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Information for Patients: Frequently Asked Questions Q. Why does my blood pressure vary so much when I monitor it? A. Everyone who starts to use a home monitor is surprised by the amount that the readings vary from each other. Even if you take three readings in a row (as we recommend) they may vary by as much as 20 points. Typically, the first of the three will be higher than the other two. Blood pressure goes up and down as we breathe in and out, so no two readings are ever the same. Q. What is the Normal Blood Pressure? The traditional numbers for a “normal” blood pressure are 120/80, but there are some other numbers you should know. 140/90 or less is the normal goal for treatment. For self-monitored (home) blood pressure, the average of all the readings should be 135/85 or less. The risks arising from high blood pressure start to increase even in the “normal” range, and when the World Health Organization issued its latest report on Health related issues it stated that a systolic pressure of 115 should be considered the “ideal” pressure, because at any number higher than this the risk starts to increase. However, it's not until the blood pressure reaches 140/90 that blood pressure lowering drugs are recommended by the leading guidelines (the JNC 7 in the US , and the world Health Organization/International Society of Hypertension guidelines in the rest of the world). The reason for taking 140 rather than 115 is that the absolute level of risk is still relatively low at 140 for most people, and getting the blood pressure down to 115 with drugs has not been achieved, so we can't say with certainty that lowering the blood pressure to this level will lower the risk. The JNC 7 report has designated a systolic blood pressure between 120 and 139 as “prehypertension”, which has confused some people, because they think that this implies that the treatment goal is 120 or less. There are some conditions where it appears that lowering the blood pressure to less than 140/90 may be particularly beneficial. If you have diabetes or kidney disease as well as high blood pressure the target blood pressure is 130/80 or less. Q. Why Is High Blood Pressure So Bad? A. Everyone has high blood pressure some of the time, and it only causes a problem when it stays high for long periods. Even then, there are many people who live normal lives with high blood pressure, and never know it. Unfortunately, not all are so lucky, and the reason why doctors are concerned about high blood pressure is that it increases the risk of a number of serious events, chiefly strokes and heart attacks. Even if these do occur, however, it may be only after ten or twenty years of the pressure being high. The damage caused by high blood pressure is of three general sorts. The first is the one everyone thinks of - bursting a blood vessel. While this is dramatic and disastrous when it happens, it's actually the lesser of the three problems. It occurs most frequently in the blood vessels of the brain, where the smaller arteries may develop a weak spot, called an aneurysm. This is an area where the wall is thinner than normal and a bulge develops. When there is a sudden surge of pressure the aneurysm may burst, resulting in bleeding into the tissues of the brain, and hence a stroke. Aneurysms can also develop in the largest blood vessel in the body, the aorta. Here they gradually enlarge over a period of several years, and because they are so large (sometimes as big as a grapefruit) they can often be detected before they start to leak, and treated surgically. The second adverse consequence of high blood pressure is that it accelerates the deposition of cholesterol plaque (atheroma) in the arteries. This too takes many years to develop, and is very difficult to detect until it causes a major blockage. It affects mainly the larger arteries, but its deposition is not uniform. It accumulates most where an artery divides into two smaller branches. The blood flow is normally smooth in the arteries, but where they divide it becomes turbulent, and this turbulence is thought to damage the delicate lining of the arteries. Wherever this occurs, cholesterol deposits are more likely to accumulate. The most important sites to be affected are the heart, where atheroma causes angina and heart attacks, the brain, where it causes strokes; the kidneys, where it causes renal failure; and the legs, where it causes a condition known as intermittent claudication, which means pain during walking. Thirdly, high blood pressure puts a strain on the heart: Because it has to work harder than normal its muscle enlarges, just as any other muscle does which is used excessively. In people with high blood pressure the volume of the heart doesn't change very much, but the thickness of the muscle increases. Thickening of the heart muscle is bad because the muscle outgrows its blood supply, rendering it more susceptible to the effects of atheroma narrowing the coronary arteries which supply the heart. Q. Is High Blood Pressure A Disease? A.Not really. The word "disease" generally implies sickness, and an inability to function properly. The vast majority of people with high blood pressure are not sick in this sense: they have no symptoms, they don't look sick, and they can do the same things as anybody else. It's only when blood pressure gets to very high levels (technically referred to as malignant hypertension) that it makes people feel sick. For those less severely affected, high blood pressure is important merely because it imposes a little extra wear and tear on the circulation. It's more appropriate to regard it as a risk factor. Q. Does High Blood Pressure Affect My Ability To Work? A. Since high blood pressure causes no symptoms or disability, the logical answer to this question would be no. Unfortunately, many doctors do not follow this logic, and may recommend that people with high blood pressure should not be hired for a job, on the grounds that they are at increased risk of having a heart attack, or perhaps because they think that the stress of the job will raise the blood pressure even more. In a survey of physicians who were members of the American Occupational Medicine Association, all of whom did pre-employment medical examinations for corporations, Dr Michael Murphy found that two thirds of the physicians would exclude people from working for the company because of hypertension. When asked what level of diastolic blood pressure would be needed for the applicant to be rejected, the answers given by the physicians ranged from 90 to 130 mm Hg. These findings are worrying because they suggest that there is a potential bias in the attitude of many physicians to hypertensive patients, and the wide range of blood pressures used as the cutoff point for employment indicates that these decisions are based on the whims of the individual doctors, rather than on any scientific basis. Q. How Do I Know When My Blood Pressure Is High? A. For the most part you can't tell if you have high blood pressure, and most hypertensive people have no symptoms. So the only way to find out if it's high is to have it measured. This statement may come as a surprise, because many people are convinced that they can tell when their pressure is high. It's certainly true that when you get angry or anxious you may feel yourself tensing up, and your heart pounding. You may even go red in the face, something that's often erroneously associated with high blood pressure. High blood pressure is of concern only when it's still high when you are not angry or tense. Q. What Are The Symptoms of High Blood Pressure? A. Usually, there are no specific symptoms which indicate that someone has high blood pressure. But some population surveys have shown that a wide variety of common symptoms, such as sleep disturbance, emotional upsets, and dry mouth, are slightly commoner in people with higher pressures. The differences are small, however. Going red in the face, or feeling flushed, is not indicative of high blood pressure. Q. Does High Blood Pressure Cause Headache? A. If you asked a hundred people what is the commonest symptom of high blood pressure, the chances are that the majority would say headache. In fact, not only do most people with high blood pressure not have headaches any more than the rest of us, but when they do, it's usually not from the blood pressure. Merely having a high level of blood pressure inside your head does not normally produce any symptoms; if you lift a heavy weight, your pressure may go up by 30 or 40 mm Hg, but you don't get a headache. What can cause headache is muscle tension. Any muscle that is tensed for long enough starts to hurt, and chronic tension in the scalp or neck muscles is a very common cause of headache. A study conducted many years ago shed some very interesting light on the relationship between headache and high blood pressure. Out of 104 people who had high blood pressure but were unaware of it, only three volunteered that they had headaches, although another 14 admitted it when asked. But of 96 people who had been told that they had high blood pressure, 71 said they had headaches. The simplest explanation for this finding is that being told that you have high blood pressure makes you start to worry, and that this in turn causes the headaches. There is a much smaller number of patients, mostly with very high pressures, in whom headaches are directly related to the height of the blood pressure. In such individuals treating the blood pressure will relieve the symptoms. Q. Which Is More Important- Systolic Or Diastolic Pressure? A. It is a common misconception that diastolic pressure is more important as a predictor of risk than systolic pressure. The reason for this partly historical. The first large scale trial of the effectiveness of blood pressure-lowering medication in preventing strokes and heart attacks, the Veterans' Administration Trial, selected patients for the trial solely on the basis of their diastolic pressures. Since that time, other similar trials have followed the same practice, so most of our knowledge about the benefits of treating high blood pressure is based on the level of diastolic pressure. But epidemiological studies of the risks associated with a particular level of blood pressure have shown that of the two measures, systolic pressure is more important. This is of special significance in older people, who often have a normal diastolic but raised systolic pressure. Such people are at increased risk, and this risk can be reduced by treatment. Q. Can High Blood Pressure Be Treated? A. The good news is that high blood pressure is eminently treatable. The objective of treatment is not simply to lower the blood pressure, but to prevent its consequences, such as strokes and heart attacks. The benefits of treatment were first convincingly demonstrated in a landmark Veterans Administration study conducted by Dr Edward Fries, the first results of which were published in 1967. Since then a large number of studies has shown that treating high blood pressure cuts the risk of stroke in half, and reduces heart attacks by aboyut one quarter. This applies to men and women, young and old. Q. What Is White Coat Hypertension? A.White coat hypertension is defined as a persistently high blood pressure (above 140/90) measured in the doctor's office, together with a normal daytime ambulatory pressure (below 135/85). The reason for including “persistently” in the definition is that many people have high blood pressure when they are first seen by a doctor, but if repeat measurements are made on subsequent visits, lower pressures are often recorded as the patient gets more comfortable with the situation. However, there is a group of people whose office blood pressure stays high no matter how many times they are seen. There is no evidence that people who have it are generally any more anxious or neurotic than other people, except perhaps when seeing their doctor. At the very least, diagnosing white coat hypertension involves a series of office visits together with some measurements made outside the office. It should be emphasized that one office visit is not enough, because in many people the blood pressure measured on subsequent visits will be lower than on the first occasion. If the blood pressure measured at home appears to be normal, the next step would be to wear an ambulatory monitor for 24 hours to check whether the pressure is still normal at work. Q. How Common Is White Coat Hypertension? A. White coat hypertension is quite common, occurring in about 20 per cent of hypertensive patients. Actually, the increase of blood pressure in a doctor's office occurs no less frequently in patients with sustained hypertension, but the implications are different, because these people are still hypertensive outside the doctor's office. White coat hypertension can occur in just about anyone. We find it to be a little commoner in women than in men, and it's surprisingly common in older people. In one study 40 per cent of hypertensives over the age of 65 had white coat hypertension. Q. How Do I Know If I Have White Coat Hypertension? A. Like any other form of hypertension, white coat hypertension can only be diagnosed by measuring the blood pressure. This means a series of measurements made in the office, which show that the average level is more than 140/90, and measurements made outside the office that are within the normal range (less than 135/85). Many patients have had measurements made in other settings, which may include visits to their gynecologist, for example, which are often much lower than the readings taken when they come for the evaluation of their hypertension. Self-monitored home readings can provide a good idea of this, but a normal blood pressure at home does not necessarily imply that it is normal all the time, because it may be high at work. For this reason we recommend that 24 hour monitoring should be used to establish the diagnosis. Q. Does White Coat Hypertension Affect the Risk of Heart Disease and Stroke? A. There are now several large studies which have examined the long-term outlook for patients with white coat hypertension. Almost all have found that patients with a diagnosis of white coat hypertension have a risk of strokes and heart attacks which is the same as or only slightly higher than people whose pressure is normal all the time, and lower than patients with “sustained” hypertension, whose pressure is still high when they are out of the office. It should also be emphasized that having a diagnosis of white coat hypertension does not confer immortality; patients with white coat hypertension can have strokes and heart attacks just like anybody else if they smoke and have a high cholesterol. Q. Should I Take Medication if I Have White Coat Hypertension? A. When people with white coat hypertension take blood presure lowering medication, what usually happens is that the mediation lowers the blood pressure measured in the doctor's office, but has little effect on the pressure outside the office, which by definition is normal to begin with. One large study, the “Syst-Eur” study, in which elderly patients with systolic hypertension were treated with either an active medication or a placebo for several years, looked at the effects of treating white coat hypertensives. In the patients with sustained hypertension, drug treatment significantly reduced the numbers of strokes, but in the white coat hypertensives there was no significant effect. The main reason for this was that the number of strokes was very small in the white coat hypertensives, whether or not they received the active drug. Thus the general consensus is that drug treatment of white coat hypertension has not been shown to have any beneficial effect, other than making the doctor happy at the time of an office visit. Q. What is Prehypertension? A. The latest national guidelines on hypertension, referred to as JNC 7, has identified a group of people with blood pressures between 120 and 139 systolic, and 80 to 89 diastolic, who have been designated as having “prehypertension”, on the grounds that some of them will go on to develop “true hypertension”, and an even smaller number will suffer a stroke or heart attack. The rationale was that such individuals should take “hygienic steps” to prevent their blood pressure going up any further. Blood pressure lowering medication is not recommended for these individuals. Q. How is High Blood Pressure Classified? A. The official set of guidelines for the classification of blood pressure in the United States is called “JNC 7” (for the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure). It has proposed the classification shown in the Table below. JNC 7 Classification of Blood Pressure
Q. Can Chronic Low Blood Pressure Cause Symptoms? A. Low blood pressure is generally thought to be a sign of good health, but there is some evidence that people whose blood pressure is low all the time (for example 90/50 mm Hg), may be more likely to complain of symptoms such as fatigue and giddiness. In Germany it is condiered to be a disease, but not in England , Canada , and the United States . It is unproven if raising the blood pressure improves the symptoms. Patients who are being treated with blood pressure lowering drugs may develop symptoms if the blood pressure goes too low at times. There is a rare condition called postural (or orthostatic) hypotension where the pressure may go too low when standing, but is high when lying down. People with this feel faint when standing. Q. What is Postural Hypotension? A. Postural or orthostatic hypotension is characterized by a fall of blood pressure on standing up, which if unchecked, may lead to a loss of consciousness. It is not common, and it mainly occurs in older people. It is caused by a deterioration of the blood pressure-regulating mechanisms. Normally when we stand up our blood pressure changes very little, because the arteries and veins in our legs constrict, and prevent the blood from pooling in the legs. This happens as a result of a reflex controlled by the brain and the sympathetic nervous system, and it's the sympathetic nerves that make the vessels contract. If the sympathetic nerves are not working properly, as is the case in postural hypotension, the blood tends to pool in the legs on standing, and fainting occurs because there is not enough blood left in the system to keep the brain properly perfused. When people with postural hypotension are horizontal for long periods of time, their blood pressure may go too high. The treatment of this condition is very difficult. The pooling of blood in the legs can be controlled to some extent by wearing tight fitting elastic stockings or pantyhose that goes up to the waist. These have to be custom made, and are quite expensive. They are uncomfortable because they are so tight, and they are a nuisance when going to the toilet. The standard medication is called florinef, which is an analogue of the hormone aldosterone, and makes the kidneys retain sodium, and hence to keep the blood pressure up. It helps a little, but is no miracle cure. A whole host of other medications have been tried, most of which constrict the blood vessels. None of them work very well, and they all tend to raise the blood pressure even further when the patient is lying flat. Q. What is a normal blood pressure in children? A. The normal range of blood pressure values in children has been established by surveys of large numbers of children of different ages. The results are usually expressed as percentiles. As in adults, some children have higher pressures than others, and the conventional method for deciding what is “high” for a particular group is to take the number that separates the 5 per cent of children with the highest readings from the other 95 percent. This number is called the 95 th percentile. As an example, the 95 th percentile of systolic pressure for an average-sized boy of 16 is 134 mmHg; that means that 95 percent of boys in this group will have a systolic pressure below this value, and 5 percent will be higher than this. The upper limits of normal blood pressure, defined according to the 95 th percentiles for both blood pressure and height, are shown for boys and girls aged from three to sixteen in the Table. Upper limit of normal blood pressure for boys and girls
Source: Task Force on high blood pressure in children and adolescents of the National High Blod Pressure Education program (1996).
Q. What is Pre-Eclampsia (Toxemia Of Pregnancy)? A. In some women the blood pressure may increase during the later stages of pregnancy (20 weeks or more), sometimes in association with swelling of the ankles. There is also a marked gain in weight, which is not due to overeating, but to retention of salt and water. This condition has various names, the commonest being pre-eclampsia. The reason for this name is that if untreated it may proceed to the more severe condition of eclampsia, characterised by very high blood pressure, headaches, and convulsions. It is also known as hypertension of pregnancy, or toxemia (which literally means blood poisoning). Having blood pressure measured regularly during pregnancy is hence very important for all women, as is testing the urine for protein (protein in the urine being another manifestation). The specific criteria used to diagnose pre-eclampsia are as follows: • An increase of systolic pressure of 30 mm Hg The cause of pre-eclampsia is not known, but it may be related to a failure of the uterus to develop normally during pregnancy. It is most likely to occur during first pregnancies, and does not necessarily recur with subsequent ones. Other risk factors for its occurrence include diabetes, previous high blood pressure, and a twin pregnancy. And as mysteriously as it develops during pregnancy, equally mysteriously it goes away after delivery. It is very important that proper treatment should be given, which can greatly reduce the risks of harm to both the mother and the baby. This consists of bed rest (often in hospital), medications, and if necessary, early delivery of the baby. Q. Is It Safe To Get Pregnant If I Have High Blood Pressure? A. Most women with mild or moderate hypertension can go through pregnancy with little problem, although it may require a change of medications, because there are some (such as angiotensin converting enzyme inhibitors) which are known to cause fetal damage. If you have kidney disease as well, you should seek out a physician who is experienced in the management of high blood pressure during pregnancy, because here the risks may be higher. Q. What is Systolic Hypertension Of The Elderly? A. Most people with high blood pressure have elevations of both systolic and diastolic pressure, but in many older people the systolic pressure may be high (above 160 mm Hg) while the diastolic is quite normal or low (below 90). This is referred to as isolated systolic hypertension, and affects about twenty per cent of people over the age of seventy. It used to be thought that the diastolic pressure is more important than the systolic, but this is wrong, and in fact the systolic pressure is more important in predicting your risk. The mechanism underlying systolic hypertension is different from the mechanism of the hypertension which occurs in younger people. As we grow older, our arteries grow stiffer, and lose their elasticity. When the heart pumps blood into the aorta (the large artery leaving the heart) of a young person, it expands to accommodate the extra volume of blood, which means that the pressure only goes up by a moderate amount. But an older and stiffer aorta cannot expand as much, so that there is a greater surge of pressure. This peak of pressure is called the systolic pressure. Q. Why Is Hypertension Commoner In Blacks Than Whites? A. Although blacks in the United States have consistently higher blood pressure than whites, this pattern is not the same in all other countries. In Africa , blood pressure tends to be relatively low in rural areas, and high in the cities. And a study of factory workers in Birmingham , England , found no difference in the pressures of black and white workers. A group that is at particular risk of developing high blood pressure (in England just as much as in the United States ) is black women, in whom obesity plays a major role. Since these populations share a common African origin and the same genetic background it is unlikely that heredity can account for all of the racial differences seen in the US . Nonetheless, heredity is an important cause of high blood pressure in blacks just as in whites, so if you're black and both your parents have high blood pressure, you have an increased chance of getting it yourself. There seems to be something about the modern western lifestyle that raises blood pressure in blacks just as much as in whites. When a group of Kenyan tribesmen was followed after they migrated from their rural village to the city of Nairobi their blood pressures increased markedly. One of the most important studies of the effects of the urban environment on blood pressure was conducted by Dr Ernest Harburg and his colleagues in Detroit , who found the highest blood pressures in black males living in "high stress" neighborhoods, which were characterised by low income, high unemployment, and high crime rates. Another factor that was found to be associated with higher pressures was suppressed anger. Thus some of the high blood pressure in blacks can be attributed to stress. Q. What is Secondary Hypertension? A. More than 95 per cent of patients with high blood pressure have essential hypertension, which means that no specific cause can be found. The other 5 per cent are potentially the lucky ones, because many of them have a form of hypertension for which there is the possibility of a permanent cure. It is sometimes referred to as secondary hypertension because the hypertension is secondary to a specific abnormality, usually in the kidneys or adrenal glands; when this abnormality is corrected, the hypertension disappears. The commonest causes of secondary hypertension are: • Renovascular hypertension (Renal artery stenosis)- blocked or narrowed artery to one or both kidneys. When your doctor first sees you for a history and physical examination, there are a number of potential clues which may raise the suspicion that you may have one of these rare forms of hypertension. Some of these are listed below. • Sudden Onset. Essential hypertension (the common sort) usually develops over several years, and many people give a history of marginally elevated readings before the pressure reached a level high enough to warrant treating. If, however, you've had annual physical exams, and after having had a pressure of 120/80 mm Hg for many years you are suddenly found to have 180/110, you could have secondary hypertension. Q. What is Renovascular Hypertension (Renal Artery Stenosis)? A. This is by far the commonest cause of secondary hypertension, and accounts for about 3 per cent of all cases of hypertension. It's caused by a narrowing in one or both renal (kidney) arteries. This reduces the blood pressure and flow in the kidney, which responds by secreting a hormone called renin, which enters the blood stream and leads to the formation of a second hormone (angiotensin), which causes the blood pressure to go up. This helps to restore the flow to the blocked kidney. There are two quite distinct causes of renovascular hypertension. The first, which occurs in young people (particularly children and young women), is called fibromuscular dysplasia. There are one or more fibrous constrictions of the artery. An important aspect of this condition is that it hardly ever affects any arteries other than the ones supplying the kidneys. Nobody knows what causes it, although smoking may be a contributory factor; it usually does not run in families. The second cause is atherosclerosis, sometimes referred to as hardening of the arteries, which is the same process that causes strokes and heart attacks. It occurs in the middle aged and elderly, and plaques may develop in the renal arteries just as they do in other major vessels. However, when an atheromatous obstruction is detected in a renal artery there is often a chicken-and-egg problem. While a plaque in the renal artery certainly can cause hypertension, hypertension itself can cause or accelerate the development of plaques, so that an atheromatous obstruction in the renal artery cannot always be assumed to be the cause of the hypertension. The important thing to establish is whether the kidney is being starved of blood: if it is, the narrowing is almost certainly contributing to the elevation of the blood pressure. Q. What are The Advantages Of Self-Monitoring of Blood Pressure? A. The readings taken by a doctor during an office visit are increasingly regarded as providing a very poor estimate of what someone's blood pressure level really is- the “true” blood pressure. The main advantage of self-monitoring is that it provides a better estimate of the true pressure. It does this in two ways: first, by increasing the number of readings that can be taken, and second, by avoiding the “white coat” effect, which makes the pressure go up by an unpredictable amount during the office visit. When patients first start taking their blood pressure, they are frequently astonished at how variable it is, and no less frequently worried about the few readings that seem excessively high. In the same way as the saying “one swallow doesn't make a summer”, one high reading does not make a diagnosis of hypertension. By looking at a large number of readings and taking the average of all of them, we can get a much better idea of what the true blood pressure is, and also whether there is any tendency for the blood pressure to change over time. This is particularly important when someone starts on treatment, or when a new medication is added. The second advantage of measuring your own blood pressure is that it avoids the potentially distorting influence of the doctor's office, or the white coat effect. This means that in the majority of patients the pressure recorded at home is substantially lower than in the doctor's office. It may still be high, but when it's definitely normal (for example below 135/85 mm Hg), it's highly questionable whether you should start taking medications. Q. How Often Should Home Blood Pressure Readings be Taken? A. When you have taken the trouble to get out your blood pressure monitor and set it up, it makes sense to take more than one reading. A lot of people find that, even when taking their own blood pressure, the first reading is higher than subsequent ones (the same as happens when a doctor is taking your pressure), so we routinely recommend taking a series of three readings on each occasion. It is also a good idea to take readings at least twice a day- when you first wake up, and when you go to bed (particularly if you are taking medications), because there is often a difference between morning and evening values. How many days a week you take your pressure depends to a large extent on where you are in your treatment program. If you are in the early stages, when it is still not clear whether you need to start taking medication, it is helpful to take readings relatively frequently (for example, three or four times a week for at least two weeks). When you are just starting on medication, or when the dose has been changed, frequent readings are again advisable. But if you are on a stable dose and your blood pressure is controlled, once or twice a month may be all that is needed. Q. What Is An Acceptable Level Of Home Blood Pressure? A. The traditional target for clinic blood pressure when you are on treatment is 140/90 or lower. The recommended level for home blood pressure is 135/85 or less. The reason for this difference is that clinic readings are in most people consistently higher than home readings. In older people (over the age of 65), slightly higher readings may be acceptable, although there are not yet any strict guidelines about this. If you have diabetes, the recommended clinic pressure is 130/80 or lower, which would translate into a home pressure of 125/75. Q. How well does Self-Monitored Blood Pressure Predict Your risk? A. Ultimately, the value of any blood pressure measurement is how well it predicts your risk of the adverse effects of high blood pressure such as strokes, heart attacks, and kidney disease. Since the readings that you will get at home will almost certainly be very different from your doctor's readings, the big question is which set of readings gives the best prediction. There are two large studies that have looked at this, and both came to the same conclusion. The first is a study from Japan , which recruited 1789 people living in a small town called Ohasama. The participants were asked to monitor their blood pressure at home for 4 weeks, and also had their blood pressures measured in the usual way by a nurse. The participants were followed for 10 years, during which time some of them had strokes and other problems related to high blood pressure. It was the home readings that predicted the risk of stroke and mortality best. The second study (called SHEAF) was conducted in France , and recruited 4939 elderly hypertensives who were currently on treatment, and found that morbid events observed over a 3 year follow-up period were predicted by the home blood pressure at baseline, but not by the clinic pressure. One particularly interesting aspect of this study was that patients who had normal clinic pressures but high home pressures were at increased risk, a phenomenon known as masked hypertension Q. What is 24 hour ambulatory monitoring?
A. This is a technique that is used to measure the blood presssure during daily life. To do this, you are hooked up with a monitor that is about the size of a Walkman radio, and is worn on a belt round the waist. It is connected by a thin tube to a blood pressure cuff on the upper arm, and is relatively unobtrusive. It can be pre-programmed to take readings at regular intervals, typically every 15 to 30 minutes, throughout the day and night, and is fully automatic, which means that it pumps up the cuff, deflates it, and stores the reading in its memory. All you have to do is to hold your arm still while the reading is being taken, and also to record what you were doing at the time. At the end of the 24 hours you have the monitor disconnected, and the readings are transferred into a personal computer. Up to 100 readings may be taken, so it's possible to get a much better idea of what your true blood pressure really is. Q. What are the Normal Values for 24 Hour Blood Pressures?
A. The upper limit of normal for ambu;atiry blood pressure is 135/85 mmHg for the daytime readings, and 130/80 for the average 24 hour level. There are two reasons for choosing the 135/85 level. Fist, studies realting ambulatory blood pressure to the risk of heart attacsk and strokes have shown that the risk increases markedly above this value, and second, it corresponds to the widely accepted treatment goal of 140/90 for office blood pressure. Q. How do Ambulatory Readings Compare with Office Readings ? A. Ambulatory blood pressure recording shows that blood pressure varies a lot in everyone. There is a marked diurnal rhythm of blood pressure, with the highest readings being recorded in the morning and working hours, lower at home in the evening, and the lowest occurring during sleep. This pattern is the same in people with normal and high blood pressure, although in hypertensives all the readings are higher than in normotensives. The relationships between the office pressures and the ambulatory pressures are not the same in normotensives and hypetensives. In normotensives the office pressures are on average not as high as the pressures measured at work, while in hypertensives they are often a lot higher than the blood pressure measured during the working hours. Why should this difference occur? One likely explanation for this is that hypertension is normally defined by how high the office blood pressure is, not by the “out-of-office” pressure, so that anyone who has a tendency to show a white coat effect (an increase of blood pressure in the presence of a doctor) will be labeled as being “hypertensive”. In about 25% of people with hypertension the blood pressure does not fall during the night (the normal ‘dipping' pattern), a phenomenon called non-dipping. This pattern is associated with an increased cardiovascular risk. Q. How can Ambulatory Monitoring be Used to Classify Blood Pressure Level? A. The blood pressure measured by ambulatory monitoring predicts risk better than the traditional office or clinic measured pressures, so this means that we can define hypertension independently by each of two methods- the traditional office measurements using a cutoff point of 140/90 mmHg, and the newer ambulatory method, using 135/85. Some people have high readings when measured by one method, but not by the other. As shown in the Figure, there are four groups of patients who are: 1. Normotensive by both methods (True Normotensives); 2. Hypertensive by both (True, or Sustained Hypertensives); 3. Hypertensive by clinic measurement and normotensive by ambulatory measurement (White Coat Hypertensives); and 4. Normotensive by clinic measurement and hypertensive by ambulatory measurement (Masked Hypertensives). Since the risks assocaited with high blood pressure are more closely related to the ambulatory than the clinic pressure, it is thought that the risk is reltively high in patients with Sustained and Masked Hypertension, and reltively low in those with White Coat Hypertenison. It is lowest in those with True Normotension.
Q. What is The Diurnal Rhythm of Blood Pressure? A.One of the unique features of 24 hour monitoring is its ability to record blood pressure throughout the day and night, and to give a profile of the diurnal rhythm of blood pressure. Actually, most of our bodily functions show some sort of rhythmicity- this is true not only of blood pressure, but also the heart rate, and many of the hormones which regulate the circulation and other bodily functions. Blood pressure is typically highest in the morning hours, at the time when we get up, and then gradually decreases dauring the day. It is thus lower in the venings than in the mornings in most people. When we fall asleep there is a further fall of blood pressure, that is most pronounced during the first few hours of sleep. The average range of blood pressure over 24 hours is 10-20 mmgHg, although individual readingsw show a much wider range. This rhythm is largely determined by the cycle of rest and activity. Shift workers show a different rhythm- higher during the night when they are working. Most patients with hypertension show the same diurnal rhythm of blood pressure, but there are some (called non-dippers) whose blood pressure stays high during the night. Q. What are Dippers and Non-Dippers? A. Normally the average blood pressure is 10 to 20% lower during the night than during the day, a pattern known as “dipping”. In some individuals, who are termed “non-dippers” the blood pressure shows little or no decrease during the night. This is seen in about 25% of patiens with hypertension. There is some evidence that non-dippers are at a greater risk than dippers for getting some of the adverse consequences of high blood pressure. Indeed, some studies suggest that the nighttime blood pressure (which is higher in non-dippers than dippers) may be the best predictor of risk. There are several known causes of non-dipping. These include interrrupted sleep, African –American race, obesity, kidney disease, and diabetes. Q. What is The DASH diet? A. One of the major advances in the non-drug treatment of hypertension in the last ten years has been the DASH diet. DASH stands for Dietary Approaches to Stop Hypertension; the basic idea behind the diet was that people who eat a diet rich in fruits and vegetables tend to have low blood pressure, and there is also evidence that taking supplements of potassium, calcium, and magnesium may help to lower the blood pressure. A study was designed to test the effects of the diet in two stages: one was the fruits and vegetables part, which restricted the intake of saturated fat, snacks, and sweets, and was also high in fiber. The second component was the addition of low fat dairy products in the form of yoghurt and low fat milk. The original study was conducted in people with mild hypertension, who were randomized to one of three groups: a typical American diet (the control group); the fruits and vegetables diet; and the combination DASH diet. For the whole group of subjects, the fruit and vegetable diet lowered the blood pressure by 3/1 mmHg, and the combination diet by 5.5/3 mmHg. This does not sound like a very dramatic change, but many of the subjects had only slightly elevated blood pressures to begin with. For the subjects who were definitely hypertensive at the start of the study (above 140/90 mmHg) the combination DASH diet reduced systolic pressure by 11.4 mmHg, and diastolic by 5.5, a change in the same ballpark as produced by drugs. The effects were bigger in African-Americans than in whites. Two points to note about the original DASH study are that the diet was not low in either salt (the sodium content was 3,000 milligrams a day for all three groups) or calories, which varied between 1600 and 3100 a day depending on the subject's size. A second and equally important study was the DASH-Sodium trial, where the effects of the combined DASH diet were tested in conjunction with different levels of salt intake. Combining the DASH diet with low salt intake further lowered the blood pressure. One of the other benefits of the DASH diet is that it lowers blood cholesterol levels. In the original DASH study it was found that total cholesterol fell by 14 mg/dl (0.35mmol/L), LDL cholesterol by 11 mg/dl (0.28 mmol/L), but triglycerides were unchanged. HDL cholesterol also fell, by 4 mg/dl (0.09mmol/L), which of course is not what is wanted, but has also been seen in other studies where people go on a low fat diet (the Ornish diet does the same thing). Nevertheless, on balance, the DASH diet should reduce the risk of heart disease. Q. Where Can I find out more about the DASH diet? A. There is a lot more information available about the DASH diet, both on the web (http://www.nhlbi.nih.gov/health/public/heart/hbp/dash/index.htm), and as a book, The DASH diet for hypertension, by Thomas J Moore and others, which is available in paperback. These provide detailed instructions for how to actually go about it, with meals plans that can be varied according to how many calories you need, and whether or not you want to restrict your sodium intake. The NIH site has a booklet that can be downloaded as a pdf file. Please contact tp2114@columbia.edu for further information.
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