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Measuring blood pressure
Hypertension is discovered most often during a routine visit to the doctor. The instrument used to evaluate blood pressure in a doctor's office is called a sphygmomanometer and typically consists of an inflating bulb, an inflatable cuff, and a mercury column gauge.
Blood pressure is measured by wrapping the cuff around the upper arm and determining how much pressure is needed to compress the brachial artery--the major artery in the arm. The amount of pressure needed is equivalent to the height of the mercury in the gauge. Thus, blood pressure is expressed in millimeters of mercury, or mm Hg.
Because of concerns about mercury contamination of the environment, the Environmental Protection Agency is encouraging doctors to switch to aneroid or electronic blood pressure devices that use dial or digital gauges, respectively, to indicate blood pressure levels. Some experts are uneasy about these devices, but when used properly they can be as accurate as mercury sphygmomanometers.
Regardless of the type of device used to measure blood pressure, the following steps will help ensure accurate results:
- Do not smoke or consume caffeine in the 30 minutes prior to having blood pressure measured.
- Be seated and at rest for at least five minutes before the measurement.
- The results of two or more readings, taken at least one minute apart, should be averaged.
Ambulatory Blood Pressure Monitoring. Ambulatory blood pressure monitors automatically measure and record blood pressure over a 24- to 48-hour period. Such measurements may be useful in the diagnosis of white coat hypertension. There is also some evidence that ambulatory monitoring may be helpful in identifying people with drug-resistant hypertension, hypotension caused by blood pressure medication, episodic hypertension, or borderline hypertension (systolic blood pressure 130 to 139 mm Hg or diastolic pressure 85 to 89 mm Hg).
In ambulatory monitoring, an inflatable cuff is worn around the arm and connected to a blood pressure monitor about the size of a Walkman. At predetermined times--typically every 15 to 30 minutes during the day and every 30 to 60 minutes during the night--the cuff inflates automatically and takes blood pressure readings that are stored in the monitor and later interpreted by a doctor.
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