DEPARTMENT OF ENGINEERING SCIENCE INSTITUTE OF BIOMEDICAL ENGINEERING Marco F Pimentel, Graduate Student, Centre for Doctoral Training in Healthcare Innovation, Institute of Biomedical Engineering, University of Oxford [email protected]. ac.uk Monitoring Blood Pressure Biomedical Signal Processing June 23, 2022
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DEPARTMENT OF ENGINEERING SCIENCE INSTITUTE OF BIOMEDICAL ENGINEERING Marco F Pimentel, Graduate Student, Centre for Doctoral Training in Healthcare Innovation,
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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
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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