| Summary: | 碩士 === 國立臺灣大學 === 工程科學及海洋工程學研究所 === 105 === Cardiovascular diseases have been the leading cause of death in recent years. Therefore, regular monitoring of blood pressure has become current trend of personalized health management. The most common and commercialized blood pressure portable device is the electronic sphygmomanometer. It is based on the principle of Oscillometry with a pressurized cuff to measure the systolic and diastolic blood pressure. However, it cannot measure the complete profile of blood pressure, and it is not a comfortable process. To overcome these limitations, current studies have turned to the direction of cuffless and continuous Sphygmomanometer.
In this study, we use laser Doppler interferometer to measure the pulse amplitude of the wrist skin. The advantage of this system is it has a resolution as high as 0.08 nm, and the directional ambiguity can be removed by the quadrature interferometer. To increase the stability, we use a wristband to fix a corner cube on wrist and identify the suitable pressure in the range between 70~114 mmHg testing by using a film pressure sensor. We compared our system with Arteriovenous Ultrasound Scanner system and ECG monitor to verify its. Different pulse amplitudes were obtained from different objects, the measurement result was in the range between 25 to 56 μm. The correlation coefficient between pulse amplitude and blood flow velocity was between 0.4 and 0.7. The mean value of heart beating cycle and the result of electrocardiogram have a 73.3% similarity with a less than 0.05 second difference. The correlations among pulse amplitude, blood flow velocity and the accuracy of heart rate measurement were evident.
To develop personalized blood pressure sensor, we further develop the fiber Bragg grating to measure the surface strain induced by wrist pulse vibrations. The Bragg wavelength offset of the fiber grating has a nearly linear relationship with surface strain. Using the four point bending test, we found that 1 micro strain could induce 0.1 pm wavelength shift with the correlation coefficient of 0.995. By adjusting the Bragg wavelength, this strain sensor can be applied to measure the profile of wrist pulse. This sensor could potentially combine with wearable device to achieve long time continuous monitoring of blood pressure.
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