Previous chapiter: Oxygenation of the heart and its blood circulation

 

The heart, located between the two lungs, is a muscular pump responsible for blood circulation. It is the engine of life.

It is fuelled by oxygen, which is delivered by the coronary arteries.

Two arteries have the crucial task of supplying the heart with oxygen: these are the coronary arteries.

Oxygenation of the heart

The left and right coronary arteries begin at the root of the aorta and lead to the heart.

They split into several branches to irrigate the entire cardiac muscle. They spread into thin arterioles to cover the heart muscle and ramify into capillaries, where red blood cells release oxygen into the cardiac muscle and collect carbon dioxide as they are everywhere else in the body.

 

Four determinants of oxygen requirements of the heart

Oxygen requirements vary depending on the filling of the left ventricle, on its resistance to emptying, on the strength of contractions and on heart rate.

 

Carriers and pipes

The oxygen supply depends mainly on the quantity of red blood cells present in the blood and on the state of the vessels that transport the blood.

 

These pipes are made of three layers

The coronary arteries, like all the other arteries of our body, are made of three layers.

Each one of these layers plays a specific role, but the middle one is particularly important in the development of the cholesterol plaques.

 

 

Internal layer:  intima

The internal layer called intima is like a thin layer of Teflon. It is responsible for the integrity of the vessel and protects it from the formation of blood clots.

It naturally produces substances used to dilate the artery when necessary. One could compare that to the nitroglycerin that certain patients must use to relieve chest pain. The intima thus helps keep the artery at a larger size where necessary.

 

Middle layer:  media

The media, in the center, is thicker and made up of smooth muscle cells. It gives the artery the ability to contract and to dilate.

The nitroglycerin spray that some people use for angina acts on this layer. It induces a vessel relaxation. The vessel becomes larger, circulation improves and angina is relieved.

 

External layer: adventitia

The adventitia is the external coating. It is the most resistant part of the artery and offers a protective effect to the vessel.

 

Pollutants of the arteries

Major pollutants such as tobacco and cholesterol can affect arterial health and cause serious diseases.

 

 

 

That cholesterol!

We often hear about bad cholesterol, which clogs arteries, but very few people know about the vital role cholesterol plays in the human body.

 

Essential for life

In fact, cholesterol is found in every cell of the body. It is essential to the integrity and proper functioning of the cell membranes, i.e., their exterior skin.

It is also involved in hormone production, in defending against infection and in the digestion of fat by bile acids.

 

Vital, but he has his dangerous side

So, how can it be so important and yet have such dangerous potential? Everything depends on the balance and quantity of cholesterol in the blood.

 

 

We all make some

Every day, our bodies produce cholesterol in the liver. This is what we call endogenous cholesterol, since we make it ourselves.

We have a natural “thermostat” that regulates its production. This production level is genetically determined and varies from one person to another.

 

 

 

 

We all eat some

Exogenous cholesterol, which comes from outside the body, is ingested through our diets. It is absorbed by the intestine and directed to the liver.

 

 

 

It needs a carriers

Cholesterol is a lipid molecule that does not dissolve in the blood. Whether eaten or produced, it needs transporters or “taxis” to be able to circulate in the blood. The good “taxi,” or good cholesterol, is called HDL. The bad “taxi,” or bad cholesterol, is called LDL.

 

 

Bad and good cholesterol

The LDL or bad cholesterol taxi carries cholesterol from the liver to the cells of the body.

The excess cholesterol that is not used by the cells is returned to the liver by the HDL or good cholesterol taxi.

From there, the cholesterol will be transformed into bile acids, which are necessary for the digestion of fats, and excreted into the gallbladder.

 

Cholesterol traces

From birth, the transportation of cholesterol leaves traces on our arterial walls. With time and age, these build up on the arterial walls and eventually form plaques.

 

 

Cholesterol plaques

The formation of atheromatous plaques begins with the deposit of bad cholesterol on the thin inner layer of the blood vessel, the intima.

It is absorbed and stored in the vessel’s muscle layer, the media.

The presence of cholesterol produces inflammation.

The cholesterol is “eaten” by macrophage cells, which serve to clean the organism. They in turn fill with cholesterol and become trapped in the vessel’s walls.

We can picture them as large frothy cells filled with foam. When they die, they release their contents, creating even more inflammation, and the cycle repeats.

 

Where does the excess of cholesterol come from

Broadly speaking, excess bad LDL cholesterol results from:

·        Poor dietary habits, especially a high consumption of saturated fats

·        Genetic predisposition

·        Certain diseases, especially certain kidney and thyroid gland diseases

 

Atheromatous plaques vary in number and size depending on the quantity of excess bad LDL cholesterol in the body and on family predisposition.

 

The taxi parts of bad cholesterol also pollute

The bad LDL cholesterol taxis also contribute to the formation of plaques.

Like the pollution caused by cars on the road, the presence of certain proteins that enter into the taxis’ composition also produce inflammation.

Researchers are currently interested in these proteins with a view to producing a medication that will reduce their numbers to improve health.

 

Small plaques have no effect on oxygen delivery

Most of the little plaques that form in the coronary arteries over time do not affect circulation or oxygen distribution in the cardiac muscle. However, it is possible that the presence of certain plaques could end up deforming the vessels and even causing aneurysms.

 

Possible aneurysms formation

An aneurysm is characterized by an alteration in the function of the muscle layer. It becomes less resistant.

The presence of this weakness in the muscle layer combined with the pressure inside the artery causes a deformation and a localized dilation. Fortunately, rupture of aneurysms is extremely rare in the heart.

We can compare aneurysms to the deformation we sometimes find on a worn out garden hose.

 

The plaque takes up space in the wall of artery

The accumulation of cells and their fatty contents swells the intima, the vessel’s interior layer.

Rather like a pimple, the top of the plaque becomes stretched and fragile.

The inflammation caused by the presence of cholesterol in the wall then activates the body’s healing mechanisms. This leads to fibrosis, this white and leathery structure found in meat. This fibrosis which takes hold and makes the plaque more rigid and firm, more stable.

 

With time, calcium deposits can appear.

 

Some people are more likely

Excess “bad” cholesterol (LDL) in the organism influences the number and size of these plaques. Moreover, some people are more predisposed to developing these plaques than others.

 

Movement of the arteries on the heart

The body’s vessels distend at each heartbeat.

You can observe this movement in your pulse in your neck or wrist. The coronary arteries undergo this distension while also being moved by the heart’s beating.

With this unrelenting movement in the coronary arteries, a cholesterol plaque can burst spontaneously.

Regardless of their size, the most brittle plaques are the most likely to rupture and produce an acute coronary event, either unstable anguna or infaction

 

Be careful with intense effort!

​​This phenomenon may explain certain plaque ruptures during intense effort made by normally sedentary individuals. Shovelling snow rapidly on a cold day after a storm is a common example. 

 

Angina

When an artery’s diameter shrinks by more than 60% due to the presence of a plaque, its ability to deliver oxygen to the heart is compromised.

Angina manifests when the arteries cannot circulate enough blood in their respective areas of the heart to provide an adequate supply of oxygen.

 Angina, the name given to the pain caused by the lack of oxygen to the heart, is felt upon physical exertion and is quickly relieved by rest.

 

Classic form of angina

Most commonly, angina takes the form of chest pain that radiates towards the jaw and the left arm. It can also be felt in many other ways, especially as back pain, or only in the jaw or the left arm.

 

 

Sometime angina is… Silent

In certain people who feel little pain or no pain at all, sudden breathlessness might be experienced under strain, followed by rapid relief with rest. We call this; silent angina.

 

Chest pain at exertion, dissipating with rest and reproducible

In every case, pain between the nose and the lower thorax occurring with exertion and dissipating with rest, and repeating with the same type of exertion, is a serious symptom. If you experience such symptoms, you should immediately make an appointment to consult a doctor.

Angina with a stable presentation of these symptoms is not usually fatal and can be treated in various ways.

 

Attention to any changes in symptoms

However, any progression in the symptoms, in intensity or frequency, or if they start to occur during rest, is a sign of instability and could lead to a heart attack.

You should consult a healthcare professional promptly in this situation. In any worry, dial 911!

 

No one is safe

No one is safe from coronary artery disease. We must be vigilant, for ourselves and for the people around us, and know the signs and symptoms as well as the aggravating factors.

 

Some factors increase the risk of coronary artery disease

Certain factors are known to increase the risk of coronary artery disease.

Some are unchangeable, like masculine sex, age and hereditary factors.

Other factors can be changed by lifestyle, such as tobacco use, cholesterol levels, sedentariness, diabetes and high blood pressure.

 

Prevention remains the best treatment

Prevention remains the best treatment against coronary artery diseases.

To reduce the risk, it is important to lead a healthy lifestyle, especially by maintaining a balanced diet and getting regular exercise.

 

Next chapiter: Unstable angina