| Hypertension Classification and external resources |
|
| ICD-10 | I10.,I11.,I12., I13.,I15. |
|---|---|
| ICD-9 | 401.x |
| OMIM | 145500 |
| DiseasesDB | 6330 |
| MedlinePlus | 000468 |
| eMedicine | med/1106 ped/1097 emerg/267 |
| MeSH | D006973 |
Hypertension, also referred to as high blood pressure, HTN or HPN, is a medical condition in which the blood pressure is chronically elevated. In current usage, the word "hypertension"[1] without a qualifier normally refers to arterial hypertension. [2]
Hypertension can be classified either essential (primary) or secondary. Essential hypertension indicates that no specific medical cause can be found to explain a patient's condition. Secondary hypertension indicates that the high blood pressure is a result of (i.e., secondary to) another condition, such as kidney disease or tumours (pheochromocytoma and paraganglioma). Persistent hypertension is one of the risk factors for strokes, heart attacks, heart failure and arterial aneurysm, and is a leading cause of chronic renal failure. Even moderate elevation of arterial blood pressure leads to shortened life expectancy. At severely high pressures, defined as mean arterial pressures 50% or more above average, a person can expect to live no more than a few years unless appropriately treated.[3]
In individuals older than 50 years, hypertension is considered to be present when a person's systolic blood pressure is consistently 140 mm Hg or greater. Beginning at a systolic pressure of 115 and diastolic pressure of 75 (commonly written as 115/75 mm Hg), cardiovascular disease (CVD) risk doubles for each increment of 20/10 mmHg.[4] Prehypertension is defined as blood pressure from 120/80 mm Hg to 139/89 mm Hg. Prehypertension is not a disease category; rather, it is a designation chosen to identify individuals at high risk of developing hypertension.[4] The Mayo Clinic specifies blood pressure is "normal if it's below 120/80".[5] Patients with blood pressures over 130/80 mm Hg along with Type 1 or Type 2 diabetes, or kidney disease require further treatment.[4]
Resistant hypertension is defined as the failure to reduce BP to the appropriate level after taking a three-drug regimen.[4] The American Heart Association released guidelines for treating resistant hypertension.[6]
Although no specific medical cause can be determined in essential hypertension, it often has several contributing factors. These include obesity[7], salt sensitivity, renin homeostasis, insulin resistance, genetics, and age.
The risk of hypertension is 5 times higher in the obese as compared to those of normal weight and up to two-thirds of cases can be attributed to excess weight. More than 85% of cases occur in those with a BMI>25.[7]
Sodium is an environmental factor that has received the greatest attention. Approximately one third of the essential hypertensive population is responsive to sodium intake[8]. This is due to the fact that increasing amounts of salt in a person's bloodstream causes cells to release water (due to osmotic pressure) to equilibrate concentration gradient of salt between the cells and the bloodstream; increasing the pressure on the blood vessel walls.
Renin is an enzyme secreted by the juxtaglomerular apparatus of the kidney and linked with aldosterone in a negative feedback loop. The range of renin activity observed in hypertensive subjects tends to be broader than in normotensive individuals. In consequence, some hypertensive patients have been defined as having low-renin and others as having essential hypertension. Low-renin hypertension is more common in African Americans than white Americans, and may explain why African Americans tend to respond better to diuretic therapy than drugs that interfere with the renin-angiotensin system.
High Renin levels predispose to Hypertension: Increased Renin → Increased Angiotensin II → Increased Vasoconstriction, Thirst/ADH and Aldosterone → Increased Sodium Resorption in the Kidneys (DCT and CD) → Increased Blood Pressure. Some authorities claim that potassium might both prevent and treat hypertension[9].
Insulin is a polypeptide hormone secreted by cells in the islets of langerhans, which are contained throughout the pancreas. Its main purpose is to regulate the levels of glucose in the body antagonistically with glucagon through negative feedback loops. Insulin also exhibits vasodilatory properties. In normotensive individuals, insulin may stimulate sympathetic activity without elevating mean arterial pressure. However, in more extreme conditions such as that of the metabolic syndrome, the increased sympathetic neural activity may over-ride the vasodilatory effects of insulin. Insulin resistance and/or hyperinsulinemia have been suggested as being responsible for the increased arterial pressure in some patients with hypertension. This feature is now widely recognized as part of syndrome X, or the metabolic syndrome.
Sleep apnea is a common, under-recognized cause of hypertension.[10] It is often best treated with nocturnal nasal continuous positive airway pressure, but other approaches include the Mandibular advancement splint (MAS), UPPP, tonsilectomy, adenoidectomy, sinus surgery, or weight loss.
Hypertension is one of the most common complex disorders, with genetic heritability averaging 30%. Data supporting this view emerge from animal studies as well as in population studies in humans. Most of these studies support the concept that the inheritance is probably multifactorial or that a number of different genetic defects each have an elevated blood pressure as one of their phenotypic expressions.
More than 50 genes have been examined in association studies with hypertension, and the number is constantly growing.
Over time, the number of collagen fibers in artery and arteriole walls increases, making blood vessels stiffer. With the reduced elasticity comes a smaller cross-sectional area in systole, and so a raised mean arterial blood pressure.
Consumption of liquorice (which can be of potent strength in liquorice candy) can lead to a surge in blood pressure[11]. People with hypertension or history of cardio-vascular disease should avoid liquorice raising their blood pressure to risky levels. Frequently, if liquorice is the cause of the high blood pressure, a low blood level of potassium will also be present.
Liquorice extracts are present in many medicines (for example cough syrups, throat lozenges and peptic ulcer treatments).
Only in a small minority of patients with elevated arterial pressure can a specific cause be identified. In 90 percent to 95 percent of high blood pressure cases, the American Heart Association says there's no identifiable cause. For the rest (5-10%), most will probably have an endocrine or renal defect that, if corrected, could bring blood pressure back to normal values.
Both adrenal glands can overproduce the hormone cortisol or it can arise in a benign or malignant tumor. Hypertension results from the interplay of several pathophysiological mechanisms regulating plasma volume, peripheral vascular resistance and cardiac output, all of which may be increased. More than 80% of patients with Cushing's syndrome have hypertension.
In patients with pheochromocytoma increased secretion of catecholamines such as epinephrine and norepinephrine by a tumor (most often located in the adrenal medulla) causes excessive stimulation of adrenergic receptors, which results in peripheral vasoconstriction and cardiac stimulation. This diagnosis is confirmed by demonstrating increased urinary excretion of epinephrine and norepinephrine and/or their metabolites (vanillylmandelic acid).
Hypertension can be caused by mutations in single genes, inherited on a mendelian basis.[12]
The congenital abnormality aortic coarctation can result in hypertension.
Certain medications, especially NSAIDs (Motrin/Ibuprofen) and steroids can cause hypertension. Licorice (Glycyrrhiza glabra) inhibits the 11-hydroxysteroid hydrogenase enzyme (catalyzes the reaction of cortisol to cortison) which allows cortisol to stimulate the Mineralocorticoid Receptor (MR) which will lead to effects similar to hyperaldosteronism, which itself is a cause of hypertension.[13]
High blood pressure that is associated with the sudden withdrawal of various antihypertensive medications. The increases in blood pressure may result in blood pressures greater than when the medication was initiated. Depending on the severity of the increase in blood pressure, rebound hypertension may result in a hypertensive emergency. Rebound hypertension is avoided by gradually reducing the dose (also known as "dose tapering"), thereby giving the body enough time to adjust to reduction in dose.
Medications commonly associated with rebound hypertension include centrally-acting antihypertensive agents, such as clonidine and beta-blockers.
Although few women of childbearing age have high blood pressure, up to 10% develop hypertension of pregnancy. While generally benign, it may herald three complications of pregnancy: pre-eclampsia, HELLP syndrome and eclampsia. Follow-up and control with medication is therefore often necessary.
As with adults, blood pressure is a variable parameter in children. It varies between individuals and within individuals from day to day and at various times of the day. The epidemic of childhood obesity, the risk of developing left ventricular hypertrophy, and evidence of the early development of atherosclerosis in children would make the detection of and intervention in childhood hypertension important to reduce long-term health risks; however, supporting data are lacking. Most childhood hypertension, particularly in preadolescents, is secondary to an underlying disorder. Renal parenchymal disease is the most common (60 to 70%) cause of hypertension. Adolescents usually have primary or essential hypertension, making up 85 to 95% of cases. [14]
Most of the secondary mechanisms associated with hypertension are generally fully understood, and are outlined at secondary hypertension. However, those associated with essential (primary) hypertension are far less understood. What is known is that cardiac output is raised early in the disease course, with total peripheral resistance (TPR) normal; over time cardiac output drops to normal levels but TPR is increased. Three theories have been proposed to explain this:
It is also known that hypertension is highly heritable and polygenic (caused by more than one gene) and a few candidate genes have been postulated in the etiology of this condition.[15][16][17]
Diagnosis of hypertension is generally on the basis of a persistently high blood pressure. Usually this requires three separate measurements at least one week apart. Exceptionally, if the elevation is extreme, or end-organ damage is present then the diagnosis may be applied and treatment commenced immediately.
Obtaining reliable blood pressure measurements relies on following several rules and understanding the many factors that influence blood pressure reading[18].
For instance, measurements in control of hypertension should be at least 1 hour after caffeine, 30 minutes after smoking or strenuous exercise and without any stress. Cuff size is also important. The bladder should encircle and cover two-thirds of the length of the (upper) arm. The patient should be sitting upright in a chair with both feet flat on the floor for a minimum of five minutes prior to taking a reading. The patient should not be on any adrenergic stimulants, such as those found in many cold medications.
When taking manual measurements, the person taking the measurement should be careful to inflate the cuff suitably above anticipated systolic pressure. The person should inflate the cuff to 200 mmHg and then slowly release the air while palpating the radial pulse. After one minute, the cuff should be reinflated to 30 mmHg higher than the pressure at which the radial pulse was no longer palpable. A stethoscope should be placed lightly over the brachial artery. The cuff should be at the level of the heart and the cuff should be deflated at a rate of 2 to 3 mmHg/s. Systolic pressure is the pressure reading at the onset of the sounds described by Korotkoff (Phase one). Diastolic pressure is then recorded as the pressure at which the sounds disappear (K5) or sometimes the K4 point, where the sound is abruptly muffled. Two measurements should be made at least 5 minutes apart, and, if there is a discrepancy of more than 5 mmHg, a third reading should be done. The readings should then be averaged. An initial measurement should include both arms. In elderly patients who particularly when treated may show orthostatic hypotension, measuring lying sitting and standing BP may be useful. The BP should at some time have been measured in each arm, and the higher pressure arm preferred for subsequent measurements.
BP varies with time of day, as may the effectiveness of treatment, and archetypes used to record the data should include the time taken. Analysis of this is rare at present.
Automated machines are commonly used and reduce the variability in manually collected readings [19]. Routine measurements done in medical offices of patients with known hypertension may incorrectly diagnose 20% of patients with uncontrolled hypertension [20]
Home blood pressure monitoring can provide a measurement of a person's blood pressure at different times throughout the day and in different environments, such as at home and at work. Home monitoring may assist in the diagnosis of high or low blood pressure. It may also be used to monitor the effects of medication or lifestyle changes taken to lower or regulate blood pressure levels.
Home monitoring of blood pressure can also assist in the diagnosis of white coat hypertension. The American Heart Association[21] states, "You may have what's called 'white coat hypertension'; that means your blood pressure goes up when you're at the doctor's office. Monitoring at home will help you measure your true blood pressure and can provide your doctor with a log of blood pressure measurements over time. This is helpful in diagnosing and preventing potential health problems."
Some home blood pressure monitoring devices also make use of blood pressure charting software.[22] These charting methods provide printouts for the patient's physician and reminders to take a blood pressure reading. However, a simple and cheap way is simply to manually record values with pen and paper, which can then be inspected by a doctor.
Systolic hypertension is defined as an elevated systolic blood pressure. If systolic blood pressure is elevated with a normal diastolic blood pressure, it is called isolated systolic hypertension. Systolic hypertension may be due to reduced compliance of the aorta with increasing age[23].
Once the diagnosis of hypertension has been made it is important to attempt to exclude or identify reversible (secondary) causes.
Tests are undertaken to identify possible causes of secondary hypertension, and seek evidence for end-organ damage to the heart itself or the eyes (retina) and kidneys. Diabetes and raised cholesterol levels being additional risk factors for the development of cardiovascular disease are also tested for as they will also require management.
Blood tests commonly performed include:
Additional tests often include:
Prevention of hypertension only goes as far as the cause; one can adjust lifestyle related causes but genetics, race, age and gender are outside the realm of change.
Modifiable factors include diet, weight, exercise levels and stress management.
Low-sodium and low-fat diets can reduce cardiovascular risks, keep arteries clear of plaque and blood volume at normal levels.
Losing even 10% of body weight can have fantastic benefits towards health, including reversal or prevention of HTN, dropping systolic pressures several points.
Exercise maintains a healthy heart, thus healthy cardiac contractions and functions. The heart is a muscle too, working out the cardiac muscles makes the heart beat more efficiently, thus pumping blood around the body more effectively.
Stressors can negatively affect blood pressure by activating the sympathetic nervous system, thus fight or flight responses which increase heartrate and blood pressure. Chronic stress can lead to regular and frequent activation of the system and repeated high blood pressure.
Effective management of stress can reduce this particular risk.
Published feasibility studies have shown that a pacemaker-like device designed to electrically activate the baroreflex, also known as Baroreflex Activation Therapy, significantly lowers blood pressure in patients with treatment resistant hypertension. One study published on a group of 16 patients reported an average systolic blood pressure reduction of 34 mmHg after three months of treatment and 35 mmHg after 24 months. A drop in systolic blood pressure of at least 20 mmHg was achieved in 12 of 16 (75%) patients at 2 years and 5 of 16 (31%) achieved a systolic BP of less than 140 mmHg at 2 years.[30] Results published on a separate group of 10 patients from another feasibility trial reported an average systolic blood pressure reduction of 24 mmHg after three months of treatment.[31] A 300 patient randomized controlled trial is currently underway. Particpants must have systolic blood pressure above 160 mmHg despite being on three or more antihypertensive medications. If the results from this trial confirm the findings published in the above studies, Baroreflex Activation Therapy may be approved by the FDA and made commercially available as early as 2012.
Unless hypertension is severe, lifestyle changes such as those discussed in the preceding section are strongly recommended before initiation of drug therapy. Adoption of the DASH diet is one example of lifestyle change repeatedly shown to effectively lower mildly-elevated blood pressure. If hypertension is high enough to justify immediate use of medications, lifestyle changes are initiated concomitantly.
There are many classes of medications for treating hypertension, together called antihypertensives, which — by varying means — act by lowering blood pressure. Evidence suggests that reduction of the blood pressure by 5-6 mmHg can decrease the risk of stroke by 40%, of coronary heart disease by 15-20%, and reduces the likelihood of dementia, heart failure, and mortality from vascular disease.
The aim of treatment should be blood pressure control to <140/90 mmHg for most patients, and lower in certain contexts such as diabetes or kidney disease (some medical professionals recommend keeping levels below 120/80 mmHg).[3] Each added drug may reduce the systolic blood pressure by 5-10 mmHg, so often multiple drugs are necessary to achieve blood pressure control.
Commonly used drugs include:
Unless the blood pressure is severely elevated, consensus guidelines call for medically-supervised lifestyle changes and observation before recommending initiation of drug therapy. All drug treatments have side effects, and while the evidence of benefit at higher blood pressures is overwhelming, drug trials to lower moderately-elevated blood pressure have failed to reduce overall death rates.
If lifestyle changes are ineffective or the presenting blood pressure is critical, then drug therapy is initiated, often requiring more than one agent to effective lower hypertension. Which type of many medications should be used initially for hypertension has been the subject of several large studies and various national guidelines.
The ALLHAT study showed better cost-effectiveness and slightly better outcomes for the thiazide diuretic chlortalidone compared with a calcium channel blocker and an ACE inhibitor in a 33,357-member ethnically mixed study group.[34] The 1993 consensus recommendation for use of thiazide diuretics as initial treatment stems in part from the ALLHAT study results, which concluded in 2002 that "Thiazide-type diuretics are superior in preventing 1 or more major forms of CVD and are less expensive. They should be preferred for first-step antihypertensive therapy."[34]
A subsequent smaller study (ANBP2) did not show the slight advantages in thiazide diuretic outcomes observed in the ALLHAT study, and actually showed slightly better outcomes for ACE-inhibitors in older white male patients.[35]
Thiazide diuretics are effective, recommended as the best first-line drug for hypertension by many experts, and much more affordable than other therapies, yet they are not prescribed as often as some newer drugs. Arguably, this is partly because they are off-patent, less profitable, and thus rarely promoted by the drug industry.[36]
The consensus recommendations of thiazide diuretics as first-line therapy for hypertension stand against a the backdrop that all blood pressure treatments have side-effects. Potentially serious side effects of the thiazide diuretics include hypercholesterinemia, and impaired glucose tolerance with consequent increased risk of developing Diabetes mellitus type 2. The thiazide diuretics also deplete circulating potassium unless combined with a potassium-sparing diuretic or supplemental potassium. On this basis, the consensus recommendations to prefer use of thiazides as first line treatment for essential hypertension have been repeatedly and strongly questioned.[37][38][39] However as the Merck Manual of Geriatrics notes, "thiazide-type diuretics are especially safe and effective in the elderly."[40]
The risk of beta-blockers provoking type 2 diabetes led to their downgrading to fourth-line therapy in the United Kingdom in June 2006[41], in the revised national guidelines.[42]
The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC 7) in the United States recommends starting with a thiazide diuretic if single therapy is being initiated and another medication is not indicated.[4]
It is based upon several factors including genetics, dietary habits, and overall lifestyle choices. If an individual conscious of their condition takes the necessary preventative measures to lower their blood pressure, they are more likely to have a much better outcome than someone who does not.
While elevated blood pressure alone is not an illness, it often requires treatment due to its short- and long-term effects on many organs. The risk is increased for:
The level of blood pressure regarded as deleterious has been revised down during years of epidemiological studies. A widely quoted and important series of such studies is the Framingham Heart Study carried out in an American town: Framingham, Massachusetts. The results from Framingham and of similar work in Busselton, Western Australia have been widely applied. To the extent that people are similar this seems reasonable, but there are known to be genetic variations in the most effective drugs for particular sub-populations. Recently (2004), the Framingham figures have been found to overestimate risks for the UK population considerably. The reasons are unclear. Nevertheless the Framingham work has been an important element of UK health policy.
Sushruta (6th century BCE) explained hypertension in a manner which matches the modern symptoms of the disease.[43]
Hypertension at the Open Directory Project
|
|||||||||||||||||||||||||||||||||||||||||