I'm glad you are paying attention to this because although this blood
pressure differential may be completely normal for you, it could also be a
sign of a problem that should be checked out by your physician.  That
problem could be an abnormality in your aorta which is the large artery
coming off your heart.  Shortly after it leaves the heart, the aorta
branches into the right and left subclavian artery, which serve the right
and left arm respectively.  If there is an abnormality at that branching, it
can give you different blood pressures in your right arm than in your left.

Another possible cause of your BP differential is called a coarctation of
the aorta. This is a narrowing of this major artery right after it leaves
the heart.

A good family physician, an internist, or a cardiologist can help you
investigate this.  Your visit should include a good history, a good
physical, blood pressures taken in both arms, and a skilled examination of
your heart sounds.  You may be asked to get some kind of imaging study after
your first visit to make sure your aorta is functioning fully.  Don't let
your doctor send you away without a definitive plan to make sure your heart
and aorta are both functioning perfectly normally!

There is a site I found for you that clearly tells about "coarctation of the
aorta".  It can help you understand some of what your physician will be
checking you for.  

Best of luck to you.  Feel free to send any follow-up information or
feedback to the innkeeper@the-doctors-inn.com!

Dr. Kerr