8

Second year medical student asking.

Does the blood pressure at the root of aorta equal the blood pressure in the brachial artery?

I've heard it does but it doesn't quite seem to make sense as I'd think the blood pressure would be lowered the further it travels? Research indicates[1] that there is not the same pressure but I can't seem to find a "why".

  1. http://www.ncbi.nlm.nih.gov/pubmed/18765967
  • 2
    Good question! I’m guessing we should assume “all things being equal” - i.e. both on the same level with respect to gravity? Also, if you’re going to include the sentence “research indicates”, it would be helpful to link to said research. – Susan Sep 17 '15 at 10:04
  • Just curious, are you contemplating the way we measure "blood pressure" (brachial artery) vs actual pressure in the aorta, and if there is a fault in this thinking? – anongoodnurse Sep 17 '15 at 19:43
  • There used to be a measurement of X/palp when without equipment, referring to being able to feel distal pulses manually, but I do not know if that is still a valid reference or not. – JohnP Sep 17 '15 at 22:00
5

The mean pressure has to be lower peripherally for blood to flow in that direction. However, it is well known that there is an amplification of systolic blood pressure in the limbs due to reflection of pressure wave from periphery (see http://hyper.ahajournals.org/content/51/1/112.full). Vascular stiffness also affects this phenomenon. See figure 4 of this article in American Journal of Physiology: http://ajpheart.physiology.org/content/299/3/H584

The phenomenon of pressure wave reflection is shown clearly in figure 5 of this article in Advances in Physiology Education http://advan.physiology.org/content/37/4/321

This phenomenon is also exaggerated in aortic regurgitation, where it is called the Hill's sign: http://www.learntheheart.com/cardiology-review/hills-sign/

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