Understanding
Blood Pressure

Professor D.G. Beevers

Published by Family Doctor Publications Limited in association with the British Medical Association

IMPORTANT

This book is intended not as a substitute for personal medical advice but as a supplement to that advice for the patient who wishes to understand more about his or her condition. Before taking any form of treatment YOU SHOULD ALWAYS CONSULT YOUR MEDICAL PRACTITIONER. In particular (without limit) you should note that advances in medical science occur rapidly and some information about drugs and treatment contained in this booklet may very soon be out of date. All rights reserved. No part of this publication may be reproduced, or stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording and/or otherwise, without the prior written permission of the publishers. The right of Professor D.G. Beevers to be identified as the author of this work has been asserted in accordance with the Copyright, Designs and Patents Act 1988, Sections 77 and 78.

© Family Doctor Publications 1999–2006 Updated 2001, 2002, 2003, 2004, 2006
Family Doctor Publications, PO Box 4664, Poole, Dorset BH15 1NN
ISBN: 1 903474 30 2

Contents

Introduction ........................................................................................................... 1

What is blood pressure? .................................................................................... 4

Measuring your blood pressure ......................................................................... 9

What is hypertension and why does it matter?............................................... 23

What causes hypertension? ............................................................................ 34

How hypertension is investigated ................................................................... 59

Treatment without drugs .................................................................................. 71

Drug treatment ................................................................................................. 79

Special cases ................................................................................................ 110

Advances in hypertension research ............................................................ 122

Questions and answers ................................................................................ 127

British Hypertension Society

Cardiovascular Risk Prediction Charts ...................................................... 130

Useful addresses .......................................................................................... 136

About the author

Professor D.G. Beevers is Professor of Medicine and Consultant Physician to the City Hospital, Birmingham. He is past president of the British Hypertension Society and the Editor of the Journal of Human Hypertension. His main interests are in clinical aspects of raised blood pressure and the importance of a population-based approach.

Introduction

How common is high blood pressure?

If you are over the age of 30 and can’t remember when you last had your blood pressure checked, you could be one of the seven to ten million people in this country who has high blood pressure. Doctors usually use the term ‘hypertension’ to describe this condition which may cause no symptoms at all for very many years, but could eventually lead to serious complications, including heart disease and strokes. In this book, the word hypertension is used to mean a blood pressure level that has been found on several separate occasions to be above normal, and that needs to be treated to prevent complications developing in the long term.

Who has high blood pressure?

The condition is very common (10–20 per cent of the population) in the UK and, the older you are, the more likely you are to have developed it. Whether you do so depends on a number of related factors, including:

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• heredity
• your diet – and especially the amounts of salt and alcohol that you consume
• your ethnic background
• whether you have diabetes
• whether you are overweight
• whether you take regbnular exercise.

How is high blood pressure diagnosed?

If all this sounds alarming, there is good news too. Hypertension can be easily diagnosed: your blood pressure can be measured quickly and painlessly at your GP’s surgery or health centre. When the reading is above normal, the check can be repeated three or four times if necessary to establish that the first figure wasn’t a chance finding.

How is high blood pressure treated?

Even if you do have hypertension, you may be one of the many people who don’t need drug treatment for some time (and possibly not ever), provided that you make some straightforward lifestyle changes that will not only lower your blood pressure but bring general health benefits too.

When treatment is required, there are a number of very effective drugs available, which are taken in tablet form usually once daily. Most people find that they have no problems at all with the treatment, but, if you do experience side effects from one drug, there are other, equally effective alternatives.

More modern drugs tend to have very few side effects. Research has shown that controlling hypertension with drug therapy can bring down the risk of a stroke by 35 to 40 per cent, and the risk of coronary heart disease by 20 to 25 per cent.

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A symptomless disease

The most important message on hypertension is that you may not know that you have it until it has done you serious damage, unless you have your blood pressure checked. Even quite seriously raised blood pressure can be controlled once it is identified and, provided that you keep taking the treatment prescribed for you and have regular check-ups, your chances of developing serious and potentially life-threatening complications are dramatically reduced.

KEY POINTS

■  Hypertension affects seven to ten million people in the UK

■  Hypertension is often not diagnosed

■  The treatment of hypertension saves lives

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What is blood pressure?

Blood pressure

When doctors talk about blood pressure, what they mean is the pressure within the large blood vessels as your heart forces blood to circulate around your body. On the whole, the lower your blood pressure, the healthier you are in the long term (except in some very rare conditions in which excessively low blood pressure is part of an underlying disease).

Blood pressure is the pressure within the arteries as the heart forces blood to circulate around your body.

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The circulatory system

Blood picks up oxygen in the lungs from the air that we breathe in. This oxygenated blood enters the heart and is then pumped out to all parts of the body in blood vessels called arteries. Larger blood vessels branch into smaller and smaller ones and then to microscopic arterioles, which eventually link to tiny networks of blood vessels known as capillaries.

This network of larger arteries, medium-sized arterioles and tiny capillaries allows blood to reach every cell of the body and deposit its oxygen, which is used by the cells to make the vital energy that they need to survive.

Once the blood has deposited its oxygen in the cells, the deoxygenated blood returns to the heart in veins, to be pumped back up to the lungs to pick up more oxygen.

During each heartbeat, the heart muscle contracts to push blood around the body. The pressure produced by the heart is highest when it contracts, and this is known as the systolic (higher value) pressure. Then the heart muscle relaxes before its next contraction, and the pressure is at its lowest, which is known as the diastolic (lower value) pressure. Both systolic and diastolic pressures are measured when you have your blood pressure checked.

The dividing line between a normal and an abnormal blood pressure is not easy to define. Perhaps the best definition is that level of blood pressure above which treatment has been shown to be worthwhile (see page 23).

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Cardiovascular system

Diagram showing the heart and circulation with veins (blue) draining the blood back to the heart where it is pumped to the lungs and back to the rest of the body through the arteries (red). Larger blood vessels branch into smaller and smaller ones and then to tiny networks of blood vessels known as capillaries, where oxygen and nutrients are passed from the blood into the surrounding cells.

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The sequence that makes up a heartbeat

The heartbeat sequence has three phases. The timing of these phases must be accurately maintained regardless of how slowly or rapidly the heart is beating.

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What determines blood pressure?

The blood pressure is determined by:

• The pumping strength of each heartbeat – the greater the strength the higher the blood pressure

• The volume of blood in the circulation – a greater volume of blood will increase blood pressure

• The diameter of the blood vessels – narrower blood vessels raise blood pressure

KEY POINTS

■  High blood pressure is caused by a narrowing of the microscopic arterioles in all tissues

■  Systolic pressure is the pressure in the larger vessels when the heart contracts

■  Diastolic pressure is the pressure when the heart relaxes between beats

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Measuring your blood pressure

How often should blood pressure be measured?

Some people will have had their blood pressure taken at least once – perhaps by the doctor or nurse at the surgery, in hospital or, in the case of a pregnant woman, at the antenatal clinic. You may possibly have opted to have it done at a pharmacy or health food shop or even have tried taking it yourself using one of the special kits that can be bought over the counter.

Around half of the adult population have, however, never had their blood pressure measured usually because they feel entirely well and have not therefore visited their doctors. As raised blood pressure is usually a symptomless condition, many of these people will be found to have raised blood pressure if they undergo a routine check. It is now recommended that all adults should have their blood pressure checked at least once every five years. If the blood pressure is not entirely normal, more frequent checks are necessary.

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How is blood pressure measured?

Although the ideal method would be to measure the blood pressure actually inside the arteries, this is clearly not feasible on a large scale because it would involve needles. However, an accurate reflection of the pressure under which blood is being pumped can be obtained using a less invasive approach. Usually you will be asked to sit down and the person performing the check wraps a rubber-lined cuff, which is part of the pressure-measuring device known as a sphygmomanometer, around your upper arm.

Determining systolic blood pressure

The cuff is inflated, either with a small hand pump or automatically by an electronic measuring device. This will stop the blood flow to your arm temporarily. The cuff is then deflated slowly until the pressure is low enough for blood to start to pass under the cuff. Electronic blood pressure measurement devices can detect this blood flow. Alternatively, the doctor or nurse may listen over the artery just below the cuff and hear the sounds as blood starts to flow.

Determining diastolic blood pressure

As the cuff continues to deflate turbulence occurs in the underlying artery because it is only partially blocked. Finally, the cuff will reach the pressure where there is no narrowing of the underlying artery and at this stage the electronic manometers (pressure-measuring device) can detect the absence of any turbulence. Alternatively, a doctor or nurse will note that turbulence sounds have disappeared.

The pressure where blood first starts to pass under the cuff is called the systolic blood pressure and the

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pressure where there is no turbulence in the artery, because the cuff pressure is low, is called the diastolic blood pressure. The systolic blood pressure coincides with the maximum pressure within the arterial tree and the diastolic blood pressure coincides with the minimum blood pressure in the system.

Measurement problems

This technique of measuring blood pressure is indirect but has the benefit of being easy to perform. There are, however, four sources of error when blood pressure is measured in this way.

The patient

Falsely raised blood pressures will occur if the patient is very anxious or involved in any animated conversation. This sort of error can be minimised if blood pressure is taken in a very quiet and peaceful environment. Sometimes the first reading of blood pressure may be raised, but the second or third readings may settle considerably as the patient becomes familiar with the technique.

The observer

Observer error is mainly a problem with the old-fashioned method of measuring blood pressure using a stethoscope and mercury column. This is because the decision about whether the doctor or nurse can hear the systolic and diastolic sounds is subjective and open to observer error or bias.

The cuff

If the cuff is too small the blood pressure is overestimated. It is also very important that the cuff be at exactly the

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How is blood pressure measured?

12

How is blood pressure measured? (contd)

13

same level as the heart. If the cuff is above the level of the heart, the blood pressure will be underestimated, and if below the blood pressure will be overestimated.

The manometer

Both the electronic and the mercury blood pressure-measuring systems may be accurate. Most electronic machines marketed now have passed criteria laid down by the British Hypertension Society (BHS). It is important that only manometers that have been passed by the BHS are used. Mercury machines can deteriorate if they are not maintained regularly.

In a small number of patients it proves impossible to measure blood pressure using electronic blood pressure-measuring devices. Under these circumstances the doctor or nurse will have to use a mercury manometer. Measurement of blood pressure using a reliable mercury system remains the ‘gold standard’, but the advent of automatic and semi-automatic systems means that mercury manometers are now rarely needed. All general practitioner health centres and hospital outpatient clinics will need to have one well-maintained mercury manometer available whereas there should be semi-automatic machines in every clinical room.

An important advantage of the electronic blood pressure equipment is that the clinician can effortlessly take several readings and obtain a truer picture of the real blood pressure as the patient becomes familiar with the technique. It is increasingly felt that a single one-off blood pressure reading measured with a mercury manometer is of little clinical value. Blood pressures that are raised should be re-checked and many settle over five to ten minutes.

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Taking a blood pressure reading

Usually, you will be asked to sit down and the cuff is applied to your upper arm so that it is at the same level as your heart. It is very important that you are as relaxed as possible and that your arm is supported by resting your elbow on a table – the effort of holding it up could otherwise produce a falsely high reading.

Everyone’s blood pressure is immensely variable and yours may go up if you’re feeling anxious or stressed, so try to relax as much as you can while it’s being measured. Your doctor or nurse will probably take the first reading as a rough guide and take a second measurement to get the actual reading. If your blood pressure is clearly settling to a lower level between the first and second reading, you may need to have a third or even a fourth reading at another visit to the clinic

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some days or weeks later to make sure that the final figure is a truly representative value. This is particularly important if the finding on the first or second measurement is only slightly above normal. There is evidence to suggest that, in most people, the blood pressure ‘bottoms-out’ at the fourth visit, with little further fall after that. There are, however, many exceptions to this rule.

Which arm should be used?

Blood pressure should be checked initially in both arms, and thereafter, if there is no important difference between the arms, the nearest arm can be used. Important differences between the arms are found in about 10 per cent of the population. If there is a difference, then the blood pressure should be measured in the arm with the highest pressure. This is common in older patients and may be the result of narrowing of blood vessels in the arm (see page 25).

If your upper arm is larger than average (more than 33 centimetres around), the person measuring your blood pressure will need to use a larger cuff, otherwise there may be a falsely high reading. About 15 per cent of people with high blood pressure have an arm circumference that is greater than 33 centimetres so it is crucially important that the correct size of cuff is used.

Standing up or sitting down?

Although it’s not normal to be asked to stand up to have your blood pressure checked because it’s more difficult to provide support for your arm, there are occasions when it is done – for example, in some people with diabetes, and in elderly people or anyone who experiences dizziness or other symptoms when

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standing up. The former is because the blood pressure of people with diabetes may fall briefly when they stand. Normally, there is no significant change in blood pressure on standing up but in certain conditions, including diabetes, this can occur, and is referred to as postural hypotension. It may or may not be associated with dizziness.

Systolic and diastolic blood pressure

As we have seen, measuring blood pressure involves recording both the highest (systolic) and the lowest (diastolic) levels in your system, so the reading will record two figures. Conventionally, blood pressure is expressed as systolic pressure over diastolic pressure, for example, 140/94 mmHg (millimetres of mercury).

The relative importance of systolic and diastolic blood pressure has been the subject of much research. In fact, contrary to what most people believe, over the age of 40 the systolic pressure is more important than the diastolic when it comes to predicting who will and who will not develop heart disease. The problem is that everyone’s systolic blood pressure varies considerably, and this is even more so with older people.

The importance of systolic blood pressure has recently been emphasised by the publication of two reliable studies which showed that reducing the

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systolic pressure was worthwhile in people whose diastolic blood pressure was normal or even below normal. This condition is known medically as isolated systolic hypertension (ISH). It mostly affects people over the age of 65 and, if it is not treated, they are at high risk of developing heart disease or stroke.

In general, the lower your blood pressure readings, the better. When treating high blood pressure, the aim is to reduce all risk factors for heart disease such as smoking, blood cholesterol levels, etc., and to keep blood pressure under 140/85 mmHg.

‘White coat’ hypertension

‘White coat’ and ‘office’ hypertension are terms applied to those people whose blood pressure is raised only when they are seeing a doctor. In recent years, it has become possible to record blood pressure over 24-hour periods at home (using automatic electronic

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equipment), and this has shown that many people’s blood pressure goes back down to the normal range within an hour or so of leaving the surgery or hospital. When this happens, the person is said to have ‘white coat’ hypertension. The technique for detecting white coat hypertension is called ambulatory blood pressure monitoring (ABPM).

The exact significance of white coat hypertension remains uncertain but the current evidence suggests that people with this condition cannot be considered to be entirely normal. There is evidence that they are more likely to have enlargement of their heart than people with normal blood pressure. Furthermore, such people may well develop sustained (or fixed) hypertension within five years and will then need treatment to lower their blood pressure.

This means that, although people with white coat hypertension may not need treatment immediately, they do need to have regular blood pressure checks every six or twelve months.

It’s also true that many people who do have genuine hypertension that requires treatment also have a large ‘white coat effect’. Thus, when they are away from the surgery or hospital, their pressures are much lower and the doctor needs to take this into account when deciding on how much medication they need to take to control their blood pressure.

Home blood pressure measurement

If it is necessary for you to have your blood pressure measured away from the hospital or clinic, there are several ways that this can be done:

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•  You may be advised to buy one of the newer and relatively inexpensive electronic automatic blood pressure machines, although some of these are as yet not very accurate. The best buys are easy to use, easy to read, cheap and portable.

•  If you do buy one of these simple desk-top blood pressure machines, you will probably be advised to take it into the hospital, clinic or health centre so that the doctor or nurse can quickly check that the equipment is accurate when compared with the mercury blood pressure ‘gold standard’. When purchasing a semi-automatic blood pressure machine, it would be sensible to ensure that the maker’s literature states that the equipment has been tested and shown to be accurate by criteria of the British Hypertension Society (BHS) or the American Association for Medical Instrumentation (AAMI).

All you have to do is place the cuff around your arm then press a button. You can take as many readings as necessary and this can provide useful information for your doctor, so long as the machine is accurate.

•  Very occasionally you may be provided with a conventional mercury blood pressure-measuring system and either you or one or your relatives can be taught how to use this in order to measure blood pressure. However, home blood pressure measurement using mercury manometers is hardly ever necessary since the advent of the semi-automatic electronic manometers.

•  In some cases, your doctor may set up a home measuring system with an automatic 24-hour ambulatory blood pressure monitor (ABPM). Several

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Electronic automatic blood pressure machines can be easy to use, but choose carefully to ensure accuracy.

reliable and accurate systems are now available which can be programmed to measure the blood pressure every half hour or so over 24 hours. Perhaps surprisingly, using these machines at night doesn’t usually cause any sleep disturbance. The value of 24-hour ambulatory blood pressure monitoring is still a little controversial, but it is an accurate method of obtaining information that will help the doctor to decide whether you have any degree of ‘white coat’ hypertension.

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• There are wrist and finger blood pressure-measuring systems becoming available. However, there remains considerable doubt as to their accuracy. For this reason, wrist and finger blood pressure machines are not recommended.

KEY POINTS

■ It is important that you are totally relaxed when your blood pressure is being measured

■ Systolic blood pressure is now known to be as important as, or even more important than, diastolic pressure

■ Automatic measuring systems can be employed to measure blood pressure away from the clinic or health centre

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What is hypertension and why does it matter?

Diagnosing hypertension

If your blood pressure reading is consistently over 160/100, you will be told that you have hypertension. If your pressure exceeds 140/90 mmHg, then you may be diagnosed as having mild hypertension.

There is a strong tendency for blood pressure to rise with advancing age. Thus, hypertension of a level where treatment would be considered necessary occurs in 10 to 20 per cent of patients aged 20 years. However, up to 60 per cent of patients over the age of 60 require treatment. For this reason blood pressures that are below 140/90 mmHg but above 120/80 mmHg are sometimes classified as being ‘high–normal’ or ‘pre-hypertensive’. This is because a very large proportion of such people will develop mild hypertension in the subsequent years

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Defining hypertension

Blood pressure readings are a remarkably accurate predictor of life expectancy: the higher the pressure the greater the risk. Even people whose blood pressures are average for the population have a slightly greater risk of heart disease than people with lower than average levels. For this reason it has been extremely difficult to find a simple working definition of hypertension. Perhaps the most sensible view is to define it as:

‘That level of blood pressure where treatment with antihypertensive drugs does more good than harm’

because there is no such thing as drug treatment that does not have some potential side effects.

If your blood pressure is more than 160/100 mmHg and if you have several different risk factors for heart disease, such as high cholesterol, being a smoker and a family tendency to heart disease, then treating your high blood pressure is likely to be very worthwhile. (This is explained in detail in the section beginning on page 79.)

The criteria for diagnosing hypertension now take into account the patient’s overall cardiovascular risk rather than just the blood pressure. Thus, in people who are at high risk (for example, patients with diabetes or those who have already had a stroke or heart attack), the criteria for starting antihypertensive treatments will be 140/90 mmHg and, in some instances, those with lower levels might even be treated if the cardiovascular risk is very high.

On the other hand, for some young people with only very marginally raised blood pressure, and no other risk factors for heart disease, the value of blood

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pressure-lowering drugs is very small and drug treatment may be held back. It is, however, crucial that such people are re-checked at intervals of roughly six months.

The silent killer

Hypertension has been called the ‘silent killer’ because it usually causes no symptoms until a late stage of the disease. Contrary to what many people believe, it is not possible to feel your own blood pressure. The only way to find out whether your blood pressure is raised is to have it measured with a blood pressure machine – see pages 9–22.

As hypertension causes no symptoms until complications begin to show themselves, about half of all those who have it remain unaware that they have a problem.

Why does hypertension matter?

Blood vessels are like rubber tubes which carry blood constantly to wherever it is needed. Arteries, which carry blood out of the heart, have to withstand the great pressures with which the blood is pumped out of the heart. If the blood pressure is higher than usual over many years, as in untreated hypertension, the vessels get damaged. The lining of the arteries can become roughened and thickened, and this eventually causes them to narrow and become less flexible, or elastic, than previously. This is known as arteriosclerosis.

If an artery gets too narrow, blood can’t get through properly, and the part of the body that relies on that artery for its blood supply is starved of blood and the all-important oxygen that it carries. As the artery narrows there is an increased tendency to develop blood clots (thrombosis) which may cause total

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blockage of the artery, so that the part of the body that it serves dies. The dead area of the heart or brain is called an infarct.

Other risk factors

High blood pressure over many years can cause all these problems and the whole point of measuring blood pressure regularly, and treating it effectively if it is high, is to prevent these complications. However, you are more likely to develop these complications if you smoke and if you have untreated high blood cholesterol levels. The reason is that cigarette smoking damages blood vessels in much the same way that high blood pressure does, making the artery itself narrower and its lining thick and rough.

High cholesterol can cause fatty deposits in the lining of the artery, called atheroma, to develop more rapidly than normal which also helps to narrow the arteries. When this ‘furring up’ process occurs in the arteries that supply the heart muscle it is called coronary heart disease (CHD). As with blood pressure it is not possible for your level of serum cholesterol to be too low, and similarly treatment to lower cholesterol also saves lives.

Another common risk factor which can also contribute to narrowing of the arteries, known as cardiovascular disease, is diabetes (type 2 diabetes mellitus) which affects four to five per cent of the white population and 10 to 15 per cent of the south Asian and African–Caribbean populations in the UK. High glucose levels in the blood damage arteries in a similar way to high blood pressure.

Type 1 diabetes mellitus usually occurs in younger people, who are more prone to develop kidney disease and damage to their retinas.

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Coronary thrombosis

A coronary thrombosis occurs when a clot forms in the coronary arteries that supply blood to the heart muscle. In a heart attack a clot typically forms on a break in the fibrous plaque in a diseased vessel.

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The purpose of measuring blood pressure

It wouldn’t do to paint too gloomy a picture, however. The whole point of checking blood pressure is that, if you are found to have hypertension, it is possible to treat it effectively and so bring your risk of heart disease and strokes back down to normal. It doesn’t matter particularly how severe the hypertension was in the first place. What really matters is how well your blood pressure is controlled over the ensuing years.

It’s better to have had severe hypertension that has been well treated than to have slightly raised blood pressure that remains untreated or neglected.

Risk factors for coronary heart disease (CHD)

Several factors have been found to influence an individual’s risk of developing CHD. The greater the number of risk factors that apply to you, the greater your chance of developing CHD.

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Long-term effects of high blood pressure

Although there are many possible serious long-term effects of high blood pressure, it must be stressed that all these complications can be prevented with effective antihypertensive treatment.

Angina

The heart is a muscle like any other that needs its own blood supply, which is brought to it by the coronary arteries. If these coronary arteries narrow, blood doesn’t get to the heart muscle efficiently. So when the heart needs to work a bit harder than usual, like when you are walking up a hill, the heart muscle cannot get the blood supply and oxygen that it needs. This causes pain in the chest, known as myocardial ischaemia or angina.

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Changes in the coronary blood vessels that cause a heart attack.

Heart attack

If a coronary artery narrows and then a blood clot forms, the part of the heart muscle that relies on that coronary artery dies. This is known as a coronary thrombosis, a myocardial infarction or a heart attack.

Heart failure and breathlessness

Over the years, as arteries narrow and become less elastic as a result of hypertension, it gets harder and harder for the heart to pump blood out efficiently to the rest of the body. The increased workload eventually damages the heart and impairs its performance. Fluid collects in the lungs, causing shortness of breath. This is known as left heart failure or left ventricular failure (LVF).

Stroke

Narrowing of an artery that carries blood and oxygen to the brain can lead to temporary loss of function in the part of the brain served by that artery; this is known as

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a transient ischaemic attack (TIA). Permanent closing off of the artery with a blood clot results in the death of the part of the brain reliant on that artery, which results in a cerebral infarction causing a stroke. Less commonly, the blood vessels in the brain may rupture, leading to a brain haemorrhage (intracerebral haemorrhage).

Peripheral artery disease

Smaller blood vessels in the legs can be damaged, resulting in less blood getting to the feet and pain in the calf muscles on walking. This is called intermittent claudication.

Kidney damage

When blood vessels supplying the kidneys are affected the result may be gradual kidney damage, which affects how the body gets rid of waste products, including

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A blockage of an artery supplying blood to the brain is called an ischaemic stroke.

drugs. This is why a blood test to check kidney function is a vital part of regular check-ups for anyone with hypertension.

Eye damage

The small blood vessels in the eyes can also be affected, although this may not become apparent until damage is extensive. Very rarely, in very severe hypertension, there may be damage to the retina with haemorrhages. This condition is called malignant hypertension, although nowadays with treatment the outlook is very good.

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KEY POINTS

■ High blood pressure is one of the three risk factors for heart attack and stroke

■ The other factors are smoking and raised blood cholesterol levels

■ Lowering blood pressure (and lowering blood cholesterol) saves lives

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What causes hypertension?

Categorising hypertension

In 95 per cent of cases there is no specific underlying cause, and this condition is known as primary or essential hypertension. The remaining five per cent of people have a problem with their kidneys or adrenal glands, located at the top of the kidneys, which causes their hypertension. Doctors refer to this as secondary hypertension.

Risk factors for high blood pressure

There are a number of different factors that may contribute to causing raised blood pressure. Heredity plays a part which means that hypertension can run in families. Blood pressure tends to increase with age but this is partly because of changes in lifestyle; many people put on weight and get less active as they get older and both these factors may contribute to the development of hypertension. More importantly, the rise in pressure with age is greater in people who eat a lot of salty foods.

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Racial background plays a part, with people of African–Caribbean origin living in western societies having a higher prevalence of hypertension than white people. This is probably because African–Caribbean people handle salt in the body differently. However, migration studies show that, although racial origins do play a part, it is the diet and other lifestyle factors that are more significant. Anyone who lives in the more affluent western countries is more prone to hypertension than those who live in developing countries.

Blood pressure always varies throughout the day and is usually higher during exercise as the heart needs to pump blood around the body faster, although people who exercise regularly will tend to have lower blood pressures than non-active people when at rest. Your blood pressure is lower when you are sleeping or resting.

You will not be diagnosed as having hypertension on the basis of a one-off reading. You will need to

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have at least two high or borderline (that is, over 140/90) readings on three separate occasions, over at least two months. Ideally, your blood pressure should be checked with you sitting down, as rested and relaxed as possible. If your blood pressure is dangerously high, or in special circumstances – for example, if you are pregnant – more urgent measures may be needed.

How does the body regulate blood pressure?

Sympathetic nervous system

There are two systems in the body that are involved in helping us to maintain normal blood pressures in all circumstances if possible. One is the sympathetic nervous system which releases chemicals such as adrenaline and noradrenaline; these can both open or vasodilate the microscopic arterioles or narrow them by vasoconstriction, as required, depending on which parts of our body need to be ready for action.

This system comes into operation to enable us to respond in a crisis by concentrating our physical resources where they are needed to help us survive a perceived threat. This means shutting down non-essential functions – such as digestion – for the duration of the crisis to prepare us to fight or run away. For early humans, this was essential when life was full of physical danger, but for most people today the system is likely to be triggered by emotional or psychological stress rather than by actual life-threatening situations most of the time. As a result of its narrowing effect on small blood vessels, this process can play a part in causing hypertension. Drugs that act on this system, for example, the alpha blockers and beta blockers, can therefore be used to control it.

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Renin–angiotensin system

The other important system is an enzyme produced by the kidneys, known as renin, which activates a hormone called angiotensin II. Angiotensin II makes blood vessels constrict. Drugs that block angiotensin, called the angiotensin-converting enzyme (ACE) inhibitors (for example, perindopril), can help to lower blood pressure.

More recently, angiotensin receptor blockers (ARBs, for example, losartan) have been introduced and are as effective as the ACE inhibitors.

Angiotensin also stimulates the release of a hormone called aldosterone from the adrenal glands. This hormone causes salt and water retention by the kidneys and may further elevate the blood pressure.

Calcium

The microscopic blood vessels, called arterioles, have smooth muscle cells in their walls which contract when calcium concentrations rise. People with hypertension have higher calcium levels in their smooth muscle cells than those with normal blood pressure, although it is still not known why.

In people with hypertension, it is thought that these rises in the calcium concentration cause the arterioles to constrict which makes it harder for the heart to pump blood through them. Long-term constriction of the arterioles is also thought to damage their walls which leads to further rises in blood pressure as the smooth flow of blood is disturbed. Drugs that block the calcium channels (calcium channel blockers or CCBs, such as nifedipine) allow the arterioles to open up again which lowers blood pressure.

Although all the hormones mentioned here (renin, angiotensin, aldosterone, adrenaline and noradrenaline)

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Constricted and dilated arterioles

The microscopic blood vessels in the circulation are called arterioles; if they constrict, they inhibit blood flow and therefore blood pressure rises. Larger arrows indicate higher blood pressure.

play a role in regulating blood pressure in all people, it seems that people with high blood pressure are more susceptible to their effects. People with hypertension do not have more of these hormones in their bloodstream, but blocking their effects with drugs lowers blood pressure only if it was raised in the first place.

The common pathway of all of these mechanisms is narrowing of the arterioles, causing increased resistance to blood flow. The heart continues to pump normally, so the pressure within the whole arterial system must rise.

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Why your lifestyle matters

As far as you as an individual are concerned, your blood pressure level depends on the interplay of genetic or inherited factors and the influences of your lifestyle. Hypertension clearly runs in families and this holds true even after allowances have been made for the fact that families tend to share the same lifestyle and diet. Excellent research conducted among twins who were brought up separately or together, and also among adopted children compared with non-adopted

Hypertension: problems throughout the circulation

Healthy artery walls are elastic, allowing the wall to flex with the blood pressure wave. If the wall stiffens, the ability to flex is lost and the pressure in the circulation will rise.

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The effect of sustained high blood pressure on the heart

With prolonged high blood pressure, the heart muscle gets thicker and more bulky as it works harder against the increased pressure. This thickened muscle is stiffer and functions less well than normal heart muscle.

children, has been able to identify how much of the similarity in blood pressure within families is the result of inheritance compared with the proportion resulting from similarities in lifestyle. Roughly speaking, about half of all the variation in blood pressure between people is the result of genetic factors and half is the result of dietary factors dating back to early childhood.

Salt intake

Salt intake has a direct effect on blood pressure. It has been shown that the rise in blood pressure as we get older, which occurs in all urban societies, is the result in large measure of the amount of salt that we eat. Reducing salt intake helps to reduce blood pressure. A high salt intake over many years probably raises

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blood pressure by raising the sodium content of the smooth muscle cells of the walls of the arterioles. This high sodium content appears to facilitate the entry of calcium into the cells; this in turn causes them to contract and narrow the internal diameter of the arteriole. There is some evidence that people with an inherited tendency to develop hypertension have a reduced capacity to remove salt from their bodies. There is, however, little evidence that such people consume more salt than anyone else, although they may tend to retain what they do eat.

Evidence from studies

The relationship between salt and hypertension has, over the years, been controversial mainly because the original research was not carried out carefully enough.

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However, during the mid-1980s a very reliable international comparative study showed convincingly that there is a close relationship between salt intake and blood pressure when comparing people in different countries. For instance, people who are Japanese, Polish and Portuguese have a high salt intake and a high frequency of raised blood pressure and strokes.

Furthermore, it was found that those populations that have a large amount of salt in their diet are also those populations in which blood pressure rises more with advancing age. By contrast populations in which salt intake is low show only a small rise in blood pressure with advancing age and thus hypertension is relatively less common. As I discuss later in this booklet, there is now good evidence that reducing the amount of salt in the diet does lower blood pressure.

It is certainly true, however, that there are variations in the way individuals’ bodies handle salt and some people are more sensitive to it than others. This is probably true of people with a strong family history of hypertension and it is also evident that older people are more salt sensitive as are people of African– Caribbean origin.

Children and salt

The relationship between salt intake and the subsequent development of hypertension has recently been confirmed by a reliable study which began by looking at babies who were weaned either on to a low-salt diet or a normal-salt diet. After six months the blood pressure was better (lower) in the low-salt babies. A proportion of these babies has now been followed up for 15 years and their blood pressures were found still to be significantly lower.

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If children could be persuaded to consume less salt then we might prevent the development of hypertension in the first place, which means that we should be seriously concerned about the amount of salt in crisps and other snacks that children nowadays consume in large quantities. The food industry is now under pressure from the Food Standards Agency to reduce the salt and fat content of processed and convenience foods, and is starting to respond.

It is interesting to note that a high salt intake has now been implicated as a cause of stomach cancer, asthma and osteoporosis (bone mineral loss).

Your weight

Overweight people tend to have higher blood pressures than thin people. This is partly because obese people’s bodies have to work harder to burn up the excess calories that they consume, partly because they tend to eat more salt than normal, and possibly because fat people have a tendency to be resistant to the hormone insulin, which deals with blood sugar, and this may be involved in causing hypertension, although it is not yet fully understood.

Although overweight people do appear to have higher blood pressure than people of normal weight, this may in part be related to a tendency for doctors and nurses using conventional blood pressure machines to over-estimate their blood pressure. The greater the circumference of the upper arm where the blood pressure cuff is applied, the greater the over-estimation of blood pressure. This can partly be overcome if they make sure that they use a larger arm cuff when appropriate.

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Body mass index

However, even when allowances have been made for this tendency to over-estimate blood pressure, there is still a convincing relationship between body weight and blood pressure. It’s not possible to say whether you are overweight just on the basis of how much you actually weigh (because tall people usually weigh more than short people), so instead doctors usually work out what’s called the body mass index (BMI). This is calculated by taking your weight in kilograms and dividing it by the square of your height in metres (see box on page 45).

A person who has a body mass index of 30 or more is considered to be obese, whereas if it is between 25 and 30 he or she would be considered to be overweight.

Waist-to-hip ratio

Recent evidence strongly suggests that body mass index is not a particularly good risk factor for the development of cardiovascular disease. Attention is now turning to ‘waist/hip ratio’. This implies that, if the waist measurement is increased (as with a paunch or beer belly) in comparison with the hip measurements, there is a greater chance of developing hypertension, diabetes, heart attacks and strokes.

The importance of losing weight

Population surveys have shown that the variation in blood pressure between people in relation to their weight is about one millimetre of mercury (mmHg) per kilogram (or two pounds) in weight. When you put on weight the amount that you gain is a good guide to the amount by which your blood pressure will rise.

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Are you a healthy weight?

• The body mass index (BMI) is a useful measure of healthy weight
• Find out your height in metres and weight in kilograms
• Calculate your BMI like this

•  You are recommended to try to maintain a BMI in the range 20-25
• The chart below is an easier way of estimating your BMI. Read off your height and your weight; the point where the lines cross in the chart indicates your BMI

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If you lose weight your blood pressure will fall by an amount that can be predicted using the same formula.

The relationship between body weight and blood pressure is more complex than was originally thought and it may also be related to important effects of certain hormones as well as to the body’s capacity to handle salt. From a practical point of view, however, losing weight is a very effective way of reducing your blood pressure.

Alcohol

Alcohol has an effect on blood pressure and, on the whole, the more alcohol you drink the higher your blood pressure, although it is not understood why this is. However, teetotallers do tend to have slightly higher blood pressures than very moderate drinkers. In men

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this means that one or two glasses of wine per day may have a very slightly protective effect against heart disease. The safe level of drinking in women is about two-thirds that of men, that is one glass per day.

People who drink more than this and also people who abuse alcohol are very likely to have raised blood pressure and have a strong tendency to develop strokes. When such people stop drinking their blood pressure comes down.

Although the relationship between alcohol and blood pressure is now well recognised, surprisingly no one has yet discovered a convincing mechanism to explain how this happens. However, from a practical point of view doctors recommend that men should drink no more than 21 units of alcohol per week (equivalent to 10.5 pints of beer or 21 small glasses of wine) and women should drink no more than 14 units per week (equivalent to seven pints of beer or 14 small glasses of wine). These units should be spread over the week, not drunk all in one session. A better recommendation is that you should consume no more than three alcoholic drinks per day if you are male and two if you are female.

Stress

Stress can put up your blood pressure in the short term but probably does not account for long-term rises in blood pressure. Relaxation techniques may help to improve your quality of life, but probably won’t be enough to control true hypertension.

The relationship between stress and blood pressure is confusing and much of the earlier research in this field was not satisfactory by modern standards.

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Short-term stress

There is no doubt that acutely stressful stimuli can cause a sharp rise in blood pressure. For example, if you are given some extremely bad or distressing news, your blood pressure may be raised soon afterwards. Similarly, in experimental situations the stress of conducting mental arithmetic in a noisy environment or even sorting out different-sized objects causes a sudden sharp rise in blood pressure.

If going to see a doctor, whether it’s your GP or in a hospital clinic, makes you feel anxious and nervous, your blood pressure is likely to go up. For this reason, you should be asked to come back and have it measured again on several occasions if it is slightly raised on your first visit. The idea is that, once you have become more familiar with the environment and the procedure, you will be better able to relax and the reading will then be a more accurate reflection of your blood pressure when you are not under any stress.

Chronic (long-term) stress

Although the effects of this kind of short-term stress on blood pressure are well recognised, there is little evidence that chronic (that is, long-term) stress causes chronic hypertension. Reliable studies have shown no relationship between levels of stress, as assessed by detailed and accurate questioning, and the height of blood pressure. People with very stressful jobs do not have more hypertension or heart disease than people with unstressful jobs. The research in this field has been seriously hampered by the lack of reliable measures of stress so the subject remains somewhat controversial. There is some evidence that people who have less control over their day-to-day life at work have higher

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blood pressures than people who can influence their working lives more effectively. Thus manual workers tend to have higher blood pressures than executives or managers. The differences between these groups, however, are also related to differences in lifestyle and diet, and it is difficult to be sure whether these differences are the result of stress alone.

Potassium and calcium

Eating lots of foods that contain potassium – such as fruit and vegetables – is good for keeping blood pressure low. However, people with high-potassium diets often have fairly low salt intake, so it’s hard to know whether it’s the low salt or the high potassium that is helping. That said, potassium does seem to be beneficial in its own right. There is quite good evidence that people who have a low-potassium diet have higher blood pressure,

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whereas those who eat a lot of fruit and vegetables have lower blood pressure and a lower incidence of stroke. This makes sense because we know that cells respond to high potassium by getting rid of sodium (in salt).

This effect of potassium intake on blood pressure is small compared with that of salt. However, it is true to say that variations in salt intake between people are also associated with parallel variations in potassium intake. In other words, people who eat a lot of potassium-rich foods generally eat relatively little salt, whereas salt fans tend to eat fewer fruit and vegetables.

This finding was confirmed in 2006 with the publication of a detailed overview of all of the population studies on fruit and vegetable intake and stroke. This demonstrated that people who consume more than five portions of fruit or vegetables each day have a significantly lower stroke incidence than those consuming fewer than three servings per day. Another study, also published in 2006, raised a strong possibility that it is the vegetable protein in pulses and nuts that keeps the blood pressure down, although there may also be an effect related to the higher potassium content.

There has been some research to suggest that a diet high in calcium may have a tiny blood pressure-lowering effect. However, these results are highly controversial and at the present state of knowledge no recommendations can be made on changing the diet accordingly.

Animal fats

Early studies on the relationship between the intakes of animal fats (mainly in the form of dairy products)

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The effect of diet on blood pressure

This shows the effects of a normal (control) diet and the DASH diet (low in dairy products and animal fats and high in fruit and vegetables) on systolic blood pressure while on a high-, intermediate- and low-salt diet. Changing from an unhealthy to a healthy diet drops the systolic blood pressure by a total of 8.9 mmHg, and is an effect roughly equivalent to that of a single antihypertensive drug.

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were unconvincing. However, a very reliable recent study from America has shown that a reduction in animal fat intake was associated with a significant fall in blood pressure. This study also showed that a low-salt diet high in fruit and vegetables lowered blood pressure even more, together with a low-fat diet.

It is clear that there are many nutritional factors that influence blood pressure and these are the subject of a major international research project, which was started in 1997. Preliminary results show that all the differences in blood pressure between individuals can be explained by nutritional and lifestyle factors, after taking into account the effects of age.

Exercise

Although your blood pressure rises sharply while you’re actually exercising, if you do it regularly you will tend to be healthier and have lower blood pressure than people who don’t take any exercise. This is partly because you are more likely to eat healthily, not smoke and not drink excessive alcohol, although exercise also seems to have a direct effect on lowering blood pressure. However, you should aim to take regular, moderate amounts of exercise rather than going in for very vigorous bouts every now and again.

The symptoms of hypertension

The vast majority of people with hypertension have no symptoms. Some people believe that they can feel their blood pressure but, in fact, it is more likely that they are feeling the emotional stress of attending hospital or some recent stressful event in their life. This short-term stress may or may not raise the blood pressure.

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The fact that hypertension causes no symptoms means that it is often not diagnosed for many years, by which time the person has subtle evidence of damage to the heart, brain or kidneys. At a later stage, the person may go to the doctor because he or she has started to feel unwell. He or she may, for example, have had a small stroke or have angina (chest pain on exertion), or even have had a heart attack. Someone who has developed heart failure may feel breathless when lying down, whereas kidney failure can be responsible for general tiredness and exhaustion as well as breathlessness.

Don’t wait to feel ill before having your blood pressure checked

These are serious problems, which is why you should never wait until you feel ill before having your blood pressure checked. The current opinion is that everyone over the age of 20 should have a routine blood pressure check by their G P. The likelihood is that your reading will be normal or require no action and, if so, you probably need to be re-checked only every three or four years, but some people with borderline pressures may need to be checked more often.

The current opinion is that all adults should have a routine blood pressure check by their G P. Younger people and even children who have a strong family history of hypertension should also be checked routinely.

How common is hypertension?

Hypertension is more common with advancing age, particularly in populations who have a high salt intake, so age must be taken into account when we consider the prevalence of hypertension.

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Premenopausal women (having monthly periods) tend to have lower blood pressure than men of the same age, although the difference between the sexes becomes less apparent over the age of 50 years. This is because, before the menopause, women may be relatively protected from heart disease by the female hormone, oestrogen. Oestrogen levels fall after the menopause and women start to catch up with men in terms of developing heart disease.

Any dividing line between so-called high blood pressure and normal blood pressure must be purely arbitrary. Even if your blood pressure is around the average for the population as a whole, you are at higher risk than someone whose blood pressure is persistently below this level. Thus a blood pressure of 140/80 mmHg carries a slightly worse prognosis (outlook) than blood pressure of 130/70 mmHg.

As explained earlier, the most useful definition of hypertension is therefore that level of blood pressure where treatment is necessary to prevent the individual developing heart disease, stroke and other complications of hypertension. At the present state of knowledge, on the basis of reliable trials of the drug treatment of hypertension compared with dummy (placebo) tablets, we know that treatment is necessary if the blood pressure is consistently 160/100 mmHg or more at all ages.

This threshold is lower in people who are at high risk by virtue of having had a heart attack or a stroke, or if they also have diabetes. In such people, treatment is now recommended if the blood pressure is consistently above 140/85 to 140/90 mmHg.

Around 25 per cent of people have a diastolic blood pressure of 90 mmHg or more, although it is worth stressing that many of them will have a lower

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reading on re-checking so that no treatment may be necessary. Should the level not fall when your blood pressure is measured again, you may need drug treatment.

If your diastolic pressure is below 90 mmHg, but your systolic pressure is over 160 mmHg, you will be diagnosed as having isolated systolic hypertension (ISH). This condition is vary rare in people under the age of 60 but affects 20 to 30 per cent of those over the age of 80. Recent research has shown that treatment to lower the systolic pressure is very effective at preventing heart attacks and strokes in patients with ISH.

If we take into consideration all types of hypertension affecting people over the age of 60, about 35 to 40 per cent of men and women in the UK need further assessment on the basis of either a raised diastolic or a raised systolic blood pressure. However, this percentage is lower among people whose consumption of salt is below the national average.

Geographical variation

Surveys suggest that between seven and ten million people in the UK have raised blood pressure levels. Socioeconomic factors seem to play a part – people who live in poorer areas are more likely to have hypertension than those who live in more affluent areas. Certainly, heart disease and strokes are more prevalent in the north and north-west of England and in Scotland than in the south-east of England, although this also reflects smoking habits.

It must be stressed that many blood pressures are only slightly raised and will be lower on re-checking. Estimates of the number of people with raised blood pressure who require drug treatment vary between

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Death rate from CHD by area in the UK

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10 and 15 per cent of the adult population. This represents a very small proportion of people aged 20 to 30 years but about half of those over the age of 70.

Hypertension is therefore the most common chronic, non-infective, medical condition in the western world. About 50 million people in the USA have blood pressure levels that require treatment and a similar figure is seen in studies from the European Union. The prevalence of hypertension in the UK is higher than in France, Italy, Spain and Greece, and similar to that seen in Sweden and Denmark. In both the UK and the USA, however, hypertension is much more common in people of African origin. The reasons for this are not entirely clear, but it is possible that these people tend to handle the salt in their diet in a different way, such that their bodies retain more of it and this puts their blood pressure up. For more on this, see page 104.

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KEY POINTS

■ Hypertension runs in families
■ Hypertension is related to a high salt intake, being overweight and drinking too much alcohol
■ Rarely, high blood pressure is the result of underlying kidney disease or excess hormones

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How hypertension is investigated

Why are further tests needed?

People whose blood pressure levels are found to be raised need to have further tests and investigations. There are three main reasons why this might be considered necessary:

•  To check your cholesterol levels: if you have a high blood cholesterol level as well as hypertension, your risk of developing heart disease and strokes (cardiovascular risk) is correspondingly greater, and you will need treatment to bring both blood pressure and cholesterol levels back down to normal.
•  To check for serious underlying disease: occasionally, hypertension may be caused by certain kidney diseases and some extremely rare diseases of the adrenal gland which is situated above the kidney.

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• To check for heart and kidney damage: this may occur after prolonged untreated hypertension, so blood tests are taken to measure kidney function and the size of the heart is estimated by an electrocardiogram (ECG). A chest X-ray does not give a reliable indication of heart size and is not recommended.

Routine tests

All people with raised blood pressure need a simple urine test; a small blood specimen is taken and an ECG must be taken. You’ll be weighed and, if necessary, given advice on how to lose weight which is likely to help reduce your blood pressure.

Next your doctor will examine your heart, chest, tummy and the pulses in your legs. This may give some indication as to whether hypertension has affected your heart or kidneys.

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The type of heart damage called heart failure results in fluid retention which causes fluid on the lungs that can be heard through a stethoscope. It can also cause an enlarged left side of the heart which the doctor can detect. Kidney damage can be diagnosed only by urine and blood tests.

If your hypertension is very severe, the doctor will probably use an instrument called an ophthalmoscope to look at the back of your eyes (the retina) where it is possible to assess the tiny blood vessels. In mild hypertension these blood vessels show only very minor changes, but in a very severe hypertension there may be haemorrhages on the retina and areas of damage that are referred to as ‘cotton-wool spots’.

Urine test

After the clinical examination, you’ll be asked to produce a small specimen of urine for testing. If sugar is

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found in the urine, this raises the possibility that you may have diabetes and, if protein is found in the urine, it could mean that you have some form of kidney condition.

Blood test

Blood tests are taken to measure your cholesterol and to test the function of your kidneys. If the kidney function is normal, the serum creatinine is usually below 120 millimoles/litre (mmol/l). The patient would be considered to have severe renal failure if the serum creatinine is greater than 600 mmol/l. If the kidneys are not working properly, levels of urea and creatinine in the blood start to rise. In addition levels of sodium and potassium in the blood are measured. These are abnormal in people with hypertension whose bodies retain sodium because of the presence of a small benign tumour of the adrenal gland; this condition is called Conn’s syndrome.

Electrocardiogram

An ECG gives a recording of the electrical activity of the heart. It has a dual purpose. First, it can give an indirect index of the size of the heart. When the blood pressure is very high, the heart enlarges in order to cope with increased load and this leads to increased voltages on the ECG. This is called left ventricular hypertrophy (or LVH) and is very important. When someone is found to have LVH, their need for treatment to lower their blood pressure becomes more urgent because it indicates that the heart muscle is under significant strain trying to cope with the effort of pumping blood out round the body at increased pressure.

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Exercise ECG

Patients with suspected disease of the coronary artery and high blood pressure may undergo an exercise ECG while walking on a treadmill. This is conducted under close medical supervision. The ECG during exercise may well show changes of ischaemia or poor perfusion of the wall of the heart that are not present at rest.

The second reason for doing an ECG is because it may show changes suggestive of narrowing or blockage of the coronary arteries, which supply the heart muscle. This process is called ‘ischaemia’ and is seen in some people who experience angina (chest pain) on exertion. Even though you may never have had symptoms of angina and have no reason to think you’ve ever had a heart attack, you may nevertheless show signs of ischaemic changes and these are important.

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The need for further tests

These are the routine investigations that will be needed by everyone with hypertension. You will require the more detailed investigations, usually done in hospital outpatient clinics, only if your hypertension is severe enough or if your doctor suspects that you have some underlying condition that is responsible for your blood pressure problems.

Two or three per cent of people with hypertension are found to have underlying medical conditions that cause their pressure to rise. These are diseases of the kidney and of the adrenal gland. In this situation, you will probably be referred to a specialist clinic in your local hospital. A further three or four per cent of people have very severe hypertension that needs more detailed investigation and care by a specialist in high blood pressure.

The vast majority of people with hypertension do not and should not attend hospital for any reason at all and can be cared for by their G P. There will be marked variations in the proportion of patients referred to hospital clinics, depending on the availability of local services and specialist blood pressure doctors. Whether you have to attend a hospital clinic will depend on your individual GP’s policy in such cases. Some may refer a large number of their patients to be seen only once or twice for a full assessment in hospital and then look after them themselves, whereas others refer only the very difficult cases to a hospital specialist.

Hospital clinics

Only a small minority of people with hypertension will need to attend hospital-based specialist clinics. As explained below, these will usually be people whose

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hypertension is associated with complications such as heart disease or kidney disease or those whose blood pressure is proving difficult to control, or if the GP suspects that they may have some underlying condition that is causing their hypertension.

Suspicion of there being some underlying cause for the hypertension would be based on the presence of protein in the urine or abnormal blood test results, showing evidence of impairment of kidney function. In addition, if levels of potassium in the blood are found to be low, this raises the possibility that there may be an underlying condition of the adrenal glands. You will also be referred to a hospital clinic if your blood pressure varies greatly from minute to minute or hour to hour or even day to day. There is an extremely rare condition called phaeochromocytoma which is caused by the intermittent secretion of large quantities of adrenaline and noradrenaline by a tumour of the adrenal gland.

When you do go to a clinic, you may have to undergo a repeat of some of the blood tests already done by your GP merely to confirm abnormalities. If there is a suspicion that you may have Conn’s syndrome, in which the hypertension is the result of excess of a hormone called aldosterone, the hospital doctor may opt to measure this in your blood.

Kidney ultrasound

To exclude any form of kidney disease, it is usual to do an ultrasound scan to investigate the size and shape of the kidneys. This test is increasingly becoming a routine investigation for severely hypertensive people because it is safe and causes no discomfort. You may also be asked to provide a 24-hour collection of urine so that

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your body’s 24-hour output of adrenaline and noradrenaline can be measured (don’t worry, the clinic will provide the bottles). Raised levels could indicate that you have a phaeochromocytoma (see above).

Echocardiogram

The clinic doctor may also measure your heart size by means of an echocardiogram, which is a type of ultrasound heart scan.

Tailoring treatments

Very often, people are referred to a hospital clinic because their blood pressure is proving a little resistant to treatment and the hospital doctor may therefore opt to alter drug combinations and formulations in order to obtain better blood pressure control.

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Echocardiography

An instrument called a transducer, which produces a beam of sound, is held against the chest. A picture of the heart is created by the reflected sound beams.

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Once your blood pressure is under control and things are sorted out you will normally be discharged from the care of the clinic back to your G P, and have to go back to the hospital only if problems arise. Once blood pressure is controlled, you should visit your practice nurse every three months and your family doctor about once a year for routine checks.

KEY POINTS

■  All people diagnosed as hypertensive should have a spot urine check, a single blood test and an ECG
■  Only a minority of patients need referral to specialist clinics for hypertension for further investigation

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Treatment without drugs

Importance of diet and lifestyle

This is sometimes called ‘non-pharmacological’ blood pressure reduction and it has been shown to work. It generally involves relatively straightforward changes to your diet and lifestyle which you can make with advice from your GP, although you may find some harder to do than others. Nevertheless, it really is worth making a big effort because, if you are successful, your blood pressure may return to normal without the need for drug treatment.

Reducing salt intake

Your GP will almost certainly advise you to reduce the amount of salt that you consume. In the UK, the average salt intake in men is 10 grams per day and in women it is about six to seven grams per day. However, a very large number of people consume about half this amount and they have lower blood pressures. Only about one gram of daily salt intake is added to food

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when it’s on the table or during cooking. The rest comes mostly in processed foods, including burgers, meat pies, sausages, salted snacks, tinned foods (such as vegetables), breakfast cereals and bread.

You can cut your intake by never adding salt to your food at the table or when cooking. Try to make more use of fresh meat and fresh fruit and vegetables, and only eat processed foods as the exception rather than the rule. All herbs and spices can be used to flavour foods in place of salt when cooking.

Making changes

Adjusting to a low-salt diet can be a little difficult at first but you will probably find that, if you can consistently keep your salt intake down, then after about a month or so you actually prefer your food with less salt.

If you were then to go back to your old eating habits, you would find that your food tastes too salty and that you have become ‘converted’.

It’s much the same process as happens to people who stop adding large quantities of sugar to their tea or coffee. Once they get used to drinking unsweetened tea or coffee, they often find that adding even a tiny amount of sugar makes it taste so repulsive that they would rather drink water. The same thing can happen when changing from a high-salt to a low-salt diet.

Salt and the food industry

Sadly, the food industry has only responded to the salt/blood pressure problem in a limited manner. Salt was once a useful preservative but modern food technology and refrigeration mean that the salt content of processed

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foods can be reduced. Unfortunately, many people have now become ‘hooked’ on salty foods.

There has been some irresponsible propaganda by some representatives of the food industry in which they have suggested that there is no relationship between salt and blood pressure, and that all the experts who have done research in this field are wrong.

Experts do not necessarily advocate a drastic reduction in salt intake; they advocate bringing it down to the same level as that in the diets of a great many people who tend to prefer good quality food without preservatives or additives.

There is some evidence that the lower blood pressures in people in senior positions in executive and managerial jobs are related to their lower salt intake, as well as to the fact that fewer of them are overweight.

Salt substitutes

There are several salt substitutes now available from chemist shops. These contain less sodium chloride and more potassium chloride. Although, in an ideal world, no one should need to add crystals of any chemical substance to their food, if you really can’t tolerate food with a low-salt content you can use the salt substitutes instead, provided that your kidney function has been shown to be normal.

Don’t forget, though, that sea salt, rock salt and ‘natural’ salt are still salt (that is, sodium chloride) and so are not salt substitutes. You need to use salt substitutes with care if you are taking a ‘potassium-sparing’ drug such as the water pills spironolactone or amiloride or the angiotensin-converting enzyme (ACE) inhibitors or the angiotensin blockers (ARBs) if your

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kidneys are not functioning well, as you may have high potassium levels anyway. If in doubt, ask your GP’s advice.

Recent reliable research from the USA has clearly demonstrated that lowering the animal fat content of the diet, and increasing the intake of potassium in the form of fruit and vegetables, cause a fall in blood pressure, with a further fall if salt intake is restricted as well. There are also benefits from increasing the intake of fish oils in the form of salmon and mackerel.

Weight control

As was pointed out earlier, for every kilogram (two pounds) of weight you lose your blood pressure will fall by about one millimetre of mercury. So, if it is only slightly elevated, say around 165/95 mmHg, it may go down to normal if you manage to lose a stone in weight. There is reliable evidence from clinical trials to show that losing weight does lower blood pressure. It’s not easy to do, however, unless you have proper advice and strong motivation, and your diet should take account of the need to cut your salt intake as well.

Research indicates that, if you are overweight, you are likely to lose more if you’re referred to a dietitian than if you’re simply told to lose weight by your doctor. You also have a better chance of reaching your target weight if you increase the amount of exercise that you take and cut down the amount of alcohol that you drink, if appropriate.

Almost all medical authorities in all specialities agree that we should all adopt ‘the prudent diet’ with:

•  less salt
•  less animal fat

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•  more fish
•  more fruit and vegetables.

This diet is associated with protection from many diseases, including cancer.

Sensible alcohol consumption

There is good evidence that drinking only moderate amounts of alcohol lowers blood pressure and you probably don’t need to give it up altogether. The Royal Colleges of Physicians, Psychiatrists and General Practitioners in the UK recommend a maximum intake of 21 units of alcohol per week for men and 14 units for women. One unit is the equivalent of half a pint of beer or a small glass of wine. Avoid binge drinking because it can cause strokes.

It may be the case that having one to two drinks every day may be associated with lower levels of heart disease. However, more than four drinks per day does appear to be associated with increased risk of hypertension and stroke, as well as having damaging effects on the liver, the nervous system and the quality of life.

Taking exercise

Research has proved a clear association between taking more exercise and a fall in blood pressure. The mechanisms are not entirely certain and may in part be related to dietary changes that people often make at the same time as they begin exercising regularly. If you have hypertension, however, you need to use your common sense when deciding on your exercise programme. For example, an overweight middle-aged man with severe hypertension who has never taken

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any exercise would be unwise to take up vigorous exercise that leaves him feeling exhausted. It is much better to opt for a graded programme of gradually increasing exercise.

Start by using stairs rather than a lift or escalator whenever you have to climb only two or three flights, and try walking to a more distant car park or bus stop on the way to and from work or the shops. Any form of sport is fine provided that you don’t exhaust yourself, but you need to put in sufficient effort to cause a small rise in your pulse rate and make you feel that you are sweating a bit.

Potassium supplements

Although there is evidence that increasing the amount of potassium in the diet lowers your blood pressure, you should not take supplements in the form of potassium salts or tablets. Instead, you should increase the amount of potassium in your diet by eating more fresh fruit and vegetables and cutting your salt intake from processed foods at the same time.

Stress counselling

As explained earlier, there is little evidence that chronic stress causes high blood pressure. However, there are many people with hypertension who are immensely stressed for a multitude of reasons, as a result of personal problems, anxieties at work or the development of anxiety states for which no obvious cause can be found.

If this applies to you, stress counselling and, in extreme cases, psychiatric treatment may help to reduce your stress and your blood pressure may come down at the same time. Otherwise, there is no reason

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to believe that most people with hypertension will derive any benefit from stress counselling, relaxation therapies, yoga, biofeedback or other related techniques.

What you may find is that, after stress counselling, you are more able to relax when you see your doctor, but this type of treatment for stress does not appear to affect the continuous 24-hour home blood pressure readings that are obtained by electronic blood pressure monitors.

This is a controversial area, but the current view is that the role of stress counselling and the like in the management of hypertension has, to date, been over-rather than understated.

Complementary therapies

A great many complementary and so-called ‘natural’ products have been tried out in the management of people with raised blood pressure.

Two large and very reliable studies show that antioxidant vitamins have no effect on blood pressure or cardiovascular risk, and these are emphatically not recommended.

Recently, a yoghurt-type product containing sour milk has been shown to have a trivial effect on blood pressure. However, for this to be effective on a long-term basis, you would need to consume two containers of this yoghurt every day for 20 to 30 years and so this regime is also not recommended.

There is some evidence that garlic may have a small effect on blood pressure. Most of the garlic that we consume is in foods that are of a higher standard and it may well be that it is these other contents of the foods that are beneficial. It is, however, true that garlic is not harmful.

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KEY POINTS

■ Relatively straightforward changes to your diet and lifestyle can reduce your blood pressure and remove the need for drug treatment
■ There is good evidence that reducing the amount of salt in the diet does reduce blood pressure
■ If you are overweight, reducing your weight will lower your blood pressure
■ Research has proved a clear association between taking regular exercise and a fall in blood pressure

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Drug treatment

Development of drug treatment

Until the 1950s there was almost nothing that doctors could do to reduce blood pressure. People with severe hypertension became unwell with strokes, heart and kidney failure, and their doctors could only stand helplessly by.

During the late 1950s and early 1960s, anti-hypertensive drugs became available that did lower blood pressure and did save lives. Many of these early drugs, which are no longer used, were, however, associated with severe side effects and their use was only justified in patients with a very poor outlook.

During the 1970s drugs with fewer and less dramatic side effects became available and these could therefore be given to people with milder hypertension who were at a lower cardiovascular risk.

A large number of well-conducted trials were performed in which active treatment was compared with dummy tablets. All of these trials were discontinued the moment it could be shown that people taking the active treatment developed fewer heart attacks and strokes.

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Pooling the results of all these trials, we now know that antihypertensive drug therapy for all grades of hypertension brings about a 35 to 40 per cent reduction of strokes and a 20 to 25 per cent reduction in coronary heart disease.

People with hypertension may of course develop heart attacks as a result of other factors, for example, cigarette smoking or having high blood cholesterol levels. It is now, however, true to say that the complications of hypertension should be avoidable if blood pressure can be controlled.

The development of antihypertensive drugs with minimal side effects and their immense benefits in terms of prevention of heart attacks and strokes has been one of the biggest advances in medical care since World War II. It is at least comparable with the revolution that was achieved with the development of effective antibiotics.

Blood pressure-lowering drugs have also been shown to be effective in reducing or preventing kidney damage in people with diabetes with or without concurrent hypertension, and more recently some drugs have been shown to prevent damage to the retinas of people with diabetes.

Furthermore, treatment with certain antihypertensive agents can reduce the likelihood of people who have had heart attacks having a second one or developing heart failure.

The publication, in 1997, of a major European study of the treatment of isolated systolic hypertension marks the end of an era. It has left no more room for doubt that nobody with hypertension should be left without treatment for more than a few weeks.

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Treating elderly people

Everyone whose blood pressure consistently exceeds 160/100 mmHg should take antihypertensive drugs, whatever their age. The only unanswered question that remains is whether people over the age of 80 benefit from such treatment and it may be that, in their case, the threshold for beginning therapy should be a little higher than 160/100. More information will become available about this point in the future. The available evidence suggests that antihypertensive treatment in people over the age of 80 does bring about a significant reduction in stroke and heart failure. There is some doubt, however, as to whether antihypertensive treatment is associated with a reduction in all-cause mortality. Research is ongoing in this area.

Antihypertensive drug treatment is particularly effective in people aged 60 to 80 years who, if not given medication of this kind, face a high risk of having a stroke. Older people often worry that they may suffer a stroke, but they can be reassured that drug treatment can largely prevent this happening, which is an excellent reason to keep taking the tablets as prescribed.

Controlling blood pressure

All drugs that lower blood pressure are roughly equally effective. They drop the systolic pressure by about 10 to 15 mmHg and the diastolic pressure by 6 or 8 mmHg. Different people respond to them in different ways: for example, older people respond better to some drugs than to others as do people of African– Caribbean origin.

It is worth bearing in mind that much the same falls in blood pressure levels can be achieved by someone

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who sticks rigorously to advice on restricting salt intake, losing weight and drinking only moderate amounts of alcohol as can be achieved by any single antihypertensive drug.

If you are on drug therapy, you should also remember that the effect of some drugs is greater if you reduce your salt consumption while taking them, so it’s worth making the necessary effort to cut down your salt intake.

Using multiple treatments

One tablet a day will be enough to control blood pressure for around one-quarter of people who are on antihypertensive drug therapy. Most of the rest require double therapy with two different drugs and about 25 per cent of people require triple therapy (that is, three different drugs) to control their blood pressure.

Fortunately, even if you need triple therapy, this usually means taking only three tablets daily. Almost all these can be taken together, either in the morning or in the evening. The older types of drugs, which had to be taken two or three times daily, are now regarded as obsolete. This is good news because the more times you need to take your tablets each day, the more likely you are to forget them sometimes.

Blood pressure that is hard to control

If you are one of the small minority of people whose blood pressure proves very difficult to control you will probably be referred to a specialist and there are a few people whose blood pressure is almost impossible to control. This is probably because they didn’t begin taking antihypertensive treatment until a late stage of the disease process, so that the structural changes to

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the small arterioles are so far advanced that the drugs don’t work very well. However, even in this situation, reducing the blood pressure does reduce heart attacks and strokes.

It must be stressed, however, that most people with hypertension have only mildly raised blood pressure which is relatively easily controlled and, if you are in this category, you can be cared for perfectly well by your GP and the practice nurse.

A long-term treatment

Many people have the mistaken idea that they will need to take drugs to lower their blood pressure only for a short while, rather like taking a short course of antibiotics, and then they can forget the whole thing. This is an extremely dangerous misunderstanding and, if you give up taking the tablets, your risk of a heart attack or stroke will be greatly increased.

With very few exceptions, antihypertensive treatment needs to be taken for the rest of your life. As you get older, the risk of a stroke increases and so the benefit of treatment is correspondingly greater. If you stop taking the drugs and your blood pressure stays down, it is necessary to question whether you ever really had hypertension in the first place, or whether your treatment was started on the basis of a single raised blood pressure reading taken when you were under stress, just because you were having it measured in an unfamiliar environment. In reality, the chances of anyone with genuine hypertension being able to stop antihypertensive tablets are small.

Changing your lifestyle

However, if your hypertension was only mild in the first

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place and if you needed no more than one tablet a day to control it, then, if you change to a low-salt, low-fat diet and consume at least five portions of vegetables or fruit per day, and also lose weight, cut down on alcohol and take more exercise, you may be able to come off drug treatment.

Even so, about half the people who do manage to do this will need to re-start therapy at some stage. If your doctor does agree that you should stop treatment, he or she will need to see you regularly for check-ups, at first monthly and thereafter three-monthly. It is very likely that your blood pressure will eventually go up again and you will need to go back on the tablets.

Anyone who needs double therapy (two different drugs) to control their blood pressure is extremely unlikely ever to be able to come off therapy altogether. There is, however, some evidence that people whose blood pressure was initially difficult to control, and who therefore needed triple or quadruple therapy, may develop easier blood pressure control as the years go by, and so be able to manage on fewer drugs.

Stopping treatment

Like many people who have been prescribed antihypertensive drugs, you may be tempted to stop taking them or actually do so without going back to your doctor. It’s all too easy to convince yourself that you don’t really need them because you’re feeling well and have no symptoms. The chances are that, if you do this, you may one day end up in the accident and emergency department of your local hospital, because you have developed one of the complications of hypertension, such as a heart attack or stroke.

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Alternatively, you may eventually go back to your doctor with very high blood pressure that is extremely difficult to control, so you then need to take three, four or even five drugs. You can avoid this happening to you if you continue to take the treatment that’s been prescribed and attend your doctor’s surgery regularly for check-ups.

Monitoring your condition and treatment

Once your hypertension has been assessed by your doctor and been brought under control by treatment, you will probably need to have your blood pressure

Regular monitoring of your condition and review of your treatment will ensure that your blood pressure is under the best possible control.

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checked only about four times a year. It is important to go back for such checks to make sure that your blood pressure is under control and, increasingly, your appointments are likely to be with a specially trained practice nurse rather than the doctor.

From time to time, you may need to have other tests besides blood pressure measurement – such as blood tests to check your kidney function or, occasionally, an ECG. Your serum cholesterol levels should also be monitored because high blood cholesterol, like high blood pressure, is an important risk factor for heart disease and cholesterol-lowering treatment also saves lives.

Antihypertensive drugs

There is now a wide choice of blood pressure-lowering drugs. This means that your doctor is able to tailor the treatment to suit your individual needs. It is important for you to know the names of the drugs that you are

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taking, how they work and their possible side effects. With improvements in drug development, it is becoming increasingly possible to minimise side effects or even avoid them altogether.

The next section of this booklet describes the currently available drugs. You need to bear in mind that there are usually many different drugs within each of the classes described here and there are minor individual variations between them.

It is a bit confusing, but all drugs have two names. The most prominent name on the box is the proprietary or trade name (for example, Istin, Zestril, Cozaar), but this can vary if several drug companies market the same drug. The small print name is the generic or chemical name (for example, amlodipine, lisinopril, losartan) and gives an idea of which class the drug is in. It is best to use the generic name even if it does seem a bit long at times.

The thiazide diuretics

These drugs work by opening up blood vessels which results in a fall in blood pressure, and also by helping the kidneys to get rid of salt and water in the urine which slightly reduces the volume of circulating blood, thus taking some pressure out of the system.

This group of drugs was introduced in the 1950s and they remain the mainstay of treatment of hypertension, particularly in older people. They are sometimes referred to as ‘water tablets’ because they slightly increase the production of urine. However, they also tend to relax the medium-sized

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blood vessels called arterioles and this helps to explain why they lower blood pressure.

In the early days, the thiazide diuretics were used in very high doses. However, it has now become apparent that it is better to take the smallest amount possible while still achieving the desired effect. Higher doses don’t work better at lowering blood pressure but do increase the risk of side effects, such as triggering gout or diabetes. In high doses, thiazide diuretics lower the potassium in the blood and increase the amount of cholesterol or lipids, but such problems are far less prominent now that they are prescribed in sensible low doses.

Among sexually active men high doses of this type of drug were shown to be associated with impotence. This again has been shown to be much less of a problem now that low doses are used, but even so they are not usually prescribed for sexually active men.

Many of the reported benefits of blood pressure reduction, in the various randomised controlled trials described earlier, were achieved with this type of drug. They work well for older people and those of African–Caribbean origin and they have almost no noticeable side effects. They may cause changes in blood chemistry but these can be minimised if low doses are used.

Some of the thiazide diuretics have a small amount of potassium chloride added to their formulation with the aim of preventing the development of low levels of serum potassium. In fact the amount of potassium in the tablets is so small that such combined preparations are no longer recommended. Thiazide diuretics in low dose do not cause a fall in potassium of any great significance but if this should happen you should be prescribed a different class of drug instead.

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How thiazide diuretics work

This class of drugs opens up blood vessels, creating more space for a given volume of blood, so the pressure in the system drops. They also force the kidneys to excrete water and salt, reducing the volume of blood in circulation and therefore the blood pressure.

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A major long-term outcome trial, published in December 2002 in the USA, demonstrated that the thiazide diuretics are quite as good as, and in some instances better than, other classes of drugs at preventing the vascular complications of hypertension.

Calcium channel blockers (also known as calcium antagonists)

These work by blocking the action of calcium in the smooth muscle of the wall of the arterioles. It is thought that constriction of the smooth muscle, caused in part by calcium, narrows these blood vessels which causes hypertension to develop. Blocking the action of calcium opens up the blood vessels which results in a fall in blood pressure. The problem is that all the arterioles open up, including ones in the brain, which can cause headaches, ones in the face, which can cause flushing, and ones in the legs, which can cause ankle swelling, but the newer, longer-acting formulations produce far fewer side effects of this kind. Nifedipine is now prescribed in this long-acting formulation and, although amlodipine and lacidipine cause few problems, high doses do cause ankle swelling. This is not the result of heart failure, and is not sinister; some women in particular find it unacceptable. Another calcium channel blocker called verapamil can cause constipation and may also be hazardous in certain forms of heart disease.

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How calcium channel blockers work

When calcium enters muscle cells they contract. Calcium channel blockers restrict the amount of calcium able to enter cells and so inhibit the contraction of the muscles that line the walls of blood vessels. As a result the blood vessels dilate (open up), reducing blood pressure.

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During 1995 anxieties were expressed about the safety of calcium channel blockers, but these anxieties have been allayed by the publication of a major trial in 1997, which showed that these drugs prevent heart attacks and strokes and are not associated with an excess of other problems. They are particularly effective in older people and those of African–Caribbean origin.

Angiotensin-converting enzyme (ACE) inhibitors

These work by preventing the activation of the hormone angiotensin II from its precursors, renin and angiotensin I by, angiotensin-converting enzyme. As angiotensin II constricts blood vessels, ACE inhibitors open up blood vessels resulting in a lowering of blood pressure.

This class of drug represents an important breakthrough in the management of hypertension. Not only do they lower blood pressure, they also protect the kidneys of people with diabetes and hypertension. More recently, they have been shown also to delay the onset of retinal damage which can impair the vision of people with diabetes. They are also prescribed for some people who have recovered from a heart attack.

The ACE inhibitors are remarkably safe but, if you are already on water pills (diuretics), you need to be monitored closely by your doctor when you first start taking them because the first dose can cause a sudden fall in blood pressure.

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How ACE inhibitors and ARBs work

ACE inhibitors block the activation of the hormone angiotensin II by angiotensin-converting enzyme (ACE) inhibitors. Angiotensin II is involved in constricting blood vessels. ACE inhibitors therefore open up the blood vessels, lowering blood pressure.

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Newer ACE inhibitors are less prone to do this but you may be advised to stop diuretics for a day or so before starting treatment with an ACE inhibitor. ACE inhibitors are also very effective in the treatment of congestive heart failure, whether or not the blood pressure is raised.

Around one in 1,000 people of African–Caribbean origin and one in 4,000 white people