High blood pressure (hypertension)
All organs in the body need a constant supply of blood. Blood is carried to tissues by arteries. Veins take the blood away from the tissues back to the heart. The heart is a specialised muscle which pumps blood through arteries. The pressure inside the arteries varies according to whether the heart is contracting (systole) or relaxong (diastole). This is why a measurement of blood pressure has two values: the systolic blood pressure and the diastolic blood pressure. The systolic blood pressure is always higher than the diastolic blood pressure.
What is hypertension?
Hypertension means high blood pressure. The level at which high blood pressure causes problems has been determined from large medical studies involving hundreds of thousands of people followed up over many years. These studies have shown that people with higher blood pressures are more likely to suffer heart attacks, strokes, kidney disease and disease of other arteries. Hypertension itself does not give rise to symptoms and blood pressure treatment will not make patients feel better. Treatment, however, will reduce the likelihood of developing these conditions.
Measuring blood pressure
We normally measure blood pressure with an instrument called a sphygmomanometer, or ‘sphyg’. This involves inflating a cuff around the arm and listening to the heart beat in an artery using a stethoscope. The blood pressure readings are shown on a tube filled with mercury or on a dial. The readings are expressed in terms of millimetres of mercury (mmHg). Blood pressure values vary between individuals and a systolic blood pressure of 120 mmHg and a diastolic blood pressure of 80 mmHg (ie. 120/80 mmHg) is considered average and normal. Because measurements always vary, measurements on several occasions are needed before deciding whether blood pressure is normal.
In the past, hypertension was diagnosed on the basis of clinic reading, but we know know that this is not accurate. This is because some patients have the so-called ‘white coat’ effect, which leads to a high blood pressure reading in clinic whilst the blood pressure outside clinic is normal. As treatment of hypertension is life-long, it is important to be sure. Before making the diagnosis, we now do an ambulatory 24-hour blood pressure profile (ABPM) and home blood pressure monitoring (HBPM).
Blood pressure (BP) has a skewed normal distribution within the population and the currently accepted model assumes risk is continuously related to BP. The National Institute for Health and Clinical Excellence (NICE) recommends the following definitions:
• Stage 1: BP in surgery is ≥140/90 mm Hg and ABPM or HBPM is ≥135/85 mm Hg.
• Stage 2: BP in surgery is ≥160/100 mm Hg and ABPM or HBPM is ≥150/95 mm Hg.
• Severe hypertension: BP in surgery is ≥180/110 mm Hg.
Although traditionally the lower blood pressure (diastolic) has been thought to be more important, we now know from from the Framingham study and the Multiple Risk Factor Intervention Trial (MRFIT) study that it is the higher blood pressure (systolic) that is more important. Systolic rather than diastolic blood pressure is the most important in determining cardiovascular risk.
Further investigations are geared towards identifying the causes of hypertension and its effects on organs such as the kidneys and the heart. In the majority of cases, no cause is found. In the minority, particularly in the young, hypertension may be due to uncommon disorders of the kidney and adrenal glands. Coronary heart disease, strokes, diabetes and high cholesterol are more common in people with hypertension, so these also need to be investigated. You may expect the following tests:
• Blood tests, such as electrolytes, glucose and cholesterol measurements, can tell us whether you have kidney disease and whether you are at risk of developing coronary heart disease.
• Urine tests can tell us whether you have protein in the urine, which can sometimes indicate kidney disease.
• Electrocardiography (‘ECG’), which can often tell us whether you have had a heart attack or whether the wall of the heart is thickened.
• Echocardiography, which can tell us about the muscle and valve function of the heart.
• Kidney ultrasound, which can provide information as to whether hypertension is the cause of hypertension and whether it has been damaged by the condition.
MRI hypertension scan: This provides pictures of the heart, the aorta, the kidneys and their blood supply. It does not involve X-rays and excludes many of the causes of 'secondary hypertension'
• Other investigations, such as magnetic resonance scans of the adrenal glands may be needed to exclude rare causes of hypertension.
The treatment is preventative. Studies involving large numbers of people have shown that treating blood pressure reduces the likelihood of developing strokes and heart attacks. The benefit is particularly good in people who also have diabetes or coronary heart disease. The medications that we normally use to treat blood pressure are as follows:
• Thiazide diuretics (mild water tablets) such as bendroflumethiazide lower blood pressure by getting rid of fluid and dilating arteries.
• Beta-blockers, such as atenolol lower blood pressure primarily by slowing down the heart rate.
• ACE inhibitors, such as enalapril reduce blood pressure by dilating the arteries.
• Calcium channel blockers, such as amlodipine also reduce blood pressure by dilating the arteries.
• Alpha blockers, such as doxazosin reduce blood pressure by dilating the arteries.
• Other drugs: Loop diuretics, aldosterone receptor blockers and methyldopa may also be used in some circumstances.
• Renal artery denervation: This procedure involves inactivation of nerves around the arteries of the kidney. It was once thought to be effective, but it has now been abandoned. Research continues.
One tablet may be enough to control hypertension in some people, but the majority of patients will need two or three tablets. Hypertension may get worse over the years so further tablets may need to be added. Treatments for other conditions such as diabetes and high cholesterol work hand-in-hand with blood pressure medications to reduce the overall risk of developing heart disease and strokes.
What you can do
There are various measures you can take to lower blood pressure and reduce the risks of heart disease:
Keep a normal body weight (body mass index 20–25 kg/m2 for adults)
Reduce dietary sodium intake to <100 mmol/ day (<6 g of sodium chloride or <2.4 g of sodium per day)
Do regular aerobic physical activity such as brisk walking (≥30 min per day, most days of the week)
Limit alcohol intake to no more than 3 units/day in men and no more than 2 units/day in women
Maintain a diet rich in fruit and vegetables (e.g. at least five portions per day)