High blood pressure (Hypertension)
Information for patients from the Renal Department
This leaflet explains the following.
What high blood pressure is, and what can cause it.
How blood pressure is measured, and why we recommend measuring blood pressure at home.
Which blood pressure monitor to buy.
How high blood pressure can be treated.
What happens if high blood pressure is not controlled.
We hope this leaflet answers some of the questions you may have. If you have any further questions or concerns, please speak to your GP.
What is high blood pressure (hypertension)? and, what causes it?
In the UK, high blood pressure is one of the most common and preventable causes of premature:
heart disease
stroke, and
vascular and kidney disease.
It affects about 1 in 4 of all adults, and more than half of those over 60 years old.
In most people affected, the cause of high blood pressure is not fully understood. These people are often described as having ‘essential hypertension’.
Many different factors are known to be important. These include:
excessive retention of salt in the body by the kidneys;
reduced blood flow in the kidneys, partly due to increased activity of nerves involved in ‘stress’ responses (the sympathetic nervous system); and
increased activity in a complex system of hormones (known as the ‘renin-angiotensin-aldosterone’ system).
How is blood pressure measured?
Blood pressure is usually measured using a sphygmomanometer or ‘blood pressure monitor’. These devices usually use a cuff placed on the upper arm. Some devices measure blood pressure at the wrist.
When measuring blood pressure, two readings are taken at the same time.
The upper reading (systolic). This reading reflects the pressure generated within the arteries when the heart is contracting.
The lower reading (diastolic). This reading reflects the pressure that remains in the artery when the heart is relaxing and filling.
Blood pressure is often shown as ‘systolic / diastolic’, with the units ‘millimetres of mercury’ (mmHg). For example: 140 / 85 mmHg, where 140 is the systolic, and 85 is the diastolic blood pressure.
Both systolic and diastolic readings are important. However, most guidelines and targets for ‘optimal’ blood pressure control, only focus on the systolic reading.
Why do you recommend that I measure my blood pressure at home?
Home blood pressure monitoring is recommended for people with hypertension. It allows us to more fully check your blood pressure, particularly if you are having a ‘virtual’ consultation with us by video or phone.
Around 1 in 4 people have the ‘white coat effect’. The 'white coat effect' is where blood pressure readings are higher at a GP surgery or hospital clinic than they are at home. For these people, home or automated devices (‘ambulatory’) are very helpful.
What blood pressure monitor should I buy?
It is important that whatever device you use is validated. Validated means its accuracy has been confirmed. For a list of validated monitors, please go to the British and Irish Hypertension Society web site.
We do not recommend or endorse any particular brand or model of blood pressure monitor. However, the monitors listed on the Society web site can be bought from pharmacies or online.
Recalibrate or replace monitors based on manufacturer instructions. This is to make sure that the readings are reliable, and is usually done every 2 to 4 years. Some manufacturers offer recalibration services. We recommend checking individual manufacturer web sites for more information on this. If your blood pressure monitor is more than 5 years old we would definitely recommend replacing it.
How should I measure my own blood pressure?
In brief
Make sure that the arm on which you are taking measurements is free of constricting (tight) clothing. Make sure the arm is comfortably supported at the level of your heart.
Place the cuff around your upper arm, as per manufacturer instructions. Make sure the cuff is an appropriate size for your arm.
After resting for 5 minutes, take a blood pressure reading and make a note of that reading. Take 2 further readings, with 1 to 2 minutes between each reading.
If you are taking your blood pressure at home for the first time, always compare readings in both arms. If one arm has a systolic blood pressure of more than 15mmHg higher than the other, always take readings on the higher arm. Always use this same arm for future readings.
In general, we will ask you to take two sets of three readings per day:
in the morning between 6am and 10am, before your blood pressure medication, if you take these; and
in the evening, between 8pm and 10pm.
Do this either on 1 day or 3 consecutive days before your appointments and on other selected occasions. For example, a few weeks after changing blood pressure medication or medication doses. Occasionally, we will ask for readings over 5 to 7 consecutive days.
A table for you to record your home blood pressure readings is at the end of this leaflet.
How is high blood pressure treated?
Treatment for high blood pressure usually includes lifestyle changes. It can also include taking blood pressure lowering medications.
Lifestyle changes recommended for people with high blood pressure include the following.
Salt intake. The average salt intake in the UK is 10 grams per day. The recommended daily salt intake for an adult is 5 grams per day (or 1 teaspoon). Reducing the amount of salt in your food lowers blood pressure. It makes blood pressure lowering medications more effective. It is important to stop adding salt to your food when cooking or at the table. However, most of the salt we eat is already in food when we buy it, so called ‘hidden salt’. Understanding food labelling can help you see where you can find these hidden sources of salt.
Healthy diet. Follow a diet that is rich in fresh fruit and vegetables, and low in saturated fat.
Weight. Try to lose weight to achieve at least a BMI of 27.5 kg / m2, but preferably lower - between 20 and 25 kg / m2. Try to lose weight if your BMI is greater than 30 kg / m2 and you have high blood pressure. See the BMI chart at the end of this leaflet.
Alcohol consumption. Follow the current weekly UK limits. Weekly limits are 14 units or less for both men and women, with at least 2 alcohol free days each week.
One unit of alcohol is equivalent to:
half-pint of average strength beer;
a small glass of wine (125ml); or
a single pub measure of spirits.
Remember that stronger beers (such as continental lager) and larger glasses of wine (175ml or 250ml) will contain more units.
Exercise. Try to do moderate to high intensity exercise for at least 30 minutes 5 times a week. If possible, exercise more than this. A variety of different types of exercise all appear to help reduce blood pressure. Different types of exercise include the following.
Aerobic / endurance, for example swimming, running, or a brisk walk that makes you breathless.
Resistance, for example weights, or exercises using resistance bands.
Isometric, for example wall squats.
For more information on changes to your lifestyle, visit the Blood Pressure UK web site.
Medicines for high blood pressure are made up of three common classes
“Renin-angiotensin system” blocking drugs. These block various parts of a complex hormone system called the “renin-angiotensin system”. Examples include:
ACE inhibitors (end in –pril) such as ramipril; and
angiotensin receptor blockers (end in –sartan) such as losartan or irbesartan.
Vasodilators directly relax muscles in the blood vessel wall. Examples include:
calcium channel blockers such as amlodipine; and
alpha-blockers such as doxazosin.
Diuretics or “water pills” encourage the kidney to excrete salt and water. Examples include:
bendroflumethiazide
indapamide, and
frusemide.
Mineralocortocoid receptor antagonists (MRAs), which block the effects of the hormone aldosterone. Examples include:
spironolactone.
For more information on blood pressure lowering medicines, visit the Blood Pressure UK web site.
Why is my blood pressure not controlled?
About half of people taking medication, will have higher than desirable blood pressure. There are many possible reasons for this.
Inadequate numbers of blood pressure medications. Many people need three or more different types of blood pressure tablet. Combinations of two medications often lower blood pressure more effectively than a high dose of a single medication.
Inadequate doses of blood pressure medications. Some people will not be able to tolerate higher doses of some tablets, due to the side effects. However, it is also quite common for less than maximal doses of medication to be prescribed without a good reason.
Not taking medications regularly or in amounts suggested by your doctor.
Not enough changes to your lifestyle.
The “white coat effect”.
“Secondary” hypertension. Underlying causes are found in 5 to 10 out of every 100 people with uncontrolled blood pressure. Underlying causes include:
over-production of certain hormones (for example aldosterone); or
kidney artery narrowing.
If you or your doctor think any of the above apply to you, you can discuss this during your clinic visits.
What is resistant hypertension?
Resistant hypertension generally means blood pressure that remains uncontrolled in someone who:
is taking at least 3 or 4 blood pressure lowering medications, at an adequate dose;
has made appropriate changes to their lifestyle, for example lowering salt intake and weight loss; and
has been investigated for underlying causes of high blood pressure.
People with resistant hypertension also need to have the ‘white coat effect’ excluded. This is done using home blood pressure monitoring.
People with resistant hypertension are more likely to suffer heart disease or stroke. This is compared to people with controlled blood pressure.
Treatment options for people with resistant hypertension include:
additional blood pressure lowering medications (spironolactone or amiloride); or
sometimes enrolment onto clinical trials of novel treatments. These can include renal denervation or other device based therapy.
Where can I get more information?
Body Mass Index (BMI) Chart
Body Mass Index is calculated by dividing your weight (in kilograms) by your height (in metres) squared.
A BMI less than 18.5 kg / m2 is underweight.
A BMI between 18.5 and 24.9 kg / m2 is a healthy weight.
A BMI between 25 and 29.9 kg / m2 is overweight.
A BMI of 30 kg / m2 or higher is obese (well above the healthy weight range for your height).
A BMI of 40 kg / m2 or higher is very obese.
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