Cambridge study reveals why blood pressure armbands give wrong readings

Researchers at the University of Cambridge have uncovered a key reason why standard blood pressure wraps often produce inaccurate readings and proposed practical solutions to improve measurement accuracy. The findings, published in PNAS Nexus, could significantly impact the detection and management of hypertension, a leading cause of premature death worldwide linked to heart disease, stroke, and heart attack.

Hypertension affects millions globally, yet current wrap-based blood pressure tests may fail to identify up to 30% of cases. According to an article by SciTechDaily, the team sought to investigate why these errors occur, using a specialised experimental model to simulate the mechanics of wrap-based measurements.

Their work revealed that low downstream pressure — the blood pressure in the part of the arm below the wrap — plays a critical role in underestimating systolic readings.

In typical auscultatory measurements, a wrap is put around the upper arm and inflated to temporarily halt blood flow to the lower arm. As the wrap gradually deflates, a healthcare provider listens through a stethoscope for the familiar tapping sounds that indicate systolic and diastolic pressures.

A reading of 120/80 mmHg is generally considered ideal. However, previous laboratory studies using rubber tubes to mimic arteries failed to replicate how arteries collapse under wrap pressure, masking key errors caused by downstream pressure.

The Cambridge team built a physical model that more accurately reflected arterial behaviour under wrap inflation. Their experiments showed that when blood flow to the lower arm is stopped, the downstream pressure becomes extremely low.

This pressure difference keeps the artery closed longer as the wrap deflates, delaying blood flow detection and causing systematic underestimation of the true systolic pressure. Essentially, many patients may appear to have “normal” readings even when their blood pressure is elevated.

Importantly, the researchers identified simple, low-tech interventions that could improve accuracy without replacing existing devices. One such approach is to raise the arm before measurement, which helps create a predictable downstream pressure and mitigates underestimation.

Agarwal, one of the researchers, noted: “You might not even need new devices; just changing how the measurement is done could make it more accurate.”

For the future, more advanced blood pressure devices could incorporate individualised adjustments for factors that influence downstream pressure, such as age, body mass index, or tissue characteristics. These inputs could help calibrate readings for each patient, further reducing the risk of undiagnosed hypertension.

By highlighting a previously underappreciated source of error in standard blood pressure testing and suggesting straightforward corrective measures, the Cambridge team’s work has the potential to improve early detection of hypertension and ultimately reduce cardiovascular risk.

These findings underscore that even minor refinements to existing protocols can have major public health implications.

By Nazrin Sadigova