Factors affecting the Development of Coronary Heart Disease (CHD).

AS BIOLOGY ESSAY

Cardiovascular disease(CVD) is the main cause of death in the UK, accounting for over 245,000 deaths a year: four out of ten of all deaths. The main forms of CVD are fundamentally coronary Heart Disease(CHD) also Stroke. Approximately half of all CVD death is from Coronary Heart Disease, and a quarter from Stroke. But CVD can also include congenital heart disease (from birth) such as a hole in the heart or valvular heart disease. CHD and Stroke have a similar cause- a blockage in an artery.

CHD causes over 120,000 deaths in the UK: around one in four deaths in women and one in six deaths in women. This compares to about 34,000 deaths a year from lung cancer and 13,000 deaths from breast cancer. It is also the most common form of premature death in the UK causing 23% of premature death in men and 14% of premature death in women. Nearly all deaths from coronary Heart Disease are because of a heart Attack (also called a coronary thrombosis or myocardial infarction). Over 270,000 people in the UK suffer a heart attack every year. About half are fatal-in around 30% of cases the patient will die before reaching the hospital. However death rates have been falling since the late 1970’s in the United Kingdom. For adults under 65 years death rate has fallen by 40% in the last 10 years. In men death rates have been falling faster in the younger age groups. E.g. there was a 43% fall in the death rate for men aged 45-54 in 1989 and 1999, but the fall in the death rate for men aged 65-74 was only 34%. Over the same period, death rates in women have fallen fastest in the 55-64 age group, where rates were down 48%. (Information sent on request from The British Heart Foundation office in London-Phoned 02079350185 on 10-12-03)

The heart is a muscle that is working constantly. To perform well it needs a constant supply of oxygen and nutrients (in order to respire to contract repeatedly about 100,000 times a day), which are delivered by the blood through the coronary arteries. This flow can be reduced by a process called atherosclerosis, on affecting the coronary arteries it is the main form of CHD. It occurs when the inside walls of the blood vessel thicken with deposits of cholesterol, dead muscle cells, fibrous tissue, and blood platelets. The deposition is named atheromatous plaque or atheroma. The blood vessels then become narrow (called ‘stenosis’) and begin to harden, decreasing elasticity, referred to as arteriosclerosis. Therefore the blood flow is restricted by the partially blocked lumen, and the blood transportation is weakened by the decreased elasticity. This is not helped by the fact that coronary arteries are only 4mm in diameter. This lack of blood flow results in under nourishment of the heart muscle, so affecting heart muscle function. If the atheroma bulge breaks through the smooth endothelial wall of an artery and penetrates into the lumen, the rough surface of the waste can cause a blood clot to form. The blood clot can remain at its origin (a thrombus) or may be transported to another artery (a embolus). If the clot is large enough, in either case, an artery may be blocked (coronary thrombosis) resulting in a heart attack. The heart muscle may fail to pump properly and cause a sudden drop in blood pressure. Abnormal heart rhythms may be triggered within minutes and a heartbeat may become erratic or even stop, resulting in Cardiac arrest. Fluid accumulation in the lungs can cause breathlessness. Long-term damage to the heart muscle maybe apparent from the death of cells that didn’t receive enough oxygen. Because heart cells cannot be replaced the cell loss is permanent. The more serious the case is when a blockage is high in the coronary artery, when at the end the effects are practically unnoticeable. ( and Advanced Biology)

The above are some of the many forms of coronary Heart Disease. Another common cause is Angina.

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Angina: -It is a less severe symptom of CHD. Atheroma in a coronary artery is the main cause of angina (angina pectoris-Latin meaning chest pain). Characteristically it is a dull or heavy chest pain or sensation around the heart, radiating into the arms, jaw, neck and back mainly at the left side. It is often triggered during exercise because the heart cannot meet the demands of oxygen, for the heart to beat faster, when blood flow is limited by a stenosis. Like a skeletal muscle it cramps up. Stable angina is more common with great exertion such as cycling or running and subsides at rest. It can also be provoked by cold weather, by strong emotions or even after a heavy meal. Unstable angina is when the atheroma forms an uneven surface resulting in blood clots. This may block the lumen more so the angina would worsen at a fast rate, and become unpredictable even at rest. Therefore requiring urgent treatment to prevent a heart attack.

(British heart foundation, posted information)

Spasm: - Repeated contractions of the muscle in the coronary artery wall may also impede the blood flow and contribute with other small factors such as atherosclerosis, and coronary thrombosis to cause a heat attack. (Understanding Biology).

Aneurysm: -This is a different form of arterial blockage, formed when the arterial wall is weakened by the atheroma mentioned previously, and it develops to form a balloon like structure. On severe weakening the aneurysm may cause wall to rupture resulting in an internal haemorrhage-blocking the artery. Any arterial blockage can deprive tissue of oxygen- damaging or killing it.

(Advanced Biology and )

Blood pressure is the pressure of the blood in the arteries. A certain amount of pressure is needed to keep the blood flowing. High blood pressure develops if the walls of the larger arteries lose their natural elasticity and become rigid, and the smaller blood vessels become narrower (constrict). High blood pressure is also called hypertension. The heart is a pump that beats by contracting and then relaxing. The pressure of the blood flowing through the arteries varies at different times in the heartbeat cycle. The highest pressure is systolic pressure because it is during systole when the ventricles are contracting to force blood around the body. The lowest pressure is diastolic pressure because it is during diastole when the heart is relaxed allowing the blood to fill.

Blood pressure is measured in millimetres of mercury (mmHg).A blood pressure reading firstly gives a systolic pressure reading and then a diastolic pressure reading. It is measured using a Sphygmomanometer wit a stethoscope just below. The target is to have a blood pressure below 140/85mmHg. But if a person has diabetes the target would be below 130/80mmHg. There is no fixed division line between normal and exaggerated blood pressure. High blood pressure can put a strain on the heart and the blood vessels, leading to a rupture, or thrombosis. CHD is more common in men (below 50) who have a blood pressure of 170/100. The risk is then halved if a similar man (below 50) has a pressure of 140/80. In 9 out of 10 people there is no definite cause of high blood pressure, but the below factors can all contribute, in the same way as CHD is affected, because they are closely linked. The treatments for high blood pressure include the use of drugs called beta blockers. They act as antagonists to adrenaline and nor adrenalin preventing them from reacting with receptors (beta-adrenoceptors on the cells in the pace maker region of the heart. Therefore beta blockers help to prevent the usual stimulatory actions of adrenaline and nor adrenaline on the heart, causing the heart rate and blood pressure to decrease. (Advanced Biology and bhf information pack)

Coronary Heart Disease is also known as coronary heart disease and ischaemic heart disease. Ischaemia means insufficient blood supply and comes from the Greek words for ‘ischein’, to restrain, and ‘haima’ meaning blood. (www.bhf.org.uk)

CHD does not have one specific cause, but a number of contributory factors. The following are the factors that affect the development of Coronary Heart Disease.

There are factors that cannot be modified;

Increasing age – The risk of CHD is greater for men over 40 years, and for women after menopause. About four out of five people who die of coronary heart disease are 65 or older. At older ages, women who have heart attacks are more likely than men are, to die from them within a few weeks.

Male sex (gender) – Men have a greater risk of heart attack than women do, and they have attacks earlier in life. This is thought to be because of the protective female sex hormones. Oestrogens reduce the proportion of low-density lipoproteins in the blood. These carry large amount of cholesterol which lead to the deposites on the arteries as mentioned previously. So after menopause, women's death rate from heart disease increases. But it's not as great as men's until both groups reach the 80s.

Heredity (including Race) – Children of parents with heart disease are more likely to develop it themselves. If a child has one parent with the disease or died from it, the risk is doubled, if both parent have or had it, the child is five times more likely to contract it. However, families often share the same unhealthy habits and it may be misleading to assume that the risk factors are entirely inherited. Nevertheless the family history can yield important information about CHD risk. High blood pressure and high blood cholesterol may be inherited risks. African Americans have more severe high blood pressure than Caucasians and a higher risk of heart disease. Heart disease risk is also higher among Mexican Americans, American Indians, native Hawaiians and some Asian Americans. This is partly due to higher rates of obesity and diabetes. Most people with a strong family history of heart disease have one or more other risk factors. Just as you can't control your age, sex and race, you can't control your family history. Therefore, it's even more important to treat and control any other risk factors you have. It will not be long before the specific genes are identified, and genetic screening will then be available to find those most at risk and to act on CHD prevention.

Factors that cannot be modified but can be helped;

Diabetes Mellitus - Diabetes seriously increases your risk of developing cardiovascular disease. Even when glucose levels are under control, diabetes increases the risk of heart disease and stroke, but the risks are even greater if blood sugar is not well controlled. About three-quarters of people with diabetes die of some form of heart or blood vessel disease. If you have diabetes, it's extremely important to work with your healthcare provider to manage it and control any other risk factors you can.

High Blood Pressure- an inherited high blood pressure can be monitored and controlled as suggested by beta-blockers.

Inherited High Cholesterol- the cholesterol levels in the blood can also be monitored and the use of highly effective drugs called statins has transformed the treatment in recent years.

Factors that can easily be modified;

Individual response to stress may be a contributing factor. Some scientists have noted a relationship between coronary heart disease risk and stress in a person's life, their health behaviours and socio-economic status. These factors may affect established risk factors. For example, people under stress may overeat, start smoking or smoke more than they otherwise would. Even acute stress can raise blood pressure temporarily and may influence blood fats. There is a probable bond with the release of high levels of adrenalin, which, as stated increases the heart rate and leads to a constriction of the arteries.

Drinking too much alcohol can raise blood pressure, cause heart failure and lead to stroke. It can contribute to high triglyceride levels, cancer and other diseases, and produce irregular heartbeats. It contributes to obesity, alcoholism, suicide and accidents. However moderate alcohol intake (14 units a week and 21 units for men) of any alcoholic drink, has been shown to have a beneficial effect on CHD.
It's not recommended that non-drinkers start using alcohol or that drinkers increase the amount they drink.

Tobacco smoke – There is no safe level of smoking. Smokers' risk of heart attack is more than twice that of non-smokers, this risk is even higher in the young. Almost 40% of CHD deaths are caused by smoking. Cigarette smoking is the biggest risk factor for sudden cardiac death. Smokers who have a heart attack also are more likely to die and die suddenly (within an hour). Cigarette smoking also acts with other risk factors to greatly increase the risk for coronary heart disease. People who smoke cigars or pipes seem to have a higher risk of death from coronary heart disease (and possibly stroke) but their risk isn't as great as cigarette smokers'. Exposure to other people's smoke increases the risk of heart disease even for non-smokers. Cigarette smoke causes the platelets to attach tot the lumen walls through weakening the lining of the blood vessels. Carbon monoxide has a similar form to oxygen; the haemoglobin does not detect the difference so it absorbs the carbon monoxide reducing the oxygen carrying capacity of the blood, to the heart where it is needed for respiration in order to contract.

High blood cholesterol –Cholesterol is a lipid, or fatty substance, together with other lipids (triglycerides) and fatty acids, it forms the bulk of body fats. It is needed as part of cell membranes and in the production of hormones and bile. Some comes from peoples diets, however most is made from saturated fats in the bowl and liver, and then carried into the blood stream as lipoproteins. The body needs some cholesterol the blood. But during the condition ‘atherosclerosis’, in the early stages of CHD Atheroma develops when LDL, cholesterol is chemically changed by the process of oxidation. It is then taken up by cells in the coronary artery walls where the narrowing process begins. Lipoproteins are classified according to their density in the blood. LDL stands for low-density lipoprotein and HDL stands for high-density lipoprotein. HDL cholesterol removes cholesterol from the circulation, and appears to protect against CHD. Therefore the ratio of HDL and LDL within the body is important. Preferably the level of HDL should be the higher. Increased amounts of saturated fats in diet increases the level of LDL above that of HDL, and increased amounts of unsaturated fats have the reverse affect. As blood cholesterol rises, so does risk of coronary heart disease. When other risk factors (such as high blood pressure and tobacco smoke) are present, this risk increases even more. A person's cholesterol level is also affected by age, sex, heredity and diet. Diabetes and an under active thyroid gland also may increase cholesterol levels.

Physical inactivity – An inactive lifestyle is a risk factor for coronary heart disease. Regular, moderate-to-vigorous physical activity helps prevent CVD and CHD. The more vigorous the activity, the greater your benefits. However, even moderate-intensity activities help if done regularly and long term. Exercise can help increase HDL, control blood cholesterol, diabetes and obesity, as well as help lower blood pressure in some people. Physical activity helps prevent blood clotting, reducing the risk of a heart attack. It also helps after having a heart attack by reducing angina and as it produces endorphins, stress and depression are overcome which prove to hinder recovery. Aerobic exercise strengthens the heart, so when it contracts the blood flow is more forceful, meaning the heart doesn’t have to work as vigorously. The stroke volume increases and the heart rate decreases.

Obesity and overweight – People who have excess body fat — especially if a lot of it is at the waist — are more likely to develop heart disease and stroke even if they have no other risk factors. Women tend to have more fat below the waist where it is less harmful, men tend to have it at the waist, this is another reason for why there is a gender difference in contracting CHD. Excess weight increases the heart's work. It also raises blood pressure and blood cholesterol and triglyceride levels, and lowers HDL ("good") cholesterol levels. It can also make diabetes more likely to develop. Many obese and overweight people may have difficulty losing weight. But by losing even as few as 10 to 20 pounds, you can lower your heart disease risk. Obesity is normally from excessive over eating, especially of fatty foods. It can easily be avoided if the energy consumption is decreased to only what is needed for daily activities and a balanced diet is strongly recommended. ( and Advanced Biology)

World wide-economics and wealth CHD is by far the leading disease and thus cause of death in the developed world.

( and British heart foundation- posted information)