There are many different devices available for measuring blood pressure but the most common is the one you’ll normally find at your doctor’s surgery – called a sphygnomanometer.
This has a cuff which you place around your arm and as pressure in the cuff is increased a column of mercury in the measurement part of the device rises. The doctor or nurse pumps up the cuff so it is tight around you arm, then listens to your pulse using a stethoscope over the brachial artery in your arm and reads the level of the mercury at the point when your heart contracts to push blood through your body and the point where it relaxes. These correspond to the two readings you get when you have your blood pressure measured in your arm.
This is the highest pressure which is registered as your heart contracts and pushes blood into your arteries.
When your heart relaxes and fills with blood, the pressure in your arteries then falls and this is known as the diastolic pressure.
Your blood pressure is always given as a systolic and diastolic pressure number, and both are an important measurement. They are always written one above or before the other number, such as 120/80 (which is a classic measurement), and always expressed in units of millimeters of mercury (mmHg).
The systolic pressure is the first or top number, and the diastolic pressure is the second or bottom number (for example, 130/90), so if your blood pressure is 120/80, it is a reading of “120 over 80″.
What is a healthy blood pressure reading?
There are no hard and fast figures which represent a normal blood pressure. And very often doctors and other experts cannot even decide between them what an ideal blood pressure range is for an adult.
However it is usually agreed that somewhere between 120/80 and 140/85 is considered to be an average normal blood pressure for a grown person, though someone with naturally low blood pressure may be closer to a range of 100/60
A blood pressure of 140/90 is considered to be high, though as you get older, this falls into the more normal range.
How often should blood pressure be measured?
As often as your doctor advises. Having you blood pressure taken is a non-invasive procedure so it does no harm to take it regularly. Up to 35, if no other health problems (for example, obesity, diabetes or kidney problems) are present your doctor might only suggest taking your blood pressure every 5 years or so. Over 35, blood pressure should be taken every 2 to 5 years in a healthy individual. However women taking the contraceptive pill or HRT should be measured every 6 months and blood pressure should be taken at every antenatal visit in pregnancy.