Definition of Hypertension
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 is summarised by 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. 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.
Cause of Hypertension
Primary (essential) 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 genetic variants with small effects on blood pressure have been identified as well as some rare genetic variants 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. Stress appears to play a minor role with specific relaxation techniques not supported by the evidence. The possible role of other factors such as 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 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.
Signs and symptoms of Hypertension
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 report 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. These symptoms, however, might be related to associated anxiety rather than the high blood pressure itself.
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 give some indication as to how long a person has been hypertensive.
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 faces, 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.
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.
Hypertension occurs in approximately 8–10% of pregnancies. Two blood pressure measurements six hours an apart of greater than 140/90 mm Hg is considered diagnostic of hypertension in pregnancy. 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).
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.
Risk factors for Hypertension
- The people who have older age
- Race or Ethnicity
- The people who have unhealthy life habits
- Family history of hypertension
- Events in early life (for example low birth weight, maternal smoking and lack of breast feeding) as risk factors for adult essential hypertension
- Endocrine conditions, such as Cushing’s syndrome, hyperthyroidism, hypothyroidism, acromegaly, Conn’s syndrome or hyperaldosteronism, hyperparathyroidism and pheochromocytoma
- Coarctation of the aorta
- Excessive liquorice consumption
Diagnosis of Hypertension
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.
Pseudohypertension in the elderly or noncompressibility artery syndrome may also require consideration. This condition is believed to be due to calcification of the arteries resulting an abnormally high blood pressure readings with a blood pressure cuff while intra arterial measurements of blood pressure are normal.
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 may 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.
AdIn 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). 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.
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.
Hypertension occurs quite commonly in children over the age of 3 years and adolescents (2-9% depending on age, sex and ethnicity) and is associated with long term risks of ill-health. 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. High blood pressure must be confirmed on repeated visits however before characterizing a child as having hypertension.
Prehypertension in children has been 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.
Prevention of Hypertension:
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. 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);
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.
Treatment of Hypertension
The first line of treatment for hypertension is identical to the recommended preventive 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. Their potential effectiveness is similar to using a single medication. If hypertension is high enough to justify immediate use of medications, lifestyle changes are still recommended in conjunction with medication.
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 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. Different programs aimed to reduce psychological stress such a biofeedback, relaxation or meditation are advertised to reduce hypertension. However, overall efficacy is not greater than health education, with evidence being generally of low quality.
Several classes of medications, collectively referred to as antihypertensive drugs, are currently available for treating hypertension. Use 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. Evidence in those with mild hypertension (SBP less than 160 mmHg and /or DBP less than 100 mmHg) and no other health problems does not support a reduction in the risk of death or rate of health complications from medication treatment. Medications are not recommended for people with prehypertension or high normal blood pressure.
If drug treatment is initiated the 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 side effects 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. For most people, recommendations are to reduce blood pressure to less than or equal to somewhere between 140/90 mmHg to 160/100 mmHg. Attempting to achieve lower levels have not been shown to improve outcomes. In those with diabetes or kidney disease some recommend levels below 120/80 mmHg; however, these are not proven. 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 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 and Europe all of these but alpha-blockers are recommended as options.
The majority of people require more than one drug to control their hypertension. In those with a systolic blood pressure greater than 160 mmHg or a diastolic blood pressure greater than 100 mmHg the American Heart Association recommends starting both a thiazide and an ACEI, ARB or CCB. An ACEI and CCB combination can be used as well.
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 centrally acting agents. 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 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. It has been proposed that a proportion of resistant hypertension may be the result of chronic high activity of the autonomic nervous system; this concept is known as “neurogenic hypertension”
Renal nerve ablation
Surgical disruption to the sympathetic nervous system was employed in the 1930s to reduce blood pressure. Although it was effective it resulted in severe side effects and by the 1970s it had been superseded by the new antihypertensive drugs. More recently selective renal nerve radiofrequency ablation has been developed. This employs a catheter-based device that uses radiofrequency (RF) energy to cause thermal damage to the nerves surrounding the renal artery without affecting abdominal, pelvic, or lower-extremity sympathetic nerves. Clinical trials indicate that this method lowers blood pressure and, so far, major side effects have been relatively infrequent, although cases of renal artery dissection, femoral artery pseudoaneurysm, excessive decreases in blood pressure and heart rate are amongst the reported adverse effects. It has been suggested that renal nerve ablation may have a role in the management of resistant hypertension but its long term efficacy and safety have not been evaluated.