Blood Pressure

 Measuring Blood Pressure

Sphygmomanometer

The pressure exerted by the blood on the walls of the auricles is called the blood pressure. It is measured by an instrument called sphygmomanometer when the heart contracts, the maximum pressure at which the blood is pumped from the heart to aorta is called systolic pressure.

Similarly, the minimum pressure at which the heart relaxes is called diastolic pressure. Thus, the value of diastolic pressure is always lower than the systolic pressure. The value of blood pressure is measured in 'mmHg'. The normal blood pressure of a person is systolic pressure: 120 mm Hg, diastolic pressure: 80mm Hg. Thus, it is written as 120/80. However, the blood pressure of a person varies from time to time and also varies with age.

When the blood pressure value is more than 150/90, it is called high blood pressure or hypertension. This may be due to an increase in the flow of blood. When the blood pressure value is less than 110/70, it is called low blood pressure or hypotension.

We shall now discuss how sphygmomanometer is used to measure blood pressure.

Measuring Blood Pressure using Sphygmomanometer

In order to measure blood pressure, we need to take two readings namely systolic pressure and diastolic pressure.

The systolic pressure can be measured when the heart is contracting and pumping out blood. Similarly, the diastolic pressure can be measured when the heart is relaxed to fill in with blood. The following steps are done to measure the blood pressure of a person using sphygmomanometer:

(a) The instrument has a flat rubber tube called rubber cuff, which is wrapped around the person's arm. Then, the rubber cuff is inflated by pumping air to give a pressure of 200mmHg to the artery, which can be noted on the scale of the instrument. If a stethoscope is placed on the artery of the arm, no sound will be heard through it.

Checking Blood Pressure

(b) Now, reduce the cuff pressure gradually by deflating the cuff and keeping stethoscope still on the artery. When you hear a 'soft tapping sound' through stethoscope, it gives us systolic pressure.

(c) When the cuff pressure is reduced further, the tapping sound through stethoscope 'disappears' and gives us the diastolic pressure.