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Research Papers

Optimization of Inflow Waveform Phase-Difference for Minimized Total Cavopulmonary Power Loss

[+] Author and Article Information
Onur Dur

Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA 15219

Curt G. DeGroff

Congenital Heart Center, University of Florida, Gainesville, FL 32610

Bradley B. Keller

Cardiovascular Innovation Institute, University of Louisville, Louisville, KY 40202

Kerem Pekkan1

Department of Biomedical Engineering, and Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15219kpekkan@andrew.cmu.edu

1

Corresponding author.

J Biomech Eng 132(3), 031012 (Feb 17, 2010) (9 pages) doi:10.1115/1.4000954 History: Received January 25, 2009; Revised October 13, 2009; Posted January 06, 2010; Published February 17, 2010; Online February 17, 2010

The Fontan operation is a palliative surgical procedure performed on children, born with congenital heart defects that have yielded only a single functioning ventricle. The total cavo-pulmonary connection (TCPC) is a common variant of the Fontan procedure, where the superior vena cava (SVC) and inferior vena cava (IVC) are routed directly into the pulmonary arteries (PA). Due to the limited pumping energy available, optimized hemodynamics, in turn, minimized power loss, inside the TCPC pathway is required for the best optimal surgical outcomes. To complement ongoing efforts to optimize the anatomical geometric design of the surgical Fontan templates, here, we focused on the characterization of power loss changes due to the temporal variations in between SVC and IVC flow waveforms. An experimentally validated pulsatile computational fluid dynamics solver is used to quantify the effect of phase-shift between SVC and IVC inflow waveforms and amplitudes on internal energy dissipation. The unsteady hemodynamics of two standard idealized TCPC geometries are presented, incorporating patient-specific real-time PC-MRI flow waveforms of “functional” Fontan patients. The effects of respiration and pulsatility on the internal energy dissipation of the TCPC pathway are analyzed. Optimization of phase-shift between caval flows is shown to lead to lower energy dissipation up to 30% in these idealized models. For physiological patient-specific caval waveforms, the power loss is reduced significantly (up to 11%) by the optimization of all three major harmonics at the same mean pathway flow (3 L/min). Thus, the hemodynamic efficiency of single ventricle circuits is influenced strongly by the caval flow waveform quality, which is regulated through respiratory dependent physiological pathways. The proposed patient-specific waveform optimization protocol may potentially inspire new therapeutic applications to aid postoperative hemodynamics and improve the well being of the Fontan patients.

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Figures

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Figure 4

Contour plots of rate of energy dissipation (Ediss), flow rate, pressure for zero caval phase difference (Φ=0 deg, highest power loss caval waveform pair) at different time points over the flow cycle. Based on the high respiratory dependent waveforms incorporated, IVC/SVC flow split is time-dependent and labeled at each time-point, on the left. Note that the time averaged flow split is fixed to 60/40.

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Figure 5

Time averaged rate of energy dissipation (Ediss) and velocity vectors for two selected phase-shift values: Φ=345 deg (top) and Φ=120 deg (bottom), leading to high and low power loss configurations, respectively. Time averaged pressure contours and vorticity indicate the source of the power dissipation within the given cross section. Each subfigure at the frontal plane (+ shaped TCPC) corresponds to a rectangle with 2.5D×2D dimensions (width x height; D: vessel diameter=1.34 cm).

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Figure 3

Power loss changes as a function of phase-shift angle between the sinusoidal caval waveforms for 1 DO TCPC models having high (top) and low (middle) RD, and 0 DO TCPC model with low RD (bottom). Error bars indicate the cyclic variation in the power loss from the converged running ensemble averages calculated at each phase-shift angle. For reference, the power loss calculated in a transient simulation with the nonpulsatile steady waveforms is also plotted.

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Figure 2

Representation of a typical patient-specific “functional” caval flow waveform (29) by its three fundamental harmonic components (left). The full spectral decomposition of these waveforms is also provided on the right.

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Figure 1

Idealized 1 diameter offset (1 DO) TCPC model, diameter=13.4 mm (top), and single harmonic of the pulsatile inlet flow waveforms for SVC and inferior vena cava with high (IVCHRD) and low (IVCLRD) respiratory dependency (bottom). Insert shows the close-up of medium density tetrahedral mesh used in CFD simulations. Dashed lines indicate the control volume for power loss calculations. The phase-shift between IVC and SVC flow waveform is increased with 15 deg increments by altering the IVC phase-shift angle, Φ=0,15,30,45,…,345 deg, relative to SVC. For clarity, only Φ=0 deg, 60 deg (dashed), and 180 deg (dotted) are plotted. RPA: right pulmonary artery, LPA: left pulmonary artery, SVC: superior vena cava, IVC: inferior vena cava.

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Figure 6

Time averaged dissipation contours (Ediss) for the original (top) and optimized (bottom) patient-specific caval waveforms. Cross section views display the rate of energy dissipation and vorticity magnitude.

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