Transonic Systems will address this problem by developing a catheter that can measure access flow changes. A saline bolus is injected into the graft's upstream section, and a downstream electrical impedance catheter measures blood conductivity changes as the saline bolus passes through the graft. Measurements take less than one minute to perform, and the procedure requires little specialized training. The Phase-I research will address instrumentation and protocol issues identified in preliminary animal and clinical studies. We will develop an electrical impedance catheter and measurement electronics that can quantify absolute, rather than relative changes in access flow. We will then develop preliminary protocols for probe insertion and injection techniques. Concept feasibility will be studied on a sheep model containing artificial grafts, where we will compare impedance-based flow measurements with independent direct flow measurements with perivascular flow -probes. Finally, our clinical collaborators will investigate methods for Inserting flow catheters into grafts. During Subsequent Phase-II research we will collaborate with key researchers to develop and clinically validate a monitor that measures angioplasty-induced flow changes in hemodialysis accesses, with the goal of quickly gaining FDA permission to proceed to market. PROPOSED COMMERCIAL APPLICATIONS: Dialysis access flow monitor for surgical and radiological intervention could become a routine tool for treatment of vascular access dysfunction. This monitor will allow immediate assessment of the effectiveness of percutaneous angioplasty or surgical revision and reduce the need for repeat interventions, improve the quality of life for ESRD patients, and reduce healthcare costs. This device is marketable in every surgical & radiological intervention unit.