Development of an Experimental and Digital Cardiovascular Arterial Model for Transient Hemodynamic and Postural Change Studies: "A Preliminary Framework Analysis".

Abstract

The ultimate goal of the present work is to aid in the development of tools to assist in the treatment of cardiovascular disease. Gaining an understanding of hemodynamic parameters for medical implants allow clinicians to have some patient-specific proposals for intervention planning. In the present work an experimental and digital computational fluid dynamics (CFD) arterial model consisting of a number of major arteries (aorta, carotid bifurcation, cranial, femoral, jejunal, and subclavian arteries) were fabricated to study: (1) the effects of local hemodynamics (flow parameters) on global hemodynamics (2) the effects of transition from bedrest to upright position (postural change) on hemodynamics, and (3) diffusion of dye (medical drug diffusion simulation) in the arterial system via experimental and numerical techniques. The experimental and digital arterial models used in the present study are the first 3-D systems reported in literature to incorporate the major arterial vessels that deliver blood from the heart to the cranial and femoral arteries. These models are also the first reported in literature to be used for flow parameter assessment via medical drug delivery and orthostatic postural change studies. The present work addresses the design of the experimental and digital arterial model in addition to the design of measuring tools used to measure hemodynamic parameters. The experimental and digital arterial model analyzed in the present study was developed from patient specific computed tomography angiography (CTA) scans and simplified geometric data. Segments such as the aorta (ascending and descending) and carotid bifurcation arteries of the experimental and digital arterial model was created from online available patient-specific CTA scan data provided by Charite' Clinical and Research Hospital. The cranial and coronary arteries were simplified arterial geometries developed from dimensional specification data used in previous work. For the patient specific geometries, a MATLAB code was written to upload the CTA scans of each artery, calculate the centroids, and produce surface splines at each discrete cross section along the lumen centerline to create the patient specific arterial geometries. The MATLAB code worked in conjunction with computer aided software (CAD) Solidworks to produce solid models of the patient specific geometries and united them with the simplified geometries to produce the full arterial model (CAD model). The CAD model was also used as a blueprint to fabricate the experimental model which was used for flow visualization via particle imaging velocimetry (PIV) and postural change studies. A custom pulse duplicator (pulsatile pump) was also designed and developed for the present work. The pulse duplicator is capable of producing patient-specific volumetric waveforms for inlet flow to the experimental arterial model. A simple fluid structure interaction (FSI) study was also conducted via optical techniques to establish the magnitude of vessel diameter change due to the pulsatile flow. A medical drug delivery (dye dispersion and tracing) case was simulated via a dye being dispersed into the pulsatile flow stream to measure the transit time of the dye front. Pressure waveforms for diseased cases (hypertension & stenotic cases) were also obtained from the experimental arterial model during postural changes from bedrest (0°) to upright position (90°). The postural changes were simulated via attaching the experimental model to a tile table the can transition from 0° to 90°. The PIV results obtained from the experimental model provided parametric data such as velocity and wall shear stress data. The medical drug delivery simulations (experimental and numerical) studies produce time dependent data which is useful for predicting flow trajectory and transit time of medical drug dispersion. In the case of postural change studies, pressure waveforms were obtained from the common carotid artery and the femoral sections to yield pressure difference data useful for orthostatic hypotension analysis. Flow parametric data such as vorticity (flow reversal), wall shear stress, normal stress, and medical drug transit data was also obtained from the digital arterial model CFD simulations. Although the present work is preliminary work, the experimental and digital models proves to be useful in providing flow parametric data of interest such as: (1) normal stress which is useful for predicting the magnitude of forces which could promote arterial rupture or dislodging of medical implants, (2) wall shear stress which is useful for analyzing the magnitude of drug transport at the arterial wall, (3) vorticity which is useful for predicting the magnitude of flow reversal, and (4) arterial compliance in the case of the experimental model which could be useful in the efforts of developing FSI numerical simulations that incorporates compliance which realistically models the flow in the arterial system.