By Dr Ananya Mandal, MD
Hypertension or high blood pressure is often diagnosed by chance during a general health check up or when visiting the doctor about an unrelated condition. This is because the condition does not usually present with symptoms, at least not during the initial stages. Typically, symptoms may present in the case of a very high blood pressure that has reached a level of around 180/110 mm Hg or higher.
Measuring blood pressure
Blood pressure is the pressure exerted against the walls of blood vessels as the heart pumps blood through them. An increased blood pressure means excess strain is placed on the artery walls and this can lead to complications such as a stroke, kidney damage or heart attack.
Blood pressure is measured in millimetres of mercury (mm Hg) using an instrument called a sphygmomanometer, which is available in the form of a traditional device with a mercury column or a modern digital version.
There are two numerical figures of blood pressure - the systolic pressure and the diastolic pressure. The systolic pressure is the higher number that indicates the pressure of the blood when the heart beats. The diastolic pressure is the lower number and indicates the pressure of the blood when the heart rests between two beats. A healthy blood pressure reading is around 120/80 mm Hg. A reading above 140/90 mm Hg is considered high.
The sphygmomanometer has an inflatable cuff that is wrapped around the upper arm and inflated with air. A dial shows when the desired pressure in the cuff is achieved. Once this pressure is higher than the pressure in the artery, the blood flow in the main artery of the upper arm is cut off, which is indicated by the absence of a pulse in the wrist. The air is then slowly released from the cuff using a valve and as the pressure in the cuff falls, the blood rushing through the artery can be heard using a stethoscope.
The dial or the calibrated mercury column shows the pressure when the sound is first heard, as the cuff is released. This is the systolic pressure. The pressure when the last sound is heard, as blood flow is uninterrupted, is the diastolic blood pressure. Digital automatic blood pressure monitors can bypass this process and provide a direct result. However, these are not always accurate.
People with a family history of blood pressure should have their blood pressure checked every two years. More frequent checks are needed in those with a family history of stroke or heart attack due to high blood pressure.
Reviewed by Sally Robertson, BSc
Last Updated: Jan 14, 2014