EXERCISE AND BLOOD PRESSURE
The figure above shows the distribution of systolic blood pressure in the population.
My very first Exercise Blog just one year ago was about blood pressure . Here is some more about exercise and blood pressure – please forgive some repetition.
What is blood pressure?
We all have “blood pressure” (BP) which is expressed as a two figure quantity – say 120/80. The higher figure is the “systolic” pressure which is the peak pressure reached when blood is pumped out from the heart to the main arteries. The arterial pressure then falls to the lower figure which is the “diastolic” pressure, the lowest level reached before it is pushed up again by the next contraction of the heart. The unit of measurement is millimetres of mercury, mmHg, which is the pressure exerted by a column of mercury of a particular height. This is a strangely antique unit which came into being because blood pressure was always measured with a mercury “sphygmomanometer” (BP measuring instrument) which uses the height of a column of mercury as the measure of pressure. Modern sphygmomanometers are electronic and no longer use mercury so it would be more logical to use the Systeme Internationale (SI) unit of pressure, the Pascal. However the long accustomed mmHg is so ingrained into doctors’ psyche (doctors are a very conservative breed) that they have clung onto this archaic unit, rather as we continue to measure distance in the UK in miles rather than kilometres.
High blood pressure – hypertension
The distribution of blood pressure (BP) in the population follows the usual distribution of most human characteristics – the bell shaped curve which I have illustrated above. This pattern is found with height, weight, intelligence and numerous other human characteristics. There are a few people at the lower end of the range, a few at the upper end of the range but most are somewhere in between. For the majority, high blood pressure is not a disease – just the top end of a continuous scale. For a few, high BP is due to some other condition, particularly kidney disease. Persistently high levels of blood pressure are labelled hypertension, thus converting BP from a risk factor into a named disease.
Normal blood pressure is usually taken as 140/90 or less. Hypertension is a very difficult disease to define – just where is the cut off between acceptable upper level of blood pressure and unacceptable hypertension? It could be the level above which the complications of raised blood pressure kick in – but unfortunately the ill effects develop insidiously and the higher your pressure the higher the risk. Wallis Simpson said that “you can never be too thin or too rich” and to that I would add “nor have too low a blood pressure”.
A better definition would be the level above which lowering the blood pressure reduces risk. Here we should be on firmer ground but unfortunately even this soil is somewhat boggy. For decades it has been assumed that when a mildly raised pressure is treated with the appropriate medication to reach a more pleasing figure the risk is automatically reduced. However there has been no evidence for reducing the level below 140 systolic – until a recent study from the US, the SPRINT Study, which has indicated that getting the pressure down to 120 systolic may have substantial advantages over the higher target of 140.
Blood pressure varies
Another confusion in the assessment of blood pressure is that it is not a fixed figure; it is a fiction of the moment. It varies with time of day, pressure of work, timing of meals and contact with other people – particularly doctors. We are all aware of “white coat” hypertension which is the condition in which blood pressure is markedly higher when measured by the doctor. If you want to know what your blood pressure really is, take it yourself. There are plenty of reliable automatic home blood pressure machines which will give you a much more accurate picture of your BP, at whatever time of day you wish, than does the occasional snapshot BP taken in the surgery. The alternative is the 24 hour blood pressure recorder which is available to most GP surgeries.
However it is measured or defined, hypertension is very common in Western societies and the prevalence rises steadily with age. A recent American study found the prevalence of hypertension to be 9% for those aged 18-44, 40% for those aged 45-64 and 75% for 65 and over.
The ill effects of raised BP
Hypertension is a leading global cause of morbidity and mortality. Some of the damage it causes include:
The arteries: Hypertension damages the walls of the arteries and this predisposes to atheroma or hardening of the arteries. This is a narrowing of the blood vessels by patchy plaques which build up over many years, reducing the lumen, the internal dimensions, of the vessels and sometimes leading to complete blockage (as in a heart attack, stroke etc). The main artery, the aorta, may expand causing an “aortic aneurysm”. When an aortic aneurysm expands beyond a certain point it almost always bursts – a frequently fatal complication.
The heart: The atheroma often involves the arteries supplying blood to the heart muscle, leading to angina or heart attack which in turn may lead to cardiac enlargement and heart failure.
The brain: Hypertension is the greatest risk factor for stroke, which I will tackle later. Also transient ischaemic attacks (a sort of mini-stroke), and vascular dementia. This is the second commonest form of dementia and is caused by chronic progressive interference of blood supply to the brain.
Kidneys: Damage to the small blood vessels supplying the kidney can cause scarring and ultimately can lead to kidney failure.
Eyes: Again damage to small vessels can cause injury to the retina with bleeding, blurring of vision and sometimes leading to partial or complete loss of sight.
Persistently high blood pressure is common and is not a nice condition – but it is treatable. Most of these unpleasant complications are potentially preventable. Next time I will discuss the management of hypertension and the place of regular exercise.
A recent Cochrane Review1 (the best source of evidence based medicine we have) looked at the results of trials of exercise for period pain, involving women under the age of 25. They found that pain intensity was reduced to about one quarter of its previous level by exercise programmes. The exercise tested was either aerobic exercise or yoga, performed for 45 – 60 minutes weekly.
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