Researchers at the University of Cambridge have uncovered a hidden flaw in the way blood pressure is commonly measured—one that could be causing millions of people to go undiagnosed for hypertension. Their study, published in PNAS Nexus, reveals that the standard cuff-based method used in clinics and homes may systematically underestimate systolic pressure, the “top” number in a blood pressure reading. This could mean that up to 30% of cases of high blood pressure are missed, leaving patients at risk for heart attacks, strokes, and other serious conditions.
The cuff-based method, known as the auscultatory technique, involves inflating a cuff around the upper arm to temporarily stop blood flow. As the cuff deflates, a clinician listens for the return of blood flow using a stethoscope, and the pressure at which the sound reappears is recorded as the systolic value. While this method is considered the gold standard, it has long been known to overestimate diastolic pressure and underestimate systolic pressure—but until now, the reason for the systolic error was unclear.
To investigate, the Cambridge team built a physical model that mimics how arteries behave under cuff pressure. They discovered that when the cuff cuts off blood flow, the pressure in the vessels downstream—below the cuff—drops significantly. This low downstream pressure causes the artery to stay closed longer during deflation, delaying the return of blood flow and leading to a falsely low systolic reading. Previous models failed to replicate this effect because they used rubber tubes that didn’t accurately simulate how real arteries collapse and reopen.
The researchers found that the degree of underestimation depends on how low the downstream pressure gets, which can vary based on arm position, tissue characteristics, and individual anatomy. In some cases, the error could be as much as 9 to 10 mmHg—enough to misclassify someone’s blood pressure status. This is especially concerning because cuff-based readings are used to calibrate automated devices in clinics and pharmacies, meaning the error could ripple across many systems.
Fortunately, the team suggests that simple changes could improve accuracy. For example, raising the arm before measurement may help stabilize downstream pressure and reduce the error. These adjustments wouldn’t require new devices—just updated protocols. If new devices are developed, they could incorporate additional data like age, BMI, or tissue density to better estimate true blood pressure.
The researchers are now seeking funding for clinical trials to test their findings in real-world settings and hope to collaborate with clinicians and industry partners to refine the approach. Their work highlights the importance of understanding the physics behind medical measurements and could lead to more reliable diagnostics and better patient outcomes.
Article from the University of Cambridge: Why common blood pressure readings may be misleading – and how to fix them
Abstract in PNAS Nexus: Underestimation of systolic pressure in cuff-based blood pressure measurement
