How is the “normal” range of any medical measurement established? The usual starting point is to measure lots of people to get a bell curve, then decide arbitrarily on a cut-off. Usually this is the lowest and highest 2.5% or 5%, sometimes other values are used (e.g. in pediatric development just the lowest 25% and 10%).
High blood pressure guidelines are put out by Consensus Committees working with national Heart & Stroke Associations. Several studies have shown a strong benefit to reducing blood pressure below 140/90, lower in diabetics, pregnant women and some other people.
But these aren’t etched in stone and as KarlGauss says will likely come down further. The top number, when the heart is pumping (systolic pressure) is now thought to be less important than the diastolic pressure (lower number) when the heart is relaxed and refilling with blood.
In reality, both are important. Your doctor would not be concerned by one high blood pressure measurement in the absence of symptoms like headache. Ideally, you would not be started on blood pressure medications unless it was persistently elevated over months… though this can be a problem in some people who just have high blood pressure due to the anxiety of getting it measured but are otherwise “normal”.
Everybody’s blood pressure changes throughout the day. A more accurate measurement of hypertension might incorporate the mean arterial pressure (which incorporates both numbers) or changes in blood pressure over time for that person.
The length of the tube is not proportional to the pressure it can handle. Tall people cannot withstand much higher pressures to my knowledge. Arteries are very elastic and very different from rigid pipes which offer quite a limited analogy. In general, the problems from high blood pressure are not just arterial rupture (some strokes) but also eye damage, kidney damage, heart damage and headaches.
The importance of salt is controversial. Where there is salt, there is water, so physiologically salt restriction makes sense. In practice though, most people with working kidneys seem to be able to compensate for this. I believe it depends on the person and recommend salt restriction only in some people, since unsalted diets taste gross.
Caffeine and alcohol likely raise blood pressure.
Dr_Pap, B.Eng, M.D.