The reason for the inaccuracy of pressure measurements explained

A new study has revealed why typical blood pressure readings using an inflatable cuff are not entirely accurate and how this accuracy can be improved, reports the journal PNAS Nexus.

Hypertension is a major risk factor for premature death, linked to heart disease, strokes, and heart attacks. However, due to inaccuracies in the most common blood pressure measurement method, up to 30% of hypertension cases may be missed.

The most commonly used and considered the "gold standard" method for measuring blood pressure is the auscultatory cuff method. After inflating the cuff around the upper arm to the point where it cuts off blood flow to the forearm, the person taking the measurement listens for the pulse with a stethoscope while the cuff is slowly deflated. Blood pressure is measured based on the readings of a sphygmomanometer attached to the deflated cuff. Two separate values are reported: the maximum (systolic) and the minimum (diastolic) pressure. A blood pressure reading of 120/80 is considered "ideal."

Scientists from the University of Cambridge have built an experimental model that explains the physical basis of blood pressure measurement inaccuracies and provides a better understanding of the mechanics of blood pressure cuff readings. Instead of the rubber tubes used in previous artery models, they used tubes that lie flat when deflated and close completely when the cuff is inflated, a key requirement for replicating the low cuff pressure observed in the body.

This simplified physical model allowed us to isolate and study the effect of blood pressure in the arm below the cuff. When the cuff is inflated and blood flow to the forearm is cut off, a very low pressure develops in the lower arm. By replicating this condition experimentally, the researchers determined that this pressure difference causes the artery to remain closed longer as the cuff deflates, delaying reopening and leading to an underestimation of blood pressure.

"Auscultation is the gold standard, but it overestimates diastolic blood pressure, while underestimates systolic blood pressure," said study co-author Kate Bassil from the University of Cambridge's Department of Engineering. "We have a good understanding of why diastolic blood pressure is overestimated, but why systolic blood pressure is underestimated has remained a mystery."

“Almost every clinician knows that blood pressure readings are sometimes inaccurate, but no one has been able to explain why they are underestimated – there is a real knowledge gap,” said co-author Professor Anurag Agarwal, also from the Faculty of Engineering at the University of Cambridge.

This physical mechanism – delayed reopening due to low cuff pressure – is the likely cause of the underestimation. “We currently do not account for this error when diagnosing or prescribing medications, which is estimated to lead to missing up to 30% of cases of systolic hypertension,” Bassil pointed out.

According to the authors, a few simple changes, not necessarily involving replacing the standard cuff measurement, could lead to more accurate blood pressure readings and improved patient outcomes. For example, raising the arm before measurement potentially produces a predictable cuff pressure, and therefore a predictable underestimation. This change does not require new devices, only a protocol modification.

“It may turn out that new devices will not even be needed; simply changing the measurement method can increase its accuracy,” Agarwal emphasized.

However, as new blood pressure monitoring devices are developed, they may require additional inputs to tailor the "ideal" readings for each individual. This could include age, BMI, or tissue characteristics.

The researchers hope to secure funding for clinical trials to test their results in patients and are seeking industry or research partners to help them refine their calibration models and validate their results in different populations. Collaboration with clinicians will also be essential.

Paweł Wernicki (PAP)

pmw/ agt/

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