Major Flaw In Blood Pressure Tests Could Be Giving Millions The Wrong Reading

High blood pressure could be missed in millions due to a flaw in blood pressure tests. (© Andrey Popov – stock.adobe.com)

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.

Source: https://studyfinds.org/major-flaw-blood-pressure-tests/