Your blood needs to travel quite some distance from the heart to various parts of the body and back again. In order for this to happen, a certain level of pressure has to be maintained in your blood vessels. This is known as blood pressure.
The blood pressure in your arteries – your arterial blood pressure – fluctuates within each heartbeat. So, the more you move the more your blood pressure will fluctuate. When we have our blood pressure measured, it is the highest and lowest pressures that are recorded – the systolic blood pressure and the diastolic blood pressure, respectively.
When a doctor takes your blood pressure, it is recorded as one number over another. The first number is your systolic pressure, and the second number is your diastolic pressure. So, if your blood pressure is 120/80, this means your systolic pressure is 120 and your diastolic pressure in 80.
Your blood pressure is determined by two things:
- the amount of blood being pumped by your heart
- the diameter of your arteries
Imagine you’re trying to blow through a drinking straw. If the diameter of the straw is large, it’s relatively easy to blow quite hard. But if you try to blow through a very thin straw, the pressure is enormously high, and you go red in the face very quickly! The same is true for your circulation. When your arteries are dilated, your blood pressure is relatively low, but when your arteries are constricted, your blood pressure will be higher.
Because blood pressure is partly related to the amount of blood pumped by the heart, your blood pressure will go up when you exercise, because your heart is working harder. Some of the world’s fittest athletes can sustain incredibly high blood pressures when they’re working flat out. But when you’re not exercising, your blood pressure is determined mainly by the diameter of your arteries.
What is high blood pressure?
As a general guide:
- ideal blood pressure is considered to be between 90/60mmHg and 120/80mmHg
- high blood pressure is considered to be 140/90mmHg or higher
- low blood pressure is considered to be 90/60mmHg or lower