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High blood pressure is potentially a danger to many pregnancies. One of the complications is pre-eclampsia, which can lead to the death of mother and the baby.
This is why regular monitoring of a pregnant woman’s blood pressure is recommended. However, errors to BP readings are as dangerous as the condition itself.
Easily operated, validated electronic blood pressure devices are becoming increasingly available and accessible for self-monitoring of blood pressure (SMBP). It is becoming more helpful in decision-making regarding treatment and effective blood pressure control.
Indeed, emerging evidence supports the beneficial impact of personal monitoring automated devices in the regular measurement and recording of blood pressure by an individual outside of the hospital.
However, there is a caveat. Researchers believe that commonly used arm positions for blood pressure measurement will give wrong readings when the arm is not supported, say on a table or a flat surface before the reading is taken on a surface.
The researchers at Johns Hopkins Medicine found that blood pressure readings from the arm supported on the lap or hanging at their side, maybe when the measurement is done at the dining table or while sitting up in bed, maybe inaccurately higher readings.
In the study, they found that systolic blood pressure readings for participants who supported their arms on their laps were overestimated by about 4 mmHg, while readings for those positioning their arms unsupported by their sides had an overestimated systolic blood pressure of almost 7 mmHg.
Blood pressure is typically expressed as the reflection of two numbers, systolic pressure and diastolic pressure. It is usually written as the systolic pressure over the diastolic pressure (e.g., 120/80 mm Hg).
The systolic pressure is the force of blood flow when pumped out of the heart, and the diastolic pressure is the pressure in the arteries when the heart rests between beats.
High blood pressure doesn’t always cause symptoms. Sometimes symptoms don’t appear until someone has had hypertension for years. But it puts a person at a higher risk of heart disease and stroke.
Dr. Tammy M. Brady, who was involved in the study, published in the journal JAMA Internal Medicine, said the trial had further emphasised that improper arm position and support can lead to overestimation of blood pressure and potentially lead to overdiagnosis of hypertension and overtreatment.
Mistakes made at home will also translate to incorrect readings that possibly lead to overtreatment of blood pressure based on these measurements.
According to her, “When the arm is either in the lap or at the side, the blood vessels in the arm are at a greater vertical distance from the heart. Gravity increases the pressure in these blood vessels.
“It also is harder for the blood to return to the heart when the arm is lower than the heart; to compensate for this and improve blood return, the blood vessels in the arm constrict.
“In addition, when the arm is unsupported, the muscle isn’t fully at rest and contracts. All of these body responses lead to a higher blood pressure reading.”
Dr Adewole Adebiyi, a heart expert at the University College Hospital (UCH), Ibadan, in a remark, said guidelines for accurate blood pressure readings entail sitting at a table, resting the arm on the table, and making sure that the blood pressure cuff is at the level of the heart before the reading is taken.
“That’s what we teach. That’s how we train people to measure blood pressure. Rest; sit at a table. Rest your arm on the table and take the blood pressure. The clinical guideline is firm on support for the arm before the reading. If you do it any other way, you likely will get a wrong reading,” he declared.
Dr. Adebiyi said the study highlighted the importance of health workers keeping to established guidelines on proper blood pressure measurement techniques regardless of whether it’s blood pressure taken at home, a hospital ward, or a clinic to be able to obtain the most accurate blood pressure readings.
For this study, the researchers at Johns Hopkins Medicine recruited 133 adult participants ages 18 to 80 between Aug. 9, 2022, and June 1, 2023.
They were randomly assigned to sets of triplicate blood pressure measurements with their arm positioned in one of three ways when the reading was taken—arm supported on a desk, arm supported on their lap, or an unsupported arm hanging at their side.
Measurements were taken during a single visit between 9 a.m. and 6 p.m. Before BP measures were taken, all participants first emptied their bladders and then walked for two minutes to mimic a typical clinical scenario in which people walk into a clinic or office before screening takes place. They then underwent a five-minute seated rest period with their backs and feet supported.
In 2005, researchers at the Olabisi Onabanjo University Teaching Hospital, Sagamu, cautioned that arm position and arm support can affect the accuracy of BP measurements and urged healthcare providers to adhere to recommended guidelines for blood pressure measurement. This was published in the Cardiovascular Journal of Africa.
The study, which involved Professor Ranti Familoni and Dr Taiwo Olunuga, compared the effects of arm position and support on blood pressure in 123 persons with hypertension and 12 persons with normal blood pressure at the hospital.
They found that the effect of arm position is more than that of arm support in blood pressure readings, although they are additive and more in persons with normal blood pressure readings.
The lowest recordings were observed when the elbow was slightly flexed and supported at this position. The highest BP was observed in the standing position with the arm hanging at the side.
Failure to support the arm at the elbow, even when it was positioned perpendicularly to the torso, led to an increase of 4.87/4.81 mmHg in hypertensives and 7.61/2.83 mmHg in normotensives.
Also, differences in the systolic BP when the arm was hanging compared to when it was perpendicular to the torso or flexed and supported at the elbow were 7.45 mmHg in those with hypertension.
Understanding how blood pressure monitoring equipment operates and the potential sources of error that could skew readings is useful for maximising its use. The most common blood pressure reading mistakes are due to using the wrong-sized blood pressure cuff, incorrect patient positioning, incorrect blood pressure cuff placement, normal reading prejudice, and not factoring in electronic units correctly.
A BP cuff that is too large will give falsely low readings, while an overly small cuff will provide readings that are falsely high. So, the most practical way to quickly and properly size a BP cuff is to pick a cuff that covers two-thirds of the distance between one’s elbow and shoulder.
Measuring BP in an extremity positioned above heart level will provide a falsely low BP, whereas falsely high readings will be obtained whenever a limb is positioned below heart level.
A seated upright position, legs uncrossed, and not talking provides the most accurate blood pressure, as long as the arm in which the pressure is taken remains at the patient’s side. Crossing the legs increases systolic blood pressure by 2 to 8 mm Hg. Lying on their side or in other positions can give inaccurate pressure measurements.
Self-monitoring of blood pressure at home, including taking drugs as prescribed, following a low-salt diet, limiting alcohol use, exercising regularly, and managing a healthy weight are all part of self-care practices showing beneficial effects on high blood control and preventing its many complications, like stroke and heart attack.
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