Normal blood pressure

Blood pressure classification

Normal and high BP readings
Current classifications are:

  • Normal blood pressure is a reading under 120/80
  • Pre-hypertension is a reading between this and 140/90
  • High blood pressure is anything over this.

(If you don't understand what these figures mean, take a look at the blood pressure readings page).

If a person has high blood pressure, both readings are usually above normal. Sometimes only the higher of the two (systolic) is raised and this is referred to as isolated systolic hypertension.

How is 'normal' determined?

Deciding upon specific levels as 'normal' for physiological measurements is somewhat artificial. Nevertheless, it has to be done.

For many years scientists couldn't decide where exactly to draw the line especially as a lot depends upon it. If the definition of normal blood pressure was set too low, too many people would end up on treatment, set it too high and people would suffer from complications.

This is why the concept of pre-hypertension has been introduced. The level of 140/90 defines hypertension, but it has become clear from research that people with levels over say 135/85 have an increased risk of complications (although slight) compared to those with 120/80 and that people lucky enough to be lower than that do better still.

The message then is that normal is relative. There are many people living happily with blood pressures significantly lower than 120/80.

It's normal to get high blood pressure every day

Blood pressure varies widely during the average day. It changes in response to emotion, stress, anxiety, changes of position and of course physical exercise - your systolic blood pressure (that's the higher reading, remember) can reach 200 mmHg or more during vigorous exercise. This is the response to the need for extra blood to flow to the hard working muscles. Your body is designed to cope with these high pressures; but only for relatively short periods.

The damaging effects of high blood pressure occur when it is sustained over a long period. It is not sensed when normal blood pressure becomes permanently higher than it should be, and unless people have medical checks, it may remain undetected for a while. This is why hypertension is often called the silent killer.

Some people get what is called 'white coat hypertension'. For some reason, whenever their blood pressure is measured at the doctor's office or clinic it is high, no matter how relaxed they are. When measured at home however, it is normal. (To learn more about white coat hypertension click here).

There is an unusual condition which is the exact reverse, this is called masked hypertension. Blood pressure is normal in the doctor's office but rises more than it should at other times.

Also unusual is exercise hypertension in which the rise in blood pressure is much greater than the normal expected response to the exertion. When measured at rest, pressures are normal in these individuals.

Fight or flight

Dilated pupil

We've all been in frightening situations at times in our lives and know that cold-sweat, heart thumping feeling. At such times your body also makes changes that you may not notice, for example, your blood pressure goes up, your pupils dilate and more blood is diverted to your muscles.

This is the body preparing for action - just in case. It's a good illustration of the varied means by which blood pressure is controlled. You haven't had to fight, or run, but the mere thought that you might have to duck a fist or climb a nearby tree in a hurry is enough to give you a burst of hypertension as your heart gears up for action.

In this example it is adrenaline (epinephrine) is the main hormone involved and there are many similar chemicals that our body produces that you will encounter as you learn more about taking control of your blood pressure.

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This page was last modified on : May 11, 2011.

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