Blood pressure is the pressure inside your vascular system (heart and arteries) and is a function of the volume of blood being pumped around the blood vessels by the heart and the tone (level of constriction or dilation) in the small peripheral arteries. Blood pressure will go up if the heart pumps harder or the small arteries constrict, and will drop if the heart pumps less or the small arteries dilate. The body has very sophisticated mechanisms for ensuring that blood pressure sufficient to perfuse the vital organs (brain, kidneys etc) is maintained at all times.
Blood pressure is measured (indirectly) by a device called a sphygmomanometer A cuff containing a balloon is wrapped around the upper arm and is pumped up to a pressure above that which occludes (shuts off) the pulses in the arm. The cuff is then slowly deflated while the doctor or nurse listens over your brachial (elbow) artery with a stethoscope. The pressure at which sounds re-emerge is called systolic pressure (the top reading) and the pressure at which sounds disappear is called diastolic pressure (the bottom reading). Blood pressure is recorded as both of these readings eg 120/80 and represents the highest and lowest pressures in the vascular system.
An increasingly common alternative to manual blood pressure measurement is the use of electronic monitors which can be programmed to measure blood pressure with the doctor or nurse out of the room. This may produce more accurate readings in individuals prone to a "white coat" effect.
24-hour ambulatory blood pressure monitoring is now (where available) the "gold standard" for diagnosis of hypertension and to exclude white coat hypertension.
Electronic home blood pressure monitors are now cheap and widely available and are an excellent tool for monitoring blood pressure long-term in patienst on blood pressure medication.
In some people (over ¼ of the adult population in fact) blood pressure becomes higher than that required to perfuse the vital organs. We call this high blood pressure, or hypertension. Over a long period of time these higher pressures cause damage to the heart and blood vessels and increase the risk for heart attacks, heart failure, strokes, and kidney disease.
High blood pressure, particularly when we are talikng about the need for medication, in general is defined as 140/90 or higher, or 130/80 or higher if you are diabetic, have kidney disease, or existing heart problems. You still have high blood pressure if only the top reading or only the bottom reading is abnormal.
In most people, there is no specific identifiable cause of high blood pressure, and we call this "essential hypertension" ("essential" in this context just means "unknown cause"). Essential hypertension (we think) is due to a complex interaction between our genetic makeup, and the environment (lifestyle factors). It is more common to have high blood pressure if other family members are affected. Environmental or lifestyle factors which increase the risk of developing high blood pressure include being overweight, excessive salt intake, and excessive alchohol intake.
A minority of people have an underlying "secondary" cause of high blood pressure;- for example a benign tumour of the adrenal glands which produces excessive amounts of the blood-pressure raising hormone aldosterone. In this case the high blood pressure may be curable with surgical removal of the offending gland. There are a number of other "secondary" causes that doctors need to consider before labelling a patient "essential hypertension", but essential hypertension is by far the commonest.
Treatment of high blood pressure to normal levels can significantly reduce the risk associated with it - almost back to the level of risk of the non-hypertensive population.
The cornerstone of treatment of established high blood pressure, is medication (tablets), and these need to be used lifelong. Most people with high blood pressure will need to take at least 2 different medications to achieve adequate control and some will require more (3, 4, 5 or even 6 medications taken in combination).
For individuals with established hypertension, lifestyle modification is important (vital in fact) in combination with the medication, but is seldom enough on its own to avoid the need for medication. Of the "lifestyle" issues, being overweight is a very important contributor to high blood pressure. 70-80% of young and middle-aged people with high blood pressure are overweight or obese. In the older age groups (particularly over 70) there is less connection between overweight and high blood pressure. Reducing sodium (salt) intake is also a very important lifestyle measure in all individuals with high blood pressure.
From a community perspective, the best way of avoiding hypertension is attention to these lifestyle issues in the young and middle-aged population at large. For example if the approximately 45% of New Zealand adults who are overweight or obese (BMI > 25) were able to achieve a healthy weight (BMI 19-25) a very substantial reduction in the prevalence of hypertension requiring medication would result:- probably agreater than 60% reduction. The incidence of Type 2 diabetes would also show a similar dramatic fall.
Blood pressure tends to rise with age and high blood pressure become increasingly common as we get older. All adults should have their blood pressure checked regularly (a minimum of annually) and people on blood pressure treatment should have their blood pressure checked at least every three months. Blood pressure can evolve with time and people who are well controlled on a particular medication or combination of medications may require adjustment to those medications from time to time.
High blood pressure is the most important, but not the only modifiable risk factor for heart attacks and strokes (the main non-modifiable risk factors are age and male sex). Other (modifiable) risk factors include high cholesterol, smoking, and diabetes. All of these need to be managed to minimise your risk and most people on blood pressure medication will also need to be on cholesterol-lowering medication and some on low dose dose aspirin (a blood thinner which reduces the risk of heart attacks and strokes).
New Zealand Heart Foundation - Go to "Heart Health" section - click on to "must do list of how to take care of your heart" - then click on to "managing your blood pressure"
Canadian Hypertension Education Programme
American patient website (click on "high blood pressure" in the heart disease section)
American patient website (National Heart Lung and Blood Institute)