Why do my blood-pressure readings vary? And am I drinking too much water?

Pressure sensitive

Pressure sensitive

Q. I have high blood pressure, which I have had for more than 10 years. I am not yet 41. I have it measured about twice a year at our local health centre. Each time the measurement is different, and recently it has climbed to its highest level yet (162/90). It is my impression that it is higher if it is measured by the doctor, and lower if it is measured by the practice nurse. I would like to be able to measure it myself at home, both to keep an eye on it and to compare my readings with the ones at the health centre. When I tried to buy a home measurement device, I was overwhelmed by the choice available. Some measure the pressure in the upper arm, some wrap around the wrist, and some measure the pressure in the tip of the finger. How should I decide which to invest in? The price range is from £29.99 (at Argos) to £100 (at Boots).

A. There are some people who seem to have high blood pressure when they visit the doctor, and normal blood pressure when they are at home. This type of raised blood pressure is sometimes known as white coat hypertension - the pressure seems to go up in the presence of a health professional (whether or not he or she is actually wearing a white coat). There is even some evidence that doctors can put blood pressure up more than nurses. So it's not a silly idea to want to measure your blood pressure at home, although I think it's important not to become too obsessional about it. And don't forget to keep a written record of your readings to take with you to the doctor. The problem is, as you say, knowing what to buy. Home monitors come in all shapes and sizes. The finger monitors are notoriously inaccurate, and I would avoid these. Some wrist monitors and some upper arm monitors have been stringently tested and found to be accurate. Others have been found to be less good. Whichever type of monitor you use, it is important that the monitor and arm cuff are at the same height as your own heart. If you measure the blood pressure in an arm which is held up in the air, the measurement will be much lower than it should be. A list of tested and validated monitors is available online at www.dableducational.com. I would not buy anything that is not recommended on this website.

Heart of the matter

Q. I have an irregular heartbeat called atrial fibrillation. Sometimes the heart beats too fast, and if I take my pulse it is always skipping about and missing beats. It was all discovered accidentally during a travel immunisation check-up. I have been advised to take something to thin the blood. This, I am told, will prevent me from having a stroke. I can't quite understand how thinning the blood will prevent a stroke occurring. While we are at it, I can't quite understand how an irregular heartbeat (which affects the heart) will cause a stroke (which affects the brain). Can you?

A. I agree that it seems odd to thin the blood in order to prevent the heart from causing a stroke in the brain. But there is some sense behind it all, which I will try to explain. When the heart beats irregularly, as it does with atrial fibrillation, blood does not flow through the heart as smoothly as it should. It has a tendency to form small stagnant areas within the upper chambers of the heart. Stagnant blood has a tendency to form clots, and these small clots can shoot off to the brain. If a clot lodges in a critical area, it will cause a stroke. By thinning the blood, you can prevent the formation of clots within the heart, and thereby prevent strokes. Two drugs are used to thin the blood in people with atrial fibrillation. The first is aspirin. A small dose of aspirin every day will certainly reduce your risk of having a stroke. For many people, aspirin may not be the ideal solution. The option is the blood-thinning drug warfarin. Warfarin is more effective than aspirin, but it has more side effects and it needs to be regularly monitored with blood tests. Discuss which drug is best for you with a specialist.

A watery problem

Q. All the health and beauty advice I read these days seems to insist that we drink 2.5 litres of water a day to keep our skin and bodies in good working order. But what are you supposed to do if you have waterworks problems? I am not talking about full-blown incontinence, just the need to rush to the loo quickly. I have started to deliberately limit my fluid intake if I know I am going out. If I limit myself to one cup of coffee or tea I am OK, but then I find myself feeling tired and headachey in the afternoon - classic signs of dehydration. What is the minimum amount I can drink without causing problems?

A. There is no absolute minimum amount that you must drink. You should be guided by your thirst, rather than any absolute rule. As long as you are passing urine that is not too dark and concentrated, you are drinking enough. Much of your true fluid intake is in fact "hidden" in food. Fruit and vegetables contain large amounts of water. Tea and coffee are probably not the best things to drink. Both contain caffeine, which is a diuretic that causes the kidneys to produce excess urine. I doubt that your afternoon headaches and tiredness are really caused by dehydration, unless you really are drinking tiny amounts of fluid.

Have your say Readers write

PP is worried by what I said about penis size:

I've seen your piece today about penis size. I'm one of those concerned about it. Now even more concerned after your measurements; surely they are wrong. I hope so.

Please send your questions and suggestions to A Question of Health, 'The Independent', Independent House, 191 Marsh Wall, London E14 9RS; fax 020-7005 2182 or e-mail to health@independent.co.uk. Dr Kavalier regrets that he is unable to respond personally to questions