MADRID, 15 (EUROPA PRESS)
High blood pressure, or hypertension, is the leading risk factor for premature death, associated with heart disease, stroke, and heart attacks. However, inaccuracies in the most common method of measuring blood pressure mean that up to 30% of high blood pressure cases may go undetected.
Anyone who has ever had their blood pressure measured will be familiar with the cuff method. This type of measurement, also known as the auscultatory method, involves inflating a cuff around the arm until blood flow to the forearm is interrupted. The doctor then listens to the tapping of the arm with a stethoscope as the cuff slowly deflates.
Blood pressure is determined by reading a manometer connected to the deflated cuff. Blood pressure is expressed in two values: the maximum (systolic) pressure and the minimum (diastolic) pressure. A blood pressure of 120/80 is considered ideal.
"Auscultatory testing is the gold standard, but it overestimates diastolic pressure, while systolic pressure is underestimated," says Kate Bassil of the Department of Engineering at Cambridge, UK, who developed a model that provided a better understanding of the mechanics of cuff blood pressure readings.
Researchers say some simple changes, which don't necessarily involve replacing standard cuff measurements, could result in more accurate blood pressure readings and better patient outcomes. Their results are published in the journal PNAS Nexus.
WHY SYSTOLIC BLOOD PRESSURE IS UNDERESTIMATED
Almost all doctors know that blood pressure readings are sometimes wrong, but no one can explain why they are underestimated: there is a real gap in understanding," said co-author Professor Anurag Agarwal, also from Cambridge's Department of Engineering.
Previous nonclinical studies on measurement inaccuracy used rubber tubes that did not fully replicate how arteries collapse under cuff pressure, masking the underestimation effect.
The researchers built a simplified physical model to isolate and study the effects of downward blood pressure (the blood pressure in the part of the arm below the cuff). When the cuff inflates and blood flow to the forearm is interrupted, a very low downward pressure is created. By reproducing this condition in their experimental equipment, they determined that this pressure difference causes the artery to remain closed longer while the cuff deflates, delaying reopening and resulting in an underestimation of blood pressure.
This physical mechanism—delayed reopening due to low downstream pressure—is the likely cause of the underestimation, a factor not previously identified. "We are currently not adjusting for this error when diagnosing or prescribing treatments, which is estimated to cause up to 30% of systolic hypertension cases to go undetected," Bassil says.
Instead of the rubber tubes used in previous physical models of arteries, the Cambridge researchers used tubes that lie flat when deflated and close completely when the cuff pressure is inflated—the key condition for reproducing the low downward pressure observed in the body.
HOW TO AVOID UNDERESTIMATING SYSTOLIC BLOOD PRESSURE
The researchers say there are several possible solutions to this underestimation, including elevating the arm before the measurement, which could generate predictable downstream pressure and, therefore, predictable underestimation. This change doesn't require new devices, just a modified protocol.
"We may not even need new devices; we just need to change the way we measure to make it more accurate," Agarwal said.
However, if new blood pressure monitoring devices are developed, they may require additional data that correlates with decreasing blood pressure to adjust "ideal" readings for each individual. This may include age, BMI, or tissue characteristics.
The researchers hope to secure funding for clinical trials to test their findings in patients and are seeking industry or research partners to help them refine their calibration models and validate their effects in diverse populations. Collaboration with clinicians will also be essential for implementing changes in clinical practice.
The research was supported by the Engineering and Physical Sciences Research Council (EPSRC), part of UK Research and Innovation (UKRI).
