The heart is the muscular pump that is located between your lungs, slightly to the left of your breastbone. It is slightly larger than a human fist, with a weight of between 200 to 425 grams. Everyone’s heart has to beat approximately 100,000 times each and every day.

The Anatomy of the Heart

Your heart comprises of four chambers, the upper chambers are referred to as the left and right atria, collectively called the atrium, whilst the lower chambers are called the right and left ventricle. A wall of muscle known as the septum separates the four chambers.

The largest of the chambers is the left ventricle, as they have to force the blood through the aortic valve into the body. The right side of the heart is small because it only has to transmit blood a short distance to the lungs.

The heart itself is merely a pump which contracts and relaxes, in the cardiac cycle. The coronary arteries feed the oxygen, and the nutrients to the heart muscles, which need it to function effectively. The two coronary arteries, exit the heart through the aorta. The left main coronary artery is less than an inch long and very thin; it later branches into two smaller arteries, which themselves branch into arteries of decreasing size. The smaller vessels are capable of penetrating the heart muscle. The capillaries are so tiny that the red blood cells can only travel in single file. The functions of these tiny blood vessels is to transfer oxygen and nutrient filled blood to the cardiac muscles, and then take the waste products such as carbon dioxide away for effective disposal by lungs, kidney’s and the liver.

The superior and inferior vena cava are the two main veins which bring the deoxygenated blood to the heart, and they empty into the right atrium. The veins from the upper torso and head empty in the superior, and the veins from the legs and lower torso feed into the inferior vena cava.

The aorta is the largest of the body’s blood vessels, being about the diameter of the thumb, and carries the reoxygenated blood from the largest heart chamber the left ventricle to the body.

The deoxygenated blood is taken from the right ventricle to the lungs, by the pulmonary artery. Arteries carry blood away from the heart, but it not always reoxygenated. Conversely veins carry blood towards the heart, and it is the pulmonary vein, which carries the oxygen rich blood from the lungs to the left atrium. At this time the left atrium is contracting and forcing the oxygenated blood through the mitral valve into the left ventricle. When the ventricle is full of blood it contracts and forces the aortic valve open and the mitral valve closes. This action causes the blood to be pumped into the left atrium. The mitral valve closes to prevent a back flow of the blood and the blood exits the heart through the aorta. The tricuspid valve separates the right atrium from the right ventricle, and assists the blood to flow through.

As the right ventricle receives the blood the right atrium contracts, which makes the ventricle fill, when this process is complete the right ventricle contracts forcing the tricuspid valve to close. The increases pressure opens the pulmonary valve to open and the blood to flow through the pulmonary artery, which transports the blood to the lungs.

GLOSSARY OF TERMS

Septum,

The wall of muscle separating the upper and lower levels of the heart.

Blood pressure is the force the blood exerts on the artery walls whilst
travelling through. Blood pressure arises from two forces, the first
arises from the heart is it pumps blood through the arties, and into
the circulatory system. The secondary force is the force of the
arteries when they resist the blood flow. When the heart pumps it
forces blood from the larger arteries, into the smaller arteries, the
interioles.

The arterioles can
contract or expand (dilate), adjusting the resistance to blood flow,
and the blood pressure. If the arterioles contract, the resistance to
blood flow increases, which reduces blood flow and increases blood
pressure. Dilation of the arterioles has the converse effect.
Alterations in the inner diameter of the arterioles are important in
regulating blood flow and determining blood pressure. If arterioles
stay constricted, they can cause Hypertension. High blood pressure or
hypertension is when this force is too high, everyone has a blood
pressure, but hypertension over a long period of time leads to other
health risks. Your blood pressure increases naturally when you exercise
or your body is subjected to stress, however it is important to make
sure that this state of hypertension is not permanent.

Blood
pressure readings are always given as two numbers, as the force of your
blood pressure is measured in two ways. They are always represented by
a fraction for example 120/90; the top pressure (120) is your systolic reading, which is measured just after your heart beats. The bottom pressure (90) is your diastolic pressure measured in between heartbeats, when your heart is relaxed and filling with blood.

To
be completely healthy it is necessary to have both pressures within a
normal limit. High blood pressure is defined as a pressure reading
greater than 140/90. However for people with diabetes, and or kidney
diseases a lower pressure is recommended. Blood pressure goals are
highly individualistic, and it is therefore imperative that you discuss
the matter of your own goals fully with your doctor.

TYPES OF HYPERTENSION

ESSENTIAL HYPERTENSION

Ninety five percent
of sufferers have as type of hypertension that is not caused by a
single cause. This is known as Essential hypertension, or primary
hypertension.

SECONDARY HYPERTENSION

In five percent of
cases of hypertension, it can be linked to one cause. This means that
the high blood pressure is in fact a symptom of another disease,

This is known as secondary hypertension.

SYMPTOMS OF HYPERTENSION.

Hypertension
is known as the silent killer, as most people do not experience any
symptoms. Sometimes, when there is a really rapid rise in your blood
pressure it can cause a headache, and impaired vision, or cause a
blackout.

RISK FACTORS.

Some
people do develop high blood pressure whilst others do not, and the
cause of this is not yet clear. However it has a tendency to run in
families.

Other risk factors are

DIAGNOSIS OF HYPERTENSION

As the majority of people have no symptoms the only sure way of knowing is to have your blood pressure monitored regularly,

TREATMENT OF HYPERTENSION

You
may be required to undergo more than one reading to establish if your
blood pressure is high permanently. You are likely to be treated by a
nurse or doctor, on a one to one basis. However if it is very severe
you may be hospitalised. It is likely to be brought down to acceptable
levels by both a change of lifestyle and medical treatment.

LIFE STYLE CHANGES

Undertake measures to manage your level of stress

AVAILABLE MEDICINES

If
your blood pressure is high on a permanent basis, then you will be
recommended to take drugs that help to reduce it. They may include

Diuretics (These drugs include bendrofluazide).

Diuretics increase the amount of both water and salts removed by the kidneys from your blood. They also widen your arteries.

Beta-blockers (These drugs include atenolol)

Beta-blockers reduce you’re your pulse rates, and this slowing down makes your heart work less hard.

ACE Inhibitors(These drugs include captopril, losartan)

There are certain enzymes, which constrict and tighten your arteries, and this group of drugs block them.

Calcium channel blockers (These drugs include nifedipine) or alpha blockers (These drugs include prazosin)

This category of drugs help to widen your arteries.

Your
lifestyle and any other diseases you are suffering from will affect the
drugs prescribed. It may take a while for the drugs to be administered
in the correct dosage for some people. However it is important to
control a condition, whose symptoms and affects you are not aware of.

A WORD OF CAUTION:

Please
do not use this information to diagnose individual cases. Every case is
unique and needs professional help to both diagnose and treament.

GLOSSARY OF TERMS

BLOOD PRESSURE

Blood pressure is the force the blood exerts on the artery walls whilst travelling through

CARDIAC CYCLE

The
complete round of cardiac systole and diastole with the intervals
between, or commencing with, any event in the heart’s action to the
moment when that same event is repeated.

DIASTOLE

Diastolic pressure is the time at which ventricular contraction occurs.

ESSENTIAL HYPERTENSION

There is no apparent single cause for the rise in blood pressure.

HEART

OBESITY

A condition characterized by excessive bodily fat

The heart is a hollow, muscular organ that pumps blood through the blood vessels by repeated, rhythmic contractions.

SYSTOLE

Systolic pressure is the time at which ventricular contraction occurs.

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Continuous wave ultrasound

Doppler Ultrasound Schematic Diagram

Continuous wave ultrasound probe techniques involve an ultrasound signal being transmitted into the skin, and the difference in frequency reflected being measured. Along with the spectral broadening, this provides an indication of blood flow in terms of turbulence and presence. It however is difficult to get a qualitative measure, to discriminate between venous, capillary, or arterial vessels, is sensitive to the angle to flow, and lacks depth resolution. On the positive side it is non-invasive and by modulating the response using a carrier signal an audible signal can be produced which sounds either dirty (turbulent flow), or clean (laminar flow), giving an indication of underlying problems. The signal is continuous which allows for monitoring during surgical applications and detection of pulse.

Venous Occlusion Plethysmography

Venous Plethysmography is a technique which looks at the performance of the venous system in a limb. The limb is enclosed within an airtight chamber, and a cuff applied at about 40mmHg such that the venous return is stopped, but arterial flow may still pass. The chamber is fluid filled, and after due calibration the rate of volume increase is indicative of the rate of arterial flow into the limb. It is a consequence of venous occlusion that the venous pressure within the limb will increase. This takes place until it reaches the 40mmHg of the cuff, and volume will not increase much further. Once the cuff is removed the rate at which the volume leaves is indicative of the efficiency of venous return, a slow return showing a low venous flow, and indicative of underlying problems. The spatial resolution is much worse than the ultrasonic method, and the depth resolution is nonexistent. The results however are quantitative, and differentiation between arterial and venous flow is a valuable feature. The apparatus is large and cumbersome to use, which limits the use of this method. Further, the measurement is not continuous, which is a disadvantage compared to the ultrasonic method.

Venous Occlusion Plethysmography

Blood flow electromagnetic

Blood flow electromagnetic methods make use of the principle that movement of a charged particle through an electromagnetic field produces an emf. Essentially two electrodes are attached along the length of a vessel, and an electromagnetic field is applied at approximately 90o to the flow. The emf between the two electrodes can be measured and gives a continuous result proportional to the flow velocity. The response is governed by uBL, where u is the velocity (typically 10mm/s), B the magnetic field strength (typically 0.1T), and L the length between electrodes (10mm). Smaller vessels will have a lower u, and will be unable to have such a great L, reducing the signal. Typical voltage signals are in the region of 0.01mV, which is in the region of the electrode contact potential (which poses a great problem to the S/N ratio), and interferes with the ECG signal. These problems however can be reduced by using a 400MHz A.C. signal. The spatial and depth resolution are better than both previous measurements, and once the angle of field to flow has been allowed for, it is potentially an accurate and continuous measurement. The disadvantage of this is that it is by no means non-invasive, unlike the previous two methods[quote]The disadvantage of this is that it is by no means noninvasive, unlike the previous two methods:MedicalEngineer.co.uk[/quote], needing exposure of a given length of vessel for electrode fitting. This however makes it suitable for measurements during surgical procedures, especially coronary bypass or plastic cosmetic surgery.

Blood pressure is symptomatic of a circulatory system, it is indeed the pressure differentials which dictate the movement of blood throughout the body, its distribution, and velocity. Blood pressure, however, influences far more than mere fluid dynamics – it is intimately involved in vascular permeability, renal function, and even human reproduction.

The measurement of blood pressure is hence a key physical assessment which may shed light upon not only the pressure management of the cardiovascular system, but upon the overall condition of the cardiovascular and other systems.

It is an unfortunate consequence of the pressure upon a medical laboratory that there is seldom time for protruded studies and repeated measurements. Demands for high throughput of patients mean that in many cases the available instrumentation is not utilised to its maximum accuracy (Gabe,I.T).

The basic principle of any device for measuring blood pressure is that the said device must transduce a physical signal into some form of analogue or digital signal. The nature of blood pressure itself, however, is not stable, and contains a complex periodic waveform.

Digital Blood Presure measurement

Where the only pressure of interest is some form of a mean pressure, the gold standard is the use of a mercury manometer, such as employed within most general practitioner’s surgeries. The important parameters for such a device are that there should be a low baseline drift (change in accuracy over time, commonly due to temperature), and a low hysterisis (decrease in response per increase in signal with higher signal levels).

Dynamic systems provide a much more complex challenge for pressure measurement. In these systems the priorities shift to incorporate response time and temporal resolution. The input signal contains rapid changes in gradient, as well as a large dynamic range, for this reason a rapid rate of response is required.

Fourier theory provides that a periodic function may be broken down into a summation of some set of sinusoidal waveforms. The same analysis may be performed for the periodic function of the heart beat. It has been reported (Gabe, I.T.) that signal above the 10th harmonic may be disregarded as it is insignificant. This provides a practical limitation upon the required accuracy of measurement.

It is to be remembered that working with derivatives of the pressure signal may accentuate higher frequency components, requiring a larger bandwidth for effective processing.

The bandwidth is the range of frequencies above the base frequency which are included. It has been suggested to fit half a cos squared trace to the beginning of a pulse and to then use a bandwidth equivalent to half the reciprocal of the trace width.

References

Gabe, I.T Pressure Measurement in Experimental Physiology Chapter 2, pp 11-50 Cardiovascular Fluid Dynamics, ed. Burgel, D.H, Academic Press, London 1972

Substance exchange with the environment and transportation of substances within
the living body are necessary conditions for the existence of life.

The basic method of substance transport in living organisms is diffusion;
diffusion is the intermingling of the molecules of one body/fluid
with the molecules of another body/fluid they come into contact with.

With primitive and smaller organisms, diffusion is sufficient to
distribute oxygen, water, nutrients, throughout the entire body and
to maintain a constant substance exchange with the environment. With
the evolution of living matter, however, the necessity of superior
means of transportation arose. So, the heart and the blood vessels,
forming a convective system, have developed, in order to provide fast
transport of substances and heat around the body.

Approximate Rates of Diffusion

For all protozoans, that are unicellular organisms, the only method of
substance transport is diffusion; the processes of digestion,
respiration and excretion are carried out by diffusion, which takes
place over the surface of the entire body. The first system of
cavities and ducts, called “œgastrovascular system”, that
communicated directly with the environment for substance
transport/intake is found in phylum Coelenterata / Cnidaria (that
contains the hydras, sea anemones, corals and jellyfish). However,
this is not a proper vascular system, carrying blood (or a body
fluid); the first vascular system appears with phylum Nemertini
(“œribbon worms”), where, in the lack of a heart, blood flows with
the aid of the contractive walls of the vessels. Although in the more
evolved organisms, a vascular system is present, diffusion still has
its role, in intracellular transport, as well as transport between
cells.

For inferior organisms that have a diffusive transport system, this is
sufficient, and even suitable for a number of reasons. First of all,
being a passive process, diffusion does not involve energy
consumption. Secondly, the diffusive transport does not require such
a high level of specialization. Thirdly, the rate of transport is
sufficient for the transportation of nutrients, since only a small
area is involved. However, over distances longer than 1mm,
diffusional transport can become hopelessly slow (it would take a
molecule over half a day to cover a distance of 1cm!).

Toget an idea of how diffusion works, here are some typical speeds:

0.1 micrometer is covered in 0.000005s
10 micrometer ..0.05s
1mm ..9.26 min
1 cm .. 15.4 hours

This is the main reason why a more rapid transport system is needed for
larger and more complex organisms.

The convective system is able to transport substances at great distances,
sweeping them along blood vessels, in a stream of fluid that is
actually pumped through them. The pump in this system is the heart,
and its role is to provide the energy input for the blood to flow. An
oxygen molecule coming from the lungs needs only approximately 30 s
to reach the extremity of the limbs in humans, using the convective
system; by comparison, if it were to get there by diffusion, it would
need 5 years!

In superior organisms, the circulatory system actually combines both
methods – convection and diffusion. In the beginning and ending
segments – that is, at the uptake of molecules and over the last
10-20 µm diffusion is used, for the molecules to be taken
on by the fine capillaries into the blood stream or delivered to
destination cells from the blood flow. For the much greater distance
between these points, convection is needed, and molecules are
transported with the speed of the blood stream that carries them.

Atherosclerosis comes from the
Greek words athero meaning gruel or paste and sclerosis meaning
hardness. It’s the name of the process in which deposits of fatty
substances, cholesterol, cellular waste products, calcium and other
substances build up in the inner lining of the large and medium
arteries. This build up is called plaque.

Atherosclerosis is a thickening of the artery wall

The
plaques can grow large enough to drastically reduce the blood flow
through the arteries. A significant of the damage occurs when they
rupture. Once ruptured plaques can cause blood clots to form, they can
then travel to other parts of the body, or they can remain in place and
obstruct the blood flow. If either of these types of clots blocks a
blood vessel that leads directly to the heart, then it causes a heart attack.
If the blood supply is constrained to the legs, then it can cause
walking difficulties, and may over a period time lead to gangrene. When
a blood vessel to the brain is restricted it causes a stroke.

Atherosclerosis also causes hypertension.
As the blood is forced through the narrowing arteries, it exerts
greater pressure on the walls. This also increases the risk of stroke
and heart attack.

Atherosclerosis
is a slow, complex disease that typically starts in childhood and gets
worse as people age. In some people it progresses rapidly, even in
there thirties. Many doctors think that it is caused by damage to the
endothelium, the interface between the blood and the artery.

SYMPTOMS

• Doesn’t produce symptoms until the artery is severely restricted or obstructed.
• Chest pain
• Leg cramps

WARNING SIGNS

When arteries to the brain are affected.

• Headaches
• Dizzy spells
• Ringing of ear
• Memory problems
• Poor concentration
• Mood changes

When arteries to the heart are affected,

• Chest pain (angina)
• Elevated blood pressure

When arteries to the arms or legs are affected.

• Aching muscles
• Fatigue
• Cramping pains in the calves (intermittent claudication)
• Pain in the hips and thighs (may be present depending on which arteries are blocked)

RISK FACTORS

• Elevated levels of cholesterol and triglyceride in the blood
• High blood pressure.
• Smoking
• Diabetes

LIFE STYLE CHANGES

If
you have a family history of congenital, premature cardiovascular
disease, then you are at risk, and this element of the risk factor
cannot be controlled. There are risks that can be controlled

• High blood cholesterol (especially LDL or “bad” cholesterol over 100 mg/dL)
• Cigarette smoking and exposure to tobacco smoke
• High blood pressure
• Diabetes mellitus
• Obesity
• Physical inactivity

Once
the endothelium has sustained damage then, cholesterol, platelets,
cellular waste products, calcium and other substances are deposited in
the artery wall. These may stimulate artery wall cells to produce other
substances that result in further build up of cells. These cells them
thicken the endothelium significantly, and further reduces the diameter
of artery and further constricts the distribution of oxygen. If a blood
clot is formed adjacent to the plaque, then this blocked artery will
stop the flow of blood to the tissue.

CHOLESTEROL AND DIET

People
get cholesterol by the body producing all it needs, and by consumption
in all animal products. Most of it is produced in the liver. Foods
containing very high levels of cholesterol are the livers of other
animals, egg yolks, meat, poultry, fish, seafood and whole milk dairy
products. There is no cholesterol in any plant food, such as
vegetables, fruits, grains and seeds.

Some
of the excess dietary cholesterol is removed from the body through the
liver. The American Heart Association recommends that you limit your
average daily cholesterol intake to less than 300 milligrams. If you
have heart disease, limit your daily intake to less than 200
milligrams. As the body is capable of manufacturing all the cholesterol
it needs, it is not necessary to consume any at all. The quantity of
animal food such as meat, poultry should be restricted to 150 grams a
day, if they have high levels of cholesterol. To reduce the levels in
dairy products switch to low fat milks and cheeses. In crease your
protein by using chickpeas and high quality grain products.

TREATMENT

Prevention
of Atherosclerosis is a life-long process. Each individual will need to
review and improve his/her own risk factor profile.

Drug
treatment can play an important role in arresting the progression of
the disease and lipid-lowering agents may be used to reduce fat levels
in the plaques.

A WORD OF CAUTION:

Please
do not use this information to diagnose individual cases. Every case is
unique and needs professional help to both diagnose and treatment

GLOSSARY OF TERMS

ARTERIOSCLEROSIS

A
chronic disease in which thickening, hardening, and loss of elasticity
of the arterial walls result in impaired blood circulation. It develops
with aging, and in hypertension, diabetes, hyperlipidemia, and other
conditions.

ATHEROSCLEROSIS

A
form of arteriosclerosis characterized by the deposition of
atheromatous plaques containing cholesterol and lipids on the innermost
layer of the walls of large and medium-sized arteries.

ATHEROMATOUS

A deposit or degenerative accumulation of lipid-containing plaques on the innermost layer of the wall of an artery.

CHOLESTEROL

Cholesterol
is a soft, waxy substance found among the lipids (fats) in the
bloodstream and in all your body’s cells. It’s an important part of a
healthy body because it’s used to form cell membranes, some hormones
and is necessary for other functions

ENDOTHELIUM

Endothelium is the interface between the blood and the artery

TRIGLYCERIDES

Triglycerides
are lipids normally found in increased levels in the blood following
the digestion of fats in the intestine. Consumed calories that are not
immediately used are stored in fat cells in the form of triglycerides
and are later released from fatty tissues when the body needs energy
between meals.

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