What is Sphygmomanometer?
A sphygmomanometer, also known as a blood pressure meter or blood pressure monitor, is an instrument used to measure blood pressure. The word sphygmomanometer is derived from the Greek word ‘sphygmos’ meaning heartbeat or pulse rate, and manometer refers to a device used to measure pressure or tension. This instrument was invented in 1881 by Samuel Siegfried Karl Ritter von Basch. However, in 1896 Scipione Riva-Rocci introduced a simplified version of the sphygmomanometer.
What are the Types of Sphygmomanometer?
Below are the three main types of sphygmomanometers:
Mercury Sphygmomanometer: It is the most traditional form of blood pressure devices and is considered the gold standard. It consists of manually inflatable cuffs attached to mercury-infused tubes. To obtain accurate readings, the instrument should be kept on a flat surface and in an upright position. There is a high probability of risk if the instrument is accidentally dropped. The advantage of this sphygmomanometer is that it can last a lifetime, is easy to use and does not need recalibration. It is banned in some countries due to its toxic content.
Aneroid Sphygmomanometer: Aneroid means “liquid free” and this instrument does not use mercury. It consists of a stethoscope attached to the cuff and also a stethoscope attached to a tubular comparator. The gauge head has a mechanical part to convert the cuff pressure to gauge pressure. The instrument needs to be recalibrated to avoid erroneous readings. There are other different types of aneroid sphygmomanometers depending on their use and they are:
- Pocket-aneroid sphygmomanometers.
- Palm aneroid sphygmomanometers.
- Clock style aneroid sphygmomanometers.
Automatic Digital sphygmomanometer: It is the most technologically advanced sphygmomanometer. It consists of an electronic sensor to measure blood pressure and the readings are displayed on a digital monitor. To measure blood pressure, the device measures the fluctuations of the arteries. These should be checked using a mercury sphygmomanometer to avoid erroneous readings.
Parts of Sphygmomanometer
Bladder: This is an inflatable bag used to compress the arm to occlude the artery. Bladders must have certain sizing parameters to ensure full arterial compression.
Cuff: This is designed to hold the bladder around the arm during measurement. For accurate measurement, the cuff must be properly designed for placement and position.
Manometer: It is a device used to measure air pressure in mmHg. The manometer used in an aneroid sphygmomanometer consists of a clock-like movement to measure the air pressure applied to the cuff. To widen the diaphragm, the gauge has a set of copper or beryllium, and there are gears to convert the linear motion of the diaphragm to get the readings in mmHg.
Valve: This is used as a lowering valve to control the cuff. This plays a vital role in obtaining an accurate measurement.
Bulb: This is used to pump air into the cuff.
SEE ALSO: Why Does Blood Have a Metallic Taste?
How to Use a Sphygmomanometer?
Here is the procedure to follow to use a sphygmomanometer:
The cuff bladder length used to measure blood pressure should be equal to 80% of the upper arm circumference.
Wrap the cuff around the upper arm so that the lower edge of the cuff is one inch above the antecubital fossa (the triangular area on the anterior aspect of the elbow). Gently press the bell of the stethoscope over the brachial artery below the rim of the cuff. Increase the air in the cuff to 180 mmHg at medium speed.
Watch for the first knocking sound by listening with the aid of a stethoscope and also observing the mercury meter. This should be done for both arms and pressure, with the subject’s position and cuff size recorded. If the pressure is greater, the blood pressure should be measured with a gap of several minutes between the two measurements. If blood pressure is above 180/120 mmHg, urgent action should be taken.