High blood pressure is the single most important risk factor for cardiovascular disease. This group of diseases, which includes heart attack and stroke, is responsible for 1 in 4 deaths worldwide and 1 in 3 deaths in Australia. Recently, the National Heart Foundation demonstrated that less than 1% of people diagnosed with high blood pressure would modify their lifestyle to reduce their risk of heart disease (1). Up to 50% of people with high blood pressure are completely unaware they are at risk.
Why is blood pressure important?
“High blood pressure doesn’t necessarily have any symptoms. Unless we measure it accurately we often don’t know if we have high blood pressure” warns Prof. James Sharman from the Menzies Institute for Medical Research.
It is critically important that blood pressure is regularly measured using a validated blood pressure device (more on that below).
What is blood pressure?
You’ve probably had your blood pressure taken during a routine check-up with your GP, or before you donate blood or plasma at the local blood bank (kudos to all you good Samaritans!). You may have noticed that the reading is one number over another number, for example, 120/80. These two numbers are measurements of the pressure of the blood moving through your arteries (tubes that carry oxygen enriched blood from the heart to your cells). The larger, top number, is the “Systolic” blood pressure – the maximum pressure your blood will reach as the blood is pumped out of the heart. The lower, bottom number, is the “Diastolic” blood pressure, which is the lowest pressure the artery will have, as the heart is refilling between beats.
So why is blood pressure so dangerous?
Generally, the pressure of our blood reduces as it travels from our heart out along our arteries to our smaller blood vessels where it is passed along to our cells via even smaller tubes called capillaries. The force of the blood being pushed through these tubes by the heart lessens as the blood gets further away from the heart and reaches its destination. When we have high blood pressure, the blood that reaches our cells can have such high forces that it damages organs including our brain, kidneys and eyes, causing rupturing of the capillaries.
Blood pressure measurement: the good, the bad and the ugly
The good:
Measuring blood pressure is extremely important to identify people at risk of problems related to high blood pressure. There are many different ways blood pressure can be measured. Doctors measure your blood pressure, either using an automated device with a cuff at your arm or manually with a pressurized cuff and a stethoscope to listen for sounds at your arm to measure blood pressure. Doctor-measured blood pressure has several limitations, including the phenomena called ‘white coat hypertension’ where the doctor records a high blood pressure reading because the patient is tense due to the situation or setting. Perhaps they’re nervous about visiting their doctor, perhaps they’re nervous about what the blood pressure reading will say, but they normally have a healthy normal blood pressure when calm. This elevated blood pressure when nervous is an evolutionary feature of the “fight or flight” response. When anxious or feeling in danger, our blood pressure increases to keep oxygen supply to the brain, and to make sure we have oxygen in our system to supply our muscles if we need to run. Think about how you might feel before a speech or presentation at work – your heart starts to race, you get flushed – what you may not be able to tell is you also have an elevated blood pressure in that moment.
Therefore, the gold standard method of measuring blood pressure is away from the doctor and using a device that measures your blood pressure automatically over 24 hours. The 24 hour method gives an indication of what your blood pressure is like when you’re undertaking your usual activities. The blood pressure numbers from the 24 hour method can be more accurately linked to risk of heart attacks and strokes than other methods of measurement. Enabling patients to measure their blood pressure at home can empower patients to have an active role in managing their cardiovascular health, and allow doctors to monitor the effect of medications.
Patients are often asked to buy a blood pressure monitor to perform at-home measurements. However, it can be quite difficult to know what type of device to buy and what the differences are. Are all blood pressure monitors created equal?
The bad:
There are rigorous international protocols developed to test the accuracy of new blood pressure monitors. If a blood pressure monitor passes this testing, it is said to be validated. However, before becoming available for sale it is not essential for new devices to undergo this validation testing. This means many monitors available on the market may not provide an accurate indication of blood pressure.
Doctor Dean Picone from the Menzies Institute for Medical Research recently investigated the types of blood pressure monitors available for purchase in Australia. He found there were almost 1000 monitors available but as few as 7% had been validated. Non-validated monitors are less likely to be accurate than validated ones (2).
“People looking to buy a blood pressure monitor are inundated with choice and are potentially more like to buy a monitor that could be inaccurate due to the high prevalence of lower cost, non-validated monitors and lack of information available on validation” says Dr. Picone
The ugly:
Now you may be thinking that even if a blood pressure monitor hasn’t been validated it’s probably better than not measuring your blood pressure at all. This is not the case. Accurate blood pressure measurement is essential to inform clinical decisions about lifelong therapy to prevent the leading cause of death worldwide. The ramifications of inaccurate measurements span from someone unnecessarily receiving lifelong medication to the flip side of someone not receiving medication when they require it, meaning they could unknowingly be left at higher risk of heart attacks and strokes.
Among the plethora of non-validated devices available, there’s the emergence of wrist-based wearables, commonly known as activity trackers, that claim to measure blood pressure. To date, the technology does not exist to accurately measure blood pressure without the inflation of a cuff and these activity trackers do not use cuff inflation to obtain the blood pressure measurement. The method of blood pressure measurement from these monitors is unclear. Essentially, activity trackers cannot be recommended for blood pressure measurement because of uncertainty about the accuracy of the readings.
The good news:
Prof. Sharman and Dr. Picone, alongside international colleagues who are experts in blood pressure, are working to improve international standards, ensuring the validation of blood pressure devices so that consumers can have confidence in their accuracy.
“To help consumers identify validated blood pressure monitors, we have developed this practical resource which describes all the validated device listings available globally and how to search them.”
The tool is designed for use by the general public, health professionals and policy makers to promote the uptake and use of validated blood pressure monitors and is currently being translated to several languages other than English.
What can you do?
Measuring your blood pressure at home is extremely valuable in helping your doctor make clinical decisions. Prof. Sharman and Dr. Picone have some helpful tips to make those readings as accurate and useful as possible.
10 easy steps to accurately measure your blood pressure at home:
- Use an upper arm device (not a wrist cuff or one you wear on a wristband) with a correct cuff size (within the range indicated on the cuff).
- Use a validated, accurate device. You can check for reliable devices here. If you don’t want to buy a device, you can hire or borrow one from some pharmacies and medical clinics.
- Measure your blood pressure at around the same time, morning and evening, over seven days (five day minimum).
- Measure before taking medication, food or exercise, and as advised by your doctor (for instance, before visiting the doctor or after a medication change).
- Don’t smoke or drink caffeine 30 minutes before measuring, and don’t measure if you’re uncomfortable, stressed or in pain.
- Avoid distractions or talking during the measurement. Sit quietly at rest.
- Perfect posture – both feet flat on the floor, back supported and the cuff applied directly to your bare upper arm with your arm supported at heart level.
- Take two measurements with one-minute rest in between.
- Keep a diary that records each measurement either by paper or electronically, templates can be found here.
- Provide your doctor with your readings, by email or via telehealth.
There are many things you can do to reduce your risk of heart disease and lower your blood pressure. We recommend you check out the Heart Foundation website for more information – they even have some heart healthy recipes.
This article was written by Niamh Chapman, Dr. Dean Picone and Prof. James Sharman from the Blood Pressure Research Group at Menzies Institute for Medical Research, University of Tasmania, with editing help from Kelsey Picard.
Guests:
Professor Sharman’s Blood Pressure Research Group is working on a series of studies ranging from understanding the basic human physiology of blood pressure to exploring new methods for improving patient diagnosis and care. People have been led to believe blood pressure measurement is easy and reliable. But unfortunately in some people this simply isn’t the case. To try and address this problem we’re collaborating with cardiologists at the Royal Hobart Hospital to try and understand the factors contributing to blood pressure measurement inaccuracies.
Dr Picone is a Postdoctoral Research Fellow with the Blood Pressure Research Group at the Menzies Institute for Medical Research. His PhD studies focused on the accurate measurement of blood pressure and he is currently continuing research in this area.
Sources:
(1) https://www.heartfoundation.org.au/media-releases/fatal-but-forgotten-high-blood-pressure-threat
(2) Picone DS, Deshpande RA, Schultz MG, et al. Nonvalidated Home Blood Pressure Devices Dominate the Online Marketplace in Australia: Major Implications for Cardiovascular Risk Management. Hypertension. 2020;75(6):1593‐1599. doi:10.1161/HYPERTENSIONAHA.120.14719
(3) Unger T, Borghi C, Charchar F, et al. 2020 International Society of Hypertension Global Hypertension Practice Guidelines. Hypertension. 2020;75(6):1334‐1357. doi:10.1161/HYPERTENSIONAHA.120.15026