Why raise the bed six inches at the head end for Inclined Therapy?

An experiment was performed to determine the optimum angle for circulation.

Using a closed water filled loop of tubing with coloured salt solution added at the pillow end and the loop stretched down the bed, the bed was elevated.

The lower elevations in the range of 4-4.5 inches resulted in the salt flowing down one side and the clean water flowing back up the same side. 2 directional flow in one tube while fascinating to watch was not the desired effect.

After raising the bed to 5 inches the downward flow was in the salt added side representing the arteries and the return flow was in the opposite salt-free side representing the venous return or indeed the return flow of the cerebrospinal fluid system or the return flow of the lymphatic system.

this return flow and return is under tension and was observed using soft walled silicon tubing showing clearly how the solutes affect the pressure of the water molecules.

The downward flowing side clearly bulged outwards under the positive pressure induced by gravity, while the return flow water only side was pulled in, indicating that the molecules were placed under tension by the gravity affect on the salt dissolved in water.

Over time this has been born out by many people sleeping inclined, while a 4 inch incline is better than sleeping flat, a 6 inch / 15 cm raise producing a five degree to the horizontal on a 75 inch long bed.

Fascinating history of the bed reveals that the oldest beds know from the ancient Egyptians some 4 thousand years ago were raised by exactly 6 inches at the head end according to a curator of a museum in Boston. USA.

Question is how did they know? Did they observe animals sleeping on an incline and imitated them and then find the benefits? We will never know but it is intriguing.