What is it?
Blood pressure is the pressure in the main arteries that carry blood from the heart to the rest of the body. It is measured as the maximum and minimum blood pressure with each heartbeat. The blood pressure depends on the force of heart contraction, the elasticity of the main arteries, the resistance in the smaller arteries, and the thickness (viscosity) of the blood.
The maximum pressure is known as the ‘systolic’ and the minimum is known as the ‘diastolic’. When blood pressure is measured, both readings are taken and are written like this: 120/80mm/Hg (where mm = Millimetre and Hg = Mercury).
What is normal blood pressure?
Blood pressure normally varies a lot, from minute to minute and even from one breath to the next. It is usually lower at night, and goes up with exercise and other forms of stress (eg anxiety). It also varies around the body.
For most purposes, it is best to measure blood pressure in the upper arm, at heart level, with the person sitting comfortably, not talking, having rested for at least five minutes and avoided cigarettes and caffeine for at least 30 minutes. Measured like this, a ‘normal’ adult’s blood pressure is around 120/80 mm Hg.
Blood pressure is often measured in a rush in outpatient clinics, without much time for rest, and often at a time of increased anxiety. Measurements taken like this shouldn’t be used as the sole basis for deciding on treatment. Repeated measurements at home (two in the morning and two in the evening over a one-week period) or ambulatory blood pressure measurements (which require the person to wear a blood pressure machine for 24 hours) give a much better idea.
- Your blood pressure is considered to be high if your blood pressure is 140/90mmHg or above, and your average daytime ambulatory or home blood pressure is 135/85mmHg or above.
- The higher your resting blood pressure, the higher your risk of heart disease, stroke, and progressive kidney damage.
There is often no obvious cause for hypertension but some groups, for example people from minority ethnic groups are more prone to developing high blood pressure.
Blood pressure and kidney disease
Hypertension is both an important cause and consequence of kidney disease. In some patients it can be difficult to determine which came first.
Healthy kidneys help to regulate blood pressure by controlling the amount of fluid in the circulation and by sending chemical messengers (called hormones) that control constriction of blood vessels.
But this process can be seriously affected if the kidneys are damaged. This can cause high blood pressure, which can, in turn, cause further kidney damage – so creating a ‘vicious cycle’ of hypertension and progressive kidney damage.
Controlling high blood pressure is the most important step towards reducing the risk of further kidney damage. It also reduces the risk of cardiovascular problems such as heart attacks and strokes that can occur in anyone with high blood pressure.
One of the biggest problems is that you cannot usually 'feel' high blood pressure, although very high blood pressure can cause symptoms such as headaches, shortness of breath, nosebleeds, and blurred vision. The only reliable way of finding out your blood pressure is to have it measured.
What can I do?
There are several things that you can do to help prevent or reduce hypertension:
- Cut down on your salt intake and increase your intake of fruit and vegetables
- Try to maintain a healthy weight
- Exercise regularly
- Avoid drinking excessive amounts of alcohol.
A number of different drugs which lower blood pressure are available:
- Drugs known as “ACE inhibitors” and Angiotensin Receptor Blockers (ARBs) prevent the action of hormones which are regulated by the kidney and increase blood pressure. They also seem to be able to protect diseased kidneys from further damage – especially in patients who have protein in their urine (proteinuria)
- They can also protect heart and blood vessels too
- Calcium channel blockers (such as diltiazerm, nifedipine)
- Diuretics (such as bendroflumethazide) reduce the amount of salt and water in the body
- Spironolactone – which is used to treat fluid retention
- Alpha-blockers (such as doxazosin) work in different ways to prevent contraction of blood vessels, reducing tension in blood vessel walls
- Beta-blockers (such as atenolol) reduce the effects of hormones such as adrenaline. Beta blockers may also be used to treat angina (chest pain caused by reduced blood flow to the heart muscles) as well as heart failure.
Speak to your GP if you want help and advice about preventing or managing high blood pressure (including advice on eating healthily, exercising and how to lose weight).
But always remember to speak to your kidney dietitian or kidney nurse before starting a new diet plan if you are on a restricted diet, due to kidney disease.
Blood Pressure in kidney disease - from Edinburgh Renal Unit.
Blood pressure – a booklet from the British Heart Foundatio.
Watch Dr Kathryn Griffith explain the link between blood pressure and kidney disease.
Reviewed April 2019
The need for more research
There’s still a lot we don’t understand about how blood pressure is regulated by the kidneys or how best to treat high blood pressure.
We’ve awarded a grant to a team of researchers to tackle the sudden drop in blood pressure some patients experience during haemodialysis using novel pressure sensors on the dialysis tubing.
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