Blood Pressure Devices
1. The mercury sphygmomanometer (sphygmo—Gr: pulse) is the usual apparatus for measuring blood pressure. It consists of an inflatable sleeve or cuff of various widths and lengths attached by tubing to a manometer tube containing Mercury. It measures the pressure required to move a column of Mercury up the tube a certain distance.
2. The aneroid (sphygmo) manometer (aneros—Gr: no liquid) uses a similar cuff to the above but air pressure elongates a metal bellows that transmits motion to the needle in a small round device that one may hang from the cuff. These are popular with physicians.
However, many are inaccurate because of infrequent calibrations.
3. The automatic electronic oscillometric instrument (i.e., Dinamap) is widely used in hospitals today. The cuff is connected to a monitor which may also display oxygen saturation and cardiac rhythm. A microprocessor senses the amplitude of arterial wall oscillations. As the cuff deflates, the first increase in amplitude is the systolic pressure;
a quick decrease is the diastolic pressure. The mean pressure is the strongest amplitude. The devise is statistically more accurate than the mercury sphygomomanometer. Recent portable devices have arm, wrist or finger cuffs (the latter two are prone to error).
A built-in algorithm calculates blood pressure based on arterial vibration patterns. Some portable monitors also have oxygen saturation capabilities.