Sphygmomanometer (BP Apparatus): Parts, Names, Types and Uses

The instrument used to measure blood pressure is called a sphygmomanometer, also known as a BP apparatus, BP machine or blood pressure monitor. A manual sphygmomanometer has five main parts: an inflatable cuff, a rubber bladder inside the cuff, an inflation bulb, an air-release valve and a manometer (pressure gauge), connected by rubber tubing. A stethoscope is used alongside manual models to listen for blood flow.

What Is a Sphygmomanometer?

A sphygmomanometer is a medical device that measures arterial blood pressure without entering the body. It records two values in millimetres of mercury (mmHg): systolic pressure, when the heart contracts, and diastolic pressure, when the heart relaxes between beats. The name comes from the Greek "sphygmos" (pulse) and "manometer" (pressure meter).

What Is the BP Instrument Called?

The BP instrument is called a sphygmomanometer. In everyday use, people also call it a BP apparatus, BP machine, BP monitor, blood pressure machine or, informally, a BP operator. In Hindi it is called a raktchap mapak yantra (रक्तचाप मापक यंत्र). Manual models are used together with a stethoscope; digital models measure automatically.

Parts of a Sphygmomanometer and Their Functions

These are the parts usually listed as the 5 parts of a sphygmomanometer: cuff, bladder, inflation bulb, air-release valve and manometer, joined by rubber tubing.

Parts of an Aneroid Sphygmomanometer

An aneroid sphygmomanometer has a cuff with bladder, an inflation bulb with air-release valve, rubber tubing and a round dial gauge with a needle that moves as pressure changes. It contains no mercury. Some models, such as this aneroid BP apparatus with a large dial and stethoscope, are sold as a set with a stethoscope.

Parts of a Mercury Sphygmomanometer

A mercury sphygmomanometer has the same cuff, bladder, bulb, valve and tubing, plus a mercury reservoir and a glass column marked in mmHg. Air pressure in the cuff pushes the mercury up the column, and the reading is taken from the top of the column. Mercury is used because it is very dense, so a short column can show a wide pressure range, and its reading does not drift over time. Because mercury is toxic, many facilities now use mercury-free alternatives.

Parts of a Digital BP Machine

A digital BP machine has a cuff with bladder, an air tube, and a main unit containing an electric pump, a pressure sensor, a release valve, a microprocessor and a digital display, powered by batteries or an adapter. It inflates and deflates the cuff automatically and shows systolic pressure, diastolic pressure and pulse rate on the screen.

Types of Sphygmomanometers

To compare models and prices, see Medikabazaar's range of sphygmomanometers (BP machines).

What Is a Sphygmomanometer Used to Measure?

A sphygmomanometer is used to measure blood pressure: the systolic and diastolic pressure of blood in the arteries, in mmHg. Digital models also measure pulse rate. Common uses include:

1. Screening for and diagnosing high and low blood pressure
2. Monitoring patients with hypertension and checking how well treatment works
3. Routine check-ups in clinics, hospitals and pharmacies
4. Monitoring before, during and after surgery and anaesthesia
5. Antenatal check-ups, to detect high blood pressure in pregnancy
6. Emergency, ambulance and intensive care monitoring
7. Home blood pressure monitoring
8. Health camps and workplace screening
9. Teaching clinical examination skills to medical and nursing students
10. Inflating a cuff to a set pressure for some clinical tests

Principle of a Sphygmomanometer

A manual sphygmomanometer works on the principle that blood flow through a compressed artery produces sounds that can be heard with a stethoscope. The cuff is inflated until it stops blood flow in the brachial artery, then slowly deflated. The pressure at which the first tapping sound (the first Korotkoff sound) is heard is the systolic pressure; the pressure at which the sounds disappear is the diastolic pressure. Digital machines use the oscillometric method instead, detecting small pressure oscillations in the cuff and calculating the readings electronically.

How to Measure Blood Pressure with a Sphygmomanometer

1. Sit quietly for about 5 minutes, with your back supported, feet flat on the floor and arm resting at heart level.
2. Wrap the cuff snugly around the bare upper arm, with its lower edge about 2 to 3 cm above the elbow crease and the artery marker over the brachial artery.
3. For a manual reading, place the stethoscope chest piece over the brachial artery at the inner elbow.
4. Close the valve and squeeze the bulb to inflate the cuff to about 20 to 30 mmHg above the point where the pulse disappears.
5. Open the valve slightly to release air at about 2 to 3 mmHg per second.
6. Note the reading at the first tapping sound (systolic) and when the sounds disappear (diastolic). On a digital machine, simply press start and read the display.
7. Release all the air and remove the cuff. For an accurate result, take two readings a minute or two apart.

Who Invented the Sphygmomanometer?

The first sphygmomanometer was invented by Samuel Siegfried Karl von Basch in 1881. In 1896, Scipione Riva-Rocci introduced the easy-to-use mercury sphygmomanometer with an arm cuff, which Harvey Cushing later helped popularise. In 1905, Nikolai Korotkov described the sounds heard through a stethoscope during cuff deflation, the basis of the manual method still used today.

Care and Calibration

1. Check that an aneroid needle rests at zero before use, and have the gauge checked against a reference at regular intervals.
2. Inspect the cuff, bladder, bulb and tubing for leaks or cracks, and replace worn parts.
3. Wipe the cuff with a suitable disinfectant between patients.
4. Store the device away from heat, and avoid kinking the tubing.