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Biology notes: Human circulatory system Part 9. More on treating heart disease

The human circulatory system Part 9. More advanced procedures for treating cardiovascular disease including coronary heart disease

Doc Brown's GCSE level Biology exam study revision notes

Index of notes on human circulatory system: heart, lungs & blood vessels


9. More on scientific developments to help treat cardiovascular disease and emergency situations!

Reminder: Cardiovascular disease (CVD) is the scientific medical term for all types of disease that affect the heart or blood vessels.  CVD includes coronary heart disease (clogged up arteries with fatty deposits), which can cause heart attacks, stroke, heart failure, and peripheral artery disease.

Appreciate that modern developments in biomedical and technological research enable us to help when the circulatory system is not working well.

Points to consider: blood vessel tissue replacement, transplant donated hear, suitable organ donor, artificial heart, valve replacement, pacemakers, artificial blood, the latest advanced procedures for treating cardiovascular disease and coronary heart disease.

Surgical techniques

Tissue replacement

A section of blocked blood vessel can be replaced by taking a section of healthy blood vessel and bypassing the affected section.

This is called coronary bypass surgery.

Transplanted donated heart or an artificial heart

In the case of a total patient heart failure and severe cardiovascular disease, surgeons may perform a heart transplant or even a combined heart and lung transplant if the lungs are diseased to.

The donor organs must come from other people who have recently died.

However, donor organs might not be immediately available, or they are not for some other medical reason not the best option, doctors may fit an artificial heart.

Even after the heart transplant operation, the new heart does not always start pumping the blood immediately - stimulation might be required.

Also, the patient has to take suppressive drugs (immunosuppressant drugs) to stop the body rejecting the 'foreign' tissue of the new heart (rejection) - these drugs can have side effects and the patient more vulnerable to infection.

Any major surgery like a hear transplant operation carries its own risk of bleeding, blood clots and infection from microorganisms including some potentially fatal bacterial infections like MRSA.

A transplant can greatly improve the quality of life (a factor that applies to all these surgical techniques), BUT the disadvantages are:

it requires major risky intrusive surgery - unforeseen complications or infection,

patients must take immunosuppressive drugs for the rest of their life,

the application of anti-rejection drugs - may cause a greater infection risk because the body's natural immune defence system is suppressed,

and, sadly, a shortage of donors - does require the death of somebody and permission to use their heart.

BUT, we are balancing risks versus survival.

 

Artificial hearts are machines inserted by surgery into a patients chest to pump the blood around the circulatory system, ideally temporarily, until a donor heart can be found.

These mechanical devices are able to pump blood around a person who's heart has failed.

They are usually a temporary fix to keep the patient alive until a donor heart can be found.

They can also be used to help a patient recover while the heart is rested and healing.

Artificial hearts can be permanent solution, with the advantage of reducing the need for a donor heart.

Artificial hearts have an advantage of being much less likely to be rejected by the body, as donor hearts can be, because the immune system doesn't recognise the plastic or metal parts as an invasive ('foreign') microorganism to be attacked - like it might with living tissue.

However, any major surgery in fitting an artificial heart or transplant carries risks eg from bleeding, infection.

Also, artificial heart machines are subject to wear and tear themselves and are not as efficient as a real heart and there are still risks from heart attacks and strokes.

Parts of the heart machine can wear out or the electric motor fail.

The blood flow is not as smooth causing blood clots leading to strokes.

Heart patients have to take drugs to thin their blood to make sure this doesn't happen.

Unfortunately, such drugs cause problems if the patient has an accident and excessive bleeding occurs.

I'm afraid it just another case of medical treatment where you are balancing risks ('bad' outcomes') versus 'good' outcomes!

 

Surgical techniques - heart valve replacement

Heart valves can be damaged or weakened by heart attacks, infection or just old age - you can't stop aging processes!

The damage may cause the valve tissue to stiffen and prevent the valve from opening and closing properly.

If the valve leaks, blood can flow in the wrong direction instead of always going forward in the right direction.

This results in poor circulation of blood, which causes its own problems.

Tiredness and lack of energy and breathlessness are symptoms of leaky valves.

Poor circulation can cause pain in the legs, feet, arms, and hands.

Cold hands and feet may ache or throb.

When the blood does not circulate correctly, oxygen and nutrients cannot reach tissues effectively, which can result in stiffness and cramping.

Badly damaged valves can be replaced with artificial valves or other animal biological valves.

Replacement valves can be taken from other humans or animals such as cows or pigs.

Defective heart valves can be replaced by m an-made artificial mechanical valves that work in the same mechanical way as a real heart and the surgery is much simpler and less risky, but still risks of blood clot problems.

Replacing a valve is a less complicated surgery, so less drastic, and therefore less risky, than doing a full heart transplant operation.

Advantages of artificial valves:

No rejection

Disadvantages of artificial valves:

They can damage red blood cells. Patients need anti-clotting agents because of blood clot risk.

Advantages of biological valves:

Red blood cells not damaged.

Disadvantages of biological valves:

Biological valves can harden and need replacing.

 

Artificial pacemakers

For some patients the problem is an inability of their body to control the heart rate.

The steady beat of the contraction and relaxation of the heart muscles is obviously important.

Artificial pacemakers can be fitted under the skin and a wire connects it to a vein to the right atrium.

The pacemaker sends electrical impulses to stimulate and control the heartbeat.

Advantage of artificial pacemakers:

No major surgery is required.

Disadvantage of artificial pacemakers:

Our immune system may reject the pacemaker ('foreign' materials) and may need replacing.

 

Use of artificial blood

Blood loss from a serious accident can lead to death indirectly - loss of available blood means less oxygen and nutrients are getting the cells of all the tissues and organs - not good!

If you can keep the volume of blood 'topped up' life can be preserved for sometime.

Therefore, artificial blood can be used temporarily as a blood substitute when a patient has lost a lot of blood, but, as long as the heart can still pump the diluted fluid (diluted plasma) containing the remaining red blood cells around the circulatory system.

The simplest artificial blood (blood substitute) is a saline solution - an aqueous sodium chloride salt solution NaCl(aq).

Its safe to use, but must NOT contain air bubbles, and it can keep people alive even if they have lost 2/3 rds of their red blood cells!

This can now give enough time e.g. to get the patient to hospital and prepared for surgery if necessary and also time for the body to produce more red blood cells.

This can be followed up by a blood transfusion if the patient cannot make enough red blood cells in time!

Research is being done to develop artificial blood containing molecules that can carry oxygen just like haemoglobin in red blood cells, but limited progress so far.

This is an ideal solution, to produce a product that can temporarily act like the haemoglobin molecules to transport oxygen to the bodies cells - a sort of haemoglobin replacement.

This would avoid the need for a blood transfusion, and presumably the body would gradually produce enough red blood cells to allow the circulatory systems to work normally.


Summary of learning objectives and key words or phrases

Be able to describe and understand CVD treatments involving blood vessel tissue replacement, transplanting a donated heart, issues with organ donors, the use of artificial heart valves replacement, pacemakers, the values of artificial blood used in advanced procedures for treating cardiovascular disease and coronary heart disease.


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