DR. MARTIN SCURR: Everyone over 30 should check their blood pressure – and here’s how NOT to…

Are you doing it all wrong? Last week, researchers in the US reported that holding your arm in the wrong position while measuring your blood pressure could significantly overestimate the reading.

As a result, many people may be misdiagnosed with high blood pressure.

So what’s the right way? I’ll get to that.

But first you might wonder why, in this age of high-tech scanners and tests, we take this low-tech measure – wrapping a cuff around your arm and inflating it tightly – so seriously?

The fact is that it could be a matter of life and death. The first number in your reading, known as the systolic pressure, reflects the pressure in the blood vessels when your heart contracts – the maximum pressure. The second number, the diastolic, is when the heart relaxes. A healthy value is around 120/60 mmHg.

When blood pressure is higher, you might expect blood flow to be faster, like when you turn on the garden hose. In fact, it is slower – this is because blood is a ‘liquid’ tissue, a fluid containing small particles such as blood cells, and higher pressure tends to cause slower blood flow.

High blood pressure is a sign of unhealthy arteries. Arteries have elastic walls and can expand or contract to change their diameter. If they are not flexible, it increases the work of the heart pumping blood. The result? A weaker heart as the muscle becomes progressively damaged, leading to heart failure, blood clots, heart attack and stroke.

Previously, a value above 140/90 was the cut-off point for diagnosing hypertension, but today it is thought that the cut-off value should be lower: 120-130 systolic, 60-70 diastolic. My opinion is that, like body weight, blood pressure is something that everyone over the age of 30 should check periodically, perhaps once a month.

The great thing is that no complicated technology is needed to measure blood pressure. For around $20, you can get a simple and accurate monitor, also known as a blood pressure monitor.

But as this latest study has confirmed, it must be used correctly.

Choose a device with an upper arm cuff. I would avoid the cuffs that go around the wrist or a finger as the measurement will not be as accurate. The point is to record the pressure in a large blood vessel, which will be much the same as the pressure in the main artery, the aorta, as it leaves the heart. The brachial artery in the upper arm is about the diameter of a pencil and, in my opinion, is the only place where blood pressure is measured.

The cuff is inflated to compress the artery, causing it to close. The pressure then automatically decreases and when the blood can just squirt through, it makes a small sound that a microphone in the cuff detects. That is the systolic blood pressure. The diastolic is when, as the cuff pressure slowly decreases, the blood flows again with each heartbeat.

The included cuffs are a standard size, but if you have a large arm (whether you are overweight or muscular), you will need to purchase a larger one. Using a small cuff on a large arm makes it much harder to pinch the artery, which will cause the reading to be much higher than your actual blood pressure because what you get is distorted by the extra work of the cuff.

Dr. Scurr recommends a number of steps before measuring your own blood pressure to ensure an accurate reading, including going to the toilet, as a full bladder can increase the reading by as much as 10 percent.

The best time to measure your blood pressure is early in the morning or late at night.

But whatever time you do it, abstain from too much coffee, smoking, alcohol or other exercise – even if you’re just biking home or walking up several flights of stairs – at least 20 to 30 minutes beforehand. These can all temporarily increase blood pressure (putting pressure on the entire cardiovascular system), causing an incorrect reading. Also go to the toilet and empty your bladder. If you are in a hurry, this can increase blood pressure by at least 10 percent.

Then sit in a quiet room for five minutes straight.

Place your forearm on the armrest of the chair or on a table, about level with your heart (this has to do with the physics of blood flow, but essentially makes it more accurate).

The bottom of the cuff – around the bare upper arm – should be a few finger widths above the elbow crease. This ensures that the microphone is above the brachial artery. The cuff should also be loose enough that a finger can slide between the cuff and your arm. Then press the start button on the blood pressure monitor.

If the pressure seems high, much above 140/90, wait a few minutes and take the pressure again.

If the temperature remains high, take a few measurements two or three times a week for several weeks, at different times of the day, for example when you first wake up, somewhere around the middle of the day, and when you go to bed .

The range of measurements is important, and taking an average will be helpful. Consistently high readings require the attention of a doctor, as high blood pressure can silently cause damage until it is irreversible and dangerous.

That’s why I encourage my patients to purchase and use a blood pressure monitor. If you want to survive, it is no less important than a scale to monitor your weight.