From the Guidelines
To measure blood pressure accurately, you should place the blood pressure monitor on a table or flat surface at heart level, not on the floor. When taking your blood pressure, sit in a chair with your back supported and feet flat on the floor, as recommended by the 2021 KDIGO clinical practice guideline for the management of blood pressure in chronic kidney disease 1. Rest your arm on the table so that the middle of your upper arm (where the cuff will be placed) is at the same level as your heart. Make sure you're relaxed, haven't consumed caffeine or exercised within 30 minutes before measurement, and empty your bladder beforehand, as suggested by the 2019 AHA/ACC clinical performance and quality measures for adults with high blood pressure 1 and the 2020 blood pressure measurement: a KDOQI perspective 1. The cuff should be placed directly on bare skin, not over clothing. These positioning details matter because blood pressure readings are affected by gravity - if the cuff is below heart level, readings may be falsely high, while positions above heart level may give falsely low readings. Some key points to consider when measuring blood pressure include:
- Using a validated BP measurement device and ensuring it is calibrated periodically 1
- Supporting the patient’s arm while taking the measurement 1
- Positioning the middle of the cuff on the patient’s upper arm at the level of the right atrium (the midpoint of the sternum) 1
- Using the correct cuff size, such that the bladder encircles 80% of the arm 1 Following these guidelines ensures you get the most accurate measurement of your blood pressure.
From the Research
Accurate Blood Pressure Measurement
To measure blood pressure accurately, it is essential to consider the position of the monitor in relation to the heart level.
- The position of the blood pressure monitor can affect the accuracy of the measurement due to hydrostatic pressure changes 2, 3, 4, 5, 6.
- Studies have shown that the difference in level between the heart and the wrist or arm can result in significant errors in blood pressure readings, with a calculated difference of ±4.8 mmHg according to one study 2.
- To minimize these errors, it is recommended to keep the monitor at the same level as the heart, which can be achieved by placing it on a table or surface that allows the arm to be at the same level as the heart 2, 3.
- Alternatively, some blood pressure monitors come with position sensors that can guide the user to place their arm at the correct angle to eliminate hydrostatic pressure effects 2.
- Another approach is to use wearable inertial sensors and deep learning models to correct for hydrostatic pressure changes, which can enable accurate blood pressure measurements even when the sensor is placed away from heart level 3.
Placement of the Monitor
When deciding where to place the monitor, consider the following:
- Placing the monitor on a table can help to keep the arm at the same level as the heart, reducing hydrostatic pressure effects 2.
- Avoid placing the monitor on the floor, as this can cause the arm to be below heart level, leading to inaccurate readings due to hydrostatic pressure changes 5, 6.
- If the monitor is placed on a surface that is not at the same level as the heart, consider using a position sensor or other correction methods to account for hydrostatic pressure effects 2, 3.