blood-pressure work-sheet part 1 & 2

Blood Pressure Monitor

By:

Keivan Mojtahedi

Mentor:

Dr. Vincent Pizziconi

Outline:

Pressure Pressure measurement techniques

(specifically in liquids) Blood pressure (BP) measurement methods History of BP measurement Automatic BP measurement techniques Wrist-type fully automatic electronic blood

pressure monitor (reverse engineering) Analysis of device Modeling Clinical needs assessment

BME 182: Biomedical Product Design & Development I

Spring 2014

After accomplishing this worksheet, we expect you to:

Understand the concept of pressure and know how to propose its physical modeling.

Learn various pressure measurement techniques and evolutionary history of blood pressure.

Acquire experience on how to analyze and be able to reverse engineerthe blood pressure device.

Explore what are the clinical needs and challenges in blood pressure.

Propose a reasonable solution for the unmet needs.

Group Number: ________________ Group Names: _________________________________________________________

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Engineering Design in Reverse Blood Pressure Monitor

I. Prologue (Est. time 20-30 minutes with presentation) A. Pressure:

Pressure is force per unit area applied in a direction perpendicular surface of an object.

B. Pressure Units:

The SI unit for pressure is the Pascal (Pa), equal to one Newton per square meter (N/m2 or kg·m−1·s−2). Other common pressure units are PSI (pound per square inch), bars, atmosphere, etc. Pressure might be measured by its ability to displace a column of liquid in a manometer, so pressures are often expressed as a depth of a particular fluid (e.g., centimeters or mm of Hg).

C. How can we measure the pressure?

Many techniques have been developed for the measurement of pressure.

1. Position: The most common method is mapping pressure to position. Manometer is placed in this category. The manometer maps the unknown pressure of desire liquid to a height level of another liquid which is known for us. A displacement of a diaphragm can also measure the pressure (e.g. pressure gauges). Other techniques can also detect the displacement due to the applied pressure and change it to pressure like magnetic methods, encoder, etc.

2. Strain: These methods are measuring the strain due to applied pressure. Depends on the applied pressure, the strain can be varied. Therefore, the applied pressure could be calculated by detecting strain. Piezoelectric, Piezoresistive Strain Gage, Potentiometric, Capacitive and optical are in this category.

Note 1: The value of pressure must have a reference point because pressure is a relative quantity. Therefore, the zero reference of the pressure sensor can be anything. The pressure sensor can show the absolute pressure (with atmospheric pressure) or gauge pressure (without atmospheric pressure). Or, it could be differential pressure which shows the difference in pressure between two points.

Note 2: Generally, the term transducer is defined as a device that converts one form of energy to another. A sensor converts a physical measurand to an electric output. The sensor should respond only to the form of energy present in the measurand, to the exclusion of all others. The sensor should interface with the living system in a way that minimizes the energy extracted, while being minimally invasive. Many sensors have a primary sensing element such as a diaphragm, which converts pressure to displacement. A variable conversion element, such as a strain gage, then converts displacement to an electric voltage.


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D. What are the methods of pressure measurements in liquids?

By using this fact “liquid pressure is exerted equally in all directions.” and any above methods we can measure the liquid pressure. The liquid pressure depends on density of liquid, gravity and height or depth of liquid which can be formulated as P=ρgh, respectively.

Fact: The pressure of fluid (liquid) at a point is the same in all directions only in the absence of flow.

When the liquid can only move through pipeline (closed system), it creates two pressure components: static (when the liquid is not moving) and dynamic (when the liquid can move in the pipeline). The pressure at any point in a fluid can be calculated by Bernoulli equations in a closed system (See the presentation file.).

II. Introduction (Est. time 20 minutes)

E. How can we measure the blood pressure?

The measurement of blood pressure was first reported by Stephen Hales, who in 1773 measured mean arterial pressure by inserting an open-ended tube in the artery of the neck of an un-anaesthetized horse. The measurement was made by noting the height to which blood rose in the tube relative to the point of insertion. Many techniques have been developed since, including direct methods which provide instantaneous data, indirect methods which provide information on the time-dependent features of the arterial pressure pulse, and microscopic methods that measure directly and indirectly the pressure in vessels as small as the mammalian capillaries.

A practical example: As we mentioned above, the pressure of a fluid at a point is the same in all directions only in the absence of flow. When the fluid is in motion, the pressure measured by a transducer includes a factor determined by the kinetic energy of the fluid and the orientation of the sensing element relative to the direction of the flow at the point of measurement. This factor is significant when pressure is transmitted to a transducer through a catheter, where the open tip is in the moving fluid. The pressure correction necessary in the presence of relative motion between fluid and sensor is given by Bernoulli’s equation as ΔP=ρv2/2 where ρ is the density of the fluid (kg/m3) and v (m/s) is the relative velocity between fluid and sensor perpendicular to the sensing surface.

Arterial blood pressure waveforms are periodic, where the maximum pressure in a cycle is called the systolic pressure and the minimum is the diastolic pressure. The mean pressure is the time-weighted average over one cardiac cycle. The range of amplitude of blood pressure in humans is variable; instrumentation that accurately measures pressure in the range of 0 to 300 mmHg is considered adequate for most applications. The fundamental frequency in humans is in the range of 50 to 120 beats per minute.


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F. Blood Pressure measurement: Direct and Indirect

Direct: The determination of blood pressure where the sensors come in direct contact with the blood, or where the fluid in the region of interest is coupled hydraulically to the pressure sensor, is termed a direct measurement. This includes contacting blood by inserting a cannula, catheter, needle, or pressure transducer into the blood vessels or heart.

Q.1: Why do we need direct measurement of blood pressure? Answer this question by giving a several medical reasons. (10 points, Est. time 15 minutes)

Indirect: Noninvasive pressure measurements in humans were first developed by Korotkoff in 1905, who described the method of sphygmomanometry, which consists in balancing the pressure in an air-filled cuff against the blood pressure of the vessels. In a routine measurement the cuff is wrapped around an arm, over the brachial artery, and is inflated to a pressure that exceeds systolic blood pressure, thus collapsing the artery and stopping blood flow. Air is then slowly released, until arterial pressure exceeds cuff pressure and a sound related to the reestablishment of blood flow (Korotkoff sound) is heard by means of a stethoscope. It is assumed that the cuff pressure at which blood flow just begins is systolic pressure and that at which it becomes continuous is diastolic pressure.

III. Methods (Est. time 40 minutes)

Automatic blood pressure mechanisms are divided to two categories:

G. Auscultatory

Q.2: Explain this method in 1-2 paragraphs (less than 500 words). (7.5 points, Est. time 10 minutes)

H. Oscillometric

Q.3: Explain this method in 1-2 paragraphs (less than 500 words). (7.5 points, Est. time 15 minutes)


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I. Ambulatory Blood Pressure Monitoring

Ambulatory blood pressure monitors measure patient blood pressure over a predetermined length of time (typically 24 hours) outside the clinic as the patients follow their normal daily routine.

Briefly described, the procedure is as follows: the patient receives instruction on the correct use of the monitor, and wears the device. Then, the patient leaves the clinic and follows a normal daily routine. Periodically, the monitor takes a measurement and stores the results. When the monitoring period is over, the patient returns to the clinic. The clinician downloads the data from the monitor to a computer for analysis. The clinician normally has between 70 and 100 blood pressure measurements available for analysis.

Q.4: What is the purpose of ambulatory blood pressure monitoring (ABPM)? Why and when do we need to perform the ABPM for the patient? Explain “white coat hypertension” and “circadian rhythm of blood pressure”. (10 points, Est. time 15 minutes)

Clinical research in the field of ABPM has led to the application of additional analysis techniques that may allow the clinician to obtain a clearer assessment of a patient's hypertensive condition.

ABPM may be cost effective by reducing the number of patients who are mislabeled as hypertensive and subsequently undergo hypertension management therapy. One twenty-four hour ABPM session using Pulse Dynamic technology may provide reliable information regarding blood pressure, arterial compliance, left ventricular contractility, and dipper/non-dipper classification. This decreases the need for exhaustive testing and allows quicker, easier diagnosis and treatment program development.


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IV. History (Est. time 35 minutes)

J. A short history of blood pressure measurement

It is Galen in ancient Greece who first proposed the existence of a circulatory system in the human body. However, building on ideas conceived by Hippocrates and because the arteries stopped bleeding when death occurred, Galen believed that this circulatory system was composed of an interconnected set of arteries filled with “pneuma” (life giving force) or air. He maintained that the human body was comprised of three systems. Nerves and the brain were responsible for sensation and thought, the heart filled the body with life-giving energy (pneuma) and the liver provided the body with nourishment and growth. Galen believed that the heart was like a fountain, constantly giving the needed pneuma and blood to the system.

In 1616 William Harvey announced that Galen was wrong in his assertion that the heart constantly produced blood, like a fountain. Harvey proposed that there was a finite amount of blood that circulated the body in one direction only. Harvey's views were initially met with a lot of skepticism and resistance. The idea that blood was not constantly produced in the body raised doubts about the benefit of bloodletting, a popular medical practice at the time. As a matter of routine, bloodletting was used as a universal panacea for just about every symptom known to man.

The first recorded instance of the measurement of blood pressure was in 1711 by the Reverend Stephen Hales. Hales inserted a glass tube into an artery of a horse and observed the rise and fall of blood in the tube and concluded that this must be due to fluctuating pressure in the arteries of the horse. However, Hales’ technique was not suitable for testing with humans, as it was very invasive and highly inappropriate for clinical use. The horse died every time...

K. Human blood pressure measurement

In 1856 Faivre recorded human blood pressure for the first time during a limb amputation. Faivre used Carl Ludwig's recently invented kymograph with catheters inserted directly into an artery. Ludwig's kymograph consisted of a U-shaped manometer tube connected to a brass pipe canula plugged directly into the artery. The manometer tube had an ivory float onto which a rod with a quill was attached. This quill would sketch onto a rotating drum hence the name “kymograph” (wave writer in Greek).

Q.5: Look for Carl Ludwig's kymograph. How did Faivre use this device in blood pressure measuring? Explain his set-up. (10 points, Est. time 15 minutes)

However, at this time, blood pressure could still only be measured by invasive means. The race was now on to find a suitable way to measure blood pressure non-invasively.

In 1855, Karl Vierordt discovered that with enough pressure the arterial pulse could be obliterated. Vierordt introduced the sphygmograph, based on this principle of obliteration. Vierordt used an inflatable cuff around the arm to constrict the artery. However, Vierordt’s device was huge and unwieldy (168 cm tall) and produced very uneven results.

Etienne Jules Mary, a French physician (also a cinematographer who is considered to be the father of modern photography) developed this idea further in 1860. His sphygmograph could accurately measure the pulse rate, but was very unreliable in determining the blood pressure. Yet this design was the first that could be used clinically was some degree of success. In 1882, Robert Ellis Dudgeon simplified and refined the Marey sphygmograph, rendering it eminently portable and easy to use. At the time, Dudgeon's device was so successful that it became standard equipment for the U. S. Navy.


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In 1881, Samuel Siegfried Karl Ritter von Basch invented the sphygmomanometer. His device consisted of a water or mercury-filled rubber ball connected to a manometer. The rubber ball was then pressed against the radial artery until the pulse was obliterated and the blood pressure was then estimated using the manometer and palpation was used to determine when the arterial pulse disappeared.

However von Basch's design never had the success it deserved, many physicians of the time being skeptical of this new technology, claiming that it sought to replace traditional ideas of diagnosis based on palpation. The real problem was however that most doctors questioned the medical usefulness of blood pressure. This did not stop some from attempting to produce a more useful device, such as the sphygmometer by Bloch, which was essentially a spring-loaded tire-gage that was applied to an artery to see how much pressure was necessary to obliterate the pulse.

In 1889, Potain improved all of the compression devices available by replacing water and mercury in the devices with air, thus substantially improving their accuracy. From this moment on, air became the compression medium of choice.

1896 was a decisive year in the history of blood pressure. Scipione Riva-Rocci developed his first mercury sphygmomanometer. This design was the forerunner of the modern mercury sphygmomanometer.

Q.6: Look for Scipione Riva-Rocci’s set-up. Explain his set-up. (10 points, Est. time 15 minutes)

An inflatable cuff was placed over the upper arm to constrict the brachial artery. This cuff was connected to a glass manometer filled with mercury to measure the pressure exerted onto the arm.

Riva-Rocci's sphygmomanometer was then spotted by the American neurosurgeon Harvey Cushing while he was traveling through Italy. Seeing the potential benefit of this device, he returned to the US with the design in 1901. After the design was modified to be more adapted for clinical use, the sphygmomanometer became commonplace. This year really marks the beginning of modern sphygmomanometry.

However, it is useful to remember that this sphygmomanometer was then only used to determine the systolic blood pressure. The importance of the diastolic pressure had not yet been clearly defined at this time. In 1905, a young Russian surgeon, Nikolai Korotkoff, observed the sounds made by the constriction of the artery, using a stethoscope. Korotkoff found that there were characteristic sounds at certain points in the inflation and deflation of the cuff. These Korotkoff sounds were caused by the passage of blood through the artery, corresponding to the systolic and diastolic blood pressures. The technique that we still use today to measure systolic and diastolic blood pressure was born.

Q.7: Korotkoff actually described five types of sounds. What are the five Korotkoff sounds? (5 points, Est. time 5 minutes)

A crucial difference in Korotkoff's technique was the use of a stethoscope to listen for the sounds of blood flowing through the artery. This auscultatory method proved to be more reliable than the previous palpation techniques and thus became the standard practice.

Modern developments have led to more accurate auscultatory sphygmomanometers, and newer oscillometric models.

In 1974, Panasonic released the first digital oscillometric device. These sphygmomanometers measure the pressure imparted onto the cuff by the blood pushing through the constricted artery over a range of cuff pressures. This data is used to estimate the systolic and diastolic blood pressures.


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V. Electronic Blood Pressure Monitoring Device (Est. time 10 minutes)

Receive and use the electronic blood pressure monitoring device, measure blood pressure for each person in your group and recordings. Answer these questions:

Q.8: What systolic and diastolic blood pressures did you record within your group? What are the average and standard deviation of systolic and diastolic blood pressures for your group? (5 points, Est. time 10 minutes) Q.9: If you are walking (standing, sitting or talking), will it change your recorded numbers? Explain your finding. What is the best position to measure BP in this device? Why? (5 points, Est. time 5 minutes)

Session one ends here. Submit your first product-sheet in the blackboard.

If you have time, you can continue and answer Q.10 in the product-sheet part 2. Do not answer Q.10-18 in the product-sheet part 1.


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VI. Engineering Design in Reverse (Est. time 50 minutes) Use tools to open the case of blood pressure device. See the main internal and external components of the device. Then, do the engineering design in reverse and answer the following questions: Q.10: Which mechanism is used in this device? Auscultatory or Oscillometric? Why? How can you support your answers based on the components of device? (10 points, Est. time 5 minutes) Q.11: Which technique used in this device for measuring the pressure? Position or Strain? Why? How can you support your answers based on the components of device? (10 points, Est. time 5 minutes) Q.12: What is the reference point for this blood pressure? Is it absolute pressure, gauge pressure or differential pressure? Why? How can you support your answers based on the components of device? (10 points, Est. time 5 minutes) Q.13: Sketch the MAIN internal and external components of the device based on your answers in Q.10-12. Be sure your sketch includes “pressure measurement system” and “cuff control system”. Your drawing should include: (20 points, Est. time 15 minutes) • Label for all components in your sketch (or diagram) • Brief description of each component’s function(s) ** Instead of drawing, you might want to take a photo and attach it in your product-sheet. Your components must be clear in the photo/drawing. Q.14: Can temperature of the environment or the patient affect on your measurement? Why? How can you support your answers based on the components of device? (5 points, Est. time 10 minutes) Q.15: How can device monitor the heart rate? How can you support your answers based on the components of device? (5 points, Est. time 5 minutes)

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10

IX. Clinical Needs Assessment (Est. time 60 minutes)

Q.18: For this step, you should come up with your clinical needs which your group already identified (e.g. hypertension and/or obesity, or anything else which you think it could be considered as an unmet need.). Your clinical need should cover different issues (e.g.: blood Pressure measurement technologies, the importance of accurate blood pressure measurement, home blood pressure monitoring application- in clinical practice, blood pressure measurement in obese patients, hypertension and obesity, low-cost device, wireless communication, cuff sizes, etc.).

* Several files were attached in the content. You can use them for your initial steps. (30 points, Est. time 60 minutes)

For performing this section, the following steps must be followed:

1. Understand the need: What is the problem? What do we want to accomplish? What are the project requirements? What are the limitations? Who is the customer? What is our goal? Gather information and conduct research - talking to people from many different backgrounds.

2. Brainstorm different designs: Imagine and brainstorm ideas. Be creative; build upon the wild and crazy ideas of others. Investigate existing technologies and methods to use. Explore, compare and analyze many possible solutions.

3. Select a design: Based on the needs identified, select the most promising idea.

4. Plan: Draw a diagram of your idea. How will it work? What environmental and cultural considerations will you evaluate? What materials and tools are needed? What analyses must you do? How will you test it to make sure it works?

5. Create: Assign team tasks. Build a prototype and test it against your design objectives. Push yourself for creativity, imagination and excellence in design. Does it work? Analyze and talk about what works, what doesn't and what could be improved.

6. Improve: Discuss how you could improve your product. Make revisions. Draw new designs. Iterate your design to make your product the best it can be.

X. Product Design and Development (Extra Credit)

Propose your design and development based on your identified clinical need. Then, model it.

• You might propose to change a material component or shape, sketch your idea using Solidworks and post the .stl file for review and 3D printing. Please attach a jpeg file for your design from the best angle of your design.

• You might propose to change an electrical component, state your method and model it in MATLAB and post the required files.

• Elevator pitch: You might work on your clinical needs assessment in depth.

Session two ends here. Submit your second product-sheet in the blackboard.

blood-pressure work-sheet part 1 & 2

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