Here's the lowdown as far as I know on Blood Pressure 101
Blood pressure is the force of the blood pushing against the walls of the arteries. Each time the heart beats, it pumps out blood into the arteries. Your blood pressure is at its highest when the heart beats, pumping the blood. This is called systolic
pressure. When the heart is at rest, between beats, your blood pressure falls. This is the diastolic
Blood pressure is always given as these two numbers, the systolic and diastolic pressures. Both are important. Usually they are written one above or before the other, such as 120/80 mmHg. The top number is the systolic and the bottom the diastolic. When the two measurements are written down, the systolic pressure is the first or top number, and the diastolic pressure is the second or bottom number (e.g., 120/80).
A blood pressure reading below 120/80 is considered normal. In general, lower is better. However, VERY low blood pressures can sometimes be a cause for concern and should be checked out by a doctor.
With high blood pressure, the arteries take a beating, and over time, one is at risk of heart disease and stroke.
Doctors classify blood pressures under 140/90 as either "normal," or "prehypertension."
"Normal" blood pressures are lower than 120/80.
"Prehypertension" is blood pressure between 120 and 139 for the top number, or between 80 and 89 for the bottom number.
FOR EXAMPLE: blood pressure readings of 138/82, 128/89, or 130/86 are all in the "prehypertension"
range. If your blood pressure is in the prehypertension range, it doesn't mean you have high BP
but it is more likely that you will end up with high blood pressure unless you take action to prevent it, like doing regular exercise, eating a good, balanced low-fat diet, reduce sodium intake to no more than 2400mg a day (read labels and don't add table salt to your food if you can help it), alcohol and caffeine in moderation and lose weight if overweight.
Hope some of this helped.