I am helping a med student do a project with PPGs. He (and I) are
     having trouble finding adequate references about technique,
     variability, etc. Does any one out there know of some good references
     about PPG. I've checked a few of the old textbooks but there really
     isn't too much written. Maybe some of the "oldies but goodies" among
     flownet land may know of some early work on PPGs. Thanks for any
     help.

     Ann Marie Kupinski