Blood Pressure Control - What You Need To Know

Hypertension, most commonly referred to as "high blood pressure" or HTN, is a medical condition in which the blood pressure is chronically elevated. It was previously referred to as arterial hypertension, but in current usage, the word "hypertension" without a qualifier normally refers to arterial hypertension.

Hypertension can be classified as 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 certain tumours (especially of the adrenal gland). 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.

Hypertension is considered to be present when a person's systolic blood pressure ("top number") is consistently 140 mmHg or greater, and/or their diastolic blood pressure ("bottom number") is consistently 90 mmHg or greater. As of 2003, the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure has defined blood pressure 120/80 mmHg to 139/89 mmHg as "pre hypertension." Pre hypertension is not a disease category; rather, it is a designation chosen to identify individuals at high risk of developing hypertension. The Mayo Clinic web site specifies blood pressure is "normal if it's below 120/80" but that "some data indicate that 115/75 mm Hg should be the gold standard." In patients with diabetes mellitus or kidney disease studies have shown that blood pressure over 130/80 mmHg should be considered high and warrants further treatment. Even higher numbers are considered diagnostic using home blood pressure monitoring devices.

Factors of Essential Hypertension

Although no specific medical cause can be determined in essential hypertension, the most common form, several factors may contribute to it, including salt sensitivity, renin homeostasis, insulin resistance, genetics and age.

Salt sensitivity

Sodium is an environmental factor that has received the greatest attention. Approximately 60% of the essential hypertension population is responsive to sodium intake. This is due to the fact that increasing amounts of salt in a person's bloodstream causes the body to draw more water, increasing the pressure on the blood vessel walls.

The effects of excess amounts of salt in the body depend on how much excess salt (or salty foods) is eaten in a specific time versus how well the kidneys functioned. When the salt content of the blood elevates, water is attracted from around the cells (in muscles and organs) and into the blood, in order to dilute blood salinity. There is salt as sodium outside every cell in the body. When the salt content of the fluid around the cells goes up, it attracts water from the blood and swelling occurs. The kidneys are responsible for regulating salt and water levels in the body. When salt and water levels increase around cells, the excess is drawn into the blood, which is filtered by the kidneys. The kidneys remove excess salt and water from the blood, both of which are excreted as urine. When the kidneys do not work well, fluid builds up around cells and in the blood. The heart is the pump that pushes the blood around. If there is more fluid in the blood, the heart has to work harder and the blood pressure can go up because there is more pressure on the walls of the blood vessels. The heart can get weaker or worn out from the extra work.

Salt has been blamed in the past as causing high blood pressure. New research suggests that too little calcium or potassium also has an impact on blood pressure.

Role of renin

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 Caucasians and may explain why they 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 Re absorption in the Kidneys (DCT and CD) ? Increased Blood Pressure.

Insulin resistance

Insulin is a polypeptide hormone secreted by 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 apneas

Sleep apnea is a common, under-recognized cause of hypertension.<Actinic:Variable Name = '5'/> It is often best treated with nocturnal nasal continuous positive airway pressure, but other approaches include the Mandibular advancement splint (MAS), UPPP, tonsillectomy, adenoidectomy, sinus surgery, or weight loss.

Genetics

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.

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.

Other etiologies

There are some anecdotal or transient causes of high blood pressure. These are not to be confused with the disease called hypertension in which there is an intrinsic physiopathological mechanism as described below.

Etiology of secondary hypertension

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). These individuals will probably have an endocrine or renal defect that, if corrected, could bring blood pressure back to normal values.

Renal hypertension

Hypertension produced by diseases of the kidney. This includes diseases such as polycystic kidney disease or chronic glomerulonephritis. Hypertension can also be produced by diseases of the renal arteries supplying the kidney. This is known as renovascular hypertension; it is thought that decreased perfusion of renal tissue due to stenosis of a main or branch renal artery activates the renin-angiotensin system.

Adrenal hypertension

Hypertension is a feature of a variety of adrenal cortical abnormalities. In primary aldosteronism there is a clear relationship between the aldosterone-induced sodium retention and the hypertension.

Cushing's syndrome (hypersecretion of cortisol)

Both adrenal glands can overproduce the hormone cortisol or it can arise in a benign or malignant tumour. 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 tumour (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).

Genetic causes

Hypertension can be caused by mutations in single genes, inherited on a mendelian basis.

Coarctation of the aorta

Drugs

Certain medications, especially NSAIDS (Non-steroidal anti-inflammatories such as Motrin/ibuprofen) and steroids can cause hypertension. Licorice (Glycyrrhiza glabra) inhibits the 11-hydroxysteroid hydrogenase enzyme (catalyzes the reaction of cortisol to cortisone) which allows cortisol to stimulate the Mineralocorticoid Receptor (MR) which will lead to effects similar to hyperaldosteronism, which itself is a cause of hypertension. [Reference: Harrisons Internal Medicine, online edition (2007-04-14)]

Spinal misalignment

Another claimed cause of hypertension is the misalignment of vertebrae within the spinal column, specifically the atlas vertebra. The Journal of Human Hypertension published the results of a clinically controlled trial in which patients with hypertension and a misaligned atlas vertebra were chosen to undergo chiropractic treatment. The study showed a significant lowering of blood pressure in hypertensive patients after only one chiropractic adjustment of the atlas vertebra. The study showed a decrease in blood pressure immediately following the adjustment as well as a full eight weeks following the adjustment. The decrease in blood pressure was equal to taking two blood-pressure drugs at once.

Source: http://en.wikipedia.org/wiki/Hypertension