Blood pressure is a measure of the force blood in major arteries (generally, the arteries leading to the arm) can overcome over resistance. It is expressed as a ratio of two numbers - the pressure in mm of mercury (mmHg) that the blood in the artery can overcome when the vessels are under direct pressure from the heart when it contracts, and the pressure the blood can overcome when the heart is at rest in the short time between beats. "Normal" blood pressure is generally 120/80, but blood pressures from about 110/70 to 140/90 are considered acceptable.

High blood pressure or 'hypertension' (generally from about 140/90 to 180/100) is considered to put the patient at a higher risk of stroke and other cardio-vasular diseases. As a result, patients with blood pressure in this range generally undergo treatment, either with medication or with lifestyle changes. There are several medications that are effective in treating blood pressure, each group of which acts in a unique way and such drugs must be targeted to the individual patient. Lifestyle changes require that the patient change behaviors that tend to raise blood pressure, such as being overweight, smoking, or drinking alcohol to excess. The role of salt in blood pressure is currently under review, but historically it has believed that excess salt intake also raises blood pressure. Regular monitoring of blood pressure is important. There are web tools that let users store and analyze their readings. One example is Blood Pressure Chart .

Very high blood pressure is a serious condition and puts the patient at immediate risk of stroke. It can be the result of such conditions as restricted major arteries, kidney disorders, or drug use.

Low blood pressure is also a serious condition and puts the patient at risk of losing consciousness (due to the inability of blood to reach the brain) and damage to other major organs, most of which require a constant flow of blood at appropriate pressure to function properly. Although several conditions can cause low blood pressure, a common cause is an overdose of depressive drugs, such as alcohol or barbituates.

Blood pressure at Wikipedia