Blood pressure is the pressure made by the blood inside blood vessels. Unless otherwise stated, "blood pressure" refers to systemic arterial blood pressure. This is the pressure in larger arteries delivering blood to body parts other than the lungs, for example the brachial artery in the arm. The blood pressure changes. Blood pressure is higher in arteries than it is in other blood vessels. Blood pressure is often measured in millimeters of mercury (mmHg).
Systolic pressure is the first number given in blood pressure readings. It is the peak pressure in the arteries during the cardiac cycle (when the heart is pumping). The diastolic pressure is the second number given in a blood pressure reading, and it is the pressure at the resting phase of the cardiac cycle (when the heart is relaxing). The mean arterial pressure (the average pressure) and pulse pressure (the difference between the systolic and diastolic) are other important values.
Typical values for a resting, healthy adult human are about 110 mmHg systolic and 70 mmHg diastolic (written as 110/70 mmHg). This can be very different for each person. Blood pressure readings change naturally during the day (in a circadian rhythm); they also change because of stress, drugs, disease or even because of what you eat. The American Medical Association says that even the stress of having your blood pressure taken can make it higher. They call this "white coat hypertension".
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- Pesola GR, Pesola HR, Nelson MJ, Westfal RE (January 2001). "The normal difference in bilateral indirect blood pressure recordings in normotensive individuals". Am J Emerg Med 19 (1): 43–5. doi:10.1053/ajem.2001.20021. PMID 11146017. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6W9K-45SRDHC-C&_user=10&_coverDate=01%2F31%2F2001&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=74f2b32e088d88986cd307f6c7219331.
- "Home Blood Pressure Monitoring". American Heart Association. http://www.heart.org/HEARTORG/Conditions/HighBloodPressure/SymptomsDiagnosisMonitoringofHighBloodPressure/Home-Blood-Pressure-Monitoring_UCM_301874_Article.jsp. Retrieved 2013-02-14.