As blood travels through the arteries of human body, it exerts pressure to its walls. This, so called blood pressure (BP), is maintained within an acceptable range by human body's regulatory mechanisms. To understand basic physiology of blood pressure, click here.
Hypertension is a condition where blood pressure is higher than what can be considered acceptable for that age/gender. An overview of Hypertension can be found here.
Blood pressure varies with the ambiance. Our body is programmed to increase the blood pressure or heart rate at times of stress or anxiety. White Coat Hypertension refers to a condition where a person's BP is elevated only during a doctor's visit. Even people who are under treatment for hypertension, it's not uncommon to see their doctor's office BP readings to be higher than that obtained at home. In all fairness, hypertension treatment decisions should be based on home BP reading because this is 'normal' physiological state of any person. This makes it very important for us to understand and adapt best practices of recording accurate BP recording at home. I will be referencing a typical digital BP monitor which uses oscillometric method, and an arm cuff.
Here is a list do's and don't's that one should follow to get an accurate and reliable BP recording.
Relax, be calm
Ensure you haven't engaged in any major physical or emotional stress in the past one hour. Also, avoid checking BP within one hour of a major meal. On the same note, having a full urinary bladder or in pain due to recent injury may be 'stressful' to the body and may give falsely higher reading. Avoid engaging in a conversation while the recording is going on.
While BP can be measured in any position, most calibration and standardization is done assuming sitting upright position. Also, its advisable that 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 reading. Keep the legs straight down and relaxed. Avoid sitting with crossed legs as this will alter venous circulation of lower body and may effect BP reading. To accommodate all these steps, dinner table and chair works better than couch/sofa or recliners.
Optimal size and position of BP cuff
Blood pressure cuff should be snugly wrapped around the mid portion of the upper arm. Position of the cuff should be roughly estimated to be at the same height at the heart. BP cuff should be loose enough to allow one finger to pass into it, but tight enough not to allow 2 fingers. Ideally, cuff should be placed on bare arms without any cloth or fabric.
Place cuff on the non-dominant arm
Its always optimal to use non-dominant arm with your palms facing up. Keep your hand still for the entire recording. Readings obtained via cuffs on arm may be more reliable compared to wrist cuffs or finger monitors.
Look out for cuff markings
Most of the available cuffs have marking to indicate which area should face the front. Make sure you follow those instructions.
A hard flat surface is the best
The recorder (monitor) should be placed flat on a hard surface, and should not be moved, shaken, or tampered with when in use.
High-quality batteries or power cable is a must
A worn out battery is more likely to give a faulty reading.
Confirm your findings with a second reading
Depending on the model and working conditions, numbers can differ by a few points and that's acceptable. It is also a good practice to check BP on both the arms. Difference of less than 10 mm of mercury is acceptable.
Accuracy of electronic machine can be checked
It's very simple. At your next doctor's visit, take your machine with you. As your blood pressure gets checked at doctor's office, you can ask the nurse/doctor to check your BP once again using your machine. If numbers don't match, your machine is likely faulty. You should go for a new machine in this case since services to re-calibrate an electronic machine may not be readily available.
Please ask any related questions on this topic and I will be glad to add those to this list