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 Monitoring Blood Pressure Biomedical Signal Processing August 3, 2015

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 2 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

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 3 The first to measure BP  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!!!

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 4 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

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 5 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!

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 6 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 which is filled with air, and a squeeze bag to inflate the rubber sleeve I had an idea!

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 7 Nowadays BP monitors

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 8 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)

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 9 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!

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 10 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

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 11 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.

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 12 Hypertension Know your numbers:

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 13 Hypertension Hypertension depends on several factors: HYPERTENSION Stress Diabetes Tobacco Age Gender Ethnicity Obesity Activity Diet

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 14 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

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 15 How to measure?  Non-invasive blood pressure  Auscultation  Oscillometry Mercury sphygmomanometer + stethoscope Mechanical manometer + stethoscope

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 16 How to measure?

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 17 The auscultation method

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 18 The auscultation method

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 19 The auscultation method Systolic BP Diastolic BP

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 20 The oscillometric method

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 21 The oscillometric method  It is based on the change of the magnitude of oscillation  MAP – Mean Arterial Pressure

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 22 The oscillometric method  It is based on the change of the magnitude of oscillation  MAP – Mean Arterial Pressure

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 22 How often should we measure? Lets first consider an example… MATLAB Demo

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 22 How often should we measure? Why is this important for blood pressure monitoring? How much does your blood pressure vary in one day?

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 22 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

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 22 How often should we measure? Treat Do not treat 8am DBP 4am 2pm 4am Treatment threshold SBP time 24hr mean BP 10pm

M F Pimentel Under-sampling August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 22 How often should we measure? Treat Do not treat 8am 4am 2pm 10pm 4am time Treatment threshold 24hr mean BP

M F Pimentel Aliasing effect August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 22 How often should we measure? Treat Do not treat 8am 4am 2pm 10pm 4am BP time Treatment threshold

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 22 Under-sampling and aliasing

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 22 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

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 22 New resources

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 22 Low-cost BP monitor

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 22 Low-cost BP monitor

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 22 Awards

M F Pimentel August 3, 2015 Blood Pressure - Biomedical Signal Processing Page 22 Break!