What is Blood Pressure (BP)
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Blood pressure is generated and maintained by two events;
i. When the heart is pumping blood out of the heart's chamber (ventricle) and into the artery - the circulation - this is the higher (systolic) pressure.
ii. The arteries have 'elastic recoil' which contributes to the BP. This is the lower (diastolic) pressure and represents the pressure in the artery when the heart is filling with blood or 'relaxing'.
The BP is a measurement of the force exerted by the blood on the artery wall.
The heart has to overcome the existing arterial diastolic pressure so that it can empty its contents into the circulation. This lower pressure (the diastolic) therefore is a very important state because it represents the minimum pressure the heart has to overcome to keep the circulation going. During the pumping-out phase this lower pressure must be exceeded by a considerable margin to empty the heart's ventricle and it must keep up this work rate to provide sufficient blood volume to satisfy the demands of the general circulation, especially during exercise. It is partly for this reason that the lower pressure is taken seriously by doctors when assessing the blood pressure for if this pressure is abnormally high it represents excessive long term work for the heart and it will eventually falter.
The BP is measured by recording at what height it supports a column of mercury (symbol Hg). The two readings are therefore expressed as for example, 140 / 80 mm Hg; 140 mmHg systolic and 80 mm Hg diastolic.
What is 'High blood pressure'?
Current recommendations by the British Heart Foundation are that, for the general population, and irrespective of age, a blood pressure reading of 140 / 85 mm Hg or less is desirable and for people who have had a heart attack or stroke the recommendations are a reading of 130 / 80 mm Hg.
For these reasons doctors now treat blood pressure readings higher than these recommendations much more aggressively than a few years ago. By these clear rules people are judged as requiring treatment or not. If the blood pressure exceeds these recommended limits the individual should make suitable modifying lifestyle changes and seek medical advice.
How is it measured?
The instrument to measure blood pressure is the sphygmomanometer.
The traditional mercury instrument together with the accompanying stethoscope has for very many years been a piece of standard equipment in the doctor's surgery. It consisted of a pressure cuff - to be placed around the upper arm at the level of the heart - connected to a hand pump with a screw pressure-release valve, a closed reservoir containing mercury and a vertical closed glass tube; the manometer. The cuff size used varies depending on the person's size.
The liquid metal mercury has the high relative density of 13.6, enabling the manometer to be a conveniently short 300mm. The device is not particularly portable and mercury itself and its vapour, even from microscopic accidental spillage, is extremely poisonous. It has been the standard accurate instrument for measuring blood pressure and any error in interpreting the result can be assigned to the operator.
The hand pump inflates the arm cuff to develop a pressure to support the mercury column at a height above the estimated blood pressure and this pressure halts the blood flow in the artery. The screw valve is opened to allow the pressure in the cuff to reduce gradually and, with the stethoscope placed over the brachial artery, the listener hears the sound of the blood entering the brachial artery under the pressure of the heart pumping blood into the circulation - this is the systolic pressure. As the cuff is released further and the pressure in the cuff falls a second sound is heard reflecting the diastolic pressure.
Over the past few years all this has changed because under COSHH regulations (Control of Substances Hazardous to Health) the mercury sphygmomanometer has been removed from use and replaced by modern aneroid and electronic BP devices. These are safe to use, free from operator error, are very portable and the electronic versions are automatic. They are calibrated to match the mercury devices.
They are a most valuable addition to personal health care monitoring and provide users with previously unseen evidence of silent disease. Since a single recording of the BP can be marginally or very erroneous - depending on how the individual responds to the experience - these devices can be used in the familiar setting of the home where relaxation is the norm, providing ideal circumstances for a correct reading. Moreover, in regular use and recording they can show a trend pattern over a suitable time period.
Electronic blood pressure devices operate by detecting oscillations in the artery and for this reason should be used in a quiet stationary environment.
How common is high blood pressure (hypertension)?
It is estimated that one person in four of the adult population in the UK are affected by high blood pressure. Approximately 30% of these do not even know they have the condition. This is understandable for more often than not it does not make a person feel any different than usual. Not without good reason therefore is it known as 'the silent killer' for if left untreated it will cause serious effects including major organ damage and even heart attack. Not knowing if it is present means not having treatment and that puts health at serious risk. Doctors are extremely keen to redress this anomaly because it is easy to diagnose and treat. Treatment can be as simple as a lifestyle change or, under medical management, with highly effective drugs.
The term 'blood pressure' is used in a popular context to describe a disease state yet we all know that the blood is indeed naturally under some pressure, without which the circulation simply wouldn't work. So when the doctor advises that a person has 'blood pressure' or 'high blood pressure' just what is being described and what are the implications for the individual?
With an estimated 1m people having undiagnosed high blood pressure and being unknown to their GP, it is an attractive option to obtain a personal electronic blood pressure device so that the blood pressure can be recorded and logged to obtain a clear trend over various periods of time - stressful and placid - and offers a better and more informed picture than a solitary recording at a specific time.
Have I got 'blood pressure'?
Medical recommendations suggest that all adults should have their blood pressure checked at least every five years, but preferably more often. Increased frequency for this is recommended for older people because blood pressure rises with age. To minimise errors, ideally three recordings should be taken - to allow the individual to relax and reduce any tension generated by the experience - and an average result is then noted. Since blood pressure varies throughout the day a single record may not reflect the true state.
It should be every person's responsibility to know what their blood pressure is and, where this is elevated above the British Heart Foundation recommendations, to take appropriate action to reduce it through lifestyle management and medical advice. This should become a part of a personal health action plan. It is primarily through this personal action route that this 'silent killer' will be corrected.
What causes it?
In over 90% of cases there is no single underlying cause but it is believed that several risk factors and conditions contribute to the development and progress of the condition:
- Obesity. The BMI (Body Mass Index) should be 25 or less.
- Excess alcohol consumption. Note the calorie value of alcohol.
- Lack of exercise. Engage in exercise to create fast breathing for 20 - 30 minutes three times per week
- Consuming too much dietary salt. Ideally not more than 6 grammes / day
- Genetics (High blood pressure appears to run in families).
- The ageing process
- Smoking (not a direct risk factor for high blood pressure, but it does increase the
chance of heart attack, heart failure and stroke).
- There are recognised medical causes such as kidney disease but these are small in
number in a generally vast 'silent killer' pool.
- Certain medication can also cause a rise in blood pressure.
What damage can it do?
Hypertension damages blood vessels throughout the body and imposes excessive work on the heart. Persistently raised blood pressure is transmitted through the large arteries and onward to the smaller arteries (arterioles) supplying the respective organs of the body and these too are not capable of tolerating such pressures and this causes 'end organ' damage resulting in organ failure.
Reducing high blood pressure by 5mm Hg can reduce the risk of having a heart attack by about 20%. If personal blood pressure is not known it is better to remove uncertainty by getting it checked and then taking the initiative for on-going personal monitoring, which is a far better process of checking than a single reading by the doctor or nurse.
How does it all work?
The circulatory system can vary the flow of blood within it for it is subject to highly sensitive nervous regulation. This regulation is under 'automatic control' through a part of the nervous system that is specialised to regulate all the essential internal processes of the body; the autonomic nervous system. Each organ of the body that is controlled in this way has a nervous network reaching it which has two parts; the sympathetic branch and the parasympathetic branch. Generally it is the sympathetic branch, together with the hormone adrenaline, that prepares the body's organ systems for extra activity, when necessary. The parasympathetic system slows it down or relaxes it to restore the normal state.
From this brief description it can be appreciated how apprehension, stress or worry - which generates the hormone adrenaline - can be associated with speeding-up organ systems and raising the blood pressure.
Daily activity can bring stress, excitement or apprehension and it can be appreciated that from the result of these experiences, in exciting the sympathetic nervous system, the blood pressure will vary throughout the working day. When we relax the parasympathetic branch becomes dominant and slows down the process, so blood pressure decreases during rest and sleep.
If the pressure remains consistently high it can damage the arterial walls causing them to lose their natural elasticity. The role of exercise is valuable in this context because not only does it diminish stress but it also exercises the elastic nature of the arteries helping to keep them responsive to the demands of the autonomic nervous system. The progressive loss in elasticity eventually limits blood flow and this also causes arterial thickening adding to the persistently elevated blood pressure. In over 90% of cases there is no single underlying cause but is generally a mixture of the above mentioned causes.
How is it treated?
There are many lifestyle changes a person can make to reduce their risk of, or help lower, existing high blood pressure.
Smoking is not a direct risk factor for high blood pressure, but it does increase the chance of heart attack, heart failure and stroke. Within two years of stopping smoking a person's risk of a heart attack is halved.
Research suggests relaxation techniques, to help with stress, may be useful for some people in managing their high blood pressure.
There are many highly effective drugs available from the doctor to help lower and control hypertension including beta-blockers, ACE inhibitors (Angiotensin Converting Enzyme inhibitors), Angiotensin11 antagonists, calcium channel blockers (calcium antagonists) and diuretics. They do of course have some side effects but are usually well tolerated and, if these are troublesome, the available drugs and their various combinations generally provide a suitable treatment alternative. Their benefits outweigh the side effects.
What about low blood pressure?
People with low blood pressure rarely have any symptoms but can experience feeling dizzy or even fainting after bending over or getting up after lying down if their blood pressure falls below 90 / 60 mm Hg. This condition does not have the life threatening risk associated with high blood pressure and they generally live longer than people with high or even 'normal' blood pressure.
High blood pressure (Hypertension), affects nearly one in four adults in the UK.
About 30% of these do not know they have the condition. That means their doctor does not know that they have this high risk condition and are therefore not receiving treatment.
Normal blood pressure for the general population should be no higher than 140 / 85 mm Hg.
Following a heart attack or stroke this should be below 130 / 80 mm Hg
Lifestyle adjustment; a healthy diet (eat more fruit and vegetables for these contain potassium, which can help keep blood pressure down) and less saturated fats. These changes can reduce the BP by 8 and 14 mm Hg. Reduce salt intake (not more than 6 grammes per day), reducing alcohol consumption, reducing overweight / obesity (BMI less than 25), and taking more exercise can all help reduce hypertension.
Drug treatment by the GP is usually very effective - perhaps requiring a combination of drugs
Personal blood pressure monitoring for accurate recording and trending is now within the reach of all and can begin reducing the incidence of this silent killer.