Sphygmomanometer: Definition, Diagram, Parts, Working Principle, Types & Uses

A sphygmomanometer is a blood-pressure monitoring device. We have all noticed doctors check our pressure with an instrument, which is usually strapped above our elbow. This essential blood pressure monitoring device is called a sphygmomanometer. It is also known as a blood pressure metre or blood pressure cuff. The name sphygmomanometer is derived from the Greek word ‘sphygmo,’ which means the pulse or heartbeat. A manometer is a device that can measure tension or pressure. Samuel Siegfried Karl Ritter von Basch invented this machine in 1881. However, a simpler version of the sphygmomanometer was brought into existence by Scipione Riva-Rocci in 1896. 

A sphygmomanometer is a medical instrument used to measure blood pressure. It measures blood pressure on the basis of the force of the moving blood in the blood vessels. It is one of the simplest pieces of equipment used in the medical field with accuracy and precision. Besides blood pressure, it is also helpful for monitoring heart rate and its rhythm. It is also useful for hearing heart and breathing sounds. Thanks to modern innovation, there are different types of sphygmomanometers used across the world. Although their construction and working are different, the final output is the same thing i.e. measuring blood pressure.

In this article, we will explain what is a sphygmomanometer? How it works, its types, different parts, and its uses in this Physics article. 

What is Sphygmomanometer?

The word sphygmomanometer comes from the Greek word “sphygmos” which means the beating of the heart and ‘manometer’ which means the device to measure the pressure using dimensional analysis. It was invented by Samuel Siegfried Karl Ritter von Basch in 1881. It is the most basic of instruments used by doctors and is used generally every time a person goes for a diagnosis. It consists of an inflatable cuff made of rubber which is attached to a scale of mercury with graduations on it. The systolic and diastolic pressure is measured by the gradual increase and release of the pressure inside the rubber cuff.

Types of Sphygmomanometer

There are three different types of sphygmomanometer, which are as follows: 

• Mercury Sphygmomanometer
• Aneroid Sphygmomanometer
• Automatic Digital Sphygmomanometer

Mercury Sphygmomanometer

It is the most used type of sphygmomanometer. It consists of a graded tube containing mercury which measures the pressure applied by the bladder of the inflatable rubber cuff on the upper arm. For correct measurements, the instrument is kept on a flat surface. The advantage of this type is that it can last for a long time, but due to the presence of mercury which is a toxic metal it is banned in some countries.

Aneroid Sphygmomanometer

It does not use any type of fluid for measuring pressure. In this type, the stethoscope is directly attached to the cuff, which is further attached to a gauge with a dial. The gauge shows the pressure inside the cuff.

Automatic Digital Sphygmomanometer

It measures blood pressure electronically based on the fluctuations of the arteries. The cuff is directly connected to the device, and it inflates and deflates with just a press of a button. It has a digital display to display the value of blood pressure. Due to these types being without any fluid, they can be transported from one place to another more easily.

Parts of Sphygmomanometer 

The sphygmomanometer consists of three different parts. The parts are as follows :

• An inflatable rubber cuff or band is tied around the upper arm, generally. But it can be tied around other parts too, in case of emergencies or for specific uses.
• The inflatable rubber cuff consists of a bladder to store the air pumped into it. It is the part which gets inflated and applies pressure to the upper arm.
• The bladder is connected with a rubber bulb which can be squeezed to pump air into the bladder.
• The bulb has a valve just above it, which is used for controlled deflation of the bladder.

Working Principle of Sphygmomanometer 

The main principle behind the working of a sphygmomanometer is that the pressure in the bladder is equal to the pressure of the artery under the cuff. Blood pressure is usually measured in the brachial artery because that artery is a major blood vessel in the upper arm. The cuff is wrapped around the patient’s arm and inflated until the brachial artery is compressed, and blood flow is stopped. After that, the pressure is slowly released and the rushing blood produces a vibration around the vessel tissue, which is heard using a stethoscope. When the pressure lowers more, then no sound is heard as the artery no longer constricts.

All of these involve two pressures
1. Systolic pressure: Pressure recorded when left ventricle contracts.
2. Diastolic pressure: Pressure recorded when left ventricle relaxes.

The values of systolic and diastolic pressures are monitored to know the blood pressure. The blood pressure is noted as systolic over diastolic, such as 120/80.

How to Use Sphygmomanometer?

The steps to be followed are as follows :

• The upper arm is tied with the inflatable cuff, keeping in mind that the cuff covers at least 80% area of the upper arm and its lower edge is above the antecubital fossa or the elbow pit or the elbow bend.
• Air is pumped into the bladder of the cuff to a pressure above the systolic and diastolic pressure.
• The stethoscope is then kept above the brachial artery on the arm.
• The air is gradually released, and thus the pressure applied by the cuff also reduces. It is released till the pressure drops to 180mm of Hg.
• The stethoscope is used to listen to the first knocking sound while depressurising the cuff. The pressure is also monitored when the sound is heard. This pressure is the systolic pressure.
• The pressure inside the cuff is then further dropped by releasing the air until no sound is heard by the stethoscope. The pressure where no sound of blood flow is heard is recorded as the diastolic pressure.

Sphygmomanometer Uses

Sphygmomanometer has a variety of applications which are :

• To measure the blood pressure of organisms.
• To find out any abnormality in the blood pressure, which can tell about any diseases.
• To monitor the efficacy of drugs which alter the blood pressure of organisms.
• As a first aid in ambulances, depending on the blood pressure, different techniques to help the aggrieved patient can be used.

Download free PDF Of Sphygmomanometer Sample Questions Here! 

Hope this article about the sphygmomanometer makes it easier to understand it than to pronounce it. There are many such Physics topics that you can learn about, just download the Testbook app and start browsing.