Definition of high blood pressure and its significance?

Answer 1

Definition of high blood pressure (aka hypertension) goes like this (Taken from Harrison's Principles of Internal Medicine, 17th Edition, Chapter 241):

Blood Pressure Classification Systolic, mmHg Diastolic, mmHg

Normal <120 and <80

Prehypertension 120-139 or 80-89

Stage 1 hypertension 140-159 or 90-99

Stage 2 hypertension >160 or >100

Isolated systolic hypertension >140 and <90

(From now on, it's not from Harrison's)

For a more specific definition from a statistical view, hypertension means being above the 95th percentile (roughly 2 standard deviations greater than the mean) of the normal blood pressure distribution for your age, sex and race. This is a sentence that sounds quite complicated, but it simply translates into the table written above :) Prehypertension means between 90th and 95th percentiles and is not a risk for diseases but is a warning sign. It can be managed by lifestyle changes.

As for the second part of the question:

As blood pressure (from now on I'll simply abbreviate it as BP) increases so does the risk for some medical conditions, some of them life threatening :

-Stroke (aka cerebrovascular accident or CVA): As a general principle, high BP can cause bleeding in any part of the body, but none of the organs are as vulnerable to bleeding as the brain is. Since the brain is located in a solid box (the skull), the increase in volume created by the bleeding has to be compensated by squeezing the brain itself, either creating compression (and compressing small blood vessels, causing other parts of the brain to be harmed or die) or resulting in parts of brain herniating through some possible paths in the skull.

-Heart attack (aka myocardial ischemia or MI): As BP increases it gets harder for your heart to pump blood (just imagine trying to simply open a door and trying to open a door that has 10 people behind it; which one would make you more tired?). The increase in difficulty means more energy requirement for your heart and this makes for an easier heart attack.

-Kidney disease: Prolonged high BP is a risk factor for end stage renal disease (meaning kidney transplant/dialysis or death)

-Blood vessels: The risk for atherosclerosis increases. The important thing here is that atherosclerosis is, by itself, a risk factor for stroke and heart attack so hypertension increases the risk for those conditions both directly and indirectly via atherosclerosis.

In order to avoid these complications, strict control of BP is required. At lower BP, this can be managed chiefly by lifestyle changes (eg, cease smoking, lose weight, be careful with what you eat, do some exercise...) but as the BP and the duration of hypertension increases, one would need medication for a better control. Unless one has very high BP or hypertension resistant to medical treatment (refractory hypertension), lifestyle changes and medical treatment is usually enough for a normal life (that is, life without too much increase in risk for the complications I mentioned above), at least until you are well into the elderly ages.

I'm sorry if it sounds too complicated, English is not my native language so sometimes I can't tell things in a simple way. I used some medical terms and abbreviations in purpose, so that you can make a better, more refined search on Google if you wish to.