High blood pressure, or hypertension,
results from abnormally high pressure in the arteries.
It is defined as a systolic pressure above 140 mmHg at rest,
and/or a diastolic pressure above 90 mmHg.
Hypertension causes thickening of the walls of blood vessels,
and is a powerful risk factor of acute myocardial infarction,
congestive heart failure (CHF), stroke,
renal failure, and aortic aneurysms.
It is the most common disease-specific reason
for medical visits in the United States.
About one-third of American adults are hypertensive.
Approximately, 90% of hypertension cases are of unknown cause,
called essential hypertension.
The remaining cases are usually caused
by kidney disease or hormonal imbalances.