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9.3 Medical Technology - Bionics 2. The heart
Extract from Senior Science Stage 6 Syllabus (Amended October 2002) © Board of Studies, NSW
[Edit: 10 Sept 08]
Prior learning: Preliminary modules 8.4 (subsections 1, and 6)
Science Stages 4-5 syllabus: Outcomes 4.8 (content 4.8.1a, b, c, d; 4.8.4 b, c, d and 4.8.5 a, b), Outcome 5.8 (content 5.8.1 a), Outcome 5.12 (content 5.12 d, f, g).
Background: The circulatory system is a vast transport system, through which red blood cells carry oxygen and nutrients to the cells of the body and remove carbon dioxide and other waste materials. The heart is the key to circulation. It pumps blood around the body and its health is critical to the overall wellbeing of a person.
gather, identify data sources, plan, choose equipment or resources, perform a first hand investigation and analyse information about changes in the heartbeat rate before and after physical activity
- Ask your teacher what equipment is available to measure heartbeat rates
and then plan your
investigation by considering issues such as the following:
- Data sources: The simple procedure of observing heart rates from a person's wrist pulse using two or three fingers can be used in the investigation.
- Equipment or resources: A person, even yourself, will be a "resource" for this investigation, and a wristwatch or stop watch can be used to measure time in the investigation.
- Experimental design: What exercise to do and for how long. Do you
take the readings while the exercise is being done or straight after exercise?
How long do you wait before taking the resting measurements? Make sure
conditions are the same for each set of measurements. What repetition is
needed? Will the same student do the activity three or four times or will
four or five different students do it? How to gather and record
your results: You could use a table to record results and a graph to see
a visual representation of the results.
- Perform the investigation, making sure you record the results carefully
and fully.
- Analyse the results of your investigation by considering if there is a definite pattern when considering different students. Comment on what effect exercise has on heart rate.
explain the relationship between the structure and function of the following parts of the heart
- valves
- atria
- ventricles
- major arteries and veins
Valves
- Valves are structures present in the heart and in veins that allow blood to flow in one direction only. Valves consist of flaps of tissue that are oriented to allow this unidirectional flow. Flow in the opposite direction will cause them to close.
Atria
- The function of the atria (singular atrium) in the heart is to receive
blood from the veins before passing it on to the ventricles.
- About 80% of the blood received in the atria flows into the ventricles
while the heart is relaxed. The first beat of a heartbeat cycle is the
contraction of the atria pushing the remaining 20% of the blood into the
ventricles.
- The atrium has thin elastic walls, as only a small amount of heart muscle is required to push the 20% of remaining blood into the ventricle.
Ventricles
- The ventricles receive blood from the atria. The function of the ventricles
is to pump the blood either to the lungs for re-oxygenation (right ventricle)
or to the body for distribution to cells (left ventricle).
- Because the ventricles must pump the full component of blood received (unlike the atria), the walls of the ventricle are much thicker and much more muscular than those of the atria.
Major arteries and veins
- Arteries carry blood away from the heart and veins carry blood back
towards the heart.
- There are two major veins, one bringing blood back to the heart from the
upper and one bringing it from the lower body.
- The walls of the major arteries and veins are composed of four layers:
- an inner layer of connective tissue
- a thick layer of elastic fibres surrounding the connective tissue, allowing the vessel to change size depending on blood flow
- a layer of smooth muscle, ensuring that the vessel does not over-expand
- an outer layer of connective fibres, giving the vessels elasticity and strength.
- Veins do not have to withstand the high pulsing pressures that arteries do, because the intricate capillary network absorbs much of the force of the heartbeat. Veins, therefore, have much thinner layers of muscle and elastic fibre.
Tour of the heart 
,
The Franklin Institute Science Museum, Philadelphia, Pennsylvania USA
plan and perform an investigation to identify individual aspects that comprise the heartbeat
An electrocardiogram records the electrical activity of the heart as it goes through its rhythmic beating process. The electrocardiogram of a normal heart consists of a regular pattern of peaks. The peaks indicate that electrical activity is occurring in an area and this electrical activity stimulates the muscles in that part of the heart, causing them to contract.
- Plan an investigation that compares the step-by-step cycle of an
operating heart with the noises heard and with the electrical activity
indicated by an electrocardiogram.
- When you perform your investigation you should be able, for instance, to indicate the relationship between the contraction of a chamber, the sound of a heartbeat and a peak on an electrocardiogram. You will need to find out what part of the heart is being stimulated at different peaks and what muscles are contracting as a result of this stimulation.
Blood
pressure Sample electrocardiogram and notes about using as sphygmomanometer.
Information from the web site of California Humboldt State University, USA
explain that specialised tissues in the heart produce an electrical signal that stimulates rhythmic contraction of the cardiac muscle
- The heart has its own natural pacemaker, a small mass of specialised cells
in the top of the right atrium. This mass of specialised cells is called
the sinoatrial (S.A.) node
or sinus node.
- The chambers of the heart will contract when an electrical impulse moves
across them.
- The sinus node sends electrical signals directly to the atria, stimulating them to pump, before sending electrical signals through other nerve connections to the ventricles.
discuss the problems that can result from interruptions to the normal rhythm of the heart
Interruptions to the normal rhythm can be as follows.
- An irregular heartbeat, referred to as an arrhythmia, may result in the heart pumping less effectively.
- An arrhythmia includes a heartbeat that is too slow (bradycardia), too fast (tachycardia) or irregular (e.g. fibrillation)
- A heartbeat that is slower than usual may cause fatigue, light-headedness or fainting.
- A heartbeat that is too fast may result in palpitations, dizziness, light-headedness or sweating.
- Fibrillation in the ventricles is life-threatening, and may be resolved by using electrical shock. Fibrillation in the atria may lead to blood clots, as the blood is not pumped out of the atrium fully, causing it to pool and clot.
identify that a pacemaker will produce a regular electrical impulse
- A cardiac pacemaker is used to correct arrhythmiasinitiating from
conduction problems with the natural pacemaker, the sinus node.
- The stimulator of the pacemaker produces an electrical current, which is
transmitted down conducting electrodes. The electrodes are positioned near
the side of the atrium.
- The pacemaker delivers an exact amount of electrical current to the heart at varying heart rates.
identify data sources, gather, process and analyse information to outline the historical development of pacemakers and use available evidence to identify types of technological advances that have made their development possible
The syllabus here requires an outline of the historical development of pacemakers.
- Consider the type of data required for this. You should be able
to explain the analysis that will be required for the data to be useful
to identify types of technological advances that have made the development
of pacemakers possible.
- Gather information from a range of sources including, encyclopaedias,
medical technology books and the Internet.
- In order to process the information, consider putting it in a table
for easy analysis. The table could have the headings Date, Type of pacemaker,
Technology involved.
- Analyse the information by sequencing your table by Date.
- Once you have sufficient information, you can use the evidence in your table to identify the technological innovations, such as new materials, medical techniques and electronic innovations, which have resulted in improvements to the design of pacemakers.
Link site
Science Stages 4, 5 and 6 Network, Port Macquarie District Office
identify the types of materials used to make pacemakers and the properties that make them suitable for implanting in the body
- A pacemaker is made up of a stimulator and electrodes.
- The stimulator is fully sealed in a titanium casing, as titanium is non-corrosive
and non-reactive in the body.
- The electrode outlets are protected by a polypropylene cuff, to prevent
loss of electrical signal during transmission.
- The electrodes are insulated with silicone or polyurethane rubber, except
for the tips, which are embedded into the cardiac wall. This ensures that
the electrical signal is controlled and focused.
- The tip of the electrode is usually made of platinum-10% iridium alloy. This alloy is chosen as it is non-corrosive and non-reactive in the body, and possesses reasonable mechanical strength.
construct a simple model to demonstrate the function of valves in the heart
- Below are some possible procedures for demonstrating the function of valves
in the heart. There are numerous other possibilities. Perform an investigation
by carrying out a procedure, looking for where and when modifications are
needed. Analyse the effect of any adjustments made.
- Investigation procedure 1: Build a model of a heart valve from four identical cardboard triangles that are attached to a square frame. The parts should interlock when closed.
- Investigation procedure 2: Connect a series of half matchsticks around the opening of a balloon using sticky tape. Cut the end of the balloon off, to form a one-centimetre rubber "ring" (the valve), strengthened with an outside ring of matchsticks (the fibres). Attachment of this structure to a 25 mL measuring cylinder (by further sticky taping) with the matchsticks oriented down will allow unidirectional flow of water only. When we attempt to pour the water from the measuring cylinder, the pressure of the water will cause the matchsticks to close the valve.
- Investigation procedure 3: With your class, design a role-play simulation. Some students can lock arms to form the walls of the heart chambers. Pairs of other students can simulate the valves by using their arms as flaps, while still other students can role-play the blood, easily passing through the valves in one direction but forcing the valves shut if they try to move in the wrong direction.
gather, process and analyse information to outline areas of current research in heart transplants and/or artificial hearts and their impact on society
-
Look in encyclopaedias, text books, magazines and journals and on the Internet
to gather
information on current research in heart transplants and
its impact on society.
- To process the information, you could put it into a table, with
columns such as
Researchers, Findings, When research was
done, Success with the method, Impact on society. Some
of the information may use medical language, so you may need to use a glossary
or dictionary to understand the research.
- Analyse the information by identifying common areas of research to see if their impact on society is consistent.
- Discuss the impacts on society with others. Who do you think are the best candidates for heart transplants? If these people are only young adults, who else would be impacted on if their lives are saved? What about their economic value to society?
Some
current research Totally artificial hearts offer hope, New Scientist, 31
October 04
And
another point of view , Mechanical 'artificial hearts' can remove need for
heart transplant by returning heart to normal, Science Daily, UK, November 06
Also try SENIOR
SCIENCE MODULE 9.3 Medical Technology- Bionics Science Stages 4, 5
and 6 Network, Port Macquarie District Office
describe the problems that can result from faulty valves in the heart
- If a valve is damaged and cannot close completely, the blood will leak
backwards and a hissing or murmuring sound may be heard.
- A damaged valve, therefore, means that a certain amount of blood will be
lost in backflow and blood will not reach the destination as efficiently
as required.
- A damaged valve may also obstruct blood flow through the heart or vessel.
- The more extensive the damage to the valve, the less efficient the heart action and the greater the strain placed on the heart.
process information to identify different types of functions of artificial valves in the heart
Some of the doctors and scientists who develop artificial heart valves try to copy nature, believing that valves work best if they are modelled on nature. Others believe that it is not important to worry about what a valve looks like but to make a valve that functions properly.
- As you gather information about the different types of artificial valves, focus on the functions of the valves. It may assist you to process information by recording your findings in table form, such as the one following.
| Type of valve | Structure | Function |
|---|---|---|
| Mechanical valves
e.g. ball-in-the-cage or disc-in-the-cage valves |
A ball or disc is placed so it has restricted movement between a ring and a cage. As the heart contracts, the ball is forced towards the cage. As the heart relaxes, the back-flow of blood forces the ball against the ring. | These types of valves function to allow blood flow through the valve opening and around the ball or disc as the heart contracts and prevent back flow of blood as the heart relaxes. |
| e.g. tilting disc or bileaflet valves. | A disc or some leaflets swing open as blood flows in the required direction and close when blood flows back. | These types of valves function more efficiently as there is less obstruction to blood flow from a ball or floating disc. They also last longer as there is less fatigue resulting from repeated ramming against a cage. |
| Bioprosthetic valves
e.g. animal tissue valves |
||
| e.g. human tissue valves |
describe properties of materials such as Teflon/pyrolytic carbon that make them versatile materials for making artificial body parts, including heart valves
- Pyrolytic carbon is used mainly as a coating in the
manufacture of artificial body parts. It is used for a number of reasons,
including the following:
- It has excellent compatibility with living tissues and therefore is less likely to be rejected by the body.
- It possesses greater elasticity than graphite, an alternative material.
- Its compressive strength is about four times the strength of graphite.
- It is not prone to lipid absorption or swelling in
the body, and therefore may be used as a coating on the ball or disc in
artificial heart valves. Earlier artificial heart valves that used silicone
swelled up and caused blockages in the flow of blood around the heart.
- Teflon (polytetrafluoroethylene) is a polymer used in
the manufacture of a wide array of artificial body parts, including blood
vessels, hip sockets and soft tissue prostheses, such as ear and nose
replacements. It has many advantages, for example:
- it is resilient
- it is easy to fabricate
- it has a high density
- it has a low coefficient of friction
- it is one of a few polymers that can be dry sterilised, and therefore made aseptic with minimal contact with other factors.
gather information from secondary sources on techniques used, including angioplasty, to ease blood flow to and from the heart and in blood vessels, when there has been a build up of plaque
- To gather information, look in encyclopaedias, health books and journals and on the Internet. If you use an Internet search engine, try entering a number of relevant words together, such as plaque, blood, flow, and angioplasty.
describe and explain the build up of plaque on the walls of major arteries and veins on blood flow to and from the heart
The build up of plaque on the walls of arteries and veins is termed atherosclerosis.
- A healthy artery or vein has a pale, smooth, glistening wall. At sites
of plaque, yellow fatty streaks are apparent under the endothelium. A fat
deposit, known as an atheroma,is built up from cholesterol that
is taken from the blood as low-density lipoproteins. Dense white tissue
may also be laid down forming a raised area in the wall of the vessel.
This leads to the smooth endothelial wall breaking down, leaving the rough
fibrous tissue exposed. The blood platelets (known for initiating clotting
in blood) selectively adhere to the rough surface, and a blood clot, or
thrombus, subsequently forms.
- Such blood clots may affect the body by raising blood pressure, leading to aneurysms(a bulging and weakening of the vessel wall), or obstructions such as embolisms(a mobile blood clot) or a thrombosis(a localised blood clot). Atherosclerosis of the coronary artery may lead to heart attack if not treated promptly.
discuss ways in which plaque could be eliminated to ease blood flow
- Methods of removing plaque, especially from arteries in the heart and brain
include the following.
- To orally take thrombolytic (clot-dissolving) agents, such as tissue plasminogen activator. However, to be effective, they must be given within a few hours after symptoms begin.
- Angioplasty: Surgery done on arteries, veins or capillaries in which a balloon is inflated inside a blood vessel to flatten any plaque that obstructs it and causes it to become narrowed.
- Athrectomy: A catheter is placed in the aorta in the groin and then moved to the heart or the location of the plaque. The instrument then mechanically removes the plaque.
Light-activated
drug shrinks plaque buildup in arteries , Stanford University, California,
USA
Enhanced
Plaque Removal Technology For Treating Peripheral Artery Disease Medical News
Today, USA April 2007
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