Blood pressure

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 under 120/80 mmHg according to the AHA and ACC, and under 120/70 mmHg according to the ESC, and over 90/60 mmHg, though low blood pressure is usually not harmful unless it causes symptoms. 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. 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...