 JUSTIFICATION To date, the measurement of regional blood flow and oxygen utilization has proven difficult. Nowhere is this more true than in the measurement of the regional blood flow and oxygen utilization of the respiratory muscles. Much of what we know about Respiratory Muscle Blood Flow RMBF stems from animal investigations or human research requiring highly invasive methods. The development of a minimally invasive technique for the measurement of RMBF has the potential to add significantly to our knowledge of respiratory energetics in research and clinical settings. 