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nerve control of BP or abnormal signals from the brain
control of the amount of fluid and salt in the circulation
control of the strength and rate of the heartbeat.
Researchers have already identified a gene that may be able to predict your future risk of hypertension. People who have inherited the angiotensinogen gene (T235) from both parents have double the risk of developing high blood pressure and coronary heart disease compared to those who do not have the gene variant, or who inherit it only from one parent.
DEVELOPMENTAL FACTORS
Fascinating research has suggests the way you develop during the first few weeks of life as an embryo may affect your future risk of high blood pressure and other cardiovascular diseases in adult life. This is probably linked with lack of micronutrients (vitamin and minerals) in the mother’s diet, which affects the way your arteries are laid down. Researchers have found, for example, that:
Low birth-weight babies maybe more likely to develop high blood pressure as adults. Average adult systolic BP increases by 11 mmHg as birth weight goes down from 7.5lb to 5.5lb.
The size of the placenta may be important – average systolic blood pressure rises by 15 mmHg as placental weight increases from 1lb to 1.5lb.
The highest blood pressures occur in men and women who were born as small babies with large placentas.
Risk of high blood pressure in later life also increases:
– as a baby’s birth length decreases
– as the ratio of a baby’s head circumference to the length of the baby increases from less than 0.65 to 0.7 or more.
– if the mother’s blood haemoglobin level was low during pregnancy
– if maternal nutrition was known to be poor.
Lack of important nutrients – including vitamins, minerals and essential fatty acids – during the first few weeks of embryonic life is thought to trigger the development of abnormal arterial and blood circulatory patterns. These probably result from an imbalance between the placenta and baby. This is supported by research linking fingerprint patterns with the risk of developing high blood pressure in later life. Fingerprints are laid down in the womb in the first few weeks following conception. Their patterns are linked to the degree of bumpiness and swelling of the developing fingertips, which is related in turn to irregular blood circulation.
Fingerprint patterns take the form of arches, loops or whorls, and the more whorls you have, the more likely you are to become hypertensive in later life. People with at least one whorl may have a blood pressure that is 6 per cent higher (8mmHg) than people with no whorls. BP then generally increases as the number of whorls increases, up to the maximum number possible, which is ten (two per digit). The average number tends to be two or three. Long, narrow hands are also associated with higher blood pressure, and both effects are more marked on the right hand.
Inherited and developmental factors are not the sole causes of high blood pressure, however. Something else has to happen in any individual before blood pressure goes up, and this is where environmental factors come in. These interact with inherited factors in individuals whose genes predispose them to hypertension to produce high blood pressure in later life. If several environmental factors linked with high blood pressure interact together, your risk of high blood pressure will be even greater.
ATHEROSCLEROSIS
One of the main causes of high blood pressure – especially a raised systolic BP – is hardening, furring up and narrowing of the arteries (atherosclerosis – see Chapter 3). This occurs naturally with increasing age and comes on more quickly if you smoke, eat an excessively fatty diet or are overweight. High blood pressure in turn puts excessive strain on the arterial wall lining and triggers damage that hastens atherosclerosis. Because atherosclerosis in turn causes hardening of arterial walls, a vicious cycle is set up in which blood vessels become even less elastic and less able to distend to even out pressure surges, so BP rises further. High blood pressure is therefore both a cause, and a consequence, of atherosclerosis, with each factor making the other worse.
DIABETES
Diabetes mellitus is a condition in which blood sugar (glucose) levels are raised due to insufficient production of insulin hormone by the pancreas. Some people also have an impaired tolerance to glucose tolerance due to an inability of their cells to respond properly to relatively normal levels of insulin (insulin resistance). Having poorly controlled diabetes significantly increases the risk of developing atherosclerosis, high blood pressure, coronary heart disease (CHD) and stroke – especially in women. The reason is not fully understood, but high blood sugar levels may trigger abnormal blood clotting, damage blood vessel linings to trigger hardening and furring up, affect nerves controlling heart and blood vessel function or weaken muscles in the heart or artery walls.
The risk of severe CHD is two to three times higher in men with diabetes and three to seven times higher in women with diabetes. Therefore, if you have both high blood pressure and are also diabetic, it is vitally important that you keep your blood sugar levels under tight control.
SMOKING
Smoking cigarettes greatly increases the risks associated with hypertension – people with high blood pressure, who also smoke, are two or three times more likely to develop coronary heart disease than hypertensive non-smokers, and life-insurance companies load their premiums accordingly.
Smoking cigarettes triggers hardening and furring up of the arteries (atherosclerosis), which is one of the most important causes of high blood pressure, coronary heart disease and stroke. It is also linked with at least 90 per cent of all cancers. The reason that cigarette smoke is so toxic is that it contains chemicals that:
damage the lining of arterial walls, triggering the build-up of clots and plaques
increase the stickiness of blood, making serious blood clots (thrombosis) more likely
displace oxygen from red blood cells in exchange for poisonous carbon monoxide – so that less oxygen is available for use by cells, including those in the heart muscle and artery walls
trigger spasm of arteries all over the body, which increases blood pressure and decreases blood flow to vital areas such as the brain and heart
produce harmful by-products of metabolism known as free radicals which damage tissues, increasing the risk of atherosclerosis and also of cancer.
For more information, see Chapter 21.
OBESITY
People who are overweight or obese are more likely to have high blood pressure than thin people, as there is a larger body tissue mass through which the heart has to pump blood. Overweight people are also more likely to eat an unhealthy diet with a high intake of saturated fat. This raises blood fat levels, which in turn hastens the onset of atherosclerosis. Another factor is that overweight people tend to be inactive.
Although not everyone who is overweight has high blood pressure, however, there seems to be an interaction between obesity and some underlying, predisposing mechanism that is inherited by some people. This may be linked to where excess fat is stored. Overweight people who carry excess weight around their middle (apple-shaped) rather than around their hips (pear-shaped) seem to be at greater risk of a number of health conditions, including high blood pressure, atherosclerosis, raised cholesterol levels, diabetes, CHD and stroke. The reasons are not fully understood but may be linked to the way the body metabolizes dietary fats.
For more information, see Chapter 21.
ALCOHOL
A high alcohol intake is also linked with an increased risk of hypertension. People who regularly consume excessive amounts (more than 3 units of alcohol per day, or 21 units per week) tend to have higher blood pressures. However, many people drink more than this and have a normal blood pressure – it depends on whether you have inherited predisposing factors that make you sensitive to these effects of alcohol.
For more information, see Chapters 11 and 21.
LACK OF EXERCISE
Lack of exercise is an important cause of high blood pressure. Inactivity means the heart is unfit, despite having to work extra hard to pump blood around the increased bulk of the body. People who exercise for at least 20–30 minutes, three times per week, have a lower risk of high blood pressure, stroke, obesity and coronary heart disease than those who are physically inactive.
To be beneficial, exercise needs to be brisk enough to raise your pulse rate, produce a light sweat and to make you slightly breathless. Unfortunately, the average level of physical activity in the UK is low. Only 30 per cent of men and 20 per cent of women are active enough to gain some protection against high blood pressure. One survey among adult males found that one in five had taken no exercise at all during the preceding month. Although exercise increases the amount of blood pumped through the heart by up to 700 per cent, and puts BP up during the period of exercise itself, this is a healthy, temporary response.
Taking regular exercise helps to prevent high blood pressure by:
burning off stress hormones that trigger arterial spasm in small blood vessels
dilating peripheral veins
increasing the efficiency of your cardiovascular system so your pulse rate falls
boosting the muscle pump action of your skeletal muscles
lowering blood fat levels
reducing the risk of atherosclerosis.
For more information, see Chapter 21.
STRESS
High blood pressure is thought to be linked with excessive levels of stress in some people. Susceptible individuals have an overactive part of the nervous system (sympathetic nervous system) which is unusually responsive to stressful stimuli that would normally be associated with only a mild, temporary rise in blood pressure. This overactivity of sympathetic nerves probably runs in families, with stress acting as the environmental factor that triggers off the process.
In people sensitive to stress, a condition known as Gaisbock’s syndrome can occur. This is a form of labile hypertension in which blood pressure levels can vary considerably. Sometimes they are high; sometimes they are low or normal. This can lead to more permanent hypertension if their lifestyle doesn’t slow down. One of the most common signs of this is so-called White Coat Hypertension – blood pressure that shoots up on being measured in the surgery or hospital (usually by someone wearing a white coat or uniform). This can increase systolic BP by as much as 100 mmHg, although this is extreme. More commonly, white coat hypertension increases systolic BP by 20–30 mmHg. This form of hypertension is confirmed by attaching the sufferer to a 24-hour BP monitoring tape and showing that BP rises in stressful conditions, including having BP measured by a doctor, then falls again in between.
Until recently, white coat hypertension was thought to be relatively harmless. However, latest research suggests that people with this condition have just as many abnormalities of the heart and blood vessels (e.g. poor left ventricular function, decreased elasticity and increased stiffness of artery walls) as those with persistently high blood pressure. They are also likely to develop hypertension in the future.
In most people, however, stress only causes only a transient rise in BP as a result of the hormone adrenaline (epinephrine). This triggers the constriction of arteries and veins which temporarily puts blood pressure up. This is an adaptive response to help you fight or flee in dangerous situations. Blood pressure can still fall when you are at rest or asleep, however, and relaxation training is usually helpful in offsetting the effects of excessive stress.
For more information, see Chapter 21.
KELOIDS
Interestingly, people who develop an excessive scar tissue reaction to a skin wound and produce a large, lumpy, keloid scar seem to be twice as likely to develop high blood pressure as people who produce normal amounts of scar tissue. This is thought to be due to a blood protein, angiotensin II, which helps to regulate blood pressure. It is now also known to stimulate production of collagen – a fibrous protein found in scar tissue. A group of drugs that block angiotensin (angiotensin converting enzyme – or ACE-inhibitors) are commonly used to treat high blood pressure. The link is the result of much research in an attempt to unravel some of the mysteries of essential hypertension.
For more information on dietary factors affecting essential hypertension, such as increased salt intake, and low intakes of calcium, magnesium, folic acid and antioxidants, see Chapters 6, 7, and 12.
Causes of Secondary Hypertension
One in ten people with hypertension have a recognizsed, underlying cause and are said to have secondary hypertension. Secondary hypertension should always be ruled out in any hypertensive person, but it is especially important to exclude other conditions in people developing high blood pressure before the age of 35.
KIDNEY DISEASE
The commonest cause of secondary hypertension is kidney disease, which accounts for 8 out of 10 cases. High blood pressure can also be the cause of kidney disease, however, and it can be difficult for doctors to tell which condition developed first. When high blood pressure is the cause of kidney disease, this occurs because essential hypertension leads to hardening and furring up of the large renal arteries and also damages small blood vessels in the kidney. As a result, blood supply to the kidneys is reduced and they may start to shrink. At the same time, poor blood supply to the kidney filtering units (nephrons) means less urine is produced. Kidney function progressively deteriorates and fluid builds up in the circulation, contributing to hypertension. Poor blood supply to the kidneys also stimulates the special pressure receptors (baroreceptors) in the kidneys that are responsible for monitoring blood pressure. If they detect blood pressure has fallen within the kidneys, they trigger increased production of renin hormone, which raises blood pressure in an attempt to increase blood supply to the kidneys. This puts BP up even more, so another vicious cycle develops.
Where kidney disease comes first, and high blood pressure develops as a consequence, the usual kidney diseases involved are:
chronic glomerulonephritis (inflammation of the kidney filtration units)
chronic atrophic pyelonephritis (shrinking of kidney tissue due to chronic infection or inflammation)
congenital polycystic kidneys (abnormal kidney structure due to the formation of multiple cysts during embryonic development).
Kidney problems are thought to cause high blood pressure by reducing filtration of excess fluid and salts from the body, which build up in the circulation to raise blood pressure. Increased secretion of renin hormone is also involved.
OTHER CAUSES
Other relatively common causes of secondary hypertension include:
pre-eclampsia during the last three months of pregnancy (which affects around one in ten pregnant women)
the side-effects of some drugs.
Rarer causes of secondary hypertension include:
anatomical abnormalities of the circulatory system such as narrowing of the aorta or renal artery
polycythaemia, in which blood stickiness is significantly increased due to over-production of red blood cells
Conn’s syndrome, in which there are high levels of aldosterone hormone
phaeochromocytoma, due to a tumour that secretes excessive amounts of adrenaline hormone and noradrenaline
Cushing’s syndrome, due to excessive exposure to corticosteroids – either from overactive adrenal glands or from steroid drug treatment
acromegaly, due to excessive production of growth hormone by the pituitary gland
hyperparathyroidism, due to overactivity of the four parathyroid glands in the neck which, if not treated, raises blood calcium levels and can damage the kidneys.
SECONDARY HYPERTENSION DUE TO DRUGS
Several drugs – both those available on prescription and those bought over the counter – can put your blood pressure up while they are being taken. These include:
nasal decongestants (e.g. ephedrine), taken to relieve a blocked nose
non-steroidal anti-inflammatory drugs (e.g. ibuprofen), taken to relieve aches and pains in the muscles and joints which – can raise BP by 5–10 mm Hg
oral corticosteroids, taken for severe inflammatory conditions such as asthma or rheumatoid arthritis
the combined oral contraceptive pill (containing both oestrogen and progestogen hormones), which can raise BP after several years’ use – recent research suggests that the average increase in BP is around 2.8/1.9 mmHg. In some women, however, rapid and more severe rises in BP can occur
monoamine-oxidase inhibitors – drugs sometimes used to treat severe depression – can cause sudden rises in BP if you eat cheese or other foods containing tyramine while on medication
carbenoxolone – a synthetic version of liquorice, sometimes used to treat stomach ulcers – can put BP up as it can trigger retention of sodium and water; a similar effect can also occur if you eat too much liquorice which has not been deglycerrizhinated.
Diagnosing High Blood Pressure
ROUTINE EXAMINATIONS
If your doctor finds your blood pressure is raised, you will probably have the following examinations:
checking your blood pressure at least twice during the first visit
feeling your pulse to see how regular and strong it is
checking pulses in your groin, feet and ankles to make sure your peripheral circulation is intact – pressing on the skin of your lower legs and then letting go will show how quickly blood flows back into the blanched area
feeling your chest to see where the tip of your beating heart is detectable – this gives a good indication of whether or not your heart is enlarged
listening to your heart with a stethoscope to check for heart murmurs and to listen to your heart beat rhythm
listening to your lungs to check for signs of fluid build-up on the chest
listening to your neck and abdomen with a stethoscope to detect any noises due to turbulent blood flow through damaged carotid or renal arteries
examining the backs of your eyes to look for any signs of arterial damage (see below).
If your blood pressure remains consistently raised, you may have the following routine investigations:
chest x-ray – to check the size and shape of the heart and to look for evidence of congestive heart failure with fluid build-up on the lungs
