BP Basics

How To Measure Blood Pressure?

Blood pressure is measured in the form of two numbers, namely, the systolic blood pressure and the diastolic blood pressure. It is written as 120/80, where 120 is the systolic pressure and 80 is the diastolic pressure.

Systolic pressure is the pressure of the blood when the heart beats. This is the highest pressure exerted by the blood. On the other hand, diastolic pressure is the pressure of the blood when the heart rests between beats. This is the lowest pressure exerted by the blood.

You can measure your blood pressure in two different manners. That is, using the cuff or by measuring it digitally.

The cuff is the most common way of measuring blood pressure. It is wrapped around your upper arm and a tube connects the cuff to a reservoir of mercury at the bottom of a vertical glass tube. There is a rubber bulb, which is used to blow air into the cuff. Thus pressure generated in the cuff moves the mercury in the column. The mercury goes up with a heart beat and comes down, when the heart is resting between the beats.

Digitally, there are two ways of measuring blood pressure. These are:

1) The Auscultatory method
2) The Oscillometric method

Auscultatory method
In the auscultatory method, a stethoscope and a sphygmomanometer are used. In this method, an inflatable cuff is placed around the upper arm, at roughly the same vertical height as the heart. This cuff is attached to mercury. The cuff is inflated manually by squeezing a rubber bulb repeatedly until the artery is completely occluded.

The pressure in the cuff is slowly reduced. When the blood starts flowing again, a whooshing or pounding sound is heard. The pressure at this point is called systolic pressure. Then the pressure in the cuff is further reduced, till no sound is heard. The pressure at this point is called diastolic blood pressure.

Both these pressures are recorded to find out the accurate blood pressure.

Oscillometric method
Oscillometric method is similar to the auscultatory method functionally. It is used in long-term measurement as well as in clinical practice.

The cuff in this type of manometer comes with an electronic pressure sensor fitted in the cuff to detect the blood flow. In this method, the mercury manometer is fitted on the wrist, elevated to the height of the heart, though the upper arm is always preferred. The cuff is inflated and released by an electrically operated pump, which then gives out a numerical readout of the blood pressure.

Oscillometric measurement does not require much skills and is easy to use by even non-trained staff and by the patient themselves.