High blood pressure-What is it exactly?

Cast your mind back if you will to the idle days of summertime. If by any chance you used your hosepipe you will know about water pressure. When the water comes out of the end of the hose the distance it travels depends on the pressure within the pipe. If you connected the end of your hosepipe to a Blood pressure machine (Sphygmomanometer)you might be able to measure the water pressure. Blood pressure is essentially the pressure exerted by our own blood on the walls of our blood vessels. Fortunately for us our hosepipes are closed at both ends except if an artery is severed. When this happens the pressure in the vessel is immediately apparent and blood from a severed artery can rise several feet into the air.

William Harvey first demonstrated the circulation of the blood (described in 'De motu cordis et sanguinis '-Concerning the movement of the heart and blood) in the seventeenth century. It is the circulation which dictates blood pressure and the contraction of the heart (known as systole)which determines the maximum or systolic pressure. During the relaxation phase (Diastole) the pressure is lower and is termed the diastolic pressure. Both pressures are measured in millimetres of mercury, this happens to be a convenient heavy liquid with which to measure pressure

In a sense every individual has a 'high' blood pressure and a 'low' blood pressure written thus 120/70.. The larger number is the systolic and the smaller number the diastolic pressure.The difference in the pressures ensures that blood flows. Normal blood pressure varies within an individual and with time and circumstances. Most people have fainted at some time or another, this occurs because the pressure has fallen too low. Surprisingly low blood pressure can be responsible for symptoms although in this country it is not usually treated. In contrast high blood pressure usually causes few symptoms and is picked up incidentally. A single measurement is of little value in establishing whether somebody really does have high blood pressure(usually termed essential hypertension). Someone with normal blood pressure on a bad day could have a blood pressure similar to that of someone with untreated hypertension on a good day. A racing driver on the starting grid of a Grand Prix will have a very high blood pressure. The system is designed to cope with this for short periods. Sustained high blood pressure however causes damaging changes in blood vessels which can .predispose over many years to stroke. Doctors treat blood pressure to prevent this.

In my view everyone should have the blood pressure checked every couple of years. If it is found to be raised significantly on one occasion then at least two further checks should be made before treatment is started unless it is exceptionally high in which case treatment might be given immediately. There is at present some debate about who is best placed to monitor blood pressure. My personal view is that there is nothing wrong with patients monitoring their own as long as they know what they are doing and use a reliable machine which is periodically checked.

A family history of high blood pressure or stroke is a risk factor for developing hypertension. Women who have high blood pressure in pregnancy (pre-eclampsia) have a one in three risk of developing high blood pressure in future. Patients with diabetes are more likely to develop the condition. The role of stress alone in causing high blood pressure is not clear. However attention to lifestyle factors such as exercise ,taking a good reduced salt diet and avoiding obesity can all reduce risk. Although alcohol in small amounts seems to offer some protection against heart disease in large amounts it can cause high blood pressure.

It has been said that only half the number of people with hypertension are treated and of these only half are adequately controlled. . If you have not had your blood pressure checked for some years you can get this done without an appointment at one of the new walk in centres in Bristol. Alternatively ask your General practitioner to check it next time you see him or her.

Raised blood pressure is common in those aged over 60 years and is associated with an increase in the absolute risk of stroke and coronary heart disease. Treatment will reduce stroke incidence by almost 40% and the risk of a major coronary event by about 20%.

When to treat

Treatment is indicated in those aged 60-79 years with a sustained (checked twice on 3 separate occasions 1-2 weeks apart) sitting systolic blood pressure of>160mmHg or diastolic blood pressure >90mmHg or both. Blood pressure should also be checked standing because of the high prevalence of orthostatic hypotension in this age group. As yet there is insufficient evidence to recommend routinely treating those over the age of 80 years who are newly diagnosed and otherwise asymptotic and free from target organ damage (TOD). In those with TOD and those who have been on treatment up to the age of 80+years, treatment should probably be continued or initiated. The results of current ongoing studies are needed to resolve some of these important issues, particularly with regard to the benefits of treatment m the very elderly and for those with raised BP levels following a stroke.

How to treat

Weight loss in the overweight, reducing salt and alcohol intake and increasing exercise (e.g. brisk walking for 30 minutes 2-3 times per week) where appropriate are always worth introducing but may be insufficient to reduce BP levels sufficiently and so anti-hypertensive drug therapy will often be needed.

Anti-hypertensive drug therapy is well-tolerated by the elderly with no significant age related increase in drug related side-effects although postural hypotension is more common. Quality of life is preserved provided low doses are used initially and increased gradually as required. Diuretic therapy reduces cardiovascular morbidity and mortality though even low dose thiazides can occasionally produce unwanted problems e.g. urinary incontinence and gout. Controversy exists as to whether beta-blockers are as effective first line agents as diuretics in this age group and it is as yet unclear whether newer antihypertensive agents, such as angiotensin converting enzyme (ACE) inhibitors and calcium channel blockers are superior to older drugs in terms of preventing CHD) and stroke. More than half elderly patients require a second line drug. The choice of drugs should take account of concomitant problems, e.g. the presence of heart failure indicating the use of an ACE inhibitor and a diuretic. Consideration must also be given to other medications that patients may be prescribed in order to prevent adverse side-effects, e.g. interaction between non-steroidal anti-inflammatory drugs and ACE Inhibitors.

The benefits of therapy are more closely related to on-treatment BP levels than pre-treatment values so regular assessment of BP control is important. Optimal BP levels on treatment are unknown at present but pragmatically it is probably beneficial to try and achieve values of at least 140-150/80-85 mmHg if reasonably achievable without inducing important side-effects. Routine checks of renal function and serum electrolytes are needed especially m those taking diuretics and ACE inhibitors. Finally, it is important to consider and, when necessary, treat other risk factors, in particular smoking, diabetes and elevated plasma lipid levels (at least in those aged up to 75 years or with a history of coronary heart disease).

Reference

British Hypertension Society: http://www.hyp.ac.uk/bhs

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