sphygmomanometer | Blood Pressure Instruments

How does a blood pressure gauge (sphygmomanometer) work? What exactly is blood pressure?

Your heart is an amazing pump. It works reliably for decades, and it safely pumps blood -- one of the trickiest liquids

around. In the same way, your blood vessels are pipes. They take the output from the pump and distribute it throughout the

body. A blood pressure gauge is simply a way to measure the performance of the pump and the pipes.
There are two numbers in a blood pressure reading: systolic and diastolic. For example, a typical reading might be 120/80.

When the doctor puts the cuff around your arm and pumps it up, what he/she is doing is cutting off the blood flow with the

pressure exerted by the cuff. As the pressure in the cuff is released, blood starts flowing again and the doctor can hear the

flow in the stethoscope. The number at which blood starts flowing (120) is the measure of the maximum output pressure of the

heart (systolic reading). The doctor continues releasing the pressure on the cuff and listens until there is no sound. That

number (80) indicates the pressure in the system when the heart is relaxed (diastolic reading).

If the numbers are too high, it means that the heart is having to work too hard because of restrictions in the pipes. Certain

hormones, like adrenaline (which is released when you are under stress) cause certain blood vessels to constrict, and this

raises your blood pressure -- if you are under constant stress, your blood pressure goes up, and it means that your heart has

to work too hard. Other things that can increase the blood pressure include deposits in the pipes and a loss of elasticity as

the blood vessels age.

High blood pressure can cause the heart to fail (from working too hard), or it can cause kidney failure (from too much

pressure).

restrict blood flow, and a mercury or mechanical manometer to measure the pressure. It is always used in conjunction with a

means to determine at what pressure blood flow is just starting, and at what pressure it is unimpeded. Manual

sphygmomanometers are used in conjunction with a stethoscope.

The word comes from the Greek sphygmós (pulse), plus the scientific term manometer (pressure meter). The device was invented

by Samuel Siegfried Karl Ritter von Basch. Scipione Riva-Rocci, an Italian physician, introduced a more easily used version

in 1896. Harvey Cushing discovered this device in 1901 and popularised it.

A sphygmomanometer usually consists of an inflatable cuff, a measuring unit (the mercury manometer), a tube to connect the

two, and (in models that don't inflate automatically) an inflation bulb also connected by a tube to the cuff. The inflation

bulb contains a one-way valve to prevent inadvertent leak of pressure while there is an adjustable screw valve for the

operator to allow the pressure in the system to drop in a controlled manner.

Contents [hide]
1 Operation
2 Significance
3 Types
4 Patents
5 References

[edit] Operation
The cuff is normally placed around the upper right arm, at roughly the same vertical height as the heart while the subject

seated with the arm supported. The cuff is inflated until the artery is completely occluded. Listening with a stethoscope to

the brachial artery at the elbow, the examiner slowly releases the pressure in the cuff. As the pressure in the cuffs falls,

a "whooshing" or pounding sound is heard (see Korotkoff sounds) when bloodflow first starts again in the artery. The pressure

at which this sound began is noted and recorded as the systolic blood pressure. The cuff pressure is further released until

the sound can no longer be heard and this is recorded as the diastolic blood pressure.

[edit] Significance
By observing the mercury in the column while releasing the air pressure with a control valve, one can read on the scale the

values of the blood pressure in mm Hg. The peak pressure in the arteries during the cardiac cycle is the systolic pressure,

and the lowest pressure (at the resting phase of the cardiac cycle) is the diastolic pressure. A stethoscope is used in the

auscultatory method. Systolic pressure ( first phase) is identified with the first of the continuous Korotkoff sounds.

Diastolic is identified at the moment the Korotkoff sounds disappear (fifth phase).

[edit] Types

Conventional (mechanical) sphygmomanometer with aneroid manometer and stethoscopeBlood pressure meters can be divided in

several types:

Digital non-portable with manual or automatic inflation. These are electronic, easy to operate and practical in noisy

environments. Many have not been validated for all patient groups, and can give very inaccurate readings).They measure mean

arterial pressure, MAP, and use algorithms to calculate systolic and diastolic values. In this sense, they do not actually

measure the blood pressure, but derive the readings. Digital oscillometric monitors are also confronted with “special

conditions” for which they are not designed to be used : arteriosclerosis, arrhythmia, preeclampsia, pulsus alternans, and

pulsus paradoxus.
Digital portable wrist blood pressure monitors with automatic inflation. These are more convenient for travel purposes.[1]
Digital portable finger blood pressure monitors with automatic inflation. Again these too are more portable and easy to

operate. They are noted as being the smallest blood pressure monitors around.[2][3]
Manual (older fashioned, though more precise). Must be operated by a trained person. Mercury manometers are considered to be

the "Gold Standard" of measurement because they do not go out of calibration. For this reason they are often required in

clinical trials of pharmaceuticals and for clinical evaluations of determining blood pressure for high risk patients

including pregnant women. Aneroid, mechanical, types are in common use, but should be checked against a mercury manometer if

they are suspected to be out of calibration.

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