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High Blood Pressure
Hypertension or high blood pressure is a medical condition where the blood pressure in the arteries is chronically elevated. While it is formally called arterial hypertension, the word "hypertension" without a qualifier usually refers to arterial hypertension.
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.
Definition
Blood pressure is a continuous variable, and risks of various adverse outcomes rise with it. Normal blood pressure is 120/80 mmHg. Hypertension is usually diagnosed on finding blood pressure above 140/90 mmHg measured on both arms on three occasions over a few weeks. Recently, the JNC VII (The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure) has defined blood pressure over 120/80 mmHg and below 140/90 mmHg as "pre-hypertension". "Prehypertension is not a disease category. Rather, it is a designation chosen to identify individuals at high risk of developing hypertension (JNC VII)."
In patients with diabetes mellitus or kidney disease studies have shown that blood pressure over 130/80 mmHg should be considered a risk factor and may warrant treatment.
Etiology
Essential hypertension
Age. Over time, the number of collagen fibres 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.
High salt intake
Sedentary lifestyle
Tobacco smoking
Alcohol abuse
High levels of saturated fat in the diet
Obesity. In obese subjects, losing a pound in weight generally reduces blood pressure by 1mmHg.
Stress
Low birth-weight
Diabetes mellitus
Various genetic causes
Inessential hypertension
Pregnancy. (See below for full details).
Kidney disease or renal artery stenosis
Certain cancers
Drugs. In particular, alcohol, nasal congestants with adrenergic effects, NSAIDs, MAOIs, adrenoceptor stimulants, and the contraceptive pill (ethinyl-estradiol) can cause hypertension while in use.
Malformed aorta
Slow pulse
Anemia
Fever
Aortic valve disease
Pathophysiology
The mechanisms behind the factors associated with inessential hypertension are generally fully understood, and are outlined below. However, those associated with essential hypertension are far less understood. What is known is that cardiac output is raised early in the disease course, with total peripheral resistance normal; over time cardiac output drops to normal levels but TPR is increased. Three theories have been proposed to explain this:
Inability of the kidneys to excrete sodium, resulting in natriuretic factor (note: the existence of this substance is theoretical) being secreted to promote salt excretion with the side-effect of raising total peripheral resistance.
An overactive renin / angiotension system leads to vasoconstriction and retention of sodium and water. The increase in blood volume leads to hypertension.
An overactive sympathetic nervous system, leading to increased stress responses.
Inessential hypertension
Pregnancy: unclear.
Kidney disease / renal artery stenosis: the normal physiological response to low blood pressure in the renal arteries is to increase cardiac output (CO) to maintain the pressure needed for glomerular filtration. Here, however, increased CO cannot solve the structural problems causing renal artery hypotension, with the result that CO remains chronically elevated.
Cancers: tumours in the kidney can operate in the same way as kidney disease. More commonly, however, tumors cause inessential hypertension by ectopic secretion of hormones involved in normal physiological control of blood pressure.
Drugs: anything with an adrenergic effect causes vasoconstriction at sites with alpha-adrenoceptors, increasing total peripheral resistance.
Malformed aorta, slow pulse: these cause reduced blood flow to the renal arteries, with physiological responses as already outlined.
Anemia: unclear.
Fever: unclear.
Aortic valve disease: unclear.
Signs and symptoms
Hypertension
Hypertension is usually found incidentally - "case finding" by healthcare professionals. It normally produces no symptoms.
Malignant hypertension (or accelerated hypertension) is distinct as a late phase in the condition, and may present with headaches, blurred vision and end-organ damage.
It is recognised that stressful situations can increase the blood pressure; if a normally normotensive patient has a high blood pressure only when being reviewed by a health care professional, this is colloquially termed white coat effect. Since most of what we know of hypertension and its outcome with or without modification is based on large series of readings in doctors' offices and clinics (eg Framingham) it is difficult to be sure of the significance of white-coat hypertension. Ambulatory monitoring may help determine whether traffic and ticket inspectors produce similar sustained rises.
Hypertension is often confused with mental tension, stress and anxiety. While chronic anxiety is associated with poor outcomes in people with hypertension, it alone does not cause it.
Hypertensive urgencies and emergencies
Hypertension is rarely severe enough to cause symptoms. These only surface with a systolic blood pressure over 240 mmHg and/or a diastolic blood pressure over 120 mmHg. These pressures without signs of end-organ damage (such as renal failure) are termed accelerated hypertension. When end-organ damage is present, but in absence of raised intracranial pressure, it is called hypertensive urgency. Hypertension under this circumstance needs to be controlled, but hospitalization is not required. When hypertension causes increased intracranial pressure, it is called malignant hypertension. Increased intracranial pressure causes papilledema, which is visible on ophthalmoscopic examination of the retina.
Complications
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:
Cerebrovascular accident (CVAs or strokes)
Myocardial infarction (heart attack)
Hypertensive cardiomyopathy (heart failure due to chronically high blood pressure)
Hypertensive retinopathy - damage to the retina
Hypertensive nephropathy - chronic renal failure due to chronically high blood pressure
Source: Wikipedia
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