In the NEVER-NEED-TO-KNOW department:
I've often thought about the gravity effect and finally decided to quantify it, to see if it was trivial or considerable.
So I pulled out a handy-dandy conversion chart from the ether and see that 1 mm.Hg (1 millimeter mercury) is equal in pressire to a column of water .53525 inches high (I think blood and water are similar in density.)
So each inch differencial between cuff and heart should give a 2 mmHg differential in BP reading (higher when the cuff is lower.)
Goodness, that's more than I'd have thought at first blush and a standing BP taken at the leg based on a difference of say 30 inches, would get a reading that is about 60 points higher on the BP meter, due to the effect of gravity alone (all else being equal.)
I guess, to run with the ball, one's numbers would show perhaps 10-20 mmHg lower if one is lying on one's side and the upper arm is measured. I think that was actually done to me in the hospital on occasion. That is a consierable percentage difference, especially on the diastolic.
Like I said: THE NEVER NEED TO KNOW DEPARTMENT