Hypertension is a term which is given to blood pressure readings that are considered to be too high. Whilst at first this may seem to be quite a simple concept it is in fact quite complicated.
The reason for this is that blood pressure when measured across the population in general varies considerably, with some people having a normal resting systolic blood pressure of around 90mm/Hg and others frequently showing blood pressures in excess of 200mm/Hg. Whilst some of the people at these extreme edges of the normal range can be shown to have underlying illnesses or problems, many cannot and therefore it is clear that within a normal population of people one can expect to find a significant number of people with a high blood pressure without any apparent cause and with no obvious illnesses or symptoms.
If this is so obviously the case you might wonder why it is that doctors are so keen to treat people with higher blood pressure. The main reason for this is because very many studies have shown that the people who have the highest blood pressure also have the highest risk of developing cardiovascular disease and in particular stroke and heart attack. Furthermore lowering their blood pressure significantly lowers their risk of subsequently developing these illnesses.
Blood pressure is usually measured indirectly by placing an inflatable cuff around the arm which is then connected to a pressure measuring device. The cuff is then inflated until the pressure within the cuff is higher than the pressure in the artery below it, therefore stopping the flow of blood down the arm. The pressure which is needed to stop the flow of blood down the arm is called the systolic blood pressure and this is the maximum pressure within the arterial system of the body as the heart generates the maximum amount of thrust to pump the blood out of the left ventricle and into the large blood vessel called the aorta and from there around the body.
We will also measure what is called the diastolic blood pressure and this is done by holding a stethoscope over the artery in the arm and gradually letting the inflatable cuff down and listening to the sounds of the blood going through the artery. The pressure when the sounds cease is measured as the diastolic blood pressure and is equivalent to the resting blood pressure within the arterial system of the body when the heart is between beats.
The blood pressure is normally therefore expressed as the systolic blood pressure over the diastolic blood pressure and is traditionally measured in figures of mmHg which means millimetres of mercury. This is because the original sphygmomanometers (blood pressure measuring machines) had a column of mercury within the tube (rather like an old fashioned thermometer or barometer) and the height to which the column of mercury in millimetres was supported by the pressure in the cuff was used as the measurement of pressure for the blood in the artery. Nowadays mercury has been removed from scientific instruments because of the potential for accidental poisoning from spillages and leakages but the modern machines are still calibrated to give the equivalent readings in millimetres of mercury.
There are many things which may make the measurement of a persons blood pressure less accurate and it is important that a well calibrated machine is used. It is also important that the right sized cuff is used around the arm. Whilst the standard sized cuff is correct for most people, if you have a large circumference around the upper arm then a larger cuff is needed and using too small a cuff will give a higher reading than that which is actually the true reading of the blood pressure. Similarly if you have a very small arm then a smaller cuff may need to be used as otherwise the reading obtained may be inaccurately low.
The way in which the blood pressure is taken is also of some importance and it is worth noting that virtually all the studies which have been conducted linking levels of blood pressure to subsequent disease have been conducted in an environment where the blood pressure has been taken from the subjects after they have been sat quietly for at least 10 minutes with the arm well supported and usually the lowest of three consecutive readings is taken. Clearly in the busy practice in the average hospital or GP setting this is rarely practicable but if doubt remains as to whether someones blood pressure is truly raised or not, it is worth taking extra time and care around taking the original measurements of the blood pressure before necessarily embarking on lifelong treatment.
It is also quite clear that some patients have what has become popularly known as white coat hypertension. Essentially this occurs when a person having their blood pressure measured in the hospital or GP surgery has a significantly higher blood pressure than when it is measured outside of the clinical environment - perhaps in their home. Some of these patients are aware of the fact that they are anxious within the hospital environment or perhaps just anxious as to the result of the blood pressure reading but many others who display this kind of result are not aware of any feelings of stress or anxiety. It can be useful in these circumstances, if there is any doubt as to whether the readings obtained in the GP surgery or the hospital outpatient clinic are accurate reflections of the hour to hour and day to day blood pressure of the person, for them to be fitted with an ambulatory blood pressure monitor which they can wear for 24 hours whilst they go about their normal daily business to see what their blood pressure readings are like throughout the period of time outside of the clinical environment. Further information on ambulatory blood pressure can be found by following the link. Ambulatory Blood Pressure Measurement
Another way of attempting to decide whether or not somebody has white coat hypertension is the use of home monitoring of the blood pressure by the patients themselves. There are many cheap and excellent machines now available that can be bought in the local pharmacy or over the internet and most of these are both reliable and accurate. My personal preference is for one that fits around the arm rather than the wrist and these can be very useful to monitor treatment responses as well as excluding white coat hypertension.
High blood pressure is extremely common within the population generally and by middle age probably a third of the population might benefit by having their blood pressure lowered by treatment. What then are the causes of high blood pressure?
95% of all patients with significantly raised blood pressure have no identifiable cause whatsoever and in these circumstances the blood pressure is called essential hypertension. Of the remaining 5% in whom an underlying cause can be found, in 4.5% the problem lies with the kidneys and in the remaining 0.5% there are a variety of problems, some hormonal and some metabolic and very occasionally in children or young adults there is an anatomical problem with a narrowing of the big blood vessel (aorta) called a coarctation.
Although essential hypertension may have no obvious underlying pathological cause, certain factors are significantly associated with an increased risk of hypertension and amongst these being significantly overweight, having a high salt intake in the diet, having a high alcohol intake and getting older are all easily identifiable risk factors. Clearly whilst the first three may be amenable to being positively influenced by a change in diet, activity and behaviour, the latter is not. The reason that aging increases the blood pressure is that the arteries in the body stiffen as we get older and therefore are less compliant and do not absorb the shock wave of pressure that is delivered into the arterial system with each heartbeat as well as they did when we were younger. This has the effect of gradually increasing our systolic blood pressure as we get older. This has been recognised for a long time and indeed many people may well say that your normal blood pressure would be 100 plus your age. Unfortunately however, whilst having a systolic blood pressure of around 180 may be normal when you are 80 years of age it also confers upon you the normal risk of having strokes and heart attacks which become very much more prevalent as we get older. Lowering blood pressure greatly reduces the risks of cardiovascular events and in particular the risk of stroke and it has been shown that at least 75% of the risk of having a stroke can be removed by bringing people's blood pressures down to the recommended levels. Other positive benefits of treating blood pressure are a reduction in heart disease and renal disease as we get older and a reduction in dementia.
Since the risk of vascular disease increases right the way up the scale from a systolic blood pressure of 95mmHg, it could be argued that lowering your blood pressure right the way down to this level would possibly be of benefit to everyone. Clearly however, given that 95% of the population have blood pressures higher than this this would be completely impracticable. Furthermore the increased risk of developing stokes and heart attacks is not uniform for each rise in blood pressure and the risk starts to increase significantly as the systolic blood pressure gets above 140mmHg and then becomes evermore steep in terms of increased risk for increased blood pressure as the blood pressure rises above 160mmHg. For this reason in normal people without any pre-existing vascular diseases or diabetes it is usually recommended that if the systolic blood pressure is above 140mmHg that they have repeated measurements over a period of time and where possible lifestyle interventions are tried in terms of losing weight, increasing levels of exercise, decreasing any excessive alcohol intake and reducing dietary salt intake but if the blood pressure remains elevated and particularly above 160mmHg then medications are introduced to try and control the blood pressure such that the systolic blood pressure is lowered to below 140mmHg.
In groups of patients who are already at risk and in particular those who have had a stroke, a heart attack, are diabetic or have renal disease, it is desirable to achieve lower levels of blood pressure to protect them to a greater degree and in these circumstances a lower target systolic blood pressure of around 130mmHg and diastolic blood pressure of 80mmHg would be recommended.
Most patients with hypertension have a raised systolic blood pressure and in a significant proportion of these the diastolic blood pressure will be raised as well. Ideally the diastolic blood pressure should be below 85mmHg and where there is combined systolic and diastolic hypertension the usual targets for treated patients would be to get the blood pressure to 140/85 mmHg or lower.
Occasionally patients have isolated diastolic hypertension and this merits treatment in its own right and again one would try to get the diastolic blood pressure down to 85mmHg or less.
Whilst there are no regulations regarding driving under the terms of a Group 1 license (cars and motorcycles), professional drivers holding a Group 2 license (HGV and PSV) should not drive if their systolic blood pressure is consistently above 180mmHg and/or their diastolic blood pressuire above 100mmHg. DVLA