Implantable arterial blood pressure sensor

Although blood pressure measurements are well developed, the existing technology in the field of Arterial Blood Pressure (ABP) measurements is not sufficient in terms of long-term ABP waveform assessment. To overcome existing limitations this dissertation proposes, models, designs and tests a new technique of ABP measurements: implantable arterial tonometry. The scope of this dissertation is to study how the geometry of the tonometer and its mechanical properties influence sensor output and stress/strain distribution inside the arterial wall. Two models of tonometer, analytical and numerical, are developed. The relationship between the tonometer response and its effective stiffness is calculated using a lumped parameter model. The contact pressure between the artery and the tonometer as well as the arterial wall stress/strain distribution is studied using a Finite Element numerical model. Based on the theoretical results three prototypes are developed. The piezoelectric dual mode transducer is designed to measure the tonometer-arterial wall contact pressure. The series of in-vitro and in-vivo experiments test the static and dynamic responses of the tonometer. The results indicate the tonometer's effective stiffness necessary to achieve less than 1% error in the dynamic response of the sensor. The geometry of the tonometer's measurement area is found, which results in less than 1% of error in quasi-static response of the sensor. In effort to find potential tissue remodeling areas, the internal arterial wall stress/strain distribution generated by the tonometer is found. The experimental results complement the numerical analysis. The static and dynamic characteristics of the prototype tonometer obtained in-vitro and in-vivo are presented. The explanted tunica media remodeling effect is compared with FE analysis results. The presented work states and solves basic problems of implantable arterial tonometry. In addition it provides the in-vitro and in-vivo examination of the theoretical results. The thesis develops tools of modeling, designs, and testing procedures for future researchers willing to develop implantable tonometers. The thesis concludes with a novel design of the implantable tonometer.