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 systemic, 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. About 95% of hypertension is essential hypertension. Secondary hypertension indicates that the high blood pressure is a result of (i.e., secondary to) another condition, such as kidney disease or tumours (adrenal adenoma or pheochromocytoma).

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. Beginning at a systolic pressure of 115 mm Hg and diastolic pressure of 75 mm Hg (commonly written as 115/75 mm Hg), cardiovascular disease (CVD) risk doubles for each increment of 20/10 mm Hg.

Classification

In individuals older than 50 years, hypertension is considered to be present when a person's blood pressure is consistently at least 140 mm Hg systolic or 90 mm Hg diastolic. 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. Guidelines for treating resistant hypertension have been published in the UK, and US.

In the United States, prehypertension is defined as blood pressure from 121/81 mm Hg to 139/89 mm Hg and although not a disease category, it is a designation chosen to identify individuals at high risk of developing hypertension.

Essential (primary) hypertension

By definition, essential hypertension has no identifiable cause. However, several risk factors have been identified, including 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 Body mass index greater than 25.A definitive link between obesity and hypertension has been found using animal and clinical studies, from these it has been realized that many mechanisms are potential causes of obesity induced hypertension.These mechanisms include the activation of the sympathetic nervous system as well as the activation of the renin–angiotensin-aldosterone system.