Bloodpressure
Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure" refers to the pressure in a brachial artery, where it is most commonly measured. Blood pressure is usually expressed in terms of the systolic pressure (maximum pressure during one heartbeat) over diastolic pressure (minimum pressure between heartbeats) in the cardiac cycle. It is measured in millimetres of mercury (mmHg) above the surrounding atmospheric pressure, or in kilopascals (kPa). The difference between the systolic and diastolic pressures is known as pulse pressure, while the average pressure during a cardiac cycle is known as mean arterial pressure.
Blood pressure is one of the vital signs—together with respiratory rate, heart rate, oxygen saturation, and body temperature—that healthcare professionals use in evaluating a patient's health. Normal resting blood pressure in an adult is approximately 120 millimetres of mercury (16 kPa) systolic over 80 millimetres of mercury (11 kPa) diastolic, denoted as "120/80 mmHg". Globally, the average blood pressure, age-standardized, has remained about the same since 1975 at approximately 127/79 mmHg in men and 122/77 mmHg in women, although these averages mask significant regional differences.
Traditionally, a healthcare worker measured blood pressure non-invasively by auscultation (listening) with a stethoscope for sounds in an arm artery as the artery is compressed by a sphygmomanometer. Auscultation is still generally considered the gold standard for non-invasive blood pressure readings in clinical settings. However, semi-automated methods have become common due to concerns about mercury toxicity, cost, ease of use, and suitability for ambulatory blood pressure or home blood pressure measurements.
Blood pressure is influenced by cardiac output, systemic vascular resistance, blood volume, and arterial stiffness. It varies depending on a person's situation, emotional state, activity level, and overall health. In the short term, blood pressure is regulated by baroreceptors, which act via the brain to influence the nervous system and endocrine system.
Blood pressure that is too low is called hypotension, pressure that is consistently too high is called hypertension, and normal pressure is called normotension. Both hypertension and hypotension have many causes and may occur suddenly or develop over time. Long-term hypertension is a risk factor for many diseases, including stroke, heart disease, and kidney failure.
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