Scientists have discovered why cuff-based blood pressure monitors often give inaccurate readings, missing up to 30% of high blood pressure cases, after building a physical model that replicates real artery behaviour, and finding that low pressure below the cuff delays artery reopening, leading to under-estimated systolic readings.
The work of University of Cambridge scientists suggests that simple tweaks, like raising the arm before testing, could dramatically improve accuracy without the need for expensive new devices.
They said that some straightforward changes, which don’t necessarily involve replacing standard cuff-based measurement, could lead to more accurate blood pressure readings and better results for patients. Their results were reported in the journal PNAS Nexus.
The cuff-based method – or auscultatory method – relies on inflating a cuff around the upper arm to the point where it cuts off blood flow to the lower arm, and then a clinician listens for tapping sounds in the arm through a stethoscope while the cuff is slowly deflated.
“The auscultatory method is the gold standard, but it over-estimates diastolic pressure, while systolic pressure is under-estimated,” said co-author Kate Bassil from Cambridge’s Department of Engineering.
“We have a good understanding of why diastolic pressure is over-estimated, but why systolic pressure is under-estimated has been a bit of a mystery.”
“Most clinicians know blood pressure readings are sometimes wrong, but no one could explain why they are being under-estimated – there’s a real gap in understanding,” said co-author Professor Anurag Agarwal, also from Cambridge’s Department of Engineering.
Previous non-clinical studies into measurement inaccuracy used rubber tubes that did not fully replicate how arteries collapse under cuff pressure, which masked the under-estimation effect.
The researchers built a simplified physical model to isolate and study the effects of downstream blood pressure – the blood pressure in the part of the arm below the cuff.
When the cuff is inflated and blood flow to the lower arm is cut off, it creates a very low downstream pressure. By reproducing this condition in their experimental rig, they determined this pressure difference causes the artery to stay closed for longer while the cuff deflates, delaying the reopening and leading to an under-estimation of blood pressure.
This physical mechanism – the delayed reopening due to low downstream pressure – is the likely cause of under-estimation, a previously unidentified factor.
“We are currently not adjusting for this error when diagnosing or prescribing treatments, which has been estimated to lead to as many as 30% of cases of systolic hypertension being missed,” said Bassil.
Instead of the rubber tubes used in earlier physical models of arteries, the Cambridge researchers used tubes that lay flat when deflated and fully close when the cuff pressure is inflated, the key condition for reproducing the low downstream pressure observed in the body.
The researchers say that there is a range of potential solutions to this under-estimation, which include raising the arm in advance of measurement, potentially producing a predictable downstream pressure and therefore predictable under-estimation. This change doesn’t require new devices, just a modified protocol.
“You might not even need new devices, just changing how the measurement is done could make it more accurate,” said Agarwal.
However, if new devices for monitoring blood pressure are developed, they might ask for additional inputs which correlate with downstream pressure, to adjust what the “ideal” readings might be for each individual. These may include age, BMI, or tissue characteristics.
The researchers are hoping to secure funding for clinical trials to test their findings in patients, and are looking for industrial or research partners to help refine their calibration models and validate the effect in diverse populations.
Collaboration with clinicians will also be essential to implement changes to clinical practice.
The research was supported by the Engineering and Physical Sciences Research Council (EPSRC), part of UK Research and Innovation (UKRI).
Study details
Under-estimation of systolic pressure in cuff-based blood pressure measurement
Kate Bassil, Anurag Agarwal.
Published in PNAS Nexus on 12 August 2025
Abstract
High blood pressure (hypertension) is the number one risk factor for premature death. Hypertension is asymptomatic, so blood pressure must be regularly monitored to diagnose it. In auscultatory blood pressure measurement, a patient’s systolic (maximum) and diastolic (minimum) blood pressure are inferred from the pressure in an inflatable cuff wrapped around the arm. This technique is the gold standard against which all other non-invasive devices are validated. However, auscultatory measurements systematically under-estimate systolic blood pressure and over-estimate diastolic blood pressure. Over-estimation is attributed to the increased cuff pressure needed to occlude the artery because of the surrounding tissue and arterial stiffness. In contrast, the cause of systolic under-estimation, which leads to potentially a third of systolic hypertension cases being missed, has remained unclear. When the cuff is inflated beyond the systolic blood pressure, the blood flow to the vessels downstream of the cuff is cut off. The pressure in these downstream vessels drops to a low plateau. We have developed a novel experimental rig that shows that the low downstream pressure is the key cause of the under-estimation of systolic blood pressure. The lower the downstream pressure, the greater the under-estimation. Our results yield a simple physical model for the under-estimation of systolic pressure in our rig and in the human body. Understanding the physics behind the under-estimation of systolic blood pressure paves the way for developing strategies to mitigate this error.
See more from MedicalBrief archives:
Why arm position matters in blood pressure checks – Johns Hopkins study
Checking BP in doctor’s rooms not always ideal
BP readings’ accuracy differences between men and women – Canadian study