Atherosclerosis


Atherosclerosis is the medical condition that occurs as a result of the walls of a blood vessel (usually arteries) thickening by build-up of materials such as low density lipoprotein (LDL cholesterol). Usually there are no symptoms until blood flow is significantly reduced or completely stopped. If the blood vessels to the heart are narrowed, it can result in little or no blood flow to the heart causing angina (chest pain) and shortness of breath. Sometimes the angina is felt more in the shoulder region. The artery becoming completely blocked would result in a heart attack; unless the blockage was in the brain, then one would experience a stroke. The possible symptoms of a stroke can be lack of feeling in parts of the body or paralysis.

Material build-up on artery walls (Embolism)
Material build-up on artery walls (Embolism)


Formation of Atherosclerosis


Atherosclerosis is formed when the wall of the artery becomes damaged by particles in the blood stream. Particles that damage the wall are toxins in the blood stream from smoking, LDL, and high levels of glucose. Hypertension, which is essentially high blood pressure, also damages the walls due to the higher stress that they experience. The damage increases the permeability of the artery wall, which results in LDL cholesterol and other adhesion molecules like monocytes being able to enter past the first layer, the endothelium.

Process of deposit build-up on artery walls (Atherosclerosis)
Process of deposit build-up on artery walls (Atherosclerosis)

Once inside the endothelium, the LDL can become oxidized. Interactions between the oxidized LDL and monocytes that have entered the artery wall leads to them combining and forming macrophage foam cells. These foam cells are the basis of the deposit that forms. They interact with more oxidized LDL to become larger as well as attract the smooth muscle cells in the artery walls and enlarge even further. Over time the deposit composed of these macrophage foam cells increases in size enough to cause a significant part of the artery to be blocked.


Particulate Fouling


The accumulation of colloidal particles suspended in the flowing stream on the inner surface of a vessel is the process of particulate fouling. It can possibly be derived in two ways: it can occur because of particulates that are previously present in the stream or by the particulate being generated under the standard conditions of the system (Sheikholeslami & Watkinson, N.D.). The most common industrial vessel that experience particulate fouling is a heat exchanger.

Particulate Fouling of HVAC Heat Exchanger (Heat Exchanger Technology 2008)
Particulate Fouling of HVAC Heat Exchanger (Heat Exchanger Technology 2008)

Some examples of heat exchangers that experience particulate fouling would be tube-bundle, HVAC, and industrial plate. The purpose of a heat exchanger is to transfer heat energy from one fluid to another. Particles that are suspended in the flowing fluid deposit on the inner walls of the tubes by the process of particulate fouling. Over time the deposit increases in size resulting in the restriction of flow within the tubes of the heat exchanger and decreases the amount of heat that is able to be transferred.


Particulate Fouling in Atherosclerosis


Particulate fouling is a result of the effects of two processes combined (Kim & Webb, 1990). These two processes are deposition and removal. The deposition process takes into account the transportation of the fine particles in the stream and the adhesion of them to the walls of the tube. In the case of atherosclerosis, this would be the transport of LDL in the blood stream and the process of how they become linked to the artery walls. The deposition flux can be shown by the following equation (Sheikholeslami & Watkinson, N.D.).


Deposition Flux Equation.jpg

The transport coefficient, Deposition Flux Eqn.jpg, can be shown to also be equal to the transfer coefficient for particles that are submicron in size. Particle concentration, Particle Concentration.jpg, is present for the concentration in the stream and the concentration on the surface of the small particle.

According to both Sheikholeslami & Watkinson and Kim & Webb, the rate of deposition can be approximated using a factor called the sticking probability, Sp, which is the portion of the particles that make it to the surface and attach. When considering the process of particulate fouling, we must analyze it in two steps. The first being the attachment of the particulates to the inner wall of the tube, and the second being the attachment of new particulates on the existing ones attached to the wall. In the case of blood vessels, this would be the process of LDL cholesterol initially attaching to the inner wall and forming macrophage foam cells, followed by further attachment of LDL on the existing deposit.

The significance of particulate fouling in formation of atherosclerosis is further explored by examining the chemical processes that occur in order to achieve the build-up of deposit on the blood vessel walls. The oxidation of low-density lipoprotein is described in more detail by looking into the process and mechanisms. The preventive measures for atherosclerosis covers different methods by which we can eliminate or at least postpone the risks associated with developing heart disease. Since research on the treatment and prevention of heart disease is quite limited, future direction looks into paths that are in the process of being explored and other alternative paths that have been hypothesized. The risk factors and demographics behind heart disease are included as well as a more detailed exploration of the make-up of low-density lipoprotein. The chemical significance in each section is explored in further detail.


References


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Davis, E. N. (2004, December 23). Atherosclerosis - An Inflammatory Process. Retrieved November 4, 2012, from The American Academy of Insurance Medicine: http://www.aaimedicine.org/journal-of-insurance-medicine/jim/2005/037-01-0072.pdf

Embolism. (n.d.). Retrieved November 4, 2012, from Human Diseases and Conditions: http://www.humanillnesses.com/original/E-Ga/Embolism.html#b

Heat Exchanger Technology. (2008, July 28). Retrieved November 3, 2012, from http://webwormcpt-wwhx.blogspot.ca/2008/07/unexpected-high-cost-of-heat-exchanger.html

Nae-Hyun, K., & Webb, R. L. (1990). Particulate fouling of water in tubes having a two-dimensional roughness geometry. Retrieved November 2, 2012, from Science Direct: http://www.sciencedirect.com/science/article/pii/0017931091902313#

Sheikholeslami, R., & Watkinson, A. (n.d.). Composite Fouling, Fundamentals and Mechanisms. Retrieved October 28, 2012, from Desware: http://www.desware.net/sample-chapters/d03/D03-010.pdf

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Falk, E., De, F., & Shah, P. K. (2009). Ischemic heart disease. London, Manson.