Toward a practical instrument system for the automatic measurement of "up-time" in chronic pain patients.

A portable low-cost instrument system for reliable and automatic measurement of "up-time" in chronic pain patients was described. The system used a miniature electronic stopwatch/calculator to accumulate up-time. A mercury tilt switch mounted on the outer thigh was used to control time accumulation. Performance assessment showed excellent reliaility, as well as high concurrent validity (r = 0.999) for the system. Initial field testing with normal subjects and chronic pain patients indicated reliable and easy operation.