A device designed to approximate shear forces on human skin (a preliminary study).

A shear force on the skin, perpendicular to the forces applying pressures, is thought to be a contributing factor to the formation of decubitus ulcers . The gage described here has been designed to give some quantitative information about the extent of shear forces that exist between human skin and a support medium. The basic operating principle of the device is the measurement of relative motion between a small area of skin surface and the larger surrounding area of skin . This is accomplished by having a small disk, in firm contact with the skin surface, mounted on steel wire so that it can move relative to the surrounding portion of the device which is in firm contact with the larger surrounding area of skin (as well as with the bedsheet or other support medium). Measurement of the deflection of the disk supported by steel wire is accomplished by means of four pneumatic flapper valves set 90 degrees apart from one another . Opposing valves are coupled giving as their output a pressure differential . The portable system is energized through the use of a can of Freon gas . Utilization of fluidics techniques in design and fabrication contributes to the device ' s precision and to its extreme thinness which is functionally very useful .