Flow induced pressure fluctuation in a model of a contorted carotid artery

Abstract

An experimental investigation into the link between the flow induced pressure fluctuations and atherosclerosis is reported in this thesis. A model of a C-shape tortuous channel was used to simulate a contorted cervical portion of the human internal carotid artery (ICA) and air was used as the flow medium. The experiment was carried out under steady flow conditions and pressure fluctuations at various positions along the wall of the ICA model were measured with a calibrated condenser microphone and a digital voltmeter. Dynamic similarity between air flow in the model and blood flow in the artery was scaled by the Reynolds number and characteristic frequencies of the pressure fluctuations scaled by the Strouhal number. A Fast Fourier Transform of the measured pressure fluctuations was performed with the aid of a Strobe Aquisition Unit and the resultant frequency spectra analysed. The root-mean-square voltage of the dominant characteristic frequency of the fluctuating pressure was measured and converted to a fluctuating pressure coefficient. The overall results were presented as a map of pressure distribution at various positions on the model. A dominant characteristic frequency of 34 Hz, as well as periodic doubling and band-broadening were observed. The dominant characteristic frequency was found to increase with flowrate. These pressure fluctuations may be attributed to the inherant instability in the separation/reattachment shear layer. High amplitude and high frequency pressure fluctuations were found to occur at the proximity of the bends along the flow path and matched the clinically reported sites of atherosclerosis. It could therefore be inferred that flow induced pressure fluctuations influenced the initiation and perhaps the progression of atherosclerosis.