HIGH BLOOD PRESSURE
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" without a qualifier
normally refers to arterial hypertension
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.
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 or when the diastolic blood pressure
is consistently 90 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.
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.
Blood pressure is "normal if it's below 120/80".
Patients with blood pressures over 130/80 mm Hg along with Type 1 or Type
2 diabetes, or kidney disease require further treatment.
Resistant hypertension is defined as the failure to reduce BP to the appropriate
level after taking a three-drug regimen.
Causes
Although no specific medical cause can be determined in essential hypertension,
it often has several contributing factors. These include obesity, salt
sensitivity, renin homeostasis, insulin resistance, genetics, and age.
Obesity
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.
Sodium sensitivity
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.
needs correction, not enough water is "pulled" out of cells
to increase volume. The inceased Na stimulates ADH and thirst mechanisms
leading to a concentrated urine and the kidneys holding onto water along
with the person increasing their intake of water. The water movement between
cells and the interstitium plays a minor role compared to this.
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 white
Americans, and may explain why African Americans tend to respond better
to diuretic therapy than drugs that interfere with the Renin / angiotension
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.
Insulin resistance
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 withhypertension. This feature is now widely recognized
as part of syndrome X, or the metabolic syndrome.
Sleep apnea
Sleep apnea is a common, under-recognized cause of hypertension. It is
often best treated with nocturnal nasal continuous positive airway pressure,
but other approaches include the Mandibular advancement splint (MAS),
UPPP, tonsilectomy, adenoidectomy, septoplasty, 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 multi-factorial or that a number of different genetic defects each have an elevated blood pressure as one of their phenotypic expressions.
However, hypertension can be caused by mutations
in single genes, inherited on a mendelian basis.
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 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.
Liquorice
Consumption of liquorice (which can be of potent strength in liquorice
candy) can lead to a surge in blood pressure.
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).
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 / angiotension 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
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).
Coarctation of the aorta
The congenital abnormality aortic coarctation can result in hypertension.
Drugs
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.
Rebound hypertension
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.