Near-infrared spectroscopy can be used to determine the relative oxygen saturation in tissues up to 2cm below the skin. It has been investigated, with success, in cerebral, gastrointestinal, and muscle tissue, and shows promise in numerous indications involving tissue ischemia. In the current study, we propose to examine one hundred patients requiring either bypass or angioplasty due to chronic critical limb ischemia resulting from peripheral arterial disease. We intend to challenge patients before and after the intervention, using either an inflated blood pressure cuff or toe raises, to determine if oxygen saturation recovery time in the affected limb is correlated with symptom resolution (i.e. treatment success). Near-infrared spectroscopy will be performed using the ODISsey tissue oximeter developed by ViOptix, Inc. The proposed study will take approximately one year to complete enrolment, and has a follow-up period of 6 months post-intervention.