Posted on 08/13/2025 9:35:38 AM PDT by Red Badger
Researchers expose problem with arm cuffs and how simple fixes could greatly improve accuracy.
In A Nutshell
* Standard arm-cuff blood pressure tests often read nearly 6 points too low, missing about 30% of people with high systolic blood pressure (140 mmHg or higher).
* Cambridge researchers found the problem stems from a hidden drop in blood pressure in vessels below the cuff during the test.
* In lab tests, low “downstream” pressure caused readings to be off by as much as 9–10 points.
* Simple fixes, like redesigning cuffs, adjusting arm position, or using small correction factors, could make readings far more accurate.
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CAMBRIDGE, England — Millions of Americans who should be diagnosed with high blood pressure are slipping through the cracks because the familiar arm cuff in doctor’s offices often gives a reading that’s nearly six points too low. That small-sounding gap can have big consequences: it’s enough that roughly one in three people with systolic hypertension (140 mmHg or higher) may go undiagnosed, leaving them at risk for heart attacks and strokes.
High blood pressure is the leading cause of premature death worldwide, yet it rarely causes symptoms until serious problems occur. New research from the University of Cambridge pinpoints the physical reason why standard blood pressure cuffs tend to underestimate the “top” number (systolic pressure), a mystery that’s puzzled doctors for decades.
The Problem With Blood Pressure Cuffs
When a cuff inflates around your arm, it squeezes the main artery shut for a short time. The researchers found that this blockage causes blood pressure in the vessels beyond the cuff (the ones further down your arm) to fall sharply, settling at about 30 to 70 mmHg. The lower that “downstream” pressure drops, the more the cuff underestimates your actual blood pressure.
This matters because systolic blood pressure is one of the most important predictors of heart health. Even a small underestimation could push someone’s reading from the “high” category into “normal” territory, leading to missed diagnoses and delayed treatment.
Recreating The Problem In The Lab
One of the most impressive parts of the study was how the researchers designed an experiment to mimic what happens inside the human arm during a blood pressure check.
In previous research, scientists had tried to study blood pressure measurement errors by using simplified models, but these often didn’t recreate the full picture, especially the way arteries completely collapse when the cuff is inflated. Without that collapse, the “downstream” pressure drop couldn’t be accurately reproduced.
To solve this, Cambridge engineers Kate Bassil and Anurag Agarwal built a custom experimental rig. It featured flexible silicone tubing that could behave like a real artery, able to fully close under pressure. The system allowed them to independently control the pressure on both sides of the “artery”:
* Upstream pressure — representing the heart pumping blood into the arm.
* Downstream pressure — representing the vessels beyond the cuff in the forearm.
* By adjusting these pressures separately, they could replicate exactly what happens when a cuff squeezes the artery shut and downstream pressure drops.
What They Found
Their results revealed a clear pattern: the lower the downstream pressure, the greater the underestimation of systolic blood pressure. In their tests, the underestimation could be as much as 9 to 10 mmHg when downstream pressure was at its lowest.
They also discovered why standard cuffs have this problem while devices applying uniform pressure don’t. A regular cuff doesn’t squeeze evenly along its length. It’s tighter in the middle and looser at the edges. When downstream pressure is low, this uneven squeeze keeps a longer stretch of the artery closed for longer, which delays the return of blood flow and tricks the reading into coming out lower than it should.
When they used a device that applied uniform pressure all the way around the artery, the downstream pressure no longer affected the reading, suggesting that a design change to the cuff itself could solve the problem.
Why This Matters For Patients
A large analysis of 74 previous studies confirms what the Cambridge experiments found: cuff-based measurements underestimate the top blood pressure number by about 5.7 points on average. And according to earlier research, a systematic 5-point underestimate would miss about 30 percent of people with systolic hypertension.
The Cambridge team calculated that with a standard cuff, the length of artery kept closed could vary from none at all to about six centimeters, depending on pressure conditions. In real-world terms, six centimeters of closure could mean your reading is four points too low.
Because the arm-cuff method is the “gold standard” for checking blood pressure, even small inaccuracies in this method ripple out to every other device. That includes the automatic machines in pharmacies and clinics, since they’re all tested against it.
What Could Fix This Blood Pressure Test Flaw?
The researchers suggest several ways to make readings more accurate, such as redesigning cuffs so the pressure is more uniform along the arm, asking patients to raise their arm before the test, or applying small corrections based on a person’s age, arm size, and other characteristics.
By revealing the physical cause of this measurement gap, the study opens the door to more reliable blood pressure readings. In a condition where catching problems early can prevent heart attacks, strokes, and other serious issues, improving accuracy could help more people get the treatment they need — before it’s too late.
Disclaimer:
This article is based on a published research paper. It is intended for informational purposes only and is not a substitute for professional medical advice. Always consult a qualified healthcare provider for diagnosis and treatment of any health condition.
10 minutes?
My doctor’s nurse takes the BP immediately when she calls you in!..................
I can’t stand the pain that those machines cause, so when they insist on using those, I make them apply the cuff below my elbow. The reading is the same without the pain.
My Mom has an Omron, supposedly they are “the best” eh, they are OK, she checks her blood pressure a few times a day since she has high blood pressure, she always adds another 10 points since she knows its not accurate..for me its always wrong, I have small arms sometimes it doesnt read at all and yes the batteries weak signal is annoying its been blinking for weeks now but the machine still functions
Oh, Bea Ess.
Not to mention how *recommended* BP levels were changed, in the 60s, to promote new BP meds...many of which only made things worse.
Systolic varies a lot more than diastolic due to involuntary nerve system factors,like “whit coat hypertension”( wmen MDs wore white coats) I think. diastolic was always considered the more important as that is the pressure the heart perceives during relaxation, supposedly.
I use my at-home pressure monitor as a relative reading device. I assume that, given I use it the same every time, it can tell me what my BP is relative to an earlier day. But I don’t take it as an actual reading.
I do not need to measure blood pressure. I simply pay attention to symptoms. When my blood pressure is higher from chomping on too much salty pizza, I can sense some loss of balance. Strangely same it symptoms are present when blood pressure is low from dehydration.
When my blood sugar is high I can feel tingling in feet below the ankles. Who says diabetes is silent disease? Just pay attention to subtle signals body sends out.
Interesting
Okay people listen up.
The old style of measurement is squeeze the arm, listen with a stethoscope at the inner elbow. Slowly unsqueeze. The value when sounds of blood movement appear is systolic. When they disappear again, diastolic.
This method has been universally discarded, and for excellent reason. Hearing of docs/nurses vary, and certainly erode with age.
The new method is called oscillometric. The device doesn’t listen at all for sounds. It senses pulsations in the tube that does cuff inflation. The matter then gets complex. There are algorithms for speeding things up. Projections of final value based on rate of change of pulsations with rate of deflation of cuff.
These are hyper accurate. They have been tested against the stethoscope method.
Heads up. 1/3 of the population has white coat syndrome. Higher pressure at the office than home. People think this is nervousness. It is not. It is a hardwiring in the brain done as a child/baby responding to medical environment, or even merely awareness of it being a medical environment. It’s not fear. You can try to relax for a very long time and it will probably persist.
You can take your home device in and measure the same as what the clinic device measures. Then when you get home, your measure is fine. And most devices now have memory so you can prove it.
And final heads up, the clinic’s device and your home device are both oscillometric. No more auscalatory (stethoscope).
Zactly
When I had it taken for an insurance policy....thwy took it 3 times...on both arms.
Doctors offices, Hospitals, Pharmacies, and pharmacy ads are everywhere. What happened?
Why are people falling for the nonsense?
If everyone’s BP ended up 10 points higher because every single BP measurement was done a new way ... then realistically the dividing line between needing or not needing BP medicine would also rise 10 points. This is much ado about nothing.
None of this really matters if the patient is somewhere that has their records. Then, the only thing that counts is the change in BP from the established baseline. A BP reading 10 too low is not really significant either.
It’s similar to the patients weight. We stand on a scale fully clothed, sometimes with wallet, keys etc on our persons. A weight reading 10 lbs. too heavy is not really significant to ones health. What counts is the change over time.
a better way to determine blood pressure will net someone a small fortune one of these days
I figured this out on my own years ago.
Can I get a cut of the grant, too? /s
Try a Walmart Apple Cider Vinegar gummie in the am. Swallow don’t chew.
Or, the automatic machines are 6 points too high: which, along with the “revised” (read: SMARTER than you™ guidelines), will push millions onto lucrative blood pressure medications.
Thanks for the advice. I’ll try the beet juice, lemon water, and hibiscus tea. And I’ll leave the KCl for later.
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