18 November, 2023

Recording blood pressure at home: Are you following the cardinal rules?

Introduction:
As blood travels through the human body’s arteries, it exerts pressure on its walls. This pressure, so-called blood pressure (BP), is maintained within an acceptable range by the body’s regulatory mechanisms. To understand the basic physiology of blood pressure, click here.

Hypertension is a condition where blood pressure is consistently higher than what can be considered acceptable for that age/gender. An overview of Hypertension by the World Heart Organization can be found here.

Blood pressure varies with the situation. Our body is programmed to increase the blood pressure or the heart rate at times of need, for example when doing any physical activity or when we are stressed or anxious. White Coat Hypertension is when a person’s BP is elevated only during a doctor’s visit. Even for people who are under treatment for hypertension, it’s not uncommon to see their doctor’s office BP readings to be higher than those obtained at home. In all fairness, hypertension treatment decisions should be based on home BP readings because this is any person’s ‘normal’ physiological state. This makes it very important for us to understand and adapt best practices for taking accurate BP recordings at home. I will be referencing a typical digital BP monitor that uses an oscillometric method and an arm cuff.

Here is a list of basic practices that one should follow to get an accurate and reliable BP recording.

Relax, be calm
Ensure that you haven’t engaged in any major physical or emotional stress in the past hour. Also, avoid checking BP within an hour of a major meal. On the same note, having a full urinary bladder or being in pain due to a recent injury may be ‘stressful’ to the body and may give a higher reading. Avoid engaging in a conversation while the recording is going on.

Sitting upright is the best position
While BP can be measured in any position, most calibration and standardization assume a sitting upright position. Also, one should sit with proper back support. On the same note, the arm that is being used to record should be well-supported on a surface rather than being up in the air. This will tense the muscles and will give false readings. Keep the legs straight down and relaxed. Avoid sitting with crossed legs as this will alter the venous circulation of the lower body and may affect BP reading. A dinner table and chair works better than a couch/sofa or recliner to accommodate all these steps.

Optimal size and position of BP cuff
The blood pressure cuff should be snugly wrapped around the mid portion of the upper arm. The inflatable bladder of the cuff (you can feel that through the fabric) should be placed over the inner portion of the upper arm and encircle more than half of the arm circumference. Most cuff manufacturers indicate the correct positioning by an indicator line or an arrow.

The position of the cuff should be roughly estimated to be at the same height as the heart. The BP cuff should be loose enough to allow one finger to pass into it but tight enough not to allow two fingers. Ideally, the cuff should be placed on bare arms without any cloth or fabric.

Place the cuff on the non-dominant arm
It is advisable to use the non-dominant arm with your palms facing up. Keep your hand still for the entire recording. Upper arm cuffs are more reliable compared to wrist cuffs or finger monitors.

A hard flat surface is the best
When in use, the recorder (monitor) should be placed flat on a hard surface and not moved, shaken, or tampered with.

High-quality batteries or a power cable are important
A worn-out battery is more likely to give a faulty reading.

Confirm your findings with a second reading
Depending on the machine model and its working conditions, BP numbers can differ by a few points and that’s acceptable. It is also a good practice to check BP on both arms. A difference of less than 10 mm of mercury is acceptable.

The accuracy of electronic machines can be checked
At your next doctor’s visit, take your machine with you. As your blood pressure is checked at the doctor’s office, you can ask the nurse or doctor to check your BP once again using your machine. Your machine is likely faulty if the numbers don’t match (a 5 mm difference is acceptable). You should get a new machine in this case since services to re-calibrate an electronic machine may not be readily available.

I am sure I didn’t answer all your questions on this topic. Feel free to message me with your queries; I will happily answer them.

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