Implantable intracardiac bioimpedance system
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An implantable intracardiac bioimpedance system has been designed to measure the real and imaginary parts of impedance in a dynamic cardiac setting. The system is broken into two parts: an implantable wireless device and a desktop base station. This measurement is performed using both tetrapolar and tripolar electrode configurations where a 20 kHz current field is applied to the intracardiac blood pool and myocardium. Epochs of discrete voltage samples from the resulting electric field are analyzed using a digital signal processing algorithm to generate impedance measurements. Measurements are then wirelessly transmitted from the implantable device to a base station where advanced signal processing algorithms are applied and the data is plotted in real-time. The final system measures 485 impedance samples/sec, consumes 50 mA when active, and has a percent of measurement error less than 1% for the intracardiac bioimpedance range. The device has been extensively tested to ensure the quality of measurements required for future human use. Instrument design, calibration, verification, experimentation, and modeling are the primary topics of this thesis. Moving forward, the system will be used in studies where dynamic bioimpedance signals measured in the right and left ventricles of the heart will be used to derive stroke volume.