3.3 - Blood Pressure

Meaning, Instrument and Unit

• Blood pressure is the pressure exerted by blood on the walls of blood vessels during blood circulation.
• It is measured using a sphygmomanometer.
• The unit is millimetres of mercury (mmHg).
• The instrument used by medical practitioners in hospitals and clinics, together with a stethoscope, provides a reading based on an accurate standard.
• A digital sphygmomanometer can be used to monitor blood pressure at home.

Measuring and Recording Blood Pressure

• A digital sphygmomanometer measures blood pressure with its cuff fitted around the upper arm.
• A blood-pressure measurement contains two readings.
• The upper number is the systolic pressure: pressure on the blood-vessel walls when the heart muscle contracts.
• The lower number is the diastolic pressure: pressure on the blood-vessel walls when the heart muscle rests between heartbeats.
• Record blood pressure as systolic/diastolic, read as “systolic over diastolic”.
• Normal blood pressure is 120/80 mmHg.

• The two pressures are stated in mmHg because mercury was used in the first accurate pressure gauge and remains the standard medical pressure unit.

Interpreting Blood-Pressure Readings

Adult blood-pressure category	Systolic / diastolic (mmHg)
Optimal	Below 120 / below 80
Normal	120–129 / 80–84
At risk	130–139 / 85–89
High blood pressure stage 1	140–159 / 90–99
High blood pressure stage 2	160–179 / 100–109
High blood pressure stage 3	180 and above / 110 and above

• Regular measurement helps assess body health.
• A high and prolonged reading indicates high blood pressure or hypertension.
• A low and prolonged reading may indicate low blood pressure.
• High blood pressure usually has no clear signs.
• Uncontrolled high blood pressure can cause a more serious problem such as stroke.
• Regular medical examinations are the best way to detect the problem.