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Hypertension

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Clive Rosendorff, M.D., Ph.D.
Professor, Medicine
Acting Director, Hypertension Section
Mount Sinai School of Medicine

What is Hypertension?

Everybody knows that high blood pressure is bad, but most people have
only a hazy idea as to why, and what the term really means. In fact,
all of us have high blood pressure some of the time, and we wouldn't
be able to function if we didn't. High blood pressure is only of
concern when it persists for long periods of time, and its adverse
effects actually take many years to develop. It's very common:
according to official government figures it affects 50 million people
in the United States. The other name for it is hypertension, a word
that often causes confusion. People who have high blood pressure are
not particularly "hyper" or tense, in the usual sense of the word. The
term simply refers to the increased tension or pressure in the
arteries.

The arteries are the elastic tubes that carry blood from the heart to
the tissues. They are configured like a tree: the central trunk, or
aorta, leaves the heart and then branches repeatedly. The smallest
branches, which are visible only under a microscope, are called
arterioles. They have muscle cells in their walls so that they can
constrict and dilate, and hence direct the flow of blood to where it
is most needed. The arterioles branch into even finer vessels, called
capillaries, which form a delicate mesh that supplies the tissues with
oxygen and other nutrients. For the blood to be able to circulate
properly, a certain level of pressure is needed to force it through
the arterioles and capillaries.

It's important to realize that blood pressure is continually varying
in order to meet the ever-changing needs of our bodies. Blood pressure
is normally regulated very tightly by the brain. When we're asleep,
and our bodies are at rest, we consume less oxygen than when we're
awake and active, and so the brain lets the pressure fall to a lower
level. At the other extreme, when we're exercising, our muscles need a
greater supply of blood to keep them going, and the pressure goes up.

How is Hypertension Diagnosed?

You probably recognize the numbers 120/80 as a normal blood pressure.
But why two numbers? The explanation is quite simple. Your heart beats
about 70 times a minute, and with each beat blood is pumped into the
arteries. As this happens, the pressure inside the arteries goes up,
until the end of that heartbeat. The peak level of pressure is called
the systolic pressure. Then the heart relaxes, and begins filling with
blood for the next beat, and the pressure in the arteries starts to
fall and reaches a minimum level just before the next heartbeat, which
is the diastolic pressure. So the number 120 refers to the systolic
pressure, and 80 to the diastolic pressure. Each heartbeat produces a
slightly different pressure, but usually the two numbers go up and
down together.

The blood pressure is expressed as millimeters of mercury, usually
abbreviated as mm Hg (Hg is the shortened version of the Latin name
for mercury). The reasons for using mm Hg are both historical and
practical. The pressure gauge used by doctors to measure blood
pressure is called a sphygmomanometer, which has a column of mercury,
the height of which is recorded in millimeters, and is a measure of
the pressure inside the cuff.

Which Doctors Treat Hypertension?

Although it is so common, hypertension has not traditionally been
treated by specialists, but by a variety of physicians, including
family practitioners, internists, cardiologists, and nephrologists.
This works fine for many patients, but others benefit from more
specialized care. Some patients have rare (but curable) causes of
hypertension that often go undiagnosed for many years, and others just
can’t seem to find the right mix of medicines to keep their blood
pressure under control. A recent development has been the recognition
of Hypertension specialists whose primary focus is on diagnosing and
treating all forms of hypertension and its complications.

How Blood Pressure Is Measured

The traditional method of measuring blood pressure is with a
sphygmomanometer and a stethoscope. The way it works is as follows:
the cuff that is wrapped around your upper arm contains a rubber bag,
which can be pumped up with air by squeezing a rubber bulb. The bag is
also connected via a tube to the column of mercury, which measures the
air pressure in the bag. To take a reading of the blood pressure, the
cuff is pumped up to a pressure of about 200 mm Hg. This is nearly
always higher than the systolic pressure, so that it completely shuts
off the circulation of blood in the arm. Then the valve on the rubber
bulb is opened a little, and the air in the bag allowed to leak out,
and gradually lower the pressure in the cuff. While this is happening
the person taking the pressure listens with a stethoscope placed on
the elbow crease just below the cuff. When the cuff pressure is
greater than the systolic pressure, there's no flow of blood and
nothing to hear. But as the pressure is reduced, it gets to a point at
which the systolic pressure in the artery is higher than the cuff
pressure, so the artery starts to open, and blood to flow. Each spurt
of blood makes a whooshing sound, which can be heard with the
stethoscope. As the cuff pressure is reduced further the sounds get
louder and last longer, but as the cuff pressure approaches the
diastolic pressure they start to fade away. The point at which they
finally disappear is the diastolic pressure. It may seem puzzling why
the sounds come and go in this way, but when the flow of blood in the
artery is not interrupted by the occlusion produced by the cuff, it's
quite smooth, and makes no noise. What we hear when the cuff pressure
is between systolic and diastolic pressure is partly the sound of the
artery opening and closing, and partly the sound of turbulent flow.

In practice, there are other ways of measuring blood pressure that
provide more information than the traditional stethosocope method.
These are 24 hour ambulatory monitoring and home or self monitoring.

Why Is High Blood Pressure So Bad?

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. The reason that 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 least 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.

The second adverse consequence of high blood pressure is that it
accelerates the deposition of cholesterol plaque (atheroma) in the
arteries. This problem, too, takes many years to develop, and it is
very difficult to detect until it causes a major blockage. It affects
mainly the larger arteries, but 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 damage 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 can also make the blood pressure go even
higher); and the legs, where it causes a condition known as
intermittent claudication, which means pain during walking.

Third, high blood pressure puts a strain on the heart: Because it has
to work harder than normal the muscle enlarges, just as any other
muscle does when it 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
that supply the heart.

Are There Different Types of High Blood Pressure?

Yes. High blood pressure can be classified in two ways, one according
to how severe it is (mainly a question of how high the blood pressure
is) and the other according to what's causing it. About 95 percent of
people with high blood pressure have what is known as essential
hypertension, which is really a fancy way of saying that it just
happens, and we don't know why. The other 5 percent of cases have
secondary hypertension, where there is an identifiable and usually
correctable cause. The commonest of these is renovascular hypertension,
where there is narrowing of the artery to one or both kidneys. Other
less common causes of secondary hypertension are small tumors of the
adrenal glands that secrete blood pressure-raising chemicals
(hormones) into the bloodstream.

The term essential hypertension is not a very specific one. It is
thought that hypertension is the end result of a number of different
factors that make the blood pressure go up, and it is probable that
different mechanisms are important in different individuals. This may
explain why a particular type of treatment may work very well in one
person, but not at all in another.

Classification of hypertension by its severity is somewhat arbitrary
because there's no precise level of pressure above which it suddenly
becomes dangerous. For no particularly good reason, blood pressure has
traditionally been classified according to the height of the diastolic
pressure, although the systolic pressure is probably more important in
determining the level of risk. Someone whose diastolic pressure runs
between 90 and 95 mm Hg may be regarded as having borderline
hypertension, and when it's between 95 and 110 mm Hg it's moderate,
and at any higher levels it's severe. The most dangerous type is
called malignant hypertension, which is regarded as an acute emergency
requiring immediate treatment in a hospital. Whatever the underlying
cause, when the blood pressure reaches a certain level for a
sufficient length of time it sets off a vicious cycle of damage to the
heart, brain, and kidneys, resulting in further elevation of the
pressure. Not surprisingly, if untreated, malignant hypertension can
be rapidly fatal. Because more people are treated nowadays than
before, malignant hypertension is not common, and is mainly seen in
people who have not had access to medical care.

White coat (or office) hypertension is a term used to describe people
whose blood pressure is only high in a doctor's office.

Systolic hypertension is mainly seen in people over the age of 65 and
is characterized by a high systolic, but normal diastolic, pressure (a
reading of 170/80 mm Hg would be typical). It's caused by an
age-related loss of elasticity of the major arteries.

Labile hypertension is a commonly used but inappropriate term for
describing people whose pressure is unusually labile or variable. In
fact, just about everyone has labile blood pressure.

What causes Hypertension?

As described in the previous section, in most people with hypertension
there is no single curable cause such as a blocked renal artery, and
they are labeled as having essential hypertension. This means
hypertension that just happens, although there are a number of factors
that we know can contribute to it. The important point is that there
is no single factor that causes it, but a combination of several
different ones that may play different roles in different people.
There is a genetic or hereditary component: if your parents both had
hypertension there is an increased chance that you will develop it as
well. That component may account for about half of the factors that
lead to hypertension. However, it is probable that no single gene is
responsible and that more likely a cluster of genes that have
different individual effects when acting in concert result in
hypertension. There is also a big environmental component.
Hypertension is, or was, relatively uncommon in the traditional tribal
societies that lived in Southern Africa and elsewhere, but when the
villagers moved to the big cities and adopted a more westernized
lifestyle their blood pressure tended to increase. Whether this
phenomenon is because of stress or changes in diet has not been
resolved, but almost certainly both are involved. The typical American
lifestyle, with a diet that is high in salt and fat and low in fruits
and vegetables, combined with physical inactivity, certainly
contributes to high blood pressure. Even more important is obesity,
which may account for at least 50 percent of cases of hypertension.
The good news here is that a lot can be done to treat and prevent
hypertension by attending to diet and exercise.

What Are The Symptoms of Hypertension?

Usually, there are no specific symptoms that 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.

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 strain 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.

Can Hypertension Be Treated?

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. This study included
143 men with severe hypertension who had diastolic pressures between
115 and 129 mm Hg. Half of the men were treated with medication to
lower the blood pressure, while the others received inert placebo
pills. After only one and a half years, the results were quite clear:
in the untreated group, four men had died, and 23 had developed
complications such as strokes and heart attacks, while in the treated
group none had died, and only two developed complications. This type
of study is called a randomized clinical trial. Since this study was
published, numerous larger trials have been conducted involving tens
of thousands of patients, which have demonstrated conclusively that
drug treatment can cut the number of strokes by about half, and of
heart attacks by a somewhat smaller amount. These studies have
included younger people in whom both systolic and diastolic are
elevated and older people in whom only systolic pressure is high. Both
groups have shown similar benefit.

Non-Drug Treatment of Hypertension

People often think that the treatment of hypertension invariably
involves having to take medications for the rest of one’s life, but
this is not necessarily the case. There is much that can be done with
diet and exercise to lower the blood pressure. The traditional
recommendation about diet was to restrict the intake of salt (to about
6 grams a day, or just over half the average American’s typical
intake), and while this method is still effective, it does not work in
everyone. Some people (about one third of the hypertensive population)
are "salt sensitive," which means that their blood pressure will
respond to changing salt intake, while the rest are "salt resistant,"
in whom cutting out salt will have little effect on the blood
pressure. Unfortunately, there is no simple test to decide who is salt
sensitive and who is not.

A major advance in the treatment of hypertension has been the DASH
(Dietary Approaches to Stop Hypertension) diet, which has been shown
to lower blood pressure as much as medications and is described at
http://www.mssm.edu/cvi/hypertensiondash.shtml.

For people who are overweight, the most effective method for lowering
blood pressure is to lose weight.

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