I periodically check my blood pressure using a conventional arm machine. I recently bought a wrist monitor but there is a large difference in readings between them. If the arm monitor reads 150 systolic, the wrist monitor will read 125. Which should I use?
George Teasdale, Leeds
This is a problem I’ve come across before. To explain this discrepancy, we have to understand how blood pressure is measured.
The standard way to measure it is by inflating a cuff around the upper arm, compressing the brachial artery within so tightly that no blood flows through.
Releasing the cuff gradually, a point is eventually reached when the pressure in the cuff equals that inside the artery (caused by the pumping of the heart).
At this point, blood starts to pulse through again (the GP will use a stethoscope to listen for this moment). The blood pressure recorded at this point is what we call ‘systolic’ — the pressure in the arteries when the heart contracts. This is the top number in a blood pressure reading you get from your doctor.
In a self-administered blood pressure test, the pumping up and reducing of pressure in the cuff occurs automatically, and a built-in sensor records the point when blood starts to pulse again.
Once the blood stops pulsating and the flow becomes smoother, we can note the diastolic pressure — when the heart rests between beats. Blood pressure is always given as two figures: the systole and diastole (the peak and trough).
If the upper arm is rather fat, or very muscular, a special wide cuff must be used. If the cuff is not big enough, it may be over-inflated in order to compress the artery properly, which can generate a falsely high reading.
Too many GPs and nurses are not equipped with wide cuffs for these circumstances, which can lead to the patient being told they have raised blood pressure when they do not.
With wrist sphygmomanometers (the formal name for a blood pressure monitor), we aim to compress the radial artery (the main artery in the forearm supplying the hand), 2-3 cm away from the base of the thumb.
However, arthritis in the wrist, or distortion of the bone from an old fracture, may make it hard to compress this artery properly. This might explain a discrepancy between upper arm and wrist measurements.
The wrist is also some way from the heart, so the pressure here may not accurately represent that of the aorta — the main artery from the heart. It is the aorta that is most significant, and all our understanding of blood pressure is based on this.
Although I cannot give a detailed explanation for your observations, I prefer to adhere to convention. It’s fine to monitor blood pressure yourself, but do it with a cuff on the upper arm (as the pressure in the brachial artery is almost identical to that in the aorta). If you have a large arm, get a wide cuff. Only then can you reliably know your blood pressure.
My sister is in a lot of pain from gout in her feet, despite taking allopurinol 300mg. My brother and I both had gout, controlled by the same medication. Why is it not working for her?
A.Watkinson, Crewe, Cheshire
Gout is one of the many forms of arthritis caused when uric acid (a waste product of digestion normally filtered out by the kidneys) builds up and forms crystals in the joints triggering inflammation and attacks of exquisite pain in the affected areas.
The aim of treatment — the mainstay is medication — is to prevent recurrent attacks by lowering levels of uric acid in the blood. Over time this will lower levels in the rest of the tissues and stop further crystals forming.
Drugs typically probenecid can be prescribed to increase the rate at which the kidneys excrete uric acid; allopurinol, which your sister is on, works by reducing production of uric acid.
The latter is preferred as it is very effective and generally well-tolerated (though side-effects — including rashes, diarrhoea and fever — do occur in up to 5 per cent of patients). Patients have regular blood tests to check they’re on the right dose — most require 300mg daily, though they can have up to 900mg.
Unfortunately reducing the overall level of uric acid in the body can take some time to achieve and attacks of gout can still occur for up to 18 months later.
Indeed starting the tablets often triggers more attacks, though it’s not clear why. A course of anti-inflammatory drugs such as naproxen or indomethacin during the first week or two of taking allupurinol helps prevent this (though the patient will still need an emergency supply of anti-inflammatories for a few weeks, to take at the first sign of attack).
Lifestyle changes can also undoubtedly help. These include weight loss and changing your diet. This might require help from a dietitian, but the principle is calorie restriction, more protein (from low-fat dairy products and plants rather than poultry, red meat and fish), and less saturated fat — this combination helps reduce intake of purines, chemicals which are broken down to produce uric acid. A final recommendation is to take 500mg of vitamin C every day as this is known to reduce uric acid levels.
I suggest your sister continues to take allopurinol as advised by her GP, with the proviso that the dose is increased if her blood uric acid level is not yet in the normal range. But patience is needed.