Measured incorrectly: When measuring blood pressure, the position of the arm plays a more important role than is generally assumed. If the arm is held incorrectly, this can cause significant measurement errors, as a study reveals. In extreme cases, this can lead to a diagnosis of high blood pressure even though the person is healthy. She may then receive medication to lower blood pressure, even though she doesn’t need any. But how do you measure blood pressure correctly?
Millions of people worldwide have high blood pressure, often due to lifestyle and obesity. If left untreated, persistent high blood pressure can damage blood vessel walls and the heart, increasing the risk of a stroke, heart attack or other cardiovascular disease. This can also damage the kidneys, brain and other organs. People with high blood pressure are therefore often given medication to lower blood pressure as a preventive measure. The standard blood pressure for healthy young people is 120/80 millimeters of mercury (mmHg).
In order to adequately determine what a patient’s blood pressure is, certain guidelines apply. When measuring blood pressure, an appropriately sized cuff should be placed on the upper arm at the level of the heart. The arm should be supported on a table or other object. The patient should also sit with their back leaning, feet flat on the floor with their legs uncrossed. However, the armrest in particular is often not adhered to in practice.
Three arm positions in comparison
A team led by Sherry Liu from Johns Hopkins University has now investigated whether and to what extent the position of the arm can distort the measured values. To do this, the doctors repeatedly measured the blood pressure of 133 adults between the ages of 18 and 80. They tested three different arm positions in different orders: supported on a table, placed in the patient’s lap or hanging down the side of the body without support.
In order to simulate a realistic measurement situation in a clinic, the blood pressure measurements were carried out using a digital measuring device between 9 a.m. in the morning and 6 p.m. Before the measurement, the test subjects were asked to walk for two minutes to the examination room, where they then waited five minutes sitting on a chair. After the three measurements in different positions, they walked around again for two minutes and then waited five minutes before their blood pressure was measured a fourth time – this time in the recommended position with their arm on the table.
Incorrect arm position results in higher readings
Comparing the different measurements revealed that arm position significantly influenced the results. When the arm was in the lap, the upper reading was an average of 3.9 millimeters of mercury (mmHg) higher than when the arm was supported, and the lower reading was increased by 4.0 units. If the arm hung loosely, these values were 6.5 and 4.4 units higher. The upper value – the systolic pressure – indicates the force with which the heart pumps blood into the body, and the lower value – the diastolic pressure – indicates the force with which the blood flows through the veins between two heart beats.
Although these measurement differences seem small, they can have significant consequences and even lead to misdiagnosis: “If you consistently measure blood pressure with an unsupported arm and that gives an overestimated blood pressure of 6.5 mmHg, that is a potential difference between a systolic blood pressure of 123 and 130 or 133 and 140 – which is considered stage 2 hypertension,” says Liu. Under certain circumstances, patients may receive medication that lowers blood pressure even though they don’t need any.
How to measure blood pressure correctly. © German Heart Foundation
Doctors and patients have a duty
“The results confirm that arm position makes a big difference when it comes to accurately measuring blood pressure,” says senior author Tammy Brady of Johns Hopkins University. “And they underscore the importance of adhering to clinical guidelines that require firm support on a desk or other surface when measuring blood pressure.”
Although the results only apply to digital blood pressure monitors, they are important for correct diagnosis in clinical settings and at home. The researchers conclude that both doctors and patients should be more careful about arm position when measuring blood pressure. (JAMA Internal Medicine, 2024; doi: 10.1001/jamainternmed.2024.5213)
Quelle: Johns Hopkins Medicine
October 8, 2024 – Claudia Krapp
