Blood pressure is the force exerted by the blood against the walls of blood vessels. High blood pressure, or hypertension, often has no symptoms, but can lead to heart attack, stroke and renal failure.
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Causes of blood pressure
The heart pumps blood around the body through arteries and capillaries which then flows back to the heart through the veins.
To pump the blood through the arteries, the heart contracts which increases blood pressure to its highest point (known as systolic pressure – the first number your doctor refers to in a blood pressure reading and measured in millimetres of mercury mmHg).
As the heart relaxes and fills with blood again, the pressure in the arteries decreases (known as diastolic pressure – the second number your doctor refers to in a blood pressure reading).
Therefore, when your GP says your blood pressure is for example '110 over 70', that means your systolic pressure is 110mmhg and your diastolic pressure is 70mmhg.
Causes of low blood pressure
Low blood pressure is known as hypotension and is classified by a blood pressure reading of 90/60 or less.
Factors that cause low blood pressure include:
• Medications – e.g. anti-depressants, high blood pressure drugs
• Injuries – Burns or trauma leading to blood loss and shock reduces the volume of blood in the body and causes low blood pressure
• Illness – Heart attacks, adrenal gland failure
• Age – As we age, arteries become stiff causing a drop in blood pressure particularly when standing up
• Nerve conditions – Conditions that affect the nerves in the legs
• Pregnancy – Early to mid stage pregnancy causes low pressure
• Diabetes Mellitus – Damage to blood vessels from this condition results in a drop in blood pressure
Causes of high blood pressure
High blood pressure is known as hypertension and is classified by a blood pressure reading of 140/90 or above.
High blood pressure has two types – essential (primary) high blood pressure and secondary high blood pressure.
Essential (primary) high blood pressure – The cause of this is unknown although evidence points to certain risk factors that increase the chances of developing the condition. These include:
• Age – As we age, the risk of high blood pressure increases
• Hereditary factors – Family history of the condition increases risk
• Ethnicity – People of South Asian or Afro-Caribbean origin are at higher risk
• Lack of physical activity
• Excessive alcohol consumption
• High levels of salt in diet
• High levels of fat in diet
There are also certain medical conditions that have been associated with the risk of developing high blood pressure including kidney disease and diabetes.
Secondary high blood pressure – In a small number of cases, high blood pressure is caused by an underlying condition or problem such as:
• Kidney disease
• Kidney infections
• Narrow arteries
• Hormonal conditions
• Medication – e.g. oral contraceptives, anti-inflammatory drugs
• Excessive alcohol
• Illegal drugs – cocaine, amphetamines
Symptoms of low blood pressure
The symptoms of low blood pressure are not always apparent but if
pressure is too low there may not be enough blood flowing to vital
organs which can result in dizzy spells or fainting. Other symptoms of
low blood pressure can include:
• Blurry vision
• Feeling light-headed
• Feeling confused
Low blood pressure can cause you to feel dizzy when moving from one posture to another such as when you stand up. This is known as postural, or orthostatic hypotension which generally occurs as you get older. Exercise can bring on similar symptoms but the problem usually only lasts for a few minutes before the body becomes adjusted to its new position.
Postprandial hypotension is the name given to low blood pressure symptoms that occur after eating and typically affects the elderly and people with diabetes or conditions such as Parkinson's disease. The digestive system requires a large amount of blood after eating a meal to break down the food and as a result the heart rate has to increase. To maintain blood pressure vessels constrict (narrow), however if they do not constrict enough, blood pressure drops resulting in dizziness or fainting.
Symptoms of high blood pressure
• Dizzy spells
• Feeling drowsy
• Blurry vision
Diagnosis of low/high blood pressure