotch.

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The other leads are known as unipolar type, which wasintroduced by Wilson in 1994.

For unipolar leads, the ECG is recorded between singleexploratory electrode and the central terminal, whichhas a potential corresponding to the center of the body.Three active limb electrodes together through resistorsof equal size.

In augmented unipolar limb leads, the electrode usedas an exploratory electrode is not used for the centralterminal. These leads are aVR, aVL and aVF.(seeupcoming figure)

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The remaining leads are unipolar chest leads.

These chest positions are called the precordial unipolar

leads and are designated V1 through V6.

All three active limb electrodes are used to obtain the

central terminal, while a separate chest electrode is

used as an exploratory electrode.

We will see the connection type of the precordial

unipolar leads also we will see the various ECG wave

forms for the particular patient by using different leads

techniques in upcoming diagrams.

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Some special modified leads are also used for the ECG

measurements. The most widely used modification for

ongoing ECG monitoring is modified chest lead I

(MCL1) also called the marriott lead, named after its

inventor.

For this lead technique, the placement of the electrodes

on the body is different.

Recordings obtained in this techniques are very useful

in differentiating left ventricular ectopic rhythms from

aberrant right ventricular or super ventricular rhythms.

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Fig.6.9: Single channel ECG

Recorder

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Fig.6.10: Three channel ECG Recorder.

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The other ECG Recorders are:

Vector Electrocardiograph (vectorcardiograph)

Electrocardiograph system for stress testing

Electrocardiograph for computer processing

Continuous ECG recording (Holter Recording)

MEASUREMENT OF BLOOD

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Blood Pressure is considered a good indicator of thestatus of the cardiovascular system.

Measurement of BP saved many life by indicating theHypertension.

In clinical measurement its usually measured usingindirect measuring instrument calledsphygmomanometer (greek word sphygmos meaningpulse).

The demerit of this system are:

We cant get the continuous reading and the detail waveforms of the BP also cant me taken.


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Fig.6.11: Wall Mounted Sphygmomanometer


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Basically two types of Blood Pressure measurements

are in use.

Indirect Measurements

Direct Measurements.

Here, we are going to discuss First Indirect

Method(Noninvasive), than some automatic methods

of measuring BP and after that we are going to discuss

Direct measurement(Invasive ) techniques.


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Indirect Measurements:

Well known method is using sphygmomanometer and the

stethoscope.

The sphygmomanometer is consists of an inflatable

pressure cuff and mercury or aneroid manometer to

measure the pressure in the cuff.

The cuff consists of a rubber bladder inside and inelastic

fabric covering that can wrapped around the upper arm.

This meter is works on the principle that when the cuff is

placed on the upper arm and inflated, arterial blood can….


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Flow past the cuff only when the arterial pressure

exceeds the pressure in the cuff.

When the cuff is inflated to a pressure that only

partially occludes the brachial artery, turbulence is

generated in the blood as it spurts through the tiny

arterial opening during each systole.

The sound generated by this turbulence (Korotkoff

sound) can be heard through a stethoscope placed over

the artery downstream from the cuff.


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Use of stethoscope while we measure the blood pressure.

When the cuff pressure reaches above the systole level, we

can not hear any sound in stethoscope.

Once the valve release the air, cuff pressure reduces

continuously, at one point the when the blood spurt from

the vessel, we can here one sound and that measure is know

as a systolic pressure.

Now we continuously decreases the pressure of the cuff, up

to certain limit we can able to here the sound, but when the

sound disappear that pressure noted down as a diastolic

blood pressure.


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Fig. 6.12: Measurement of Blood flow using

Sphygmomanometer.


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This familiar method of locating the systolic and

diastolic pressure values by listening to the korotkoff

sound is called the auscultatory method of

sphygmomanometery.

An alternative method is known as the palpatory

method, by which the physician identifies the flow of

the blood in the artery by feeling the pulse of the

patient downstream from the cuff.

Diastolic pressure is more difficult to measure using

this technique.


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Automated Indirect Methods.

The method of measurement is same as the ausculatory

indirect method which is done manually but here, the

pressure transducer is connected to cuff and for the

sound recording microphone is placed beneath the

cuff(Over the artery).

The pressure cuff is automatically inflated to about 220

mm Hg and allowed to deflate slowly.

This instrument is still semiautomatic because the

recording must be interpreted by the observer.


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False indications are there due to motion artifacts.

The fully automated machine are recording the firstand last sound and also preserve the display indicationof both the pressure value.

This type of machine are very much user-friendly andavailable in market.

While doing some activity, many of the automaticmeasuring instruments shows errors in readings.

So, some advance machine are invented. HereProgrammed electrosphygmomanometer PE-300 willbe discussed.


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In PE-300, we can simultaneously measure the soundof blood or pulse and pressure value.

This can be done repeatedly by adjusting the timeintervals.

There are sound sensors, pressure sensors, controllingunit for pump and valve with comparator circuit isused as shown in the diagram.

We can use one more advanced Pressure measuringunit for indirect measurement which gives a MAP(mean arterial pressure) which can also be very usefulinformation related to blood pressure.


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The value of MAP can be found out by using the

simple equation.

Most of the electrical monitor provides both diagnostic

systolic/diastolic waveforms information and added

option of a single value MAP indication.

Some instruments are using large gauge for easy

reading.( See the diagram 6.15)

1( )

3MAP systolic diastolic diastolic


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Inflation and Deflation of Cuff can be done manually,

so this instrument is called semiautomatic electronic

sphygmomanometer.

In Dinamap the MAP can be measure using

oscillometric method.

See the diagram of the Dinamap in figure 6.16.

Some advanced ambulatory automatic blood pressure

monitor are also very useful which uses the halter

method for the monitoring.


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Using this type of the blood pressure monitor we

can able to record around 26 hours of blood

pressure values in magnetic tape. The controlling

unit is always taking care of time interval and

inflation deflation of the cuff.

The recording can be read with in 12 minutes by

using specific scanner and abnormal reading of

pressure can be automatically given by the

machine.

The advantage of this unit is that, it can also be

used for the ECG measurements.

We can see the diagram in upcoming figure. 6.17


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Another approach utilizes ultrasound to measure thepulsatile motion of the brachial artery wall.

High frequency sound energy is transmitted into thepatients arm and is reflected back from the arterialwalls.

By means of Doppler effect, the movement of thearterial walls can be detected as they snap open andclosed with each pulsation of blood.

The advantage of this type of instrument is that resultscloser to direct instruments can be obtain. Its good touse this instruments for the patient under shock.


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Direct measurements.

First experiment done in1728 by Hales by inserting

glass tube into the artery of horse.

That continuous measurement is taken and is called

kymograph.

Recently the strain gage used for the measurement and

kymograph where piezo sensors are used.

There are specifically three methods for Direct

measurements.


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1. Percutaneous insertion

2.Catheterization (Vessel cutdown)

3. Implantation of a transducer in a vessel or in theheart.

For first two methods we can see the diagram number6.18.

In that one before percutaneous insertion, a localanesthetic injected near the site of invasion.

Catheter is fed through the hollow needle.

The blood pressure sensed directly by attaching atransducer to the tube.


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Catheter is used in many measurements.

Using catheterization we can do measurement by

using two methods.

1. After insertion of saline solution we can check

the pressure outside the body using the

transducer.

Or we can attach a transducer at the tip of the

catheter and get the direct measurements.

Implantation techniques involves major surgery

so that method is normally used for experimental

purpose only.


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Specific direct measurement techniques.

Basically two types.

1. By the clinical method

2.By the electrical principle involved.

There are different types of blood pressure

measuring transducers are used for various

methods.

Here we are going to see the diagrams of the

different transducers.


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MEASUREMENT OF BLOOD FLOW

AND THE CARDIAC OUTPUT

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All the organs required an adequate amount of blood.

So, by measuring the flow rate of the blood we can

diagnosis the diseases.

We can not use the industrial principles to measure the

flow rate of liquid because here we could not cut the

Wessel every time.

So some basic principles on which the measurements

are to be done are described.



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Electromagnetic Induction

Ultrasound transmission or reflection

Thermal Convection

Radiographic Principles

Indicator dilution



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PLATHYSMOGRAPHY

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Instruments measuring volume changes or providing

outputs that can be related to them are called

‘Plethysmographs’, and measurement of these volume

changes, or phenomena related thereto, is called

plethysmography.

The upcoming diagrams shows a various techniques

for plethysmogrphy.

PLATHYSMOGRAPHY

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PLATHYSMOGRAPHY

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PLATHYSMOGRAPHY

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PLATHYSMOGRAPHY

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PLATHYSMOGRAPHY

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PLATHYSMOGRAPHY

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MEASUREMENT OF HEART

SOUND

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The sound technology by which we can diagnosis thedisease related to heart its known asphonocardiography.

Initially the method was by putting ears on the chest ofthe patient.

Then after the stethoscopes are invented.

Now the electronics stethoscopes are also in use.

We can record the frequency spectrum using thephonocardiogram.

The upcoming waveform shows one of the output ofthe phonocardiogram machine.

MEASUREMENT OF HEART

SOUND

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QUESTIONS?

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?

REFERENCE

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Book: “Biomedical instrumentation and

measurements “ ,by L. Cromwell, F .Weibell, and

E. Pfeiffer. PHI publication 2nd Edition.

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THANK YOU

gtu topic 6_cardiovascular measurement

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