Blood pressure is usually measured in millimetres of mercury (mmHg) and recorded as two numbers - systolic pressure - the top number - (as the heart beats) "over" diastolic pressure - the bottom number - (as the heart relaxes between beats) - for example, 130/80 mmHg or '130 over 80'. The top number (systolic) can be anywhere from 90 to 240 and the bottom number (diastolic) can be anywhere from 60 to 140. The pressure does not fall to zero when the heart relaxes because of the elasticity of the arterial walls which means there is always some pressure present. The Systolic Pressure is the force of blood in the arteries as the heart beats, and represents the maximum pressure exerted when the heart contracts. In other words if you were taking a weightlifting analogy this is like the pressure when you are exerting full-out to lift the weight. The Diastolic Pressure shows the lowest pressure in the blood vessels between heartbeats, when the heart is at rest. Looking to our weightlifting analogy this is when you have done all the hard-graft and are returning the bar back from whence it came. So, in other words, the top reading in a blood pressure test shows the pressure when your heart is working hard to push out the blood, and the bottom reading shows when it is relaxed.

Both are important and tend to correlate very closely anyway, but it is now generally thought that the systolic reading is the more important. One reason is because systolic hypertension is the most prevalent risk factor in heart failure, stroke and kidney failure and is also the most common type of hypertension, with 2/3rds of high blood pressure sufferers having elevated systolic rather then diastolic readings. Also, systolic readings gradually rise as you get older, but diastolic readings rise until age 55, and then actually decline. So that in older persons, diastolic blood pressure is inversely related to cardiovascular risk. Thus, an older individual (applies to those aged over 60 in the study where this is stated) whose blood pressure is 160/70 is at a greater risk than an individual whose blood pressure is 160/100 mmHg. If you are aged over 55 it is probably worth getting your blood pressure tested (at least initially) by a Doctor just to avoid any confusion about what your results mean. It used to be thought to be the case that diastolic readings were more important than systolic. And in younger adults both diastolic and systolic readings correlate very closely. However, a much quoted study in May 2000 (read it here) for example now recommends that for middle aged and elderly adults, systolic readings are a more accurate measure of hypertension.

Ok. Third step. So you now have your reading. What exactly represents 'High' Blood Pressure?

The following are useful guidelines when considering blood pressure in adults. This chart is a slightly simplified version of one issued by the US Department of Health.