Blood pressure is normally measured with the cuff of the sphygmomanometer around the arm. Suppose the blood pressure were measured with the cuff around the calf of the leg of a standing person. Would the reading of the blood pressure be the same here as it is for the arm?
The blood pressure measured at the calf would be larger than that measured at the arm. If we imagine the vascular system of the body to be a vessel containing a liquid (blood), the pressure in the liquid will increase with depth. The blood at the calf is deeper in the liquid than that at the arm and so it is is at higher pressure.
Blood pressures are normally taken at the arm because it is at approximately the same height as the heart. If blood pressures at the calf were used as a standard, adjustments would need to be made for the height of the person and the blood pressure would be different if the person were lying down.
On the same note, here are seven tips to ensure you get an accurate blood pressure reading:
1. Wait! Don’t measure your blood pressure the moment you reaches the medical examination room. Wait at least five minutes to stabilize your heart rate. If you had been rushing for your medical appointment, your blood pressure will be a lot higher than its true reading. Have a good rest before measuring your blood pressure.
2. Don’t Talk. This might be a bit weird but talking to the medical personnel during the measurement can throw the blood pressure numbers off.
3. Sit correctly. An incorrect posture will have an effect on your blood pressure. Sit with your back on the back of the chair, feet flat on the floor and legs uncrossed.
4. Ensure that the cuff is of the right size. If the cuff is too large, the blood pressure reading will be higher than its true value.
5. Check blood pressure on both arms. If there is a blocked major blood vessel in one of the arm, the blood pressure measured on that arm will be different from the other arm.
6. Do not drink coffee prior to the appointment. Drinking tea, coffee, cola or other caffeinated drinks within 30 minutes will raise your blood pressure.
3 thoughts on “Why must we measuring blood pressure at the arm?”
If taking blood pressure at rest is the best way to take it, then why not take it at true rest while lying down? personally my blood pressure is on average 5-10 points lower lying down. And if lying down is acceptable, then why does the arm have to be by the side? because when I’m lying down, & I place my arm at shoulder level on my back with my elbow slightly bent, my arm is still the same height as my heart, but I find this much more comfortable because my arteries are fully opened allowing proper circulation which is what we all strive for subconsciously without even realizing it every minute of every day. This in turn gives me another 5-10 point lower BP reading because of the way my body is shaped. Could someone please respond who has researched, & understands this? Thanks in advance.
Re: Why must we measure blood pressure in the arm?
Just a comment that I would recommend revising your statement in point #4; it is incorrect. Too small of a cuff would result in a higher reading and overestimate the blood pressure. This problem is referred to as “under-cuffing”. The oversizing of a cuff is generally not that much a problem and will generally detect hypertension if a patient truly has hypertension.
Please see: http://www.ncbi.nlm.nih.gov/books/NBK83269/
Craig Wong, MD
Division Chief of Pediatric Nephrology
University of New Mexico Health Sciences Center