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Meaurement of Flow Mediated Dilation Using Photoplethysmography

Goldoozian, Layli Sadat | 2011

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40643 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Zahedi, Edmond
  7. Abstract:
  8. Endothelial cells cover the inner surface of blood vessels. In response to different physical (such as reactive hyperemia-RH) and pharmacological stimuli, they maintain homeostasis by changing the vascular diameter (by releasing chemical agents like nitric oxide). The endothelium inability to respond to metabolic need (endothelial dysfunction) is an early marker of cardiovascular diseases such as atherosclerosis. Flow mediated dilation (FMD) measurement using ultrasound imaging (FMD-US) has been established as a standard method for assessing the endothelial function. Recently, a less skilled-operator demanding method has been proposed based on the photoplethysmographic (PPG) signal changes during reactive hyperemia. It was shown that the amplitude of the PPG pulse (FMD-PPG) changed in a quite similar manner to that of the artery diameter in the method of the FMD-US i.e. increases following releasing the cuff and then gradually returns to baseline. In this project, models are proposed for the FMD-PPG signal after releasing the occlusion. First, two numerical models with exponential components are presented and fitted to the PPG-AC signal in two populations: healthy and subjects with one cardiovascular risk factor (hyperlipidemia). For the first model (with two time constants), one of the time constants was significantly lower (P<0.01) in healthy (47 people) versus subjects with hyperlipidemia (36 people). The only time constant of the second model was also significantly lower (P<0.055) in healthy versus subjects with hyperlipidemia. Besides these numerical models, PPG changes were modeled using passive electrical elements (R, L and C). Time varying circuit elements values were determined according to the PPG signal changes after cuff release. In the best state, the output signal of the electrical analog model matched relatively well (fitness of 82.47%) to the PPG-AC signal for one subject.

  9. Keywords:
  10. Endothelial Function ; Reactive Hyperemia ; Flow Mediated Dilation ; Photoplethysmography

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