Hypertension
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Classification and
external resources
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 Automated arm blood pressure meter showing arterial hypertension (shown a systolic blood pressure 158 mmHg, diastolic blood pressure 99 mmHg and heart rate of 80 beats per minute). |
Hypertension (HTN) or high blood
pressure, sometimes called arterial hypertension, is a chronic medical condition in which the blood pressure in the arteries
is elevated. This requires the heart to work harder than normal to circulate
blood through the blood vessels. Blood pressure involves two measurements,
systolic and diastolic, which depend on whether the heart muscle is contracting
(systole) or relaxed between beats (diastole). Normal blood pressure at rest is
within the range of 100-140mmHg systolic (top reading) and 60-90mmHg diastolic
(bottom reading). High blood pressure is said to be present if it is
persistently at or above 140/90 mmHg.
Hypertension is classified as
either primary (essential) hypertension
or secondary hypertension;
about 90–95% of cases are categorized as "primary hypertension" which
means high blood pressure with no obvious underlying medical cause. The
remaining 5–10% of cases (secondary hypertension) are caused by other
conditions that affect the kidneys, arteries, heart or endocrine system.
Hypertension is a major risk factor for stroke, myocardial infarction
(heart attacks), heart failure, aneurysms of the arteries (e.g. aortic aneurysm), peripheral arterial disease
and is a cause of chronic kidney disease.
Even moderate elevation of arterial blood pressure is associated with a
shortened life expectancy. Dietary
and lifestyle changes can improve blood pressure control and decrease the risk
of associated health complications, although drug treatment is often necessary
in people for whom lifestyle changes prove ineffective or insufficient.
Classification
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Adults
In people aged 18 years or older
hypertension is defined as a systolic and/or a diastolic blood pressure
measurement consistently higher than an accepted normal value (currently
139 mmHg systolic, 89 mmHg diastolic: see table — Classification
(JNC7)). Lower thresholds are used (135 mmHg systolic or 85 mmHg
diastolic) if measurements are derived from 24-hour ambulatory or home
monitoring. Recent international hypertension guidelines have also created categories
below the hypertensive range to indicate a continuum of risk with higher blood
pressures in the normal range. JNC7 (2003) uses the term prehypertension
for blood pressure in the range 120-139 mmHg systolic and/or
80-89 mmHg diastolic, while ESH-ESC Guidelines (2007) and BHS IV (2004)
use optimal, normal and high normal categories to subdivide pressures below 140 mmHg
systolic and 90 mmHg diastolic. Hypertension is also sub-classified: JNC7
distinguishes hypertension stage I, hypertension stage II, and isolated
systolic hypertension. Isolated systolic hypertension refers to elevated
systolic pressure with normal diastolic pressure and is common in the elderly.
The ESH-ESC Guidelines (2007) and BHS IV (2004), additionally define a third
stage (stage III hypertension) for people with systolic blood pressure
exceeding 179 mmHg or a diastolic pressure over 109 mmHg. Hypertension
is classified as "resistant" if medications do not reduce
blood pressure to normal levels.
Neonates and infants
Hypertension in neonates is rare, occurring in around 0.2 to 3% of neonates,
and blood pressure is not measured routinely in the healthy newborn.
Hypertension is more common in high risk newborns. A variety of factors, such
as gestational age,
postconceptional age and birth weight needs to be taken into
account when deciding if a blood pressure is normal in a neonate.
Children and adolescents
Hypertension occurs quite
commonly in children and adolescents (2-9% depending on age, sex and ethnicity)
and is associated with long term risks of ill-health. It is now recommended
that children over the age of 3 have their blood pressure checked whenever they
attend for routine medical care or checks, but high blood pressure must be
confirmed on repeated visits before characterizing a child as having
hypertension. Blood pressure rises with age in childhood and, in children,
hypertension is defined as an average systolic or diastolic blood pressure on
three or more occasions equal or higher than the 95th percentile appropriate
for the sex, age and height of the child. Prehypertension in children is
defined as average systolic or diastolic blood pressure that is greater than or
equal to the 90th percentile, but less than the 95th percentile. In
adolescents, it has been proposed that hypertension and pre-hypertension are
diagnosed and classified using the same criteria as in adults.
Signs and symptoms
Hypertension is rarely accompanied by any symptoms, and its identification is usually through screening, or when seeking healthcare for an unrelated problem. A proportion of people with high blood pressure reports headaches (particularly at the back of the head and in the morning), as well as lightheadedness, vertigo, tinnitus (buzzing or hissing in the ears), altered vision or fainting episodes.
On physical examination,
hypertension may be suspected on the basis of the presence of hypertensive retinopathy
detected by examination of the optic fundus found in the back of the eye using ophthalmoscopy. Classically, the severity of the hypertensive
retinopathy changes is graded from grade I–IV, although the milder types may be
difficult to distinguish from each other. Ophthalmoscopy findings may also
indicate how long a person has been hypertensive.
Secondary hypertension
Some additional signs and
symptoms may suggest secondary hypertension,
i.e. hypertension due to an identifiable cause such as kidney diseases or endocrine diseases. For
example, truncal obesity, glucose intolerance, moon facies, a "buffalo hump" and purple striae
suggest Cushing's syndrome. Thyroid disease and acromegaly can also cause hypertension and have characteristic
symptoms and signs. An abdominal bruit may be an indicator of renal artery stenosis (a
narrowing of the arteries supplying the kidneys), while decreased blood
pressure in the lower extremities and/or delayed or absent femoral arterial pulses may indicate aortic coarctation (a
narrowing of the aorta shortly after it leaves the heart). Labile
or paroxysmal hypertension accompanied by headache, palpitations, pallor, and
perspiration should prompt suspicions of pheochromocytoma.
Hypertensive crises
Severely elevated blood pressure
(equal to or greater than a systolic 180 or diastolic of 110 — sometime termed
malignant or accelerated hypertension) is referred to as a "hypertensive
crisis", as blood pressures above these levels are known to confer a high
risk of complications. People with blood pressures in this range may have no
symptoms, but are more likely to report headaches (22% of cases) and dizziness
than the general population. Other symptoms accompanying a hypertensive crisis
may include visual deterioration or breathlessness due to heart failure or a
general feeling of malaise due to renal failure. Most people
with a hypertensive crisis are known to have elevated blood pressure, but
additional triggers may have led to a sudden rise.
A "hypertensive
emergency", previously "malignant hypertension", is diagnosed
when there is evidence of direct damage to one or more organs as a result of
the severely elevated blood pressure. This may include hypertensive encephalopathy,
caused by brain swelling and dysfunction, and characterized by headaches and an
altered level of consciousness
(confusion or drowsiness). Retinal papilloedema and/or fundal hemorrhages and exudates are another sign of target organ
damage. Chest pain may indicate heart muscle damage (which
may progress to myocardial infarction) or
sometimes aortic dissection, the
tearing of the inner wall of the aorta. Breathlessness, cough, and the expectoration of blood-stained
sputum are characteristic signs of pulmonary edema, the swelling of lung tissue due to left ventricular failure
an inability of the left ventricle of the
heart to adequately pump blood from the lungs into the arterial system. Rapid deterioration of kidney
function (acute kidney injury) and microangiopathic hemolytic
anemia (destruction of blood cells) may also occur. In these
situations, rapid reduction of the blood pressure is mandated to stop ongoing
organ damage. In contrast there is no evidence that blood pressure needs to be
lowered rapidly in hypertensive urgencies where there is no evidence of target
organ damage and over aggressive reduction of blood pressure is not without
risks. Use of oral medications to lower the BP gradually over 24 to 48 h is
advocated in hypertensive urgencies.
In pregnancy
Hypertension occurs in
approximately 8-10% of pregnancies. Most women with hypertension in pregnancy
have pre-existing primary hypertension, but high blood pressure in pregnancy
may be the first sign of pre-eclampsia, a serious condition of the
second half of pregnancy and puerperium. Pre-eclampsia is characterised
by increased blood pressure and the presence of protein in the urine. It occurs in about 5% of pregnancies and
is responsible for approximately 16% of all maternal deaths globally. Pre-eclampsia also doubles the risk
of perinatal mortality.
Usually there are no symptoms in pre-eclampsia and it is detected by routine
screening. When symptoms of pre-eclampsia occur the most common are headache,
visual disturbance (often "flashing lights"), vomiting, epigastric pain, and edema.
Pre-eclampsia can occasionally progress to a life-threatening condition called eclampsia, which is a hypertensive emergency and
has several serious complications including vision loss, cerebral edema, seizures or convulsions, renal failure, pulmonary edema, and disseminated
intravascular coagulation (a blood clotting disorder).
In infants and children
Failure to thrive, seizures, irritability, lack of energy, and difficulty
breathing can be associated with hypertension in neonates and young
infants. In older infants and children, hypertension can cause headache,
unexplained irritability, fatigue, failure to thrive, blurred vision, nosebleeds, and facial paralysis.
Complications
Diagram illustrating the main
complications of persistent high blood pressure.
Hypertension is the most
important preventable risk
factor for premature death worldwide. It increases the risk of ischemic heart disease strokes, peripheral vascular disease,
and other cardiovascular diseases, including heart failure, aortic aneurysms, diffuse atherosclerosis, and pulmonary embolism.
Hypertension is also a risk factor for cognitive impairment and dementia, and chronic kidney disease.
Other complications include:
Cause
Primary hypertension
Primary (essential) hypertension
is the most common form of hypertension, accounting for 90–95% of all cases of
hypertension. In almost all contemporary societies, blood pressure rises with aging
and the risk of becoming hypertensive in later life is considerable.
Hypertension results from a complex interaction of genes and environmental
factors. Numerous common genes with small effects on blood pressure have been
identified as well as some rare genes with large effects on blood pressure but
the genetic basis of hypertension is still poorly understood. Several
environmental factors influence blood pressure. Lifestyle factors that lower
blood pressure, include reduced dietary salt
intake, increased consumption of fruits and low fat products (Dietary
Approaches to Stop Hypertension (DASH diet)), exercise, weight loss and reduced alcohol intake. The
possible role of other factors such as stress, caffeine consumption, and
vitamin D deficiency are less clear cut. Insulin resistance, which
is common in obesity and is a component of syndrome X (or the metabolic syndrome), is
also thought to contribute to hypertension. Recent studies have also implicated
events in early life (for example low birth weight, maternal smoking and lack of breast feeding) as risk factors for adult essential
hypertension, although the mechanisms linking these exposures to adult
hypertension remain obscure.
Secondary hypertension
Secondary hypertension results
from an identifiable cause. Renal disease is the most common secondary cause of
hypertension. Hypertension can also be caused by endocrine conditions, such as Cushing's syndrome, hyperthyroidism, hypothyroidism, acromegaly, Conn's syndrome or hyperaldosteronism, hyperparathyroidism and pheochromocytoma. Other causes of secondary hypertension
include obesity, sleep apnea, pregnancy, coarctation of the aorta,
excessive liquorice consumption and certain prescription medicines,
herbal remedies and illegal drugs.
Pathophysiology
A diagram explaining factors
affecting arterial pressure
In most people with established essential (primary)
hypertension, increased resistance to blood flow (total peripheral resistance)
accounting for the high pressure while cardiac output remains normal. There is evidence that some
younger people with prehypertension or 'borderline
hypertension' have high cardiac output, an elevated heart rate and normal
peripheral resistance, termed hyperkinetic borderline hypertension. These
individuals develop the typical features of established essential hypertension
in later life as their cardiac output falls and peripheral resistance rises
with age. Whether this pattern is typical of all people who ultimately develop
hypertension is disputed. The increased peripheral resistance in established
hypertension is mainly attributable to structural narrowing of small arteries
and arterioles, although a reduction in the number or density of capillaries
may also contribute. Hypertension is also associated with decreased peripheral
venous compliance which may increase venous return, increase cardiac preload and, ultimately,
cause diastolic dysfunction.
Whether increased active vasoconstriction plays a
role in established essential hypertension is unclear.
Pulse pressure (the difference between systolic and diastolic
blood pressure) is frequently increased in older people with hypertension. This
can mean that systolic pressure is abnormally high, but diastolic pressure may
be normal or low — a condition termed isolated systolic hypertension.
The high pulse pressure in elderly people with hypertension or isolated
systolic hypertension is explained by increased arterial stiffness, which
typically accompanies aging and may be exacerbated by high blood pressure.
Many mechanisms have been
proposed to account for the rise in peripheral resistance in hypertension. Most
evidence implicates either:
- Disturbances in renal salt and water handling, particularly abnormalities in the intrarenal renin-angiotensin system
and/or
- Abnormalities of the sympathetic nervous system
These mechanisms are not mutually
exclusive and it is likely that both contribute to some extent in most cases of
essential hypertension. It has also been suggested that endothelial dysfunction
and vascular inflammation may also contribute to
increased peripheral resistance and vascular damage in hypertension.
Diagnosis
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Hypertension is diagnosed on the
basis of a persistently high blood pressure. Traditionally, this requires three
separate sphygmomanometer measurements at one monthly intervals. Initial assessment of the
hypertensive people should include a complete history and physical examination. With
the availability of 24-hour ambulatory blood pressure
monitors and home blood pressure machines, the
importance of not wrongly diagnosing those who have white coat hypertension has
led to a change in protocols. In the United Kingdom, current best practice is
to follow up a single raised clinic reading with ambulatory measurement, or
less ideally with home blood pressure monitoring over the course of 7 days.
Once the diagnosis of
hypertension has been made, physicians will attempt to identify the underlying
cause based on risk factors and other symptoms, if present. Secondary hypertension is
more common in preadolescent children, with most cases caused by renal disease. Primary or essential hypertension is
more common in adolescents and has multiple risk factors, including obesity and
a family history of hypertension. Laboratory tests can also be performed to
identify possible causes of secondary hypertension, and to determine whether
hypertension has caused damage to the heart, eyes, and kidneys.
Additional tests for diabetes and high cholesterol levels are usually performed because these
conditions are additional risk factors for the development of heart disease and require treatment.
Serum creatinine is measured to assess for the presence of kidney
disease, which can be either the cause or the result of hypertension. Serum
creatinine alone may overestimate glomerular filtration rate
and recent guidelines advocate the use of predictive equations such as the Modification of
Diet in Renal Disease (MDRD) formula to estimate glomerular filtration
rate (eGFR). eGFR can also provides a baseline measurement of kidney function
that can be used to monitor for side effects of certain antihypertensive drugs
on kidney function. Additionally, testing of urine samples for protein is used as a secondary indicator of kidney disease. Electrocardiogram (EKG/ECG) testing is done to check for
evidence that the heart is under strain from high blood pressure. It may also
show whether there is thickening of the heart muscle (left ventricular hypertrophy)
or whether the heart has experienced a prior minor disturbance such as a silent
heart attack. A chest X-ray or an echocardiogram may also be performed to look for signs of
heart enlargement or damage to the heart.
Prevention
Much of the disease burden of high blood pressure is experienced by people who are not labelled as hypertensive. Consequently, population strategies are required to reduce the consequences of high blood pressure and reduce the need for antihypertensive drug therapy. Lifestyle changes are recommended to lower blood pressure, before starting drug therapy. The 2004 British Hypertension Society guidelines proposed the following lifestyle changes consistent with those outlined by the US National High BP Education Program in 2002 for the primary prevention of hypertension:
- maintain normal body weight for adults (e.g. body mass index 20–25 kg/m2)
- reduce dietary sodium intake to <100 mmol/ day (<6 g of sodium chloride or <2.4 g of sodium per day)
- engage in regular aerobic physical activity such as brisk walking (≥30 min per day, most days of the week)
- limit alcohol consumption to no more than 3 units/day in men and no more than 2 units/day in women
- consume a diet rich in fruit and vegetables (e.g. at least five portions per day);
- consume a diet with reduced content of saturated and total fat.
Effective lifestyle modification
may lower blood pressure as much an individual antihypertensive drug.
Combinations of two or more lifestyle modifications can achieve even better
results.
Management
Lifestyle modifications
The first line of treatment for
hypertension is identical to the recommended preventative lifestyle changes and
includes: dietary changes physical exercise, and weight loss. These have all
been shown to significantly reduce blood pressure in people with hypertension.
If hypertension is high enough to justify immediate use of medications,
lifestyle changes are still recommended in conjunction with medication.
Different programs aimed to reduce psychological stress such as biofeedback, relaxation or meditation are advertised to reduce hypertension. However, in
general claims of efficacy are not supported by scientific studies, which have
been in general of low quality.
Dietary change such as a low sodium diet is beneficial. A long term (more than 4 weeks)
low sodium diet in Caucasians is effective in
reducing blood pressure, both in people with hypertension and in people with
normal blood pressure. Also, the DASH diet, a diet rich in nuts, whole grains, fish,
poultry, fruits and vegetables promoted by the National Heart,
Lung, and Blood Institute lowers blood pressure. A major feature of
the plan is limiting intake of sodium, although the diet is also rich in potassium, magnesium, calcium, as well as protein.
Medications
Several classes of medications,
collectively referred to as antihypertensive drugs,
are currently available for treating hypertension. Prescription should take
into account the person's cardiovascular risk (including risk of myocardial
infarction and stroke) as well as blood pressure readings, in order to gain a
more accurate picture of the person's cardiovascular profile. If drug treatment is initiated
the National Heart, Lung, and Blood Institute's Seventh Joint National
Committee on High Blood Pressure (JNC-7) recommends that the physician not only
monitor for response to treatment but should also assess for any adverse reactions
resulting from the medication. Reduction of the blood pressure by 5 mmHg can decrease the risk of stroke
by 34%, of ischaemic heart disease by
21%, and reduce the likelihood of dementia, heart failure, and mortality
from cardiovascular disease.
The aim of treatment should be to reduce blood pressure to <140/90 mmHg
for most individuals, and lower for those with diabetes or kidney disease (some
medical professionals recommend keeping levels below 120/80 mmHg). If the
blood pressure goal is not met, a change in treatment should be made as therapeutic inertia is a
clear impediment to blood pressure control.
Guidelines on the choice of
agents and how to best to step up treatment for various subgroups have changed
over time and differ between countries. The best first line agent is disputed.
The Cochrane collaboration, World Health Organization
and the United States guidelines supports low dose thiazide-based diuretic as first line treatment. The UK guidelines emphasise calcium channel blockers
(CCB) in preference for people over the age of 55 years or if of African or
Caribbean family origin, with angiotensin
converting enzyme inhibitors (ACE-I) used first line for younger
people. In Japan starting with any one of six classes of medications including:
CCB, ACEI/ARB, thiazide diuretics, beta-blockers, and alpha-blockers is deemed reasonable while in Canada all of
these but alpha-blockers are recommended as options.
Drug combinations
The majority of people require
more than one drug to control their hypertension. JNC7and ESH-ESC guidelines
advocate starting treatment with two drugs when blood pressure is >20 mmHg
above systolic or >10 mmHg above diastolic targets. Preferred combinations
are renin–angiotensin system inhibitors and calcium channel blockers, or
renin–angiotensin system inhibitors and diuretics. Acceptable combinations include
calcium channel blockers and diuretics, beta-blockers and diuretics,
dihydropyridine calcium channel blockers and beta-blockers, or dihydropyridine
calcium channel blockers with either verapamil or diltiazem. Unacceptable
combinations are non-dihydropyridine calcium blockers (such as verapamil or
diltiazem) and beta-blockers, dual renin–angiotensin system blockade (e.g.
angiotensin converting enzyme inhibitor + angiotensin receptor blocker),
renin–angiotensin system blockers and beta-blockers, beta-blockers and
anti-adrenergic drugs. Combinations of an ACE-inhibitor or angiotensin
II–receptor antagonist, a diuretic and an NSAID
(including selective COX-2 inhibitors and non-prescribed drugs such as
ibuprofen) should be avoided whenever possible due to a high documented risk of
acute renal failure. The combination is known colloquially as a "triple
whammy" in the Australian health industry. Tablets containing fixed
combinations of two classes of drugs are available and while convenient for the
people, may be best reserved for those who have been established on the
individual components.
In the elderly
Treating moderate to severe
hypertension decreases death rates and cardiovascular morbidity and mortality in people aged 60 and older. There are
limited studies of people over 80 years old but a recent review concluded that
antihypertensive treatment reduced cardiovascular deaths and disease, but did
not significantly reduce total death rates. The recommended BP goal is advised
as <140/90 mm Hg with thiazide diuretics being the first line medication in America,
and in the revised UK guidelines calcium-channel blockers
are advocated as first line with targets of clinic readings <150/90, or
<145/85 on ambulatory or home blood pressure monitoring.
Resistant hypertension
Resistant hypertension is defined
as hypertension that remains above goal blood pressure in spite of concurrent
use of three antihypertensive agents belonging to different antihypertensive
drug classes. People who require four or more drugs to control their blood
pressure are also considered to have resistant hypertension. Guidelines for
treating resistant hypertension have been published in the UK and US.
Epidemiology
As of 2000, nearly one billion people or ~26% of the adult population of the world had hypertension. It was common in both developed (333 million) and undeveloped (639 million) countries. However rates vary markedly in different regions with rates as low as 3.4% (men) and 6.8% (women) in rural India and as high as 68.9% (men) and 72.5% (women) in Poland.
In 1995 it was estimated that 43
million people in the United States had hypertension or were taking
antihypertensive medication, almost 24% of the adult United States population.
The prevalence of hypertension in the United States is increasing and reached
29% in 2004. It is more common in blacks and native Americans and less in
whites and Mexican Americans, rates
increase with age, and is greater in the southeastern United States.
Hypertension is more prevalent in men (though menopause tends to decrease this
difference) and in those of low socioeconomic status.
In children
The prevalence of high blood
pressure in the young is increasing. Most childhood hypertension, particularly
in preadolescents, is secondary to an underlying disorder. Aside from obesity,
kidney disease is the most common (60–70%) cause of hypertension in children.
Adolescents usually have primary or essential hypertension, which accounts for
85–95% of cases.
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