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.
The real problem is that these stupid new automatic devices have wildly-varying results... truly all over the map. And they’re laughable when the batteries are anywhere near weak.
The studies that came up with the original results for BP would have been done with the same cuffs so the base line would be off by the same amount.
Does this mean all the problems associated with high blood pressure are off by the same 6-10 points? If so, why does it make a difference?
I have had issues with HBP for 30 years. On several medications. Need to lose about 30 pounds. Have reduced salt in my diet drastically.
My cardiologist says to take my BP first thing every morning immediately after emptying my bladder.
Two things:
1. If my arm rests on the table about 12” below my heart level reading are about 10mm higher than if I have it resting on a surface at the level of my heart. (Which is how it is supposed to be read.)
2. I normally take evening pills about 8:00 PM. If I delay even a half an hour the readings are another 10-15mm lower than if I take meds at 8:00. Almost like I’m catching their effectiveness just before it drops off.
I’ve found that those *&#^@ machines ALWAYS read too high and I’ve had plenty of nurses tell me so.
When I get a manual, done by a real human being, blood pressure, it’s almost always close to my usual.
When they use that blankety-blank machine, it adjusts the pressure and about squeezes my arm off and takes FOREVER to deflate.
And they wonder why it reads high.
And then of course, they show concern and start talking blood pressure meds.
What I finally did with my PCP was told her to look at the readings from my allergy shots and when she did, she dropped the subject.
So many variables when measuring BP....My primary care and cardiologist have both actually cautioned me against monitoring it TOO much.
For these and other factors the best method IMO is aggregation of data; several readings across different days/times to discern the average and median.
My wife has high blood pressure. Her is always lower at the DR when done manually as opposed to the auto.
For home I bought an Oxiline ($100) that is tested to be 99% accurate and comes with a lifetime warranty. It’s proven to live up to that for us.
As regards the people in the article that might get a reading of 135 when it might read 142 when done manually - too bad, you’re gonna die. And soon.
Seriously, docs are pushing meds on anyone that is above 130 anyway. They are not “missing” people who *need* treatment because of 5-7 points. That’s just hooey.
IOW, the supposed high blood pressure is actually 20 higher than the supposed healthy average. Panic porn. 😎
They’re all broken. Just like the doctor scales are broken. All of them claim I am fat.
My doc practice is a traditional MD and holistic MD.
When my BP slightly high, the holistic MD said, “Do you want the traditional med approach or my recommendation. I said both. So she prescribed a med, but then said, lose weight, take beet juice, drink lemon water and hibiscus tea. And use potassium chloride but be ready to adjust it based on diet etc (I.e., don’t overdose on potassium)
I haven’t lost all the weight I want, but even with her natural approaches, my BP dropped by 15-20.
And I haven’t taken the med
Hey, wait a minute - mine does too! I think it’s a conspiracy.
Crap. I was hoping they’d say they were reading too high. Wah!
I use a wrist monitor. It seems to be reliable.
I have a machine at home and check my blood pressure every morning for both arms. The readings are sometimes quite a bit different even though it’s just a couple of minutes between one reading and the other. I usually get better readings from the Red Cross when I give blood.
Exactly!
140/90 used to be considered normal.
People who are obsessed with taking their blood pressure are usually the first to die.
billions of bp readings taken over decades, and they claim to come up with one systemic error? That goes beyond Occam’s razor to some quantized demon.But it will promote more prescriptions. I do wonder how many higher readings are accepted by not allowing 10 minutes between first and second readings at doctor’s office.
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