I had a question; what is the proper position for taking a blood pressure reading? I’m using a cuff-type unit which auto-inflates.
When I took a reading by sitting in a chair and resting my forearm on a table, in such a way that my forearm is well below the chest. In this position, my BP is in the higher side. But when I rest my wrist up on something so that it is almost at the level of the upper arm and just a little lower than my chest, my BP reading is significantly lower.
For example, I just took a reading with my forearm resting on the table and my BP was 138/84. I then took it by supported the arm by a small box and make it almost straight and the BP was 129/77. This difference is not after any relaxation in-between.
I've came across information that a proper reading should be taken with the arm level with the heart. Does this mean propping the arm up is the right position, just below the chest? Does anyone have any correct input on this subject?
Some of the factors that can affects pressure reading; exercise, alcohol or nicotine consumption, caffeine (Coffee & Coco) containing food consumption, arm position, tension in the muscle, bladder distension and talking.
The recommended cuff sizes are:
* Arm circumference of 22 - 26 cm; cuff should be "small adult" size: 12*22 cm
* Arm circumference of 27 - 34 cm; cuff should be "adult" size: 16*30 cm
* Arm circumference of 35 - 44 cm; cuff should be "large adult" size: 16*36 cm
* Arm circumference of 45 - 52 cm; cuff should be "adult thigh" size: 16*42 cm
Effects of Body Position
Blood pressure measurement is normally taken in either sitting or supine position, but these 2 positions give different measurements. The diastolic pressure measured while sitting is higher (by 5mm HG) than supine. When the arm position is precisely adjusted so that the cuff is exactly at the level of the right atrium in both positions, the systolic pressure has been approximately 8 mm Hg higher in the supine than the upright position.
Other body position to be in considerations includes the back and legs. If the back is not supported (that is the patient is seated on table instead of a chair; no support for the back), the diastolic reading may be increased by 6 mm Hg from actual. Crossed legs during measurement may increase systolic pressure by 2 to 8 mm Hg from actual.
In the supine position, the right atrium is at halfway between the bed and the level of the sternum; thus, if the arm is rested on the bed, then it would be below heart level. That’s why, the reading taken in the supine position the arm should be supported with a pillow.
Arm Position Effects
The position of the arm can also have impact on the blood pressure measurements; if the upper arm is below the level of the right atrium; when the arm is hanging down while sitting, the pressure readings will be too high. Otherwise, if the arm is above the heart level, the pressure readings will be too low. These differences may be 10 mm Hg or more, or 2 mm Hg for every inch above or below the heart level.
Other physiological factors that may impact the blood pressure measurement include; muscle tension - the arm is held up by the patient instead of supported, the isometric exercise before reading will raise the pressure.
Differences in reading between the Two Arms
Several studies reported that there is some blood pressure reading variations between 2 arms (right & left arm). But there is no clear pattern; there is no systematic differences between the 2 arms, but 20% of subjects had differences of >10 mm Hg, these findings are disturbing, it is not clear to what extent the differences were consistent & reproducible. It is recommended that blood pressure should be taken in both arms at the first diagnosis. When there is a consistent inter-arm difference, then the arm with the higher reading should be used.