There are several factors that contribute to the development of atherosclerosis, and hence lead to a majority of the cardiovascular diseases. Some of these risk factors can not be altered, whilst others, the external risks, can.
External risks for CVD include:
High Blood Cholesterol: Cholesterol is carried in the blood and is in all the body cells. It is carried through the body by two types of lipoproteins; high density lipoprotein (HDL) and low density lipoprotein (LDL), also known as good cholesterol and bad cholesterol respectively. As mentioned, atheroma forms from LDLs therefore high intake of this type of cholesterol leads to atherosclerosis which increases chances of myocardial infarction and ischemic stroke. HDLs, on the other hand, remove cholesterol from the peripheral tissues and transport it to the liver, where it can be excreted from the body.
Triglycerides are another type of fatty substance in the blood. They're found in foods such as dairy products, meat and cooking oils. They can also be produced in the body, either by the body’s fat stores or in the liver. People with high triglyceride levels have a greater risk of developing cardiovascular disease than people with lower levels
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High Blood Pressure (Hypertension): Hypertension occurs when the diastolic pressure exceeds 95mm Hg and the systolic pressure exceeds 169 mm Hg[1]. High blood pressure can damage the endothelium of the arteries which makes it more vulnerable to atherosclerosis and thrombosis which can then lead to angina, myocardial infarction and ischemic strokes. The damaging of the endothelium weakens the arteries and constant pressure of blood continues to flow through these weakened arteries. This can cause a section of the artery’s wall to enlarge and form a bulge called an aneurysm[4], figure 2[2].The aneurysm could potentially rupture, and this is what leads to the haemorrhagic stroke.
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Stress: The sympathetic nervous system (SNS) is one of the many nervous systems which helps to manage the internal affairs of the body, and under normal conditions will secrete small amounts of a neurotransmitter substance called noradrenaline directly on the organs it is stimulating. Stressful situations, however, activate the SNS and stimulate the adrenal gland to secrete additional noradrenaline into the bloodstream along with adrenaline, which is a more powerful neurotransmitter[5]. This secretion of adrenaline and additional secretion of noradrenaline increases the amplitude of the heart beat and hence increases the body’s heart rate, which in turn increases blood pressure. Also, fatty acids are released into the bloodstream to be used as energy at times of stress which increases cholesterol and triglyceride levels.
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Smoking: smoking damages the endothelium of the arteries which makes it more prone to the build-up of atheroma, narrowing the artery and restricting blood flow. Also, carbon monoxide in the smoke reduces the amount of oxygen the blood can carry to the heart which, as mentioned, can lead to angina. Furthermore, nicotine in the cigarette stimulates the body to produce adrenaline, increasing blood pressure as the heart beats faster[5].
- Physical inactivity: Exercise burns calories therefore can help to control cholesterol levels and may lower blood pressure. Exercise also strengthens the heart muscle and makes the arteries more flexible. Lack of exercise develops atherosclerosis and, as well as malnutrition, can lead to obesity which will increase blood pressure as the heart needs to pump faster in order to supply blood to all the excess body fat due to the larger body mass.
Risk factors that can not be altered:
- Genetics: There are genetic tendencies in some families and ethnic groups to develop high blood pressure or have arteries that are more easily damaged or have problems with cholesterol.
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Age: Ageing reduces the elasticity of the arteries and stiffens its wall which makes it easier for atheroma to build up inside the arteries[6]. Also thehardening of the arteries makes the heart less able to pump blood around the body.
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Gender: Under the age of 50 it is more likely for men to suffer from CVD, but after menopause the chance of a female developing a CVD is similar to that of a male. This is because in vitro animal studies have shown that oestrogen effects many of the processes involved in the development of atherosclerosis; it inhibits platelet aggregation, LDL levels and decreases collagen and elastin production[6].
Cardiovascular diseases can be treated by a number of non-surgical methods as well as just simply changing lifestyle.
Non-surgical treatments for cardiovascular diseases:
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Aspirin: Aspirins block the enzyme cyclooxygenase which means the body is less able to produce a substance called prostaglandin[7] (prostaglandin is what causes the blood platelets to stick to the atheroma and form blood clots). Therefore when the aspirin inhibits the formation of prostaglandin, it inhibits the formation of blood clots as well, reducing the risk of myocardial infarction and ischemic stroke.
However, aspirin can increase the risk of stomach ulcers and abdominal bleeding. Also during a stoke, aspirin can increase the risk of bleeding into the brain[7].
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Heparin: Heparin is an anticoagulant medication which means that it helps clots from forming in the blood. It works by slowing down the process of clot formation and also prevents growth of a clot[7]. This reduces the chances of a stroke and myocardial infarction.
However, intake of heparin can lead to a condition called Heparin Induced Thrombocytopenia, which can cause deep thrombosis or even death[8].
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Statins: Statins are drugs used to lower blood cholesterol. They work by blocking the enzyme in the liver that makes the cholesterol, called hydroxy-methylglutaryl-coenzyme A reductase[7] which therefore reduces the formation of atheroma inside the arteries, therefore inhibits the developing of atherosclerosis and reduces the chances of having many of the CVDs.
However, a serious but rare risk associated with this treatment is liver failure and rhabdomyolysis. Rhabdomyolysis often begins as muscle pain and can progress to loss of muscle cells, kidney failure and death.
- Beta blockers: Beta blockers block the effects of the hormone adrenaline. This means that the heart beats slowly with a reduced force which therefore lowers blood pressure. Beta blockers also help blood vessels relax and open up to improve blood flow, reducing the symptoms of angina.
Side effects of beta blockers include bleeding, dizziness and depression.
- Calcium channel blockers: Calcium channel blockers, also called calcium antagonists, relax and widen blood vessels by affecting the muscle cells in the arterial walls. This increases blood flow in the heart, reducing symptoms of angina. The calcium channel blockers also slow the hearts pulse and therefore controls blood pressure.
Side effects of calcium channel blockers include drowsiness, increased appetite and constipation.
- Nitrates: Nitrates relax and widen the blood vessels allowing more blood to flow to the heart. This easy flow of blood means there is no build-up of pressure inside the blood vessels and no need for oxygen to go to the heart.
Side effects of nitrates include blurred vision, shortness of breath and weak and fast heartbeat.
Lifestyle changes are a very most powerful way to prevent developing a CVD or worsening an existing CVD. These include:
- Exercising: Exercising strengthens the heart and lowers blood pressure. It also reduces LDL and increases HDL
- Lower blood cholesterol to recommended level of 5mmol/litre, although LDL cholesterol would be less than 3mmol to keep plaque from building up inside the arteries.
- Reducing fat and salt intake: less than 60g of fat per day for an adult
- Do not smoke
- Stress reduction techniques, such as meditation, in order to prevent secretion of adrenaline and reduce blood pressure.
References
[1] Adds, J., Larkcom, E. and Miller, R., (2003) ‘Respiration and Coordination’ pp.98-165
[2] http://www.biosbcc.net/doohan/sample/htm/vessels.htm, accessed 21/11/2011
[3] http://www.bupa.co.uk/individuals/health-information/directory/s/stroke#textBlock216342, accessed 21/11/2011
[4] http://www.mayoclinic.com/health/high-blood-pressure/HI00062, accessed 21/11/2011
[5] http://www.hearthealthyonline.com/heart-disease-overview/stress-management/stress-effect-on-heart_1.html , accessed 22/11/2011
[6] Dollemore, D, et al. (2008), ‘Aging Hearts & Arteries: A Scientific Quest’ 4
[7] http://www.webmd.com/heart-disease, accessed 24/11/2011
[8] http://www.stoptheclot.org/learn_more/blood_clot_treatment.htm, accessed 24/11/2011
