Sensor for Catheter-Based Measurements of Electncal Conductivity

Measurements of the electrical conductivity of blood have found useful application for almost 100 years. Yet the technology of making those measurements has progressed relatively slowly. To facilitate intravascular conductivity measurements we have developed, refined, and validated a microminiature four-terminal conductivity cell which mounts flush with the surface of a catheter and permits continuous calibrated measurement of conductivity. This, together with our previously published model of blood conductivity, permits continuous measurements of indicator concentration as well as monitoring of blood composition. Discussed here is the rationale for this particular sensor design, including issues which are common to any sensor mounted on the surface of a catheter. The sources and forms of noise, drift, and clotting are discussed, as well as the considerations for optimizing performance.