DEPARTMENT OF ENGINEERING SCIENCE INSTITUTE OF BIOMEDICAL ENGINEERING Marco F Pimentel, Graduate Student, Centre for Doctoral Training in Healthcare Innovation,

DEPARTMENT OF ENGINEERING SCIENCEINSTITUTE OF BIOMEDICAL ENGINEERING

Marco F Pimentel,Graduate Student,Centre for Doctoral Training in Healthcare Innovation,Institute of Biomedical Engineering,University of Oxford

marco.pimentel@eng.ox.ac.uk

Monitoring Blood PressureBiomedical Signal Processing

April 19, 2023

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Outline

Short history

Definition of Blood Pressure What is hypertension?

Various methods used for measurements of blood pressure

How often should we measure blood pressure? Sampling and Aliasing

New resources – An Oxford University Project

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The first to measure BP

1733 - Reverend Stephen Hales first to measure BP

Measured the height of a column of blood after cannulating the carotid artery in a horse with a brass pipe.

I’m that good!!!

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The first measurement of BP

The brass pipe was attached to a 12 inch glass tube

Tube was connected to the pipe via a trachea of a goose

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A second try…

100 years later: a mercury manometer connected to the artery was used to measure the BP

However:

Both of these methods are invasive

… And maybe… a bit uncomfortable for the patient!

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Eureka!

In late 1890s, an Italian physician – Scipione Riva Rocci invented the Sphygmomanometer

Shygmo (from the Greek) => pulse

Manometer => pressure meter

- Consisted of a mercury column Manometer, a rubber sleeve whichis filled with air, and a squeeze bagto inflate the rubber sleeve I had an

idea!

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Nowadays BP monitors

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What is Blood Pressure?

Blood Pressure is a measurement of the force against the walls of the arteries as the heart pumps blood throughout the body

Blood pressure is measured in mmHg (millimeters of mercury)

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What is Blood Pressure?

Blood Pressure is a measurement of the force against the walls of the arteries as the heart pumps blood throughout the body

Blood pressure is measured in mmHg (millimeters of mercury)

1,000 Pa is about 7 mmHg!

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What is Blood Pressure?

The blood pressure reading is taken in 2 numbers:systolic and diastolic.

Systolic

Diastolic

Measure of pressure as the heart is beating

Measure of pressure while

the heart is at rest between beating

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Hypertension

Blood pressure changes all the time: It decreases when we sleep, or when we are at rest It increases when we are active, excited, practicing sports,

stressed and nervous

Changing blood pressure is a vital part of a healthy cardiovascular system

Hypertension, or high blood pressure, happens when the blood pressure stays too high over an extended period of time:

Can cause the heart to have to work too hard and the force of the blood flow can damage your arteries, heart, kidneys, brain and eyes.

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Hypertension

Know your numbers:

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Hypertension

Hypertension depends on several factors:

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How to measure?

Invasive blood pressure (IBP):

It measures the BP internally by using a sensitive IV catheter inserted into an superficial artery. This is the procedure taken where continuous BP monitoring is required.

Non-invasive blood pressure (NIBP):

Auscultation

Oscillometry

Doppler (determines the flow distal to the artery)

Arterial tonometry, Arterial volume clamp are other types of NIBP measure

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How to measure?

Non-invasive blood pressure

Auscultation

Oscillometry

Mercury sphygmomanometer+ stethoscope

Mechanical manometer + stethoscope

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How to measure?

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The auscultation method

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The auscultation method

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The auscultation method

Systolic BP

Diastolic BP

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The oscillometric method

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The oscillometric method

It is based on the change of the magnitude of oscillation

MAP – Mean Arterial Pressure

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The oscillometric method

It is based on the change of the magnitude of oscillation

MAP – Mean Arterial Pressure

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How often should we measure?

Lets first consider an example…

MATLAB Demo

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How often should we measure?

Why is this important for blood pressure monitoring?

How much does your blood pressure vary in one day?

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How often should we measure?

Why is this important for blood pressure monitoring?

How much does your blood pressure vary in one day?

Kotsis et al. Hypertension, 2005

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How often should we measure?

Treat

Do nottreat

8amDBP

4am2pm 4am

Treatment threshold

SBP

time

24hr mean

BP

10pm

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Under-sampling

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How often should we measure?

Treat

Do nottreat

8am4am2pm

10pm 4amtime

++

+

Treatment threshold24hr mean

BP

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Aliasing effect

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How often should we measure?

Treat

Do nottreat

8am4am2pm

10pm 4am

BP

time

++

+

Treatment threshold

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Under-sampling and aliasing

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Sampling and Aliasing

Under-sampling looses (important) wave details!

It also may change the wave form/shape due to Aliasing

Sampling is a discrete observation or measurement, while Aliasing is an illusion, appearance of something that is not, due to shortcomings of sampling

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New resources

http://www.worldlifeexpectancy.com/cause-of-death/hypertension/by-country

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Low-cost BP monitor

http://code.google.com/p/ewh-bp-project/

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Low-cost BP monitor

http://code.google.com/p/ewh-bp-project/

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Awards

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Break!