What is sphygmomanometer?
A sphygmomanometer is an instrument used to measure blood pressure which is also known as a blood pressure meter or blood pressure gauge or blood pressure monitor. The word sphygmomanometer is derived from the Greek word ‘sphygmos’ meaning beating of the heart or the pulse and manometer mean the device used for measuring the pressure or tension. This instrument was invented by Samuel Siegfried Karl Ritter von Basch in the year 1881. But in the year 1896, Scipione Riva-Rocci introduced a simplified version of the sphygmomanometer.
Types of sphygmomanometer
Following are the three major types of sphygmomanometer:
- Mercury sphygmomanometer: It is the most conventional form of blood pressure apparatus and is considered to be the golden standard. It consists of manually inflatable cuffs that are attached to the mercury-infused tubes. In order to get the correct readings, the instrument should be kept on a flat surface and in an upright position. If the instrument is dropped accidentally, there are high chances of risks. The advantage of this sphygmomanometer is that they can last for a lifetime, easy to use and there is no need for recalibration. Due to its toxic contents, it is banned in some countries.
- Aneroid sphygmomanometer: Aneroid means “without fluid” and in this instrument, there is no use of mercury. It consists of a stethoscope that is attached to the cuff which is further attached to a dial gauge with tubing. To convert the cuff pressure to gauge pressure, the gauge head has a mechanical part. The instrument needs to be recalibrated to avoid faulty readings. There are other different types of aneroid sphygmomanometer depending upon their use, and they are:
- Pocket-aneroid sphygmomanometer
- Palm aneroid sphygmomanometer
- Clock-style aneroid sphygmomanometer
- Automatic digital sphygmomanometer: It is the most technologically advanced sphygmomanometer. It consists of an electronic sensor to measure the blood pressure and the readings are displayed on the digital monitor. In order to measure the blood pressure, the instrument measure the fluctuations of arteries. These need to be checked using a mercury sphygmomanometer to avoid inaccurate readings.
Parts of sphygmomanometer
- Bladder: This is an inflatable bag that is used to compress the arm to occlude the artery. To ensure full arterial compression, bladders must have specific sizing parameters.
- Cuff: This is designed to hold the bladder around the arm during the measurement. For accurate measurement, the cuff must be designed properly with respect to placement and the position.
- Manometer: This is a device used to measure the air pressure in mmHg. The manometer used in an aneroid sphygmomanometer consists of a watch-like movement to measure the air pressure applied to the cuff. To expand the diaphragm, the gauge has a series of copper or beryllium and there are gears to convert the linear movement of the diaphragm to get the readings in mmHg.
- Valve: This used as a deflation valve to control the cuff. This plays a vital role in getting an accurate measurement.
- Bulb: This is used to pump the air into the cuff.
How to use a sphygmomanometer?
Following is the procedure to be followed to use a sphygmomanometer:
- The length of the cuff bladder used for the measurement of blood pressure should be equal to 80% of the circumference of the upper arm.
- Wrap the cuff around the upper arm such that the lower edge of the cuff is one inch above the antecubital fossa.
- Press the stethoscope’s bell lightly over the brachial artery which is below the cuff’s edge.
- Release the air from the cuff at a moderate rate to 180mmHg.
- Monitor the first knocking sound by listening with the help of a stethoscope and also by observing the mercury gauge.
- This should be done for both the arms and the pressure, the position of the subject and the size of the cuff should be recorded.
- If the pressure is more, then the blood pressure should be measured with few minutes of gaps between the two measurements.
- If the blood pressure is more than 180/120mmHg, immediate actions should be taken.
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