Blood Presssure
Blood pressure (BP) is the pressure (force per unit area ) exerted by circulating blood on the walls of blood vessels, and constitutes one of the principal vital signs. The pressure of the circulating blood decreases as it moves away from the heart through arteries and capillaries , and toward the heart through veins. When unqualified, the term blood pressure usually refers to brachial arterial pressure : that is, in the major blood vessel of the upper left or right arm that takes blood away from the heart . Blood pressure may, however, sometimes be measured at other sites in the body, for instance at the ankle. The ratio of the blood pressure measured in the main artery at the ankle to the brachial blood pressure gives the Ankle Brachial Pressure Index (ABPI).
Home monitoring
For some patients, blood pressure measurements taken in a doctor's office may not correctly characterize their typical blood pressure. In up to 25% of patients, the office visit blood pressure reading is higher than their typical blood pressure. This type of error is called white coat hypertension and can result from anxiety related to an examination by a health care professional. The misdiagnosis of hypertension for these patients can result in needless and possibly harmful medication. On the other hand, in some cases a lower than typical blood pressure reading occurs at the doctor's office and these patients may fail to get needed treatment for hypertension.
Ambulatory blood pressure devices that take readings every half hour throughout the day and night have been used for identifying and mitigating these problems. Except for periods during sleep, home monitoring could be used for these purposes instead of ambulatory blood pressure monitoring. Home monitoring may also be used to improve hypertension management and to monitor the effects of lifestyle changes and medication related to blood pressure. Compared to ambulatory blood pressure measurements, home monitoring has been found to be an effective and lower cost alternative.
Aside from the white coat effect, arterial pressure readings outside of a clinical setting are usually slightly lower in the majority of people. The studies that looked into the risks from hypertension and the benefits of lowering the arterial pressure in affected patients were based on readings in a clinical environment.
When measuring blood pressure, an accurate reading requires that one not drink coffee, smoke cigarettes, or engage in strenuous exercise for 30 minutes before taking the reading. A full bladder may have a small effect on blood pressure readings, so if the urge to urinate exists, one should do so before the reading. For 5 minutes before the reading, one should sit upright in a chair with one's feet flat on the floor and with limbs uncrossed. The blood pressure cuff should always be against bare skin, as readings taken over a shirt sleeve are less accurate. During the reading, the arm that is used should be relaxed and kept at heart level, for example by resting it on a table.
Since arterial pressure varies throughout the day, measurements intended to monitor changes over longer time frames should be taken at the same time of day to ensure that the readings are comparable. Suitable times are:
- immediately after awakening (before washing/dressing and taking breakfast/drink), while the body is still resting,
- immediately after finishing work.
Automatic self-contained blood pressure monitors are available at reasonable prices, some of which are capable of Korotkoff's measurement in addition to oscillometric methods, enabling irregular heartbeat patients to accurately measure their blood pressure at home.
Classification
The following classification of blood pressure applies to adults aged 18 and older. It is based on the average of seated blood pressure readings that were properly measured during 2 or more office visits
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