BMTS 353 1

Chapter 5

Part Two

Blood Pressure and flowby Ibrhim AlMohimeed

12/3/2013

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Blood Pressure

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• Originates from the left ventricle of the heart.

• One of the oldest physiological measurements.

• Observation of blood pressure allows dynamic tracking

of pathology and physiology affecting to the

cardiovascular system.

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Blood Pressure Reading

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• Systolic: the top number, which is also the

higher of the two numbers, measures the pressure

in the arteries when the heart beats (when the

heart muscle contracts).

• Diastolic: the bottom number, which is also the

lower of the two numbers, measures the pressure

in the arteries between heartbeats (when the left

ventricle muscle is resting between beats and

refilling with blood).

Read as "117 over 76 millimeters of

mercury"

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Blood Pressure Reading

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Blood PressureCategory

Systolicmm Hg (upper #) Diastolic

mm Hg (lower #)

Normal less than 120 and less than 80

Prehypertension 120 – 139 or 80 – 89

High Blood Pressure

(Hypertension) Stage 1

140 – 159 or 90 – 99

High Blood Pressure

(Hypertension) Stage 2

160 or higher or 100 or higher

Hypertensive Crisis(Emergency care

needed)Higher than 180 or Higher than 110

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Blood Pressure Reading

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• Mean arterial pressure (MAP) is a term used in

medicine to describe an average blood pressure in an

individual.

• It is defined as the average arterial pressure during a

single cardiac cycle and given by:

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Blood Pressure Risks

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• High blood pressure (hypertension) increases the risk of: Chest pain (angina).

Heart attack.

Heart failure.

Kidney failure.

Stroke.

Blocked arteries in the legs or arms (peripheral arterial disease.

Eye damage .

Aneurysms (permanent cardiac or arterial dilatation).

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Cont. Blood Pressure Risks

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Cont. Blood Pressure Risks

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• Low blood pressure (hypotension) increases the risk of: Reduces the blood flow to the brain and other vital organs.

Dizziness or fainting.

Lack of concentration.

Blurred vision.

Fatigue.

Cold and clammy skin.

Rapid shallow breathing.

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Blood Pressure Value

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Generally, the blood pressure value

depends on two main factors:

1) Cardiac output (Blood Volume): The

more blood present in the body, the

higher the rate of blood return to the

heart and the resulting cardiac output,

potentially resulting in higher arterial

pressure.

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Cont. Blood Pressure Value

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2) Resestance of blood flow: The higher the resistance, the

higher the arterial pressure. Resistance is related to

vessel radius, blood viscosity, and the smoothness of

the blood vessel walls.

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Invasive & Non-invasive

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• In general, there are two main categories which describe

the invasiveness of a medical measurement:

Invasive: requiring the entry of a needle, catheter, or other

instrument into a part of the body.

Non-invasive: not requiring entering or penetrating the

body or disturbing body tissue.

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Blood Pressure Measurement

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Inva

sive

No

n-I

nva

sive

Blood Pressure

Palpatory Method(Riva-Rocci Method)

Auscultatory Method

Ultrasonic Method

Oscillometric Method

Extravascular Sensor

Intravascular Sensor

Automatic Method

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Blood Pressure Measurement

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Blood Pressure

Non-invasive (Indirect) Method of Blood Measurement

1

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Measurement Site

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Blood Pressure

• Brachial artery is the most common

measurement site:

Close to heart

Convenient for measuring

• Other sites are radial artery and wrist.

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Palpatory Method

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Blood Pressure

• aka Riva-Rocci Method.

1) When the cuff pressure

is higher than SBP,

artery is closed, no

pulse can be sensed.

2) When the cuff

pressure drops below

SBP, blood can pass

through the artery and

the pulse will be felt.

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Cont. Palpatory Method

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Blood Pressure

3) The pulse will continue to be felt

as the pressure in the cuff falls

down to zero.

4) The pressure indicated on the

gauge when the pulse reappears is

noted. This is the systolic

pressure.

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Cont. Palpatory Method

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Blood Pressure• The blood pressure can be measured in noisy

environment.

• It is a simple technique.

• Only the systolic blood pressure (SBP) can be measured

(not DBP).

• The technique does not give accurate results for infants

and hypotensive patients.

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Auscultatory Method

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Blood Pressure

• Auscultation: the act of listening, either directly or

through a stethoscope or other instrument, to sounds

within the body.

• This method is based on the fact that pulse waves when

first propagate through the brachial artery, generate

Korotkoff sounds.

• Video

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Korotkoff sounds

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Blood Pressure• If a stethoscope is placed over the brachial artery in a normal

person (without arterial disease), no sound should be audible.

• As the heart beats, these pulses are transmitted smoothly via

laminar (non-turbulent) blood flow throughout the arteries, and no

sound is produced.

• Similarly, if the cuff of a sphygmomanometer is placed around a

patient's upper arm and inflated to a pressure above the patient's

systolic blood pressure, there will be no sound audible because the

pressure in the cuff is high enough such that it completely blocks

the blood flow.

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Cont. Korotkoff sounds

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Blood Pressure• If the pressure is dropped to a level equal to that of the patient's

systolic blood pressure, the first Korotkoff sound will be heard.

• As the pressure in the artery rises above the pressure in the cuff and

then drops back down (because of beating), resulting in turbulence

that produces an audible sound.

• As the pressure in the cuff is allowed to fall further, thumping

sounds continue to be heard as long as the pressure in the cuff is

between the systolic and diastolic pressures, as the arterial pressure

keeps on rising above and dropping back below the pressure in the

cuff.

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Cont. Korotkoff sounds

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Blood Pressure• Eventually, as the pressure in the cuff drops further, the sounds

change in quality, then become muted, and finally disappear

altogether.

• This occurs because, as the pressure in the cuff drops below the

diastolic blood pressure, the cuff no longer provides any restriction

to blood flow allowing the blood flow to become smooth again

with no turbulence and thus produce no further audible sound.

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Auscultatory Method Procedure

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Blood Pressure

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Auscultatory Method Procedure

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Blood Pressure1) The cuff pressure is inflated quickly to a

pressure higher than the systolic pressure.

Then the air is let out of the cuff at a small

rate.

2) When the cuff pressure equal to that of the

patient's systolic blood, a korotkoff sound

will be heard with each heartbeat. This point

marks the systolic pressure.

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Auscultatory Method Procedure

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Blood Pressure

1) As the pressure is lowered further, the

character of the Korotkoff sounds change.

At some point, the sounds will disappear.

The pressure reading at this point gives the

diastolic pressure.

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Using Auscultatory Method

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Blood Pressure

• Auscultatory technique is considerd simple.

• It may be difficult to be done in a noisy environment.

• The effect of human error is large.

• It could be difficult to be used with infant.

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Oscillometric Method

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Blood Pressure• the observation of oscillations of blood flow during the

pulsation.

• It uses a sphygmomanometer cuff, like the auscultatory

method, but with pressure sensor (transducer) to observe cuff

pressure oscillations

• The pressure sensor (within the inflated cuff) detects the

pulsation of the artery wall as a pressure vibration. The

interpretation of these small vibrations amplitude provide the

blood pressure value.

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Cont. Oscillometric Method

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Blood Pressure

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Cont. Oscillometric Method

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Blood Pressure

• In the recent years, oscillometric methods have become

popular for their simplicity of use and reliability.

• It can be used with case of hypotension and infant.

• It use algorithms that may leads to large variance in

blood pressures measurement.

• Motion artifact is considered a major drawback of this

method.

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Automatic Method

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Blood Pressure• Many limitations of manual intermittent blood pressure

measurement have been overcome by automated non-

invasive blood pressure (NIBP) devices.

• There are now used widely in medical care.

• NIBP devices provide consistent, reliable values for

systolic, diastolic, and mean arterial pressure (MAP).

• Automated NIBP devices provide alarm systems to draw

attention to extreme blood pressure value.

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Cont. Automatic Method

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Blood Pressure• The greatest advantage of automated NIBP devices

compared with manual methods of blood pressure

measurement is that they don’t require an operator to

perform the measurement.

• It can easily provide a repetitive blood pressure

measurements.

• Most automated NIBP devices are based on the

oscillometry method.

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The Device Diagram

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Blood Pressure

Pressure sensor

Pressure sensor

Air pumpAir

pumpBleed valveBleed valve

Micro-processo

r

Micro-processo

r

Display

Display

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Automatic Method Errors

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Blood Pressure• Sources of error for the automatic method:

I. Cuff size: Oscillations are direct result of BP cuff application

- Cuff too small = overestimation of BP

- Cuff too large = underestimation of BP

II. Cuff position: Bladder needs to be placed over brachial

artery.

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Cont. Automatic Method Errors

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Blood PressureIII. Movement:

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Cont. Automatic Method Errors

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Blood PressureIII. Beat to beat variation: Oscillometric method requires

reasonably stable BP during cuff deflation. If BP varies due to

arrhythmia, difficult to estimate BP accurately.

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Ultrasonic Method

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Blood Pressure

• The ultrasonic Doppler technique is applied by this

method.

• The motion of blood-vessel walls of occlusion (opining

and closing) is measured by Doppler technique.

• The vessel opens and closes with each heartbeat when

DP < Pcuff < SP

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Doppler Effect

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Blood Pressure

• It is the change in frequency of the returned sound wave

(echo) from a moving object.

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Cont. Doppler Effect

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Blood Pressure

• Video

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Principle of Ultrasonic Method

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Blood Pressure

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Cont. Ultrasonic Method

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Blood Pressure

• Can be also used in noisy environment.• The device is considiered contatin compicated part.• Highly affect by motion.

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Blood Pressure Measurement

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Blood Pressure

Invasive (direct) Method of Blood Measurement

2

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The first invasive bloodpressure measurement

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Blood Pressure

• The first invasive attempt to measure blood

pressure was made by Stephen Hales in

1733.

• He inserted tubes directly into the arteries

of animals.

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Invasive Method

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Blood Pressure

• This technique involves direct measurement of arterial

pressure by inserting a catheter (thin, hollow, and

flexible tube).

• Invasive (intra-arterial) blood

pressure (IBP) monitoring is a

commonly used technique in

the Intensive Care Unit (ICU)

and in the operating theatre.

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Con.t Invasive Method

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Blood Pressure

• IBP technique also allows accurate blood pressure

readings specially the very low pressures, for example

in shocked patients.

• it allows continuous ‘beat-to-beat’ blood pressure

monitoring.

• It complex procedure involving many risks.

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Invasive Method Types

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Blood Pressure

• Generally, the Invasive technique can be divided into

two division:

Extravascular Sensor System

Intravascular Sensor System

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Extravascular Sensor System

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Blood Pressure• The sensor is located behind the catheter and the vascular

pressure is transmitted by hydraulic connection.

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Cont. Extravascular Sensor System

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Blood Pressure

• The actual pressure sensor can be:

strain gage

variable inductance

variable capacitance

optoelectronic

piezoelectric

etc…

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Intravascular Sensor System

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Blood Pressure

• The sensor is located in the tip of the catheter (inside the

body).

• The sensor connected by an electrical or optical

connection.

• The frequency response is not limited by the hydraulic

properties of the system. No time delay.

• Breaks easily.

• More expensive.

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End of the Chapter

12/3/2013