# different bp readings in right and left arms



## Explorer127 (May 28, 2009)

What can cause a patients right arm to have a systolic pressure of 20 more than the patients left arm?


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## Lifeguards For Life (May 28, 2009)

As far as I know it is normal to have a systolic difference of up to 10mmhg in each arm.  I would guess that an inter arm systolic bp difference of 20 mmhg would be caused by a congenital anomaly. possibly thinning of vessels in one of the arms?


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## Porky1 (May 28, 2009)

Poor circulation in one arm versus the other could explain. As the previous person said it is not unusual to have a slight difference but a 20 mmHg difference could mean some circulation difficulties. Another could be size differences. Is one arm bigger than the other?


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## MSDeltaFlt (May 28, 2009)

A thoracic aortic anreuysm that begins somewhere between the bifurcations of the subclavian arteries.  Which is why when you get a pt with a poss TAA/AAA, they want BP's in *both* arms.


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## medicdan (May 28, 2009)

As far as I understand, a buildup of plaque in an artery (decreasing it's size), related to stenosis, diabetes, etc, can cause a significant difference in BPs.

Side question: Patients with Peripheral Vascular Disease suffer from calcified arteries-particularly in the legs-- so would it affect blood pressure (using a thigh cuff, of course).


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## BruceD (May 28, 2009)

Coarctation of the aorta is typically the 'book' answer you'll see when asked this question.

There are other possibilities of course.

Here is a pretty good rundown on coarctation

http://www.patient.co.uk/showdoc/40000428/


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## Lifeguards For Life (May 28, 2009)

there are multiple conditions that could cause this. in addition to what everyone else has chipped in it could be an aortic disection, atheroma, embolus or thrombus. I believe the most probable and simplest explantaion would be either the subclavain, axillary or brachial arteries becoming thinned, or an aortic coarctation as Bruce said.


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## Explorer127 (May 28, 2009)

Can an MI cause this?


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## Lifeguards For Life (May 28, 2009)

Explorer127 said:


> Can an MI cause this?



no. not that i am aware of. anybody else?


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## Explorer127 (May 29, 2009)

Okay, I was thinking a clogged artery could decrease BP..


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## Lifeguards For Life (May 29, 2009)

Like an embolus or thrombus as mentioned before?


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## BruceD (May 29, 2009)

Lifeguards For Life said:


> no. not that i am aware of. anybody else?



I do not see how it could, there is only the single systemic outflow tract from the heart (Aorta), so any MI would affect the systemic blood pressure, not just one arm.


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## BruceD (May 29, 2009)

Explorer127 said:


> Okay, I was thinking a clogged artery could decrease BP..



Symptomatic arterial thrombus is relatively rare in the upper extremities.
If you think about it, most arterial blockage is due to atherosclerotic plaque which tends to, almost exclusively, cause blockage in small arteries such as the coronaries long before it could affect large arteries like the axillary or radial artery.  Also, emboli from the legs or elsewhere would tend to be caught in the lungs (the dreaded P.E.) before they could ever get to an artery in the arm, with some exceptions for people with septal defects allowing paradoxical embolism.

There are a few possible exceptions, I've seen a few articles talking about things such as thoracic outlet syndrome, cancer, and some congenital hypercoagulable states(more commonly affect veins) mentioned as possible causes for upper extremity arterial occlusion.

Upper Extremity Arterial Thrombosis

Hypercoagulable disorders

Interestingly, 9% of patients (for lack of a better term) in an autopsy series were found to have left subclavian stenosis or occlusion.

Subclavian Artery Thrombosis

Aortic dissection can affect the subclavian artery as well, possibly resulting in decreased blood flow.

Aortic Dissection

However, depending on the artery affected and the amount of collateral circulation, and your skill in taking an accurate BP, I don't see why it couldn't cause a unilateral decrease in upper extremity BP.  It just wouldn't be at the top of the differential for different BPs in the arms.


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