Development of volumetric blood flow measurement

Frohmann, Philipp (2019-04)

Thesis (MEng)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: This thesis entails the development of a proof-of-concept device which may be used for measuring volumetric blood flow. Blood circulation is primarily determined by measuring blood velocity in arteries. This does not take into account that blood vessel diameter can vary with various medical conditions and result in insufficient oxygenated blood being delivered to organs. Insuffi- cient volume blood flow to the brain and kidney can cause strokes, death of brain tissue, heart attacks and even death. A device capable of measuring diameter and velocity was developed. Diameter was measured using a bioimpedance catheter while velocity was measured using a self-mixing interferometer. Validation testing as well as in vitro testing was performed on each. Validation testing and in vitro testing of the bioimpedance catheter was performed in various sized vials filled with horse blood to simulate various sized blood vessels. The voltage over the catheter electrodes was measured and recorded. It could be seen that there is an inverse relation between vial diameter and measured voltage due to the varying impedance in different sized vials. The self-mixing interferometer was validated by tracking the excitation frequency of a speaker diaphragm. A magnitude peak could be seen on a FFT at various excitation frequencies of the speaker. During in vitro testing it was found that the signal-to-noise ratio was insufficient to reliably measure the Doppler frequency of red blood cells in flow. Various iterations were made to the device to decrease noise, but ultimately it was determined that the sensitivity of the photodiode used to monitor the self-mixing signal was limiting the device. It was apparent that the signals reflected from the red blood cells were too small to be detected by the specific photodiode used. It was concluded that it is feasible to measure volume flow by using a combination of bioimpedance and a self-mixing interferometer provided a higher grade laser module with a higher sensitivity photodiode is used. In vivo testing will be necessary to determine the effiects of tissue surrounding blood vessels on bioimpedance measurements.

AFRIKAANSE OPSOMMING: Hierdie tesis behels die ontwikkeling van 'n bewys-van-konsep toestel wat gebruik kan word om volumetriese bloedvloei te meet. Bloedsirkulasie word hoofsaaklik bepaal deur die spoed van bloed in arteries te meet. Hierdie meting is egter nie voldoende nie, aangesien dit nie in ag neem dat die deursnee van arteries kan wissel weens verskeie mediese toestande nie. In so 'n geval kan bloed wat onvoldoende geoksigineërd is aan die organe gelewer word. Onvoldoende bloedvloei na die brein en niere kan lei tot die dood van breinweefsel, hoë bloeddruk en selfs dood. As antwoord op hierdie problem is 'n toestel ontwerp wat die deursnee van die arterie en bloedsnelheid afsonderlik kan meet. 'n Bio-impedansie kateter meet die deursnee van die arterie en die bloedsnelheid word met 'n selfmengende interferometer gemeet. Beide metodes het validasie toetse sowel as in vitro toetse ondergaan. Die toetse op die bio-impedansie kateter is op verskillende grootte skale uitgevoer om verskillende deursnee bloedvate te simileer. Die skale is met perdebloed gevul. Die spanning oor die kateter se elektrodes is gemeet en aangeteken. Daar is opgemerk dat skale met kleiner deursnee groter spannings veroorsaak as gevolg van hoër impedansies. Gedurende validasie toetse is dit bewys dat die selfmengende interferometer die opwekkingsfrekwensie van 'n luidspreker kan optel. Die sein word met behulp van 'n Fast Fourier Transform (FFT) waargeneem, waar die verskillende opwekkingsfrekwensies van die luidspreker as amplitude pieke waargeneem kan word. Tydens in vitro toetsing is te veel geraas in die sein waargeneem om die Doppler-frekwensie van die rooibloedselle betroubaar te meet. Verandering in die ontwerp van die stroombaan is aangebring om die geraas te verminder, tog het die probleem voortgeduur. Dit is uiteindelik gevind dat die sensitiwiteit van die fotodiode onvoldoende was om die selfmengende sein waar te neem, veral as gevolg van die baie lae amplitudes van die seine van die rooibloedselle. Na aanduiding van die toetse is dit bevind dat dit moontlik is om volumetriese bloedvloei te meet deur 'n kombinasie van bio-impedansie en 'n selfmengende interferometer te gebruik mits 'n beter lasermodule met 'n meer sensitiewe fotodiode gebruik word. Verdere in vivo toetse is nodig om die effek van weefsel rondom die bloedvate op die bio-impedansie te bepaal.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105860
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