Why Do We Measure Resting Blood Pressure?
By Dr Joe
On this page you are going to learn about why we measure resting blood pressure. Not just that. You are also going to know what blood pressure is; why we measure blood pressure at all in the first place, and I also discuss what ambulatory blood pressure monitoring is and when and why we do it..
Some of the commonest questions that bothers peope with high blood pressure is; why do we measure resting blood pressure. Why don’t we measure blood pressure when we are active instead? Does resting blood pressure represent our true blood pressure?
I have lost count of how many times I have had to answer this question in our blood pressure forum. So, I felt it will be a good idea to write this resting blood pressure piece here.
That way I can just direct such enquiries here. Saves me writing the same response all the time.
And if you are not one of those people in that forum, well, you are in luck, because you will now know the answer in advance of other people.
Why do we measure blood pressure at all?
Before I delve into why resting blood pressure measurements are important, let me quickly talk about why we measure blood pressure at all in the first place.
May be we should start with the definition of blood pressure first.
What is blood pressure?
Blood pressure is an index of the pressure generated in the circulatory system during a cardiac cycle. A cardiac cycle includes when your heart ventricles contract and when the ventricles are relaxed. Ventricular contraction followed by relaxation represents one cycle.
Every time your heart contracts to push blood out of it into the circulatory system, there is a force behind it. That represents the systolic blood pressure. That is the top figure you see when you take your blood pressure reading.
In between the contractions (when the heart is relaxed) there is still some pressure within the circulatory system otherwise, blood flow will cease. That will not be compatible with life and as you know life has to go on.
The pressure within the blood vessels between those ventricular contractions represent the diastolic blood pressure. That is the bottom figure you see when you measure your blood pressure.
So, your blood pressure is a measure of the force or resistance within the circulatory system at that point in time.
Why should we bother measuring the pressure within the circulatory system? Why not let it do its own thing…
Why is it important to measure our blood pressure?
It is important to measure our blood pressure because it gives an idea of how much force the heart is generating with each pump and how much resistance there is in the receiving vessels downstream.
Measuring our blood pressure also provides us an ‘implied measure’ of the diameter (thickness) and elasticity of the walls of our arteries.
- Because thicker arteries are not very compliant to allow blood flow through them easily, hence diameter.
- Inelastic arteries are also fairly resistant to free blood flow too.
Therefore thicker, inelastic blood vessels will give rise to higher blood pressure. The net effect is, the heart has to pump harder i.e work harder, to get blood through in that scenario.
Hence thicker, inelastic blood vessels will rebound on the heart, leading to enlarged heart with thicker muscle too. Ultimately leading to heart failure, if high blood pressure is undiagnosed and untreated for a long time.
Another complication of high blood pressure when the blood vessels have become thicker and inelastic is such vessels are prone to becoming narrower.
When blood vessels are narrower, they can become clogged up readily. This can lead to blood clots which can result in heart attack, stroke, vascular dementia, peripheral vascular disease and even kdney disease.
Why do we measure resting blood pressure?
From the above analysis, if you have high blood pressure, then your blood vessels are becoming thicker and inelastic. The higher your blood pressure is, the more inelastic your blood vessels have become.
Or put in another way, the higher your blood pressure is, the more the resistance they are putting up against free flow of blood.
The American Heart Association (AHA), the European Society of Cardiology (ESC), the European Society of Hypertension (ESH) and other bodies have come out with guidelines for blood pressure measurement.
These guidelines have recommended a resting time of between 3 minutes to at least 5 minutes before blood pressure measurement at home. Also make sure you are using an upper arm monitor as opposed to wrist monitor.
Wrist monitors are not accurate. You may also want to read my piece on wrist blood pressure monitors pros and cons here.
So, why do we recommend checking your blood pressure at rest?
Well, it’s very simple. Your blood pressure fluctuates throughout the day. In fact, whilst you are out and about, your blood pressure changes from minute to minute.
If I left my phone upstairs in the bedroom and I am downstairs in the living room and I hear my phone ringing and I rushed upstairs to get the phone, my blood pressure will change dramatically having done one flight of stairs very quickly.
Even if I went upstairs leisurely, my blood pressure will change. Heck, just talking on the phone answering the call, my blood pressure will change.
Worse still, if I was getting irritated over the phone by the attitude of my Energy Company’s Customer Service consultant because I have been mistakenly overcharged for my energy use in the last 3 months and he was fobbing me off, my blood pressure will hit the roof.
The point is; your blood pressure is affected during the day by all sorts of environmental and human factors like:
- Physical activity
- Cold weather
- Physical pain
- Emotional pain etc
With that in mind, it is better to measure your blood pressure at rest. Check your blood pressure when you have rested for those mandatory 3 – 5 minutes.
Those 3 – 5 minutes gives your body and your circulatory system an opprtunity to come to rest. Because measuring your blood pressure when those other factors are in play would give a skewed unreliable results.
A lot of those rises in blood pressure as a result of those environmental and human factors are temporary.
Temporary readings do not reflect your true blood pressure. Your at-rest blood pressure is a better reflection of your true blood pressure reading. Measure your blood pressure when the sea is calm before the storm begins.
A second point is this:
Your resting blood pressure is your baseline reading. Your starting point. Your best reading. Because we know that your blood pressure will change during the course of the day. That’s a fact.
So, if your resting blood pressure is normal, we don’t have to worry about what it does during the day as you go about your business.
Now imagine a scenario where your at-rest blood pressure is 190/135 mmHg. And we know that the only way is up once you are active.
Can you then imagine what could possibly happen with a blood pressure like that; if say that individual gets that customer service irritation or went out in the freezing cold winter weather or received some terrible news?
If that’s not a recipe for a heart attack or a stroke, I don’t know what is. This is an individual who needs attention. Urgently.
Compare that to someone else whose resting blood pressure is 125/70 mmHg. We know that barring something really calamitous happening to this individual, it’s unlikely his/her blood pressure rises during the day will do him/her any harm.
You should see your resting blood pressure as a baseline that either reassures us or tells us we need to do something…like adjusting your treatment. But of course, you need more than one reading.
In fact, there was a study that was carried out sometime ago that suggested the 5-minute resting rule before measuring blood pressure is not adequate.
The authors of this study are actuallly suggesting 25 minutes resting time before checking your blood pressure. In their study, the researchers found a steady decrease in both the systolic and diastolic blood pressure reading over the 25-minute period. A bigger decrease in systolic than diastolic.
This steady decrease in blood pressure was noted in all the study participants regardless of whether they were on blood pressure medications or not.
The researchers opined that the 5-minute resting blood pressure rule may be leading to over-diagnosis of hypertension and called for the resting time to be extended in the guidelines.
…because the minimal resting time before blood pressure measurement to obtain a stable Systolic Blood Pressure in 90% of the population is 25 minutes according to their research.
“Our study suggests that the current recommended practice of measuring Systolic Blood Pressure after 5 minutes of resting may not allow for adequate stabilization of SBP, which we find could take at least 25 minutes. Public Health Policies should take into account this result to organize the best way to diagnose hypertension in our societies and avoid overdiagnosis”
What is Ambulatory Blood Pressure Monitoring?
Now you know why we measure blood pressure at rest, I need to say a few words about ambulatory blood pressure monitoring. Because it sort of ties in with the concerns of those who feel their blood pressure should be measured in active periods instead of resting times.
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Ambulatory blood pressure monitoring is a technique where your blood pressure is monitored with a portable meter and you wear the attached blood pressure cuff for 24 hours.
The blood pressure machine will measure your blood pressure at fixed intervals and it’s recorded digitally. You may assist your doctor by writing down some of the activities you were engaged in during the day. That way your doctor can match the readings with the activities.
Indeed, the main concerns by individuals who feel that measuring blood pressure at rest is not ideal is because they feel that at-rest blood pressure reading mechanism is missing out on the blood pressure fluctuations that occur during the day and may be at night.
Valid concern…I must admit.
But for most people though, this is really not an issue if your blood pressure is well controlled. Even when your blood pressure is marginally elevated, those diurnal blood pressure fluctuations are not clinically significant.
In fact, this underscores why a good blood pressure control is important, if you have high blood pressure. Because you don’t have to worry about these diurnal blood pressure excursions, if your blood pressure control is good.
But there are circumstances where ambulatory blood pressure monitoring is indicated.
When is ambulatory 24-hour blood pressure monitoring necessary?
It may be wise to perform ambulatory blood pressure measurements in these individuals:
- Anyone with suspected wild blood pressure swings during the day
- Individuals with suspected huge blood pressure rises at night
- Someone with suspected sustained high blood pressure
- If white coat hypertension is thought to be an issue
- An individual who may actually have masked high blood pressure
- Poor response to high blood pressure medications
- Borderline high blood pressure individuals
- A need for prediction of risk of blood pressure complications
In all of those scenarios above, it may be wise to undertake 24-hour ambulatory blood pressure assessment. That way the right treatment strategy can be mapped out between you and your doctor.
Also se: Does drinking water reduce blood pressure?
Suggested further reading:
How To Supercharge Your Life and Restore Glowing Good Health