There probably is a test, but common sense suggests that gravity will drain fluids lower. Being involved with the trades, I can tell you that fluids will drain downhill when the drop is 1/4" per linear foot the entire line. Selma is point on with this advice. If you raise the head of your bed about four inches with boards, it will help keep acids from rising into the esophagus.
Hi...it is not just the raining of the head...it is really from the pelvis up...u r more on an incline...if it is just ur head that is raised it will not help....u need to use gravity to help keep the acids down where they belong...so raising the head of the bed, puts in on an incline...a bunch of pillows will not work as u can roll off them and it is usually not enuff of an incline to help.
"selma"