bmi Unit 3_opt

8/11/2019 bmi Unit 3_opt

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An Overview . . .

Measurement of blood pressure

Cardiac output

Cardiac rate

Heart sound

Respiratory rate

Gas volume

Flow rate of Co2, o2 in exhaust air

pH of blood,

ESR, GSR measurements

Plethysmography.

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Cardiac Output

It is the amount of blood delivered by the heart to the aorta per minute

For normal adults it is 4 -6 litres / minute

Any decrease may be due to

Low Blood Pressure

Reduced Tissue Oxygenation

Poor Renal Function

Shock

Acidosis

Methods of cardiac output measurements

Ficks Method

Indicator Dilution Method

Measurement of Cardiac Output by Impedance Changewww.eeecube.com

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Ficks Method :

Based on analysis of gas - keeping of the organism

Cardiac output can be calculated by continuously

infusing oxygen into the blood or removing it from the

blood and measuring the amount of oxygen in the blood

before and after its passage

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Oxygen uptakeby Ventilation

Heart Catheter

Mixed Venous Blood Arterial BloodHeartandLungs

Q

Q2

AortaVenaCava

Ficks Method for Cardiac Output Measurement

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Let I be the amount of infused or removed oxygen per unit time

It is equal to the difference between the amounts in the blood arriving at and

departing from the site of measurementI = CAQ CVQ

Q = I

CA CV

where

Q cardiac output in litres / minute

CA - Concentration of oxygen in the arterial blood in millilitres

of oxygen per litre of blood

CV - Concentration of oxygen in the mixed venous blood in

millilitres of oxygen per litre of blood

I - Volume of oxygen uptake by ventilation in millilitres of

blood

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Indicator Dilution Method

Principle

A known amount of dye or radioisotope is introduced as an indicator in the

blood circulation

The concentration of the indicator is measured with respect to time and the

volume of blood flow is estimated

Let M mg of an indicator be injected into a large vein or preferably into the

right heart itself

After passing through the right heart, lungs and the left heart, the indicator

appears in the arterial circulation

The presence of the indicator in the peripheral artery is detected by a

detector

The output of the detector is directly proportional to the concentration of

the indicatorwww.eeecube.com

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Letan increment volume dV pass through the sampling site in time dt

Let the mass of the indicator in dV = dM

Therefore the concentration of the indicator, c = dvdt

dMdt

dV

dtc=Now

dVdt

Q=But

Therefore dM = Q c dt

Integrating over the time of the experiment,

M = Q c dtt

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Considering the flow as constant,

M = Q c dt

t

0

(or) Q = M

c dtt

0

Here concentration of the indicator c is a function of time

By drawing a curve between concentration and time, the area of the

curve gives directly the value of the denominator in the above equation

Q = M

Area of the curve

Thus

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A bolus of about 10 millilitres of 5% Dextrose in water at room

temperature is injected as a thermal indicator into the right atrium

After mixing it is detected in the pulmonary artery by means of a

thermistor mounted at the tip of a miniature catheter probe

The temperature difference between the injectate temperature and

the circulating temperature in the pulmonary artery is measured

The reduction in temperature is integrated with respect to time

After applying proper corrections, a meter reads the cardiac output

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SA1 A2

CurrentElectrodes

Potential Electrodes

Oscillatorf = 100kHz

Amplifier andDemodulator Differentiator

z

d

Cardiac Output Measurement by Impedance Method

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Electrodes 1 and 4 are used as current electrodes

Electrodes 2 and 3 are used to pick up the voltage across the thorax

If p - resistivity of the patients haematocrit

A - cross sectional area of the thorax

L - separation between the potential electrode 2 and 3

Then the resistance of the thorax is given by

R pLA

= pL2

AL= pL

2

V=

VpL2

R=(or) (V volume of the thorax)

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dV- pL2

R2=

During ejection of stroke volume, the change in volume is dV and

the corresponding decreasing in resistances is dR

Differentiating the above expression,

dR

Since a.c. excitation is used, R should be replaced by impedance Z

dV- pL2

Z2

= dZTherefore

Taking dZ = tdZ

dtmax

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where,

dZ

dtmax

- corresponds to the peak negative value of

(dZ/dt) found during systole and

t - corresponds to the interval between (dZ/dt) = 0 and

the second heart sound

dV- pL2

Z2=Thus

dZ

dtmax

t .

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o

VOUT

+

-

VOL

Lh

r

Patientair intoBellows

Linkage

kR

R

.

VBB

Spirometer

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Spirometer

Used for respiratory volume measurements

All lung volumes and capacities can be measured

Consists of light weight bellows

These bellows are mechanically articulated to a biased potentiometer such that the wiper voltage is proportional

to volume of the bellows

The maximum volume of the bellows is given by

VOLmax = L(Pi)r2

If k is the proportionality constant giving the fractional position of the wiper arm on the potentiometer R such

that

k = Vout = VOL

VBB VOLmax

Therefore VOL = Vout (VOLmax)

VBB

Better Linearity can be obtained in measuring respiratory volumes

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Gas Analysers

Used to

Determine the quantitative composition of inspired and expired gas

Assess the lung function

Types

Infrared Gas Analyser based on infrared absorption of carbon dioxide

Paramagnetic Oxygen Analyser - based on paramagnetic behaviour of

oxygen

Thermal Conductivity Gas Analyser based on thermal conductivity of

carbon dioxide

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o

Diaphragm

Panel Meter Recorder

SampleCell

Sample TubeMotor

Amplifier

Detector Unit

Reference Tube

Infra redSourceMirror Mirror

Block Diagram of Infrared CO2 Analyzer

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By means of mirror assembly two infrared beams with same intensity are produced

A high speed rotating chopping disc is present which occludes each beam twice per motion

The chopped lights pass through the reference and sample tubes

When the opaque portions of the choppers are not in the way, the beam falls on the balanced

condenser microphone detector after passing the gas

The sample beam falling on the detector will be weaker than the reference beam since there is

absorption in the sample cell by the component of interest

The heating of the gas in the detector situated in the reference beam side will cause rise in

pressure

The diaphragm vibrates at the chopping frequency

The diaphragm forms one half of the capacitor

Thus, the change in position of the diaphragm produces a periodic change in the capacity of thecapacitor

This change is amplified and demodulated and the output is displayed on a meter or a recorder

in terms of concentration of the wanted component

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DUMB CELL

o

O2

NS

MIRROR

SCALE

Simplified Block Diagram of Oxygen Analyzer

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There is a small glass dumb cell shaped assembly containing a

weakly diamagnetic gas such as nitrogen

It is suspended from a platinum iridium thread between the polesof a powerful permanent magnet

The pole pieces are wedge shaped in order to produce a non linear

field

If the gas surrounding the dumb shell is also nitrogen there will be

no force acting on the dumb shell

If oxygen is added to the gas, the oxygen molecules experience a

force, displacing the diamagnetic dumb shell

The resulting rotation of the suspension turns a small mirror and

deflects a small beam of light over a scale calibrated in percentages

by volume of oxygen or partial pressure of oxygenwww.eeecube.com

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uA

A

R1

R2

S1

S2

Reference GasFlow

Sample GasFlow

Hot Wire Cell Thermal Conductivity Analyzer

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There are four platinum filaments as heat sensing elements

Each of these is placed in a brass black

These are maintained at constant temperature and form the four arms of a bridge

Two filaments R1 and R2 act as reference gas arms

S1 and S2 act as sample gas arms

Initially reference gas is made to flow through all the filament cells and the

bridge is balanced

When the sample gas flows through the sample gas filament cells, the

temperature of the filaments in those cells are changed

If the thermal conductivity of the sample gas is more, then cooling of the

filaments takes place

This changes the resistances of the filaments

The bridge becomes unbalanced and a current flows through the meter which is

calibrated in terms of concentration of CO2 gaswww.eeecube.com

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VOUT = Er EIN - YT

YT

o

-10 mV / oCFrom

TemperatureSensor

EIN

( From Solution )

-Er

( From Reference )

VOUT

.

+

+

+

-

-

-Digital

Voltmeter

AnalyzedSolution

Glass Membrane

Buffer Solution

ElectricalConductor

ReferenceElectrode

Digital pH Meter

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Used to measure pH at a given temperature and also at different

temperature

Consists of a glass electrode terminal and reference terminal

The calomel or silver silver chloride in potassium chloride electrolyte acts

as the reference terminal

A salt bridge consisting of a fiber wick saturated with KCl is at the tip of the

reference electrode

This keeps the reference terminal potential the same regardless of the

solution under test

The active terminal is sealed with common glass except for the tip

The tip is made of sensitive glass consisting of hydrated gelatinous glass

layer

Its membrane potential is proportional to the pH of the solution under test

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Plethysmography

Used to measure the volume changes in any part of the body that result from the

pulsations of blood occurring with each heart beat

Used to measure Total Lung Capacity (TLC)

Consists of a rigid cup or chamber placed over any part of the body in which the

volume changes are to be measured

The cup is tightly sealed

The changes in the volume reflect the pressure changes of air inside the chamber

The pressure change is measured at constant volume or vice versa

Types based on nature of sensor

Capacitance Plethysmograph

Impedance Plethysmograph

Photoelectric Pltehysmograph

Mercury Strain Gauge Plethysmograph

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Measurement of Total Lung Capacity

The principle operation is the Boyles Law which states that at a

Kelvin Temperature, the pressure of a given mass of gas is inversely

proportional to its volume

i.e. P * (VOL) = k1T

where k1 is a constant

Since the patient is made to sit inside an air tight chamber whosetemperature is constant,

P * (VOL) = constant

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The patient cannot breathe with the valve closed, so the air

pressure in the mouthpiece is equal to the lung pressure PT

In the body,d TLC

d PT

TLC

PT

= -

where TLC = Thorax Volume

PT = Thorax Pressure

In the chamber,d (VOLC)

d PC

VOLC

PC

= -

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where VOLC = Chamber Volume

PC = Chamber Pressure

Since the chamber is closed, any increase in the thoracic volume

causes a decrease in the chamber volume of air ,

i.e. d (VOLC

) = - d (TLC)

TLC

PT

VOLC

PC

= -d PT d PC

Since the changes in pressure induced by breathing motions are

small when the patient is sitting normally, PC = PT

TLC

d PT

= -d PCVOLCTherefore

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Procedure

First mouthpiece valve is closed when the patient is sitting inside

the sealed chamber

Now the patient is asked to make breathing motions

The change in pressure reading in the pressure gauge 1 is noted

down, this gives dPT

The change in pressure reading in the pressure gauge 1 is noted

down, this gives dPC

Thus knowing the value of VOLC, the TLC can be calculated using

the formula,

TLCd PT

=d PCVOLC

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Blood Pressure

Blood pressure (BP) is a force exerted by circulating blood on the wallsof blood vessels

The term blood pressure usually refers to the pressure measured at a

person's upper arm.

For each heartbeat, BP varies between systolic and diastolic pressures.

Systolic pressure is peak pressure in the arteries, which occurs near the end

of the cardiac cycle when the ventricles are contracting.

Diastolic pressure is minimum pressure in the arteries, which occurs near

the beginning of the cardiac cycle when the ventricles are filled with blood.

A person's BP is usually expressed in terms of the systolic pressure and

diastolic pressure, for example 120/80 millimetres of mercury (mmHG)

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Measurement

Noninvasive measurement

Palpation method

Auscultatory method

Oscillometric method

White-coat hypertension

Home monitoring

Invasive measurement

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Auscultatory method

Uses a stethoscope and a sphygmomanometer

Comprises an inflatable (Riva-Rocci) cuff placed around the upper armat roughly thesame vertical height as the heart, attached to a mercury or aneroid manometer

The mercury manometer measures the height of a column of mercury giving an

absolute result

A cuff of appropriate size is fitted smoothly and snugly, then inflated manually byrepeatedly squeezing a rubber bulb until the artery is completely occluded.

Listening with the stethoscope to the brachial artery at the elbow, the examiner

slowly releases the pressure in the cuff

When blood just starts to flow in the artery, the turbulent flow creates a "whooshing"

or pounding (first Korotkoff sound).

The pressure at which this sound is first heard is the systolic BP.

The cuff pressure is further released until no sound can be heard (fifth Korotkoff

sound), at the diastolic arterial pressure.

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Auscultatory method aneroid sphygmomanometer with stethoscope

Mercury manometer

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Invasive measurement

Arterial blood pressure (BP) is most accurately measured invasivelythrough an arterial line.

Involves direct measurement of arterial pressure by placing a cannula

needle in an artery (usually radial, femoral,dorsalis pedis or brachial)

The cannula must be connected to a sterile, fluid-filled system, which is

connected to an electronic pressure transducer

The advantage of this system is that pressure is constantly monitored beat-

by-beat, and a waveform (a graph of pressure against time) can be

displayed

Regularly employed in human and veterinary intensive care

medicine, anesthesiology, and for research purposes

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Classification of blood pressure for adults

Category systolic, mmHg diastolic, mmHg

Hypotension < 90 < 60

Normal 90120 and 6080

Prehypertension 121139 or 8189

Stage 1 Hypertension 140159 or 9099

Stage 2 Hypertension 160 or 100

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Heart sounds

The heart sounds are the noises (sound) generated by the beatingheart and the

resultant flow of blood through it.

In healthy adults, there are two normal heart sounds often described as a lub and

a dub (or dup), that occur in sequence with each heart beat. These are produced by

the closing of the AV valves and semilunar valves respectively

In addition to these normal sounds, a variety of other sounds may be present

including heart murmurs,adventitious sounds, and gallop rhythms

Heart murmurs are generated by turbulent flow of blood, which may occur inside or

outside the heart.

Abnormal murmurs can be caused by stenosis restricting the opening of a heart

valve, resulting in turbulence as blood flows through it.

Abnormal murmurs may also occur with valvular insufficiency which allows

backflow of blood when the incompetent valve closes with only partial effectiveness

b

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