A Novel Flexible Distributed Pressure Sensing Strip for a Urethral Catheter
2017-06
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A Novel Flexible Distributed Pressure Sensing Strip for a Urethral Catheter
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2017-06
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This dissertation develops, designs, fabricates and evaluates an instrumented catheter for instantaneous measurement of distributed urethral pressure profiles. The developed catheter has important clinical applications in urodynamic testing for analyzing the causes of urinary incontinence in patients. A flexible sensor strip is fabricated with an array of nine pressure sensors and integrated electronic pads for an associated sensor IC chip. The flexible sensor strip and associated IC chip are assembled on a 7 Fr Foley catheter for the urology application. There are two major challenges in the development of the sensor strip. First, a highly sensitive sensor strip that is flexible enough for urethral insertion into a human body is required and second, the sensor should work reliably in a liquid in-vivo environment in the human body. Capacitive force sensors are designed and micro-fabricated using polyimide/PDMS substrates and copper electrodes. To remove the stray influence of urethral tissues which create fringe capacitance that can lead to significant errors, a reference fringe capacitance measurement sensor is incorporated on the strip and the whole sensor area is actively shielded in a Faraday cage made of gold. By supplying the active sensing voltage simultaneously to the deformable electrode of the capacitive sensor and to the Faraday cage, the stray capacitance during in vivo measurements can be largely eliminated. Due to the transparency of the Faraday cage, the top and bottom portions of a capacitive sensor can be accurately aligned and assembled together. Experimental results presented in the thesis show that stray capacitance is reduced by an order of magnitude by the Faraday cage when the sensor is subjected to a full immersion in water. Since the catheter enables a new type of urological measurement, a process for accurate ex-vivo validation of the catheter is also developed. A sheep bladder and urethra are extracted and used in an ex-vivo set up for validation of the developed instrumented catheter. The bladder-urethra are suspended in a test rig and pressure cuffs placed to apply known static and dynamic pressures around the urethra. An algorithm based on use of reference stray transducers is used to compensate for the remaining portion of stray capacitance. Extensive experimental results verify that the developed compensation method works effectively. Results on pressure variation profiles circumferentially around the urethra and longitudinally along the urethra are presented. Finally, the developed sensing catheter is tested in vivo in live female sheep to construct real-time urethral pressure profiles. The results are presented and discussed.
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University of Minnesota Ph.D. dissertation. June 2017. Major: Mechanical Engineering. Advisor: Rajesh Rajamani. 1 computer file (PDF); vii, 75 pages.
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Ahmadi, Mahdi. (2017). A Novel Flexible Distributed Pressure Sensing Strip for a Urethral Catheter. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/190481.
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