High blood pressure develops if: the walls of your larger arteries lose their elasticity and become rigid the small blood vessels become narrower Measuring blood pressure Blood pressure is measured with a monitor called a sphygmomanometer. This is a digital box attached to a tube with a cuff on the end. The cuff is placed around the upper arm and inflated to a certain level, then deflated slowly. A sensor in the cuff provides information about the blood pressure or a doctor or nurse will listen to the blood flow using a stethoscope. The result is expressed as two numbers, such as 120/80 mm HG ( one hundred and twenty over eighty millimetres of mercury ). The top figure - the systolic blood pressure - is a measure of the pressure when your heart muscle is contracting and pumping blood. This is the maximum pressure in your blood system. The bottom figure - the diastolic blood pressure - is the pressure between heart beats when the heart is resting and filling with blood. This is the minimum pressure in your blood system. In the UK, high blood pressure is defined as a consistently increased systolic blood pressure of 140 or over and/or a diastolic blood pressure of 85 or over. If your blood pressure is around this level, your doctor will probably want to monitor it regularly. If you suffer from diabetes, it is even more important that your blood pressure is lower than this - ideally less than 130/80. Types of high blood pressure Primary hypertension More than 9 in 10 people with high blood pressure have what s called primary or essential hypertension . This means that there s no single clear cause of it. Although the exact cause of high blood pressure isn t fully understood, it s known that some factors to do with your lifestyle can contribute. These include: smoking your family history obesity (being very overweight) drinking a lot of alcohol - especially if you binge drink a lack of exercise your diet Secondary hypertension Around 5 in 10 people with high blood pressure have secondary hypertension . This means your condition can be linked to a recognised cause - in fact, it may be a symptom of another underlying disease or factor such as: kidney disease endocrine disease narrowing of the aorta steroid medicines the contraceptive pill pregnancy, which can cause pre-eclampsia its not how it can go as there is a number of factors to consider as you know high blood pressure can cause other things to happen Complications People with high blood pressure have an increased risk of major illnesses including: cardiovascular disease such as angina, stroke, heart attack or atrial fibrillation kidney damage damaged sight