Abstract

Hypoplastic left heart syndrome (HLHS) is a type of heart defect where the left ventricle is underdeveloped or not developed, resulting in only a single functioning right ventricle. Approximately 7.5% of patients with congenital heart disease are born with a single ventricle (SV) which is accompanied by a spectrum of other malformations such as atrophied ascending aorta, atrial septal defects, and ventricular septal defects (VSD). The existing three-hybrid staged surgical approach serving as a palliative treatment for this anomaly entails multiple complications and achieves a survival rate of only 50%. To reduce the trauma associated with the second stage of the hybrid procedure the hybrid comprehensive stage 2 (HCSII) operation can be a novel palliation alternative for a select subset of SV patients with adequate antegrade aortic flow. The procedure reduces surgical trauma in newborns by introducing a stented intrapulmonary baffle to avoid dissection of the pulmonary arteries and reconstruction of the aortic arch while obviating the dissection of the ductal continuation and distal arch. It is the purpose of this dissertation to undertake a computational investigation to elucidate the complex hemodynamics of patients who have undergone HCS II. This was accomplished in a multiscale manner coupling a 0D lumped parameter model (LPM) of the peripheral circulation with 3D pulsatile Computational Fluid Dynamics (CFD) model providing the details and enabling investigation of the HCS II complex hemodynamics. The use of CFD allows modeling of blood flow, the study of the effect of different surgical procedures, suggestion of potential improvements from investigation of areas of concern which are: the pressure drop across the baffle, the loading of the baffle itself, shear stress and shear rates that might lead to thrombus formation, as well as oxygen transport and particle residence time. A 3D anatomical model representative of a patient having undergone the HCSII was rendered utilizing the solid modeling software Solidworks based on anatomical landmarks from CT scans, and a 0D LPM was tuned to produce flowrates and waveforms that matched catheter data. The pulsatile CFD computations were carried out using the commercial STARCCM+ solver. Several cases of baffle strictures relevant to surgical implementations were considered and results showed that the largest pressure drop across the baffle reported was about 3 mmHg while for the same narrowing size and accounting for the distal arch kink, a four-fold increase is observed yielding a 12.15 mmHg drop. Moreover, the analysis showed that for averaged blood flow velocity of 0.5 m/s, no vortex shedding from the baffle was observed in the computational model due to the short distance from the baffle to the aortic arch apex. The velocity and pressure-flow fields were examined at different points throughout the cardia cycle: late diastole, early systole, peak systole, and early diastole. Reverse flow was observed towards late diastolic phase due to the presence of an adverse pressure gradient, and a stagnant flow in the aortic arch apex was also noticed. For the pulmonary circulation and due to the low flow velocity and low pulsatility, the T-junction shape of the SVC presented no risk of recirculation or swirling that may promote thrombogenesis. The wall shear stress on the baffle surface was also reported in pulsatile flow. It was observed that the flow detaches in systole and subsequently reattaches to the baffle surface. Moreover, the baffle surface experiences high wall shear stress magnitudes during systole and uneven distribution of WSS during diastole. The variation in the baffle related narrowing had a little impact on the flow hemodynamics, as shown by the nearly constant oxygen transport across the models. The geometrical modification applied to the models had little effect on the oxygen delivery for up to a 15% change between a 4 mm increment of MPA minimum diameter. The results showed consistency with the published data of Glenn patients. Particle residence time was also reported to identify any blood recirculation or flow stagnation that may lead to platelet activation leading to clot formation rate. On average particles take about 0.5(s) to exit the fluid domain. This time span is equal to the time of one cardiac cycle. Finally, the energy loss and energy efficiency were calculated as a function of split ratio and baffle related narrowing. Across all models, the efficiency was shown to be high.

Notes

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Graduation Date

2019

Semester

Fall

Advisor

Kassab, Alain

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering and Computer Science

Department

Mechanical and Aerospace Engineering

Degree Program

Mechanical Engineering

Format

application/pdf

Identifier

CFE0007813

URL

http://purl.fcla.edu/fcla/etd/CFE0007813

Language

English

Release Date

December 2020

Length of Campus-only Access

1 year

Access Status

Doctoral Dissertation (Open Access)

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