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Research Papers

Increased Energy Loss Due to Twist and Offset Buckling of the Total Cavopulmonary Connection

[+] Author and Article Information
Gokce Nur Oguz, Senol Piskin, Erhan Ermek, Samir Donmazov, Naz Altekin

Department of Mechanical Engineering,
Koç University,
Sarıyer,
Istanbul 34450, Turkey

Ahmet Arnaz

Department of Cardiovascular Surgery,
Acıbadem Bakırköy Hospital,
Istanbul 34450, Turkey

Kerem Pekkan

Department of Mechanical Engineering,
Koç University,
Rumeli Feneri Campus, Sarıyer,
Istanbul 34450, Turkey
e-mail: kpekkan@ku.edu.tr

1G. N. Oguz and S. Piskin contributed equally to this work.

Manuscript received August 1, 2016; final manuscript received January 27, 2017; published online May 3, 2017. Assoc. Editor: Marc Horner.

J. Med. Devices 11(2), 021012 (May 03, 2017) (8 pages) Paper No: MED-16-1294; doi: 10.1115/1.4035981 History: Received August 01, 2016; Revised January 27, 2017

The hemodynamic energy loss through the surgically implanted conduits determines the postoperative cardiac output and exercise capacity following the palliative repair of single-ventricle congenital heart defects. In this study, the hemodynamics of severely deformed surgical pathways due to torsional deformation and anastomosis offset are investigated. We designed a mock-up total cavopulmonary connection (TCPC) circuit to replicate the mechanically failed inferior vena cava (IVC) anastomosis morphologies under physiological venous pressure (9, 12, 15 mmHg), in vitro, employing the commonly used conduit materials: Polytetrafluoroethylene (PTFE), Dacron, and porcine pericardium. The sensitivity of hemodynamic performance to torsional deformation for three different twist angles (0 deg, 30 deg, and 60 deg) and three different caval offsets (0 diameter (D), 0.5D, and 1D) are digitized in three dimensions and employed in computational fluid dynamic (CFD) simulations to determine the corresponding hydrodynamic efficiency levels. A total of 81 deformed conduit configurations are analyzed; the pressure drop values increased from 80 to 1070% with respect to the ideal uniform diameter IVC conduit flow. The investigated surgical materials resulted in significant variations in terms of flow separation and energy loss. For example, the porcine pericardium resulted in a pressure drop that was eight times greater than the Dacron conduit. Likewise, PTFE conduit resulted in a pressure drop that was three times greater than the Dacron conduit under the same venous pressure loading. If anastomosis twist and/or caval offset cannot be avoided intraoperatively due to the anatomy of the patient, alternative conduit materials with high structural stiffness and less influence on hemodynamics can be considered.

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Figures

Grahic Jump Location
Fig. 1

Schematic static mock-up setup used to acquire three-dimensional nonfunctional conduit shapes (left). The setup is filled with a blood analog fluid. The height of the fluid column is adjusted to apply the required venous pressure level via gravity, and the pressure is measured by taking average of the data from the two pressure transducers. On the right, the PTFE conduit mounted to the setup corresponds to the surface deformations under 9 mmHg pressure. The baseline configuration shown on the left is a straight cylindrical conduit at zero-stress state. The configurations located at the middle and right have caval offset and pulmonary artery anastomosis twist in the specified directions, respectively. The conduit surfaces are marked with a uniform grid to improve three-dimensional laser scanning. IVC: inferior vena cava, PA: pulmonary artery.

Grahic Jump Location
Fig. 2

The deformation of porcine pericardium conduit mounted to the setup with three different configurations under 15 mmHg venous pressure is presented. All three configurations have 1D caval offset in the direction shown but variable in the anastomosis twist. The left conduit has 0 deg twist angle, middle conduit has 60 deg twist in the clockwise direction, and the right one features 60 deg twist in the counterclockwise direction. Porcine pericardium conduits are produced from a planar tissue segment before the surgery by a pediatric cardiovascular surgeon. Associated “initially straight” suture lines can be identified in all the three plots.

Grahic Jump Location
Fig. 3

For three caval offset levels, the differences in computed pressure drop values are presented under 15 mmHg intramural venous pressure (left plot). In these experiments, PTFE conduits with 0 deg and 60 deg twist angles are used. Reported percent differences are calculated relative to the straight ideal conduit at the same flow conditions, which results in a pressure drop of 1.96 Pa under Poiseuille flow condition for the same conduit length. Corresponding IVC flow streamlines are presented on the right, shaded with the local velocity magnitude. These CFD simulations correspond to PTFE under 60 deg twist angle, 15 mmHg venous pressure at 0D, 0.5D, and 1D offset levels displayed from left to right.

Grahic Jump Location
Fig. 4

For the three PA-IVC anastomosis twist angle levels, the differences in computed pressure drop values are presented corresponding to the PTFE under 0D offset configuration subjected to 12 mmHg and 15 mmHg venous pressure (left plot). Reported values are in percentage and are relative to the straight conduit at the same flow conditions, which results in a pressure drop of 1.96 Pa under Poiseuille flow condition for the same conduit length. Corresponding IVC flow streamlines are presented on the right, shaded with the local velocity magnitude. These CFD simulations correspond to PTFE under 0D offset, 12 mmHg venous pressure with 0 deg, 30 deg, and 60 deg twist angle displayed from left to right.

Grahic Jump Location
Fig. 5

For the three internal venous pressure levels, the differences in computed pressure drop values are presented corresponding to the PTFE under 0D offset, 60 deg twist angle configuration (left plot). Reported values are in percentage and are relative to the straight conduit at the same flow conditions, which results in a pressure drop of 1.96 Pa under Poiseuille flow condition for the same conduit length. Corresponding IVC flow streamlines are presented on the right, shaded with the local velocity magnitude. These CFD simulations correspond to PTFE under 0D offset, 60 deg twist angle with 9, 12, and 15 mmHg systemic venous pressure displayed from left to right.

Grahic Jump Location
Fig. 6

Critical deformation angle with respect to the increase in systemic venous pressure is presented for the three different conduit materials with 0D offset: Dacron, PTFE, and porcine pericardium. Critical deformation angle is defined as the first visually detectable surface wrinkling (as the anastomosis twist is increased slowly) from our mock-up setup.

Grahic Jump Location
Fig. 7

For the three conduit materials studied, the differences in computed pressure drops are presented corresponding to the 1D offset and 60 deg twist angle configuration subjected to 15 mmHg venous pressure (a). Reported values are in percentage and are relative to the straight conduit at the same flow conditions, which results in a pressure drop of 1.96 Pa under Poiseuille flow condition for the same conduit length. Snapshots of the PTFE, porcine pericardium, and Dacron conduits obtained from the mock-up setup are displayed corresponding to the 1D offset, 60 deg twist angle configuration subjected to 15 mmHg venous pressure from left to right (b). Corresponding three-dimensional conduit flow pathways are shaded with the local velocity magnitude in m/s for PTFE, pericardium, and Dacron (from left to right) under 1D offset, 60 deg twist angle and 15 mmHg venous pressure condition (c). The surface irregularities of the Dacron conduit that are resolved by the CFD model are also visible in (c). ΔPressure refers to the percent pressure drop difference.

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