Blood pressure is the pressure of blood against the wall of the artery, traditionally measured at the upper arm, and computed in millimetres of mercury (mmHg), although more often than not an aneroid gauge is used. The prescribed “normal” meaning average for a healthy adult is recorded as 120/80, by which is meant when the wave of pressure due to left ventricle contraction is at it s maximum, the pressure on the arterial wall is 120 mms Hg, and between waves the pressure falls to 80 mms Hg.
The maximum is known as systole the minimum as diastole derived from the Greek meaning for systole drawing together or contracting, and diastole the reverse of that. Systole is more labile than diastole, more likely to rise in excitement, and to some persons a raised diastole is of more significance. Hypertension is a defined term, it means a persistently raised blood pressure above an arbitrarily set desired level, and typically the upper acceptable level is 140/90, although some experts set it even lower.
It is very common for persons to mistake the tension part of the word, and suppose because they are emotionally tense, that is what is meant. Emotionally tense might cause a rise in blood pressure, but that is not in any sense at all what is meant by hypertension.
A higher than normal blood pressure indicates a higher than normal resistance to the flow of blood through the arteries. The heart is a muscle, it has to contract 70 or so times a minute to drive the blood round the body. If the resistance to flow is increased, then the heart has to contract harder. There comes a point after years of trying and getting thicker (just like the biceps would) it has decided it can do no more and quits, usually slowly, sometimes suddenly – hypertension is known as the “silent killer” because many persons die from a condition they never knew they suffered.
There is substantial variation around the world, figures are never contemporary, but it has been recently reported that the incidence of hypertension in males in India is 3% compared with 69% in Poland; the USA falls between, at 30%. All regions show the rate for women is a few percentage points higher than for men. In the USA Afro Americans and Native Americans are as a group more prone to hypertension than are those of Mexican or Caucasian descent. The market for medication in this group is phenomenal, approximately a third of US adults are on anti-hypertensive medication.
The numbers are bizarre. Although hypertension is among the commonest causes of visits to a doctor, only a third of hypertensive patients have their blood pressure under control, and the cost of hypertension to the US economy approaches 50 billion dollars.
There are different causes for the raising of blood pressure. Primary hypertension (also known as essential hypertension) comprises 90% of the cases, and is less obviously vascular in origin than was once thought.
Secondary hypertension by definition is hypertension due to some other identified cause and comprises the other 10%. Some are endocrine in origin, adrenal, renal, thyroid, some are associated with the pre-eclampsia of pregnancy, some with structural abnormalities such as coarctation of the aorta, and some with illicit drug use such as cocaine or methamphetamine.
Too often when a reason is obvious, the conclusion turns out to be fallacious. It was at one time supposed that hypertension was due to peripheral vascular disease which made it harder for the heart to do its job. To an extent that is true, but it is far from the whole picture.
There is a genetic component, reflected in the international disparity. There are environmental components such as diet and stress which act on a susceptible individual who bears the “genetic stamp” of a potential hypertensive. It is thought by many that there must be several factors involved (mosaic theory), including the sympathetic nervous system, and the hormones released by the kidneys, as well as genetic inheritance, diet and exercise. And then there is a reverse of these theories, postulating that the problem is not, or not only due to vasoconstriction, but may be due in part to the absence of normal vasodilatation factors.
Whether hypertension can always be prevented is arguable, but certainly an attempt can be made by keeping body weight to a reasonable minimum, by caution in dietary intake of sodium and lipids, not taking illicit drugs, not smoking, and by developing a routine of exercise. Those genetically disposed, those with a family history of hypertension, should in particular observe these precautions.
Regular blood pressure measurements may not prevent the onset of hypertension but might be considered preventive of complications if an early diagnosis is made and treatment started before irreversible complications are caused.
All the measures outlined for prevention should be followed. The objective in treatment is to restore blood pressure to beneath the diagnostic level of 140/90 mms Hg., or ideally to attain the normal level of 10/80.
The standard initial medication ordered is a thiazide diuretic, there are numerous combinations of drugs that can be employed with little to choose between them, the physician consulted will have his own favourites and it is better he use a regime with which he has gained experience than follow some other person’s directions.
Any part of the body that needs a blood supply, which means almost every part of the body, may be affected by hypertension, in particular it is a leading cause of strokes, of blindness, of heart attacks, of heart failure and of kidney failure.