Noninvasive fluid dynamic power loss assessments for total cavopulmonary connections using the viscous dissipation function: A feasibility study

The total cavopulmonary connection (TCPC) has shown great promise as an eff ective palliation for single-ventricle congenital heart defects. However be cause the procedure results in complete bypass of the right-heart, fluid dy namic power losses may play a vital role in postoperative patient success. Past research has focused on determining power losses using control volume methods. Such methods are not directly applicable clinically without highly invasive pressure measurements. This work proposes the use of the viscous dissipation function as a tool for velocity gradient based estimation of fl uid dynamic power loss. To validate this technique. numerical simulations w ere conducted in a model of the TCPC incorporating a 13.34 min (one caval d iameter) caval offset and a steady cardiac output of 2 L . min(-1), Inlet f low through the superior vena cava was 40 percent of the cardiac output, wh ile outflow through the right pulmonary artery, (RPA) was varied between 30 and 70 percent, simulating different blood flow distributions to the lungs . Power losses were determined using control volume and dissipation functio n techniques applied to the numerical data. Differences between losses comp uted using these techniques ranged between 3.2 and 9.9 percent over the ran ge of RPA outflows studied. These losses were also compared with experiment al measurements from a previous study. Computed power losses slightly excee ded experimental results due to different inlet flow conditions. Although a dditional experimental study is necessary to establish the clinical applica bility of the dissipation function, it is believed that this method, in con junction with velocity gradient information derived from imaging modalities such as magnetic resonance imaging, can provide a noninvasive means of ass essing power losses within the TCPC in vivo.