Implantable electrolyte conductance-based pressure sensing catheter, I. Modeling

Direct measurements of arterial blood pressure most commonly use bulky external instrumentation containing a pressure transducer connected to an ex vivo fluid-filled arterial line, which is subject to several sensing artifacts. In situ blood pressure sensors, typically solid state piezoresistive, capacitive, and interferometric sensors, are unaffected by these artifacts, but can be expensive to produce and miniaturize. We have developed an alternative approach to blood pressure measurement based on deformation of an elastic tube filled with electrolyte solution. We have constructed an analytical model describing the deformation of a fluid-filled tube part of which is exposed to external pressure, with the remaining part unexposed. The model predicts pressure-induced change in dimension of the internal electrolyte-filled volume and a resultant change in its electrical resistance, which can be measured to determine the pressure and is the basis for the sensor operation. We have applied the model to find the pressure sensitivity of fractional change in resistance as a function of device material and dimensional parameters. Construction and testing of a device is described in the following paper.