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First introduced in 1881 by Austrian-Jewish physician Samuel Siegfried Karl von Basch, and brought into broad U.S. use at the turn of the 20th century by neurosurgeon Harvey Cushing, M.D., the inflatable cuff, or sphygmomanometer, has changed little in more than a century.
Now, University of Cambridge researchers say the familiar test may be missing thousands, even millions, of cases of high blood pressure.
Published August 12 in PNAS Nexus, a new study reveals a physical quirk in the gold-standard auscultatory method that can cause systolic pressure readings to register lower than they really are. As a result, as many as 30% of patients with systolic hypertension could go undiagnosed.
High blood pressure — a leading risk factor for premature death — often shows no symptoms until serious complications strike. That makes accurate readings essential.
The physics behind the error
In the auscultatory method, the cuff inflates around the upper arm to stop blood flow. As it deflates, clinicians listen for Korotkoff sounds — the telltale taps that signal blood is once again moving through the artery — to determine systolic and diastolic pressures.
While overestimation of diastolic pressure is well understood, underestimation of systolic pressure has been harder to explain.
“We have a good understanding of why diastolic pressure is overestimated,” said co-author Kate Bassil, of the University’s engineering department. “But why systolic pressure is underestimated has been a bit of a mystery.”
Using a custom-built model, the team showed that when the cuff fully closes the artery, pressure in the vessels downstream drops to a steady, low level. This low pressure delays the artery’s reopening as the cuff deflates, meaning the first Korotkoff sound — and the systolic reading — comes later than it should.
Meta-analyses indicate that cuff-based devices can underestimate systolic blood pressure by close to 6 mmHg on average, which is enough to miss roughly one in three cases of systolic hypertension.
Because automated devices are validated against manual auscultatory measurements, the same error often carries over to newer technologies.
“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 Anurag Agarwal, a professor in Cambridge’s Department of Engineering.
What’s the fix?
Researchers say the solution might be as simple as adjusting technique.
One promising option: raising the patient’s arm before inflating the cuff. This simple step reduces venous pressure in the limb, creating a more predictable downstream pressure. Because the degree of underestimation is tied to downstream pressure, having a consistent, known value makes it easier to adjust the reading accurately.
Plus, the change wouldn’t require any new equipment, only a slight modification to the existing auscultatory protocol.
In practice, it could be combined with a short rest period before measurement to stabilize pressures and ensure repeatability.
For longer-term improvements, the team envisions integrating correction factors directly into blood pressure devices. New or updated models could use patient-specific data — age, arm circumference, body mass index or pulse wave velocity — to estimate downstream pressure and automatically adjust systolic readings in real time.
“You might not even need new devices, just changing how the measurement is done could make it more accurate,” said Agarwal.