A Sphygmomanometer is an instrument that measures arterial blood pressure. The first sphygmomanometer was invented by Samuel Siegfried Karl Ritter von Basch in 1881. It consisted of a rubber bulb filled with water to restrict blood flow in the artery. The bulb was connected to a mercury column, which would record the pressure. Newer versions of this device were introduced by Scipione Riva-Rocci and Harvey Cushing. The first fully automated oscillometric blood pressure cuff was invented by Donald Nunn.
Today there are roughly two kinds of blood pressure instruments – manual and digital. The manual type is considered more accurate and is usually operated by trained professionals.
It consists of an inflatable rubber cuff, which is connected to an air bladder and an apparatus that records pressure. The pressure is measured with reference to a mercury pressure gauge.
The examiner wraps the inflatable cuff on the arm of the patient. A stethoscope is simultaneously placed on the arm of the patient to listen to the brachial artery (which is the major blood vessel in the upper arm).
The air bladder is pumped to inflate the rubber cuff on the patient’s arm. The cuff is inflated till the artery is completely occluded (blocked). Now the pressure is released slowly at the rate of 2-3 mm per heartbeat. As the pressure is released, a ‘whooshing’ sound is heard as the blood starts flowing back again into the artery. The corresponding pressure is recorded and this is called the ‘systolic’ blood pressure.
The cuff pressure is slowly released till the sound is heard no more. The corresponding pressure is recorded and this is known as the ‘diastolic’ blood pressure. These sounds are known as Korotkov sounds. They are named after Nikolai Korotkov, a Russian physician who discovered them in 1905.
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