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(2) High Blood Pressure

What is high blood pressure (BP)?

High BP is not an illness or disease – rather it is a risk marker for illnesses that you wish to avoid. These include stroke, heart attacks, kidney problems and other problems affecting the circulatory system (blood circulation). Most people who have high BP do not have any symptoms. However, not having symptoms does not imply that you are not at risk of having any of the potentially harmful consequences of having high BP. The risk of suffering complications from having high BP can be reduced by either nondrug or drug treatments or by both.

 What types of high BP are there?

High BP is traditionally classified into two main groups: ‘essential’ or primary hypertension where no cause can be found and ‘secondary’ hypertension where high BP is caused by other conditions.

(‘Hypertension’ is just a medical name for high BP.) Secondary hypertension is very uncommon and mostly caused by various sorts of kidney disease, or occasionally by irregular anatomy of the aorta (‘coarctation’); overproduction of some BPraising hormones by tumours of the pituitary gland, adrenal glands or kidneys; or by disorders involving compression of the brain. These ‘classical’ secondary causes altogether account for less than 1% of all treated cases of high BP.

 What causes high BP?

There is still a lot of uncertainty about the causes of high BP. For the vast majority of people, over 95%, an underlying cause is not found. These are the people who have ‘essential’ hypertension. It is likely that several factors contribute to high BP in most people. The chief suspects include:

• An overactive hormone system that relates to the kidney (the renin–angiotensin system);

• An overactive autonomic nervous system (the part of the nervous system responsible for our unconscious nervous responses);

• A fault in the cells of the smaller blood vessels that produce substances leading to blood a vessel narrowing and increased BP (endothelial cell dysfunction);

• Genetic predisposition (when you may have inherited a tendency to high BP);

• Intrauterine factors, particularly birth weight that may reflect undernourishment in the fetus, and that ‘programme’ our body to develop high BP in later life.

 How is high BP measured?

Accurate BP measurement is important for diagnosis. Raised BP is a symptomless condition that, if left untreated, contributes to a substantial risk of heart disease and stroke. Clinical trials of BP-lowering drugs have shown that reducing BP reduces the risk of heart disease and stroke. BP can be measured in several ways: by means of an electronic, mercury or aneroid sphygmomanometer. Electronic monitors are being increasingly used in GPs’ surgeries. Provided that a machine is selected that has been shown to be accurate and reliable, electronic monitoring offers several advantages over the older mercury sphygmomanometers. Aneroid sphygmomanometers are unreliable and are not recommended.

 How many readings and visits are needed before high BP is diagnosed?

There is no universally accepted number of visits that are necessary for a doctor to make a firm diagnosis of high BP. However, all national guidelines recommend multiple visits and multiple readings before high BP is diagnosed. Clinical trials that have established the benefits of BP-lowering treatments generally used two or three BP readings on two or more clinic visits to confirm a diagnosis. A minimum of three BP readings per visit over at least four or more separate visits are needed to confirm a diagnosis of hypertension.

 What is white coat hypertension?

This is when your BP is high when measured during a surgery or outpatient clinic but is otherwise normal. It usually occurs in response to the measurement of BP by a doctor or nurse. In people with normal BP, there is generally little or no difference between their BP reading at a clinic or in a surgery compared to their usual BP reading. However, in some people, substantial differences between clinic and usual BP are consistently found, with the higher readings occurring in situations where a doctor or nurse has made the BP reading. This phenomenon of ‘white coat hypertension’ is more commonly seen in women and older people.

As many as 20% of people diagnosed with high BP at clinics or in surgery may have entirely normal BPs when it is measured during the rest of the day. Other BP measuring techniques are recommended in these people so that their usual pressure is accurately recorded.

 Why do some people have their BP measured with a portable machine?

What you are describing is ‘ambulatory’ BP monitoring. Ambulatory BP monitoring is a much better way of measuring BP in somebody who has one of the following factors:

• White coat hypertension

• Unusual variability in the measurement of BP at the clinic;

• Uncontrolled hypertension – this is high BP that has not been reduced to a target BP level after intensive drug treatment has been given;

• Very low BP, particularly after suddenly standing up when someone may feel dizzy or light-headed (postural hypotension); in more severe cases this can cause fainting or a fall.

What tests might I need if I suffer from high BP?

The ‘classical’ causes of secondary high BP are all rare, accounting for less than 1% of all cases of treated high BP. In practice this means that detailed tests are not usually necessary when high BP is first diagnosed. The following are usually performed by your GP:

• Urine test to check for protein and sugar in the urine. Leakage of protein may indicate that the kidneys have been damaged from high BP and you will need more detailed assessment of your kidney function. Testing for sugar is a relatively straightforward way of checking for diabetes. Similarly, if sugar is present, then blood tests will be needed to confirm or rule out diabetes.

• Blood tests for urea, electrolytes and creatinine levels; total cholesterol/HDL cholesterol.

What about other risk factors? Do they need to be measured when considering treatment for high BP?

It is now recognized that high BP should not be seen and treated as a single risk factor. Guidelines now recommend that the choice of treatment depends on a person’s ‘cardiovascular’ risk (your risk of suffering a stroke or heart attack). To assess your cardiovascular risk, the doctor will take any factors into account, such as age, sex, history of diabetes, whether you smoke or not, cholesterol levels, family history and past history of cardiovascular disease. Charts that place people into levels of cardiovascular risk have now been published, and many general practitioners use these charts to assess a person’s risk of stroke or heart attack. A consequence of taking all these factors into account is that treatment recommendations are likely to include non-drug solutions, such as taking more exercise or stopping smoking. It also means that different types of drug treatments can be considered by your doctor, such as cholesterol-lowering drugs, BP-lowering drugs and drugs that prevent clotting (aspirin).

What are the best treatments without resorting to drugs?

The best thing you can do is to change your lifestyle: altering your diet, doing exercise and stopping smoking will lower the many risks that can cause high BP or that can increase you cardiovascular risk level. Increasing exercise, losing weight, lowering alcohol consumption and changing your diet (reducing salt intake and increasing fruit and vegetable intake) will result in a reduction of about 4 mmHg systolic BP on average if you stick to these changes.

Though these falls in BP are not as substantial as drug treatment, other risk factors will be improved at the same time, resulting in an overall reduction of your cardiovascular risk. Such changes are also highly beneficial in older patients as well. Lastly, if you are a smoker, stopping smoking is the most effective way of reducing your risk of suffering a stroke or heart attack. Counselling, nicotine replacement therapy and buproprion (Zyban), have all been shown to be effective in helping people quit smoking.

Why are BP-lowering drugs recommended? What is the purpose of taking them?

The doctor will hope to:

• Decrease your risk of cardiovascular disease (heart attack and stroke), which can raise BP;

• Decrease any risk of coexisting cardiovascular risk factors such as raised cholesterol, diabetes, left ventricular hypertrophy, and other conditions that raise your risk of having a cardiovascular problem; this often requires additional drug therapy, aside from BP-lowering drugs;

• Improve your quality of life and encourage a healthy lifestyle.

Your risk factors, treatment preferences and social circumstances will be taken into account to match the drugs to your ‘risk profile’. So treatment is chosen to ensure that any side effects of drugs are minimized.

There are several different classes of BP-lowering drugs. You will probably be given a thiazide diuretic first. Depending on other risk factors, other BP-lowering drugs can be chosen to reduce BP and minimize side effects – so called ‘tailoring’ of BP-lowering medication. Over two-thirds of people with raised BP require two or more different BP-lowering drugs before the ideal BP level is reached.

 Follow-up

People with high BP will be registered, reviewed and recalled regularly in order to get the best out of your treatment, so you will have to be prepared to take part in an organized system of monitoring and care.

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