Pat:

     You're talking about the basement when most of us only know the ground
     floor (for me, this translates into...arms are nice, legs--sorry, not
     that much experience).

     Very generally speaking, a significant lesion will usually cause a
     >100% increase in PSV when compared to the adjacent, normal segment.

     In Radiology, September 1998, Vol 208, #3, 655-661, Robbin et al use a
     focal 2 to 2.9 X PSV for 50-74% and a threefold increase for 75% and
     above, BUT, this was in the upper extremity.

     Other, UPPER extremity articles you might reference:

        Silva Berry's 1989, Journal of Vascular Technology, Vol 13, April
     1989: "Hemodynamic flow parameters in grafts with adjunctive
     arteriovenous fistulas".

        Gerald Walter's 1992, Journal of Vascular Technology 16(3),
     May/June 1992: Color duplex evaluation of potential hemodialysis
     graft failure".

     Someone who might be able to help you in greater detail would be Carol
     Miranda, RVT, RDMS, RDCS.

     My lower extremity, synthetic loop, thigh access graft diagnosis of
     the month (a pre-Christmas holiday special by the way) is randomly
     pointing somewhere between "more or less" normal and "snow within 6
     months"...BUT...why does your vascular surgeon suspect a venous
     outflow obstruction (problems with dialysis--vascular surgeon
     intuition?).

     Hope this has been of some help.

     Bob Scissons