Why common blood pressure readings may be misleading – and how to fix them
University of Cambridge
Researchers have found why common cuff-based blood pressure readings are inaccurate and how they might be improved, which could improve health outcomes for patients.
High blood pressure, or hypertension, is the top risk factor for premature death, associated with heart disease, strokes and heart attacks. However, inaccuracies in the most common form of blood pressure measurement mean that as many as 30% of cases of high blood pressure could be missed.
The researchers, from the University of Cambridge, built an experimental model that explained the physics behind these inaccuracies and provided a better understanding of the mechanics of cuff-based blood pressure readings.
The researchers say 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 are reported in the journal PNAS Nexus.
Anyone who has ever had their blood pressure taken will be familiar with the cuff-based method. This type of measurement, also known as the 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.
Blood pressure is inferred from readings taken from a pressure gauge attached to the deflating cuff. Blood pressure is given as two separate numbers: a maximum (systolic) and a minimum (diastolic) pressure. A blood pressure reading of 120/80 is considered ‘ideal’.
“The auscultatory method is the gold standard, but it overestimates diastolic pressure, while systolic pressure is underestimated,” said co-author Kate Bassil from Cambridge’s Department of Engineering. “We have a good understanding of why diastolic pressure is overestimated, but why systolic pressure is underestimated has been a bit of a mystery.”
“Pretty much every clinician knows blood pressure readings are sometimes wrong, but no one could explain why they are being underestimated — 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 underestimation 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 underestimation of blood pressure.
This physical mechanism — the delayed reopening due to low downstream pressure — is the likely cause of underestimation, 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 underestimation, which include raising the arm in advance of measurement, potentially producing a predictable downstream pressure and therefore predictable underestimation. 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).
Journal
PNAS Nexus
Article Title
Underestimation of systolic pressure in cuff-based blood pressure measurement
Article Publication Date
12-Aug-2025
Better calibration for cuff-based blood pressure readings
PNAS Nexus
video:
Co-author Kate Bassil explains the role of the experimental rig in the study in a short video.
view moreCredit: Kate Bassil
A study explains why cuff-based blood pressure readings systematically underestimate systolic blood pressure. High blood pressure is the most important risk factor for premature death. Yet the gold standard method for measuring blood pressure, the inflatable cuff, is known to systematically underestimate systolic (maximum) blood pressure and overestimate diastolic (minimum) blood pressure. To measure blood pressure, a cuff is placed around the upper arm and inflated to constrict the brachial artery, collapsing it. The pressure is then slowly released, until blood begins to flow through the artery again. With each blood pressure pulse, the blood pressure briefly exceeds the cuff pressure, and the artery opens, producing a tapping sound heard by the clinician. The cuff pressure continues to decrease, until the blood pressure exceeds the cuff pressure throughout the whole cardiac cycle. The artery is then fully open, and the tapping sounds disappear. The cuff pressures at which the tapping sounds appear and disappear are noted as the systolic and diastolic pressures, respectively. The reason for the overestimation of the minimum pressure is well understood: to fully occlude the artery, the cuff needs a little extra pressure to counteract the tissue around the artery and the stiffness of arterial walls. But the reason for the underestimation of systolic pressure has been unknown. Kate Bassil and Anurag Agarwal use a novel experimental rig that more accurately reproduces the behavior of the human circulatory system than previous rigs. The authors show that when the artery is closed, the blood pressure downstream of the cuff drops, as pressure equalizes in the isolated vasculature of the arm and hand. The cuff does not apply even pressure, and this, in combination with the low downstream pressure, changes the length of the closed section of artery under the cuff. The artery opens from the upstream side to the downstream side, but the detectable signal won’t be present until the whole length is open—and the longer it takes to open, the lower the pressure readings will have fallen before the clinician notes it. In sum, the lower the downstream pressure, the longer the section of artery that closes, the more time the artery takes to reopen, and the greater the underestimation of the systolic blood pressure. According to the authors, the study could inform improved calibration methods or refinements to the cuff protocol.
Journal
PNAS Nexus
Article Title
Underestimation of systolic pressure in cuff-based blood pressure measurement
Article Publication Date
12-Aug-2025
Image of the artery model under the compressive blood pressure cuff in the experimental rig.
Overview of the experimental rig.
Credit
Kate Bassil and Anurag Agarwal
Kate Bassil and Anurag Agarwal
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