| Summary: | 碩士 === 國立成功大學 === 數學系應用數學碩博士班 === 104 === Stiffness index (SI) of vessel is an important physiological index and a predictor of cardiovascular disease such as myocardial infarction and stroke. In practice, the stiffness index is computed by finding the time difference of two peaks in a period of the photoplethysmogram (PPG) wave from fingertip. In this study, we use delayed wave decomposition to estimate the time difference instead. The key idea is to decompose the
PPG signal into the velocity waves from the carotid arteries measured by ultrasound transducer and its delayed wave, which is considered as the reflection wave from main branch of artery. The method of the wave decomposition is used to determine the delayed time, which is a parameter relating to the stiffness index; and the ratio of delayed wave and dominant wave, which is used to estimate the reflection index. We determine the time delay and the amplitude of the delayed wave by minimizing the difference between the average waveform and the heart waveform and its delayed wave in a period. We also compared with the Nelder-Mead method. And we used the penalty functions to balance the errors and the delayed coefficients. Moreover, we increase the number of delayed waves and we found that the reconstruction wave is almost the same as the averaged waveform if we used twelve delayed waves at least.
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