Significance and types of Sphygmomanometer

Significance

By observing the mercury in the column while releasing the air pressure with a control valve, one can read the values of the blood pressure in mm Hg. The peak pressure in the arteries during the cardiac cycle is the systolic pressure, and the lowest pressure (at the resting phase of the cardiac cycle) is the diastolic pressure. A stethoscope is used in the auscultatory method. Systolic pressure (first phase) is identified with the first of the continuous Korotkoff sounds. Diastolic is identified at the moment the Korotkoff sounds disappear (fifth phase).

Types

There are three types of sphygmomanometers:

• Digital with manual or automatic inflation. These are electronic, easy to operate, and practical in noisy environments. They measure mean arterial pressure (MAP) and use oscillometric detection to calculate systolic and diastolic values. In this sense, they do not actually measure the blood pressure, but rather derive the readings. Digital oscillometric monitors are also confronted with "special conditions" for which they are not designed to be used: arteriosclerosis; arrhythmia; preeclampsia; pulsus alternans; and pulsus paradoxus. Some wrist cuff blood pressure monitors have been found to be quite inaccurate, and the monitor has to be at the level of the heart when the reading is taken.
• Digital portable finger blood pressure monitors with automatic inflation. These are more portable and easy to operate, although less accurate. They are the smallest blood pressure monitors.
• Manual. Ideally operated by a trained person, mercury manometers are considered to be the gold standard and cannot be decalibrated , they are consistently accurate. Due to their accuracy, they are often required in clinical trials of pharmaceuticals and for clinical evaluations of determining blood pressure for high risk patients including pregnant women. Aneroid, (mechanical types with a dial) are in common use but they require regular calibration checks, unlike a mercury manometer. The prime reason for such maintenance is their susceptibility to bumps which can alter their accuracy. Wall mounted and mobile aneroids avoid this shortcoming. The aneroid sphygmomanometer should be checked for accuracy (usually every 6 months)by using a mercury manometer, as the gold standard. The unit of measurement of blood pressure is millimeters of mercury (mmHg) and are usually given as an even number.Manual sphygmomanometers require a stethoscope for auscultation. Although it is possible to obtain a basic reading through palpation, this only yields the systolic number