anatomy of the heart blood pressure, blood flow and … pressure, blood flow ... • similar to...

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Blood Pressure, Blood Flowand Volume of Blood

Achmad RizalBioSPIN

ARL - EL4703 - Isntrumentasi Biomedis 2Basic structure of the heart. RA is the right atrium, RV is the right ventricle; LA is the left atrium, and LV is the left ventricle.

Anatomy of The Heart

ARL - EL4703 - Isntrumentasi Biomedis 3

Lower body

Upper body

Leftatrium

Rightatrium

Leftventicle

Rightventicle

Oxygenatedblood

Deoxygenatedblood

Lung

The simplified circulatory system. The blood is delivered from the right ventricle to the lung. The oxygenated blood from the lung is then returned to the left atrium before being sent throughout the body from the left ventricle. Deoxygenated blood from the body flows back to the right atrium and the cycle repeats. ARL - EL4703 - Isntrumentasi Biomedis 4

In the top figure, the electrocardiogram (ECG) initiates the cardiac cycle. The cardiac sounds are also shown. The bottom figure shows that ejection occurs when the pressure in the left ventricle exceeds that in the arteries.


Duration and characteristics of each major event in the cardiac cycle.

AV valves closed.Semilunar valves open.Blood pumped into aorta and pulmonary artery.

AV valves open.Semilunar valves closed. Ventricular filling.

AV valves opened.Semilunar valves close.Ventricular filling.

Characteristics

0.3 seconds Atrial diastoleVentricular systole

0.1 seconds Atrial systoleVentricular diastole

0.4 seconds Atrial diastoleVentricular diastole

Duration at 75 bpm(0.8 second cycle) Event


Blood Pressure Measurement (1)

• Ave = 0,5 (Syst + Dias)• Mean = 1/3 (Syst- Dias) + Dias

• Syst 115 to 140mmHg• Dias 60 to 90 mmHg• Mean 80 to 105 mmHg

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Blood Pressure Measurement



Indirect Blood Pressure Measurement- Pressure Cuff Methods

Riva-Rocci MethodOscillometryContinuous Vascular Unloading

- Tonometry


General Facts

Indirect measurement = non-invasive measurement

Brachial artery is the most common measurement site

Close to heart

Convenient measurement

Other sites are e.g.:

forearm / radial artery

wrist (tends to give much higher SP)

The most common indirect methods are auscultationand oscillometry


Riva-Rocci Method

The occlusive cuff is inflated until the pressure above systolic pressure,And then is slowly bled off (2-3 mmHg/s). When the systolic peaks are higher than the occlusive pressure, the blood spurt under th cuff and causes a palpable pulse In the wrist ARL - EL4703 - Isntrumentasi Biomedis 12

Korotkoff Method (1)

Korotkoff’s method

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Korotkoff Method (2)• Cuff is inflated until cuff pressure exceeds systolic

pressure. Brachial artery is occluded below the cuff and no blood passes through it.

• Cuff pressure is slowly reduced at 2-3 mm Hg/s.When cuff pressure = systolic pressure, blood beginspassing through artery under cuff. Stethoscope picks upkorotkoff sounds.

• As cuff pressure drops below diastolic pressure Korotkoff sounds disappear.

cuffoccluded

blood vessel



Korotkoff sounds undergo 5 phases:• Phase I: initial ‘tapping” sounds (cuff

pressure =systolic pressure)• Phase II: sounds increase in intensity• Phase III: sounds at maximum intensity• Phase IV: sounds become muffled (cuff

pressure = diastolic pressure)• Phase V: sounds disappear




Korotkoff Method (5)• Origin of Korotkoff Sounds

-several theories exist:- Turbulence- Vibration of vessel walls

• Accuracy of korotkoff method :- underestimates systolic pressure by 5-20 mm Hg- overestimates diastolic pressure by 12-20 mm Hg.- errors are compounded in hypotensive, & elderly.- in some subjects sounds disappear during phase III,

then reappear: auscultatory gap, get erroneous diastolic reading,


Korotkoff Method (6)Cuff Size and Dynamics• Too small a cuff length will not occlude artery properly.• Cuff width should be about 0.4 limb circumference.• Different cuff sizes are available for different limb/patient

sizes.• Cuff volume is not linearly related to cuff pressure. This

suggests that some of the cuff pressure is used to deform the cuff rather than occlude the artery. Introduces nonlinear distortion, particularly at low pressures (< 50 mm Hg).


Oscillometry (1)

• Similar to Korotkoff method, looks at cuff pressure rather than Korotkoff sounds.

• Used in automated blood pressuremonitors.

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Top: Cuff pressure with superimposed Korotkoff sounds, which appear between systolic and diastolic pressures. Bottom: the oscillometric method detects when the amplified cuff pressure pulsations exceed about 30% of maximal pulsations.

From Geddes, L. A. Cardiovascular devices and their applications. New York: Wiley. 1984.8.9.2 Direct measurement

Oscillometry (2)


Block diagram of the major components and subsystems of an oscillometric blood-pressure monitoring device, based on the Dinamapunit, I/O = input/output; MAP = mean arterial pressure; HR = heart rate; SYS= systolic pressure; DYS = diastolic pressure. From Ramsey M III.

Blood pressure monitoring: automated oscillometric devices, J. Clin. Monit. 1911, 7, 56-67.

MAP

HR

SYS

Microcomputerwith memoryand I/O

Multiplexerand analogto digitalconverter

Deflate valve

Dumpvalve

Over-Pressureswitch

Auto-zerovalve

Pressuresensor

Cuff pressure

Cuff pressureoscillations

InternalExternal

BP cuff

Inflationsystem

DYS


Tonometry

• A tonometry test measures the pressure inside your eye, which is called intraocular pressure (IOP). This test is used to check for glaucoma, an eye disease that can cause blindness by damaging the nerve in the back of the eye (optic nerve).

• Arterial tonometry using linear of pressure array sensor pressed against radial artery so that at least one sensor is directly over the lumen.


Tonometry

A sensor array is used here, because at least one of the pressure sensors must laydirectly above the artery

Linear array of pressure sensors is pressedagainst a superficial artery, which is supported from below by a bone (radial artery).

The pressure is increased continuously and the measurements are made when the artery is half collapsed

When the blood vessel is partly collapsed, the surrounding pressure equals the arterypressure.

The hold-down pressure varies betweenindividuals and therefore a ’calibration’ mustbe done


Tonometry (2)


Tonometry (cont.)

ADVANTAGES

+) Can be used for non-invasive, non-painful, continuous measurement

DISADVANTAGES

-) Relatively high cost-) The wrist movement and tendons result

in measurement inaccuracies

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Blood Pressure Direct Measurement

• Arterial & venous blood pressure can be measured by inserting a catheter into the blood vessel and maneuvering it until the end is at the site at which the blood pressure is to be measured

• Catheter can be inserted into the artery inside a needle

• The alternative method catheter tip sensor• Very invasive procedure



• Sterile saline filled catheter is inserted into blood stream

• The pressure at the tip of catheter is transmitted to an external pressure transducer

• Some blood vessel :Artery: carotid, brachial, femoralVeins : femoral, brachial, subcalian, internal jugulas, CVP central venous pressureRAP right atrium pressure


Figure 7.3 Extravascular pressure-sensor system A catheter couples a flush solution (heparinized saline) through a disposable pressure sensor with an integral flush device to the sensing port. The three-way stopcock is used to take blood samples and

zero the pressure sensor.

Sensing port

Roller clamp

Flush solution under pressure

Sample and transducerzero stopcock

Electrical connectorDisposable pressure transducer with an integral flush device




Fluid resitance how fluid flows in a catheter, flow f

p = RCf p = p1 – p2p = pressure (N/m2), p1, p2 = gauge pressure at two specific

pointRC = resitance of the tube (Ns/m5)f = flow (Kg/s)



• Gauge pressure pressure relative to atmospheric pressure

• If f = 0 , p1 = p2 , in other word, when the flow in a closed tube is zero, pressure at the input equal the pressure at the output

• Tube resistanceRC = 8ηl/(πr4)

η = viscosity, l = tube length, r = radius


Blood Flow (2)

Normal blood flow velocity 0,5 m/s – 1 m/s (Systolic, large vessel)

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Blood Flow Measurement

How to make blood flow / volumemeasurements? Standard flow meters, such as turbine flow meters, obviously cannot be used!– Indicator-dilution method: cont./rapid injection,

dye dilution, thermodilution– Electromagnetic flowmeters– Ultrasonic flowmeters / Doppler flowmeters– Plethysmography: Chamber / electric

impedance / photoplethysmographyARL - EL4703 - Isntrumentasi Biomedis 32

Indicator Dilution with Continuous Injection

• Measures flow / cardiac output averaged over several heart beats

• Fick’s technique: the amount of a substance (O2) taken up by an organ / whole body per unit time is equal to the arterial level of O2minus the venous level of O2 times the blood flow

va CCdtdm

Cdtdm

dtdVF

−=

Δ==

Blood flow, liters/min(cardiac output)

Consumption of O2 (mL/min)

Arterial and venousconcentration of O2 (mL/L of blood)

dtdVdtdmC =Δ

Change in [] due to continuously added indicator m to volume V


Fick’s technique

• How is dm/dt (O2 consumption) measured?• Where and how would we measure Ca and Cv? (Exercise)

minL/5mL/L140L/mL190

minmL/250][O][O

min)(mL/O

22

2

=−

=

−=

va

nconsumptioOutputCardiac


Indicator Dilution with Rapid Injection

• A known amount of a substance, such as a dye or radioactive isotope, is injected into the venous blood and the arterial concentration of the indicator is measured through a serious of measurements until the indicator has completely passed through given volume.

• The cardiac output (blood flow) is amount of indicator injected,divided by average concentration in arterial blood.

∫= t

dttC

mF

0)(


Indicator – Dilution Curve

After the bolus is injected at time A, there is a transportation delay before the concentration begins rising at time B. After the peak is passed, the curve enters an exponential decay region between C and D, which would continue decaying alone the dotted curve to t1 if there were no recirculation. However, recirculation causes a second peak at E before the indicator becomes thoroughly mixed in the blood at F. The dashed curve indicates the rapid recirculation that occurs when there is a hole between the left and right sides of the heart.


An Example

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Dye Dilution• In dye-dilution, a commonly used dye is indocyanine green

(cardiogreen), which satisfies the following– Inert– Safe– Measurable though spectrometry– Economical– Absorption peak is 805 nm, a wavelength at which absorption of

blood is independent of oxygenation– 50%of the dye is excreted by the kidneys in 10 minutes, so

repeat measurements is possible


Thermodilution

• The indicator is cold – saline, injected into the right atrium using a catheter

• Temperature change in the blood is measured in the pulmonary artery using a thermistor

• The temperature change is inversely proportional to the amount of blood flowing through the pulmonary artery


Measuring Cardiac Output

Several methods of measuring cardiac output In the Fick method, the indicator is O2; consumption is measured by a spirometer. The arterial-venous concentration difference is measure by drawing simples through catheters placed in an artery and in the pulmonary artery. In the dye-dilution method, dye is injected into the pulmonary artery and samples are taken from an artery. In the thermodilution method, cold saline is injected into the right atrium and temperature is measured in the pulmonary artery. ARL - EL4703 - Isntrumentasi Biomedis 40

Electromagnetic Flowmeters

• Based on Faraday’s law of induction that a conductor that moves through a uniform magnetic field, or a stationary conductor placed in a varying magnetic field generates emf on the conductor:

When blood flows in the vessel with velocity u and passes through the magnetic field B, the induced emf emeasured at the electrodes is.

∫ ⋅×=L

de0

LBu

For uniform B and uniform velocity profile u, the induced emf is e=BLu. Flow can be obtained by multiplying the blood velocity u with the vessel cross section A.


B

N S

B

u −

+

e

l

Figure 8.16 Principle of an electromagnetic flowmeter.

e = Blu


ElectromagneticFlowmeter Probes

• Comes in 1 mm increments for 1 ~ 24 mm diameter blood vessels

• Individual probes cost $500 each

• Made to fit snuggly to the vessel during diastole

• Only used with arteries, not veins, as collapsed veins during diastole lose contact with the electrodes

• Needless to say, this is an INVASIVE measurement!!!

• A major advantage is that it can measure instantaneous blood flow, not just average flow

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Ultrasonic Flowmeters• Based on the principle of measuring the time it takes for an

acoustic wave launched from a transducer to bounce off red blood cells and reflect back to the receiver.

• All UT transducers, whether used for flowmeter or other applications, invariably consists of a piezoelectric material, which generates an acoustic (mechanical) wave when excited by an electrical force (the converse is also true)

• UT transducers are typically used with a gel that fills the air gaps between the transducer and the object examined


Near / Far Fields• Due to finite diameters, UT transducers produce diffraction

patterns, just like an aperture does in optics.• This creates near and far fields of the UT transducer, in which

the acoustic wave exhibit different properties– The near field extends about dnf=D2/4λ, where D is the

transducer diameter and λ is the wavelength. During this region, the beam is mostly cylindrical (with little spreading), however with nonuniform intensity.

– In the far field, the beam diverges with an angle sinθ=1.2 λ/D, but the intensity uniformly attenuates proportional to the square of the distance from the transducer

Higher frequencies and larger transducers should be used for nearfield operation. Typical operating frequency is 2 ~ 10 MHz.


Figure 8.17 Ultrasonic flowmeter. The sensor at the scan head transmits the signal from the oscillator and receives the reflected wave from the blood cells. The RF (radio frequency) amplifier amplifies the received signal and the carrier frequency, then AF (audio frequency) signal is produced by a detector. Adapted from Picot, P. A. and Fenster, A. 1996. Ultrasonic blood volume flow rate meter. US Patent, 5,505,204.

Blood vessel

Doppler angle

Scan head

Skin surface Image plane

RF amplifier

Detector AF

amplifier F/V

converter

Computer

Oscillator


UT Flowmeters

Zero-crossingdetector / LPF

Determine direction

High acoustic impedance material


Transit time flowmetersEffective velocity of sound in blood: velocity of sound (c) +velocity of flow of blood averaged along the path of the ultrasound (û)

û=1.33ū for laminar flow, û=1.07ū for turbulent flowū: velocity of blood averaged over the cross sectional area, this is differentthan û because the UT path is along a single line not over an averaged of cross sectional area

Transit time in up/down stream direction:

Difference between upstream and downstream directions

θcosˆvelocityconductiondistance

ucDt

±==

2222cosˆ2

)cosˆ(cosˆ2

cuD

ucuDt θ

θθ

≅−

=Δ


Transit Time Flowmeters

The quantity ∆T is typically very small and very difficult to measure, particularly in the presence of noise. Therefore phase detection techniques are usually employed rather then measuring actual timing.

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Doppler Measurements (3) Ultrasound Doppler

The ultrasound Doppler device can be either a continuous wave or a pulsedDoppler

CW DOPPLER PULSED DOPPLER

Range ambiguity

Low flow cannot bedetected

No minimum range

Simpler hardware

Minimum range

Accuracy

No minimum flow

(Maximum flow) x (range)= limited


Doppler Flowmeters

• The Doppler effect describes the change in the frequency of a received signal , with respect to that of the transmitted signal, when it is bounced off of a moving object.– Doppler frequency shift

cuff o

dθcos2

=

Speed of sound in blood(~1500 m/s)

Angle between UT beamand flow of blood

Speed of blood flow(~150 cm/s)

Source signal frequency


Doppler Flowmeters

cufF s )cos(cos φθ +±=Δ


Problems Associated withDoppler Flowmeters

• There are two major issues with Doppler flowmeters– Unlike what the equations may suggest, obtaining direction

information is not easy due to very small changes in frequency shift that when not in baseband, removing the carrier signal without affecting the shift frequency becomes very difficult

– Also unlike what the equation may suggest, the Doppler shift is not a single frequency, but rather a band of frequencies because

• Not all cells are moving at the same velocity (velocity profile is not uniform)

• A cell remains within the UT beam for a very short period of time; the obtained signal needs to be gated, creating side lobes in the frequency shift

• Acoustic energy traveling within the beam, but at an angle from the bam axis create an effective ∆θ, causing variations in Doppler shift

• Tumbling and collision of cells cause various Doppler shifts


Directional Doppler• Directional Doppler borrows the quadrature phase detector

technique from radar in determining the speed and direction of an aircraft.

• Two carrier signals at 90º phase shift are used instead of a single carrier. The +/- phase difference between these carriers after the signal is bounced off of the blood cells indicate the direction, whereas the change in frequency indicate the flowrate


Figure 8.10 Doppler ultrasonic blood flowmeter. In the simplest instrument, ultrasound is beamed through the vessel walls, back-scattered by the red blood cells, and

received by a piezoelectric crystal.

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Directional Doppler

(a) Quadrature-phase detector. Sine and cosine signals at the carrier frequency are summed with the RF output before detection. The output C from the cosine channel then leads (or lags) the output S from the sine channel if the flow is away from (or toward) the transducer. (b) Logic circuits route one-shot pulses through the top (or bottom) AND gate when the flow is away from (or toward) the transducer. The differential amplifier provides bi-directional output pulses that are then filtered.

Plethysmographyin

Blood Flow Measurements


Plethysmography (1)Strain Gage Method

Plethysmography means the methods for recording volume changes of an organ or a body part (e.g. a leg)

Strain gage is made of silicone rubbertubes, which are filled with conductiveliquid (e.g. mercury) whose impedancechanges with volume.

Venous occlusion cuff is inflated to 40 – 50 mmHg. In this way there will bethe arterial inflow into the limb but no venous outflow.

If only a segment of limb is measured, there is a need for arterial occlusioncuff also. ARL - EL4703 - Isntrumentasi Biomedis 58

Plethysmography (2)Chamber Method

Chamber plethysmograph is the only accurate non-invasive way to measure changes in the blood volume

As the volume of the leg increases, the legsqueezes some kind of bladder and decreasesits volume

Volume transducer can be e.g. water filled tube(level) or air (pressure)

The speed of the return of the venous blood is measured


Plethysmography (3)Electric-Impedance Method

Different tissues in a body have a different resistivity. Blood is one of the bestconductors in a body ( = 1,5 Ωm)ρ

A constant current is applied via skin electrodes

The change in the impedance is measured

The accuracy is often poor or unknown

I = 0,5 – 4 mA rms (SNR)f = 50 – 100 kHz (Zskin-electrode+shock)

ZZLVol Δ=Δ 2

0

2

ρ


Plethysmography (4)Photoelectric Method

A beam of IR-light is directed to the part of the tissue which is to bemeasured for blood flow (e.g. a fingeror ear lobe)

The light that is transmitted / reflected is collected with a photodetector

The blood flow modulates the attenuated/ reflected light which is recorded.

Poor measure for changes in volumeVery sensitive to motion artefacts

Method is simpleHeart rate is clearly seen

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Other Methodsin

Blood Flow Measurements


RadioisotopesA rapidly diffusing, inert radioisotope of lipid-soluble gas ( Xe or Kr) is injected into the tissue or passively diffused

133 85

The elimination of the radioisotope from microcirculatory bed is related to the blood flow:

( )ktCtC −= exp)( 0

2/1/2ln tk =


Thermal Convection ProbeThe rate of heat removal from the tissue under probe is measured

The concentric rings areisolated thermally & electricallyfrom each other

The central disk is heated1 – 2 C over the temperatureof tissue

A temperature difference of 2- 3 C is established betweenthe disks

o

o

The method is not very common due extreme nonlinear properties and difficultiesin practical use (e.g. variable thermal characteristics of skin)

This is one of the earliest techniques for blood flow measurements


Summary (1)BLOOD PRESSURE

Describes the physiology and pathology of cardiocvascular system

”Normal” values are 120 / 80 mmHgHigh values may lead to heart attack and strokes

Low values may lead to low oxygen perfusion

All direct methods require skin punctuation and a useof catheter. Methods are used only when continuous and

accurate measurements are needed.

Almost all indirect methods rely on an occlusivecuff which is placed on the bracial artery. The actual

measurement is done when the cuff is deflated


Summary (2)BLOOD FLOW

Used for understanding physiological processes (e.g. medicinedissolution). Also used for locating clots in arteries

Usually more invasive methods are used than with bloodpressure measurements

Normal velocity is 0,5 - 1 m/s

Indirect measurements are done by using ultrasound orplethysmographic method

Direct measurements are done by dilution methods (dye / thermal)

anatomy of the heart blood pressure, blood flow and … pressure, blood flow ... • similar to...

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