What is blood pressure?
Hypertension or high blood pressure is a common condition in which the blood is pumped around the body at too high a pressure. The blood pressure is the force exerted on the arteries by blood passing through them.
The blood pressure varies from person to person as well as in the same individual at different times of the day and under different circumstances. Blood pressure normally rises in the early morning, varies during daily activities and then falls at night during sleep. This natural 24 hour rhythm is set by the bodies biological clock and is known as the ‘circadian rhythm’. It is normally lower when resting and higher during periods of activity or when stressed.
The maximum pressure in the arteries occurs as the heart beats and is called the systolic blood pressure. The lowest pressure occurs in the arteries when the heart is slowly refilling, before the next contraction, and is called the diastolic pressure. Blood pressure is normally expressed as the systolic value written over the diastolic value, for example 130/70mmHg. A person’s blood pressure alters from minute to minute and usually increases as we get older. It is generally agreed that a normal blood pressure is less than 140/90mmHg.
Hypertension is one of those peculiar conditions that does not usually cause symptoms or warning signs. In a very small minority of patients in whom the blood pressure is excessively high, it may cause headaches, altered vision or nosebleeds but these are rare. As the majority of patients have no symptoms, it is not uncommon for the condition to go undetected. However, left untreated hypertension is associated with an increased risk of:
- Hardening of the arteries (known as atherosclerosis)
- Coronary heart disease and heart attacks
- Heart failure
- Kidney failure
What causes blood pressure?
The reason blood pressure becomes elevated is due mainly to narrowing of small arteries (called arterioles) but also due to the walls of the larger arteries becoming more rigid (a process known as atherosclerosis). Because there are so many arterioles in the body, even a small change in their size can have a large effect on the available volume of the circulation and this leads to an increase in the pressure.
In the majority of patients there is no clear cause for hypertension. This is called primary or essential hypertension. Recognised factors linked with developing high blood pressure fall into the following categories:
- A history of blood pressure in the family.
- Being over the age of 35.
- Women taking oral contraceptives.
- Other medical conditions, for example diabetes and kidney disorders.
- Medications used to treat arthritis, depression and ulcers.
Also known to influence the development of blood pressure are lifestyle factors such as:
- Being overweight.
- Exercising too little.
- Too much alcohol or salt.
In a small percentage of patients high blood pressure can be caused by specific abnormalities. This is called secondary hypertension. Identifying these abnormalities can be important, as correcting them may cure the high blood pressure. Examples of abnormalities that can lead to hypertension are:
- Some kidney diseases.
- Excessive production of hormones from the thyroid gland.
- Excessive production of hormones from the adrenal glands including too much adrenaline or steroids.
- Obstruction of the arteries to the kidney (called renal artery stenosis)
- Narrowing of the main blood vessel in the body, the aorta, a condition known as coarctation of the aorta
How is blood pressure diagnosed?
Measuring the blood pressure using a machine that incorporates a cuff around the arm (called a sphygmomanometer) together with a stethoscope helps the doctor make a diagnosis of hypertension.
The cuff is pumped up until the pulse below the cuff disappears. The pressure in the cuff is then slowly lowered until the pulse reappears (this can be heard with the stethoscope) and is called the systolic pressure. The cuff is gradually deflated until the doctor or nurse can no longer hear any sounds (this is called the diastolic pressure).
As a person’s blood pressure varies continuously, a single blood pressure reading represents only a snapshot and not the whole picture. Many patients find that their blood pressure only goes up as a result of anxiously waiting to see the doctor or nurse, the so-called ‘white coat hypertension’.
Prior to making a final diagnosis of hypertension your doctor will arrange to take your blood pressure on several occasions. This allows the doctor to gain a more representative picture of the blood pressure levels. An alternative is to perform 24-hour ambulatory monitoring. During this the blood pressure is checked at frequent intervals over a 24-hour period away from the surgery or hospital.
If you have hypertension your doctor will want to check for evidence of harmful effects on the eyes, the kidneys and the heart. If other causes are thought to have contributed to the development of raised blood pressure then more detailed tests could be required:
- Blood tests to look for electrolyte (chemicals that conduct electricity in the blood) abnormalities, thyroid disease or evidence of kidney damage.
- A chest X-ray to see if the heart is enlarged or if there is congestion on the lungs.
- An electrocardiogram (ECG) to look for any evidence of enlargement of the heart muscle.
- An ultrasound scan of the heart, called an echocardiogram. This is a painless test that provides important information about the way the heart is working. It provides pictures of the heart in motion and allows the doctor to assess the pumping action of the heart.
How is blood pressure treated?
Once correctly diagnosed, hypertension is usually present for life. There remains some debate as to what level of blood pressure should be treated. The decision can be influenced by whether or not the patient has other conditions such as diabetes, kidney disease or heart disease. If these are present, treatment for blood pressure may be recommended even when levels are below the generally accepted level of 140/90mmHg.
Marginally raised blood pressure may come back to normal with the lifestyle changes that are important in the treatment of all patients with hypertension. These include:
- Loosing weight if you are overweight.
- Keeping salt intake in the diet to a minimum and eating a healthy balanced diet.
- Reducing alcohol intake to less than 21 units per week for men and less than 14 units per week for women.
- Taking regular exercise. Ideally a minimum of 30 minutes continuous exercise at least three times per week.
- Stopping smoking.
If these lifestyle changes alone are not successful then drug treatment is likely to be needed. If medication is prescribed, it is important that it is taken. Treatment has been shown to both reduce the risk of the long-term damage caused by high blood pressure and to prolong life.
High blood pressure generally produces no symptoms. The aim is to find the most appropriate treatment for individual patients circumstances. Patients with raised blood pressure are generally well and remembering to take regular tablets in such circumstances can be very difficult but is very important! There are many different types of drugs that can be used to treat hypertension:
- Diuretics (commonly known as ‘water tablets’) help the body to lose salt and water through the kidneys.
- Beta-blockers slow the speed and the force of the heartbeat reducing the pressure generated.
- Vasodilators, which include ACE-inhibitors, angiotensin II receptor antagonists, calcium channel blockers and alpha blockers, all act by dilating blood vessels in the body. By doing so they reduce pressure within the circulation.
- Drugs that act on the blood pressure control centres in the brain.
It is important that once the question of blood pressure has been raised, or treatment started, that the blood pressure is checked regularly.