PPCD use will continue until the presenting symptoms resolve or traditional revascularization becomes necessary to achieve limb salvage. Each patient serves as his/her own control. Three "pairs" of blood specimens will be analyzed per patient. A "pair" includes phlebotomy prior to and immediately after two hours of PPCD. The first pair is obtained on enrollment in the study. The second pair will be done 2 weeks later 18-24 hours after the last dose of G-CSF. The third pair will be done 30 days into the study, 18-24 hours after the last dose of G-CSF. The patient will return for standard of care clinical evaluation, with repeat hemodynamic testing, 6 months after the 30 day clinic evaluation.