Why your blood pressure is different every time you measure it
Two measurements two minutes apart, two different numbers – and both were measured correctly. Why blood pressure fluctuates from second to second and what that means for your blood pressure diary.
You measure, write down 128/82, wait two minutes, measure again – and the device shows 141/88. No mistake, no faulty device. Both values may have been correct at that moment.
The reason is a property of the circulation that hardly anyone has explained to them: Blood pressure is not a number, but a course. It changes with every breath.
Blood pressure breathes along with you
In physiology, blood pressure fluctuations are distinguished by their cause. First-order fluctuation is the heartbeat itself – the difference between systole and diastole. Second-order fluctuation follows breathing.
When you breathe in, your chest expands, the pressure in the chest cavity falls, and blood flows back to the heart differently. When you breathe out, the effect is reversed. As a result, blood pressure rises and falls rhythmically without anything having changed in your state of health.
The fact that pressure, pulse and rhythm are three observations of the same process is summarised on Pulse, pressure, rhythm.
How big is this effect?
In healthy people, the systolic value typically falls by up to about 10 mmHg during inhalation. This is normal and nothing to worry about.
Important to know: a much larger drop – more than about 10 mmHg – has its own name, pulsus paradoxus, and is a finding that should be assessed by a doctor. You cannot judge this yourself at home; however, conspicuously large differences between consecutive measurements are a good reason to raise the matter.
Why two measurements can be 20 mmHg apart
Breathing alone does not explain the whole range. It adds up with everything else that changes between two measurements:
- Breathing phase at the moment of measurement – up to around 10 mmHg
- Arm position: 10 cm below heart level – around 7.5 mmHg
- Talking during the measurement – up to 10 mmHg
- Full bladder, coffee, nicotine, no rest period – each potentially double digits
Two technically flawless measurements can therefore easily be 20 mmHg apart. That is exactly the gap between “unremarkable” and “requiring treatment” – and the reason why a single value does not make a diagnosis. Where the limits lie in detail is shown in the blood pressure values table.
What this means in practice
The way out is not to keep measuring until a nice number appears. The way out is to measure the fluctuation along with it, rather than wishing it away.
- Always two measurements one to two minutes apart – and write both down.
- Morning and evening, for seven days. The average of this series is the value that counts.
- Breathe calmly and evenly, do not consciously breathe in deeply and do not hold your breath.
- Always measure under the same conditions: same time of day, same sitting position, same arm.
- Do not delete outliers. An outlier in the diary is information, not a mistake.
How to eliminate the avoidable mistakes is explained in Measuring blood pressure correctly: 7 mistakes that distort your readings. Why arm position makes such a difference is explained in Wrist or upper arm. And what the gap between the upper and lower value additionally reveals is explained in Pulse pressure: what the gap between your blood pressure values reveals.
The idea that the range of fluctuation can say more clinically than a single high value has also been taken up by daily media – the articles are collected under Media coverage.
When you should seek medical advice
If the average of your seven-day series is at or above 135/85 mmHg, it should be assessed by a doctor. The same applies if the values scatter extremely despite careful measuring conditions, if individual values above 180/110 mmHg occur, or if symptoms such as dizziness, visual disturbances, shortness of breath or chest pain occur as well.
Take your diary with you – complete, with all the outliers. It is precisely these that make it meaningful.
How to describe your symptoms so your doctor can actually work with them
Five steps for your next doctor’s appointment – plus a printable template for noting down your observations.
This is how it usually sounds
“I felt strange again last night. A kind of stumble, and it gave me a fright.”
“Let’s keep an eye on it.”
The guide shows you how to describe it instead and which questions to ask. What is usually missing are the numbers from exactly those two minutes – and those are what the BPER records, beat by beat.
Frequently asked questions
Why does my device show different values for two consecutive measurements?
Because blood pressure changes continuously. In healthy people, breathing alone shifts the systolic value by up to about 10 mmHg, and arm position, tension and timing add to this. Differences between two measurements are normal and not a device fault.
Which of the two values should I write down?
Both. What counts for the assessment is the average of a series over seven days, not a single value. Writing down only the lower one makes the diary useless.
Should I breathe deeply or hold my breath while measuring?
Neither. Keep breathing calmly and evenly. Consciously altered breathing distorts the value further.
When is the fluctuation no longer normal?
A systolic drop of significantly more than 10 mmHg on inhalation is called pulsus paradoxus and should be checked by a doctor. It cannot be reliably assessed at home – conspicuously large differences are a reason to raise the subject.
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Sources
- Julien C: The enigma of Mayer waves – Facts and models, Cardiovascular Research 70(1):12–21, 2006
- Deutsche Hochdruckliga e. V. DHL: Richtig Blutdruck messen
- Deutsche Herzstiftung e. V.: Woher kommen plötzliche Blutdruck-Schwankungen?
- Nationale VersorgungsLeitlinie Hypertonie (2023)
- European Society of Hypertension: 2023 ESH Guidelines for the management of arterial hypertension
This article is for general information only and does not replace a medical diagnosis or treatment. If you have symptoms or questions about your treatment, please consult your doctor.