title: Nonlinear power loss during exercise in single-ventricle patients after the Fontan: insights from computational fluid dynamics.
abstract: BACKGROUND
  We previously demonstrated that power loss (PL) through the total cavopulmonary connection (TCPC) in single-ventricle patients undergoing Fontan can be calculated by computational fluid dynamic analysis using 3-dimensional MRI anatomic reconstructions. PL through the TCPC may play a role in single-ventricle physiology and is a function of cardiac output. We hypothesized that PL through the TCPC increases significantly under exercise flow conditions.
  
  
  RESULTS
  MRI data of 10 patients with a TCPC were analyzed to obtain 3-dimensional geometry and flow rates through the superior vena cava, inferior vena cava, left pulmonary artery, and right pulmonary artery. Steady computational fluid dynamic simulations were performed at baseline conditions using MRI-derived flows. Simulated exercise conditions of twice (2x) and three times (3x) baseline flow were performed by increasing inferior vena cava flow. PL, head loss, and effective resistance through the TCPC were calculated for each condition. Each condition was repeated at left pulmonary artery/right pulmonary artery ratios of 30/70 and 70/30 to determine the effects of pulmonary flow splits on exercise PL. For each patient, PL increases dramatically in a nonlinear fashion with increasing cardiac output, even when normalized to calculate head loss or resistance. Flow splits had a significant effect on PL at exercise, with most geometries favoring right pulmonary artery flow.
  
  
  CONCLUSIONS
  The relationship between cardiac output and PL is nonlinear and highly dependent on TCPC geometry and pulmonary flow splits. This study demonstrates the importance of studying the TCPC under exercise conditions, because baseline conditions may not adequately characterize TCPC efficiency.
authors.affiliation: Children's Hospital of Philadelphia, Division of Cardiology, Main Hospital, 2 Floor, 34 and Civic Center Blvd, Philadelphia, PA 19104, USA. whiteheadk@email.chop.edu
authors.forename: Kevin K
authors.initials: KK
authors.lastname: Whitehead
authors.forename: Kerem
authors.initials: K
authors.lastname: Pekkan
authors.forename: Hiroumi D
authors.initials: HD
authors.lastname: Kitajima
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Paridon
authors.forename: Ajit P
authors.initials: AP
authors.lastname: Yoganathan
authors.forename: Mark A
authors.initials: MA
authors.lastname: Fogel
mesh_terms: D000293:Adolescent; D002302:Cardiac Output / Q000502:physiology; D002648:Child; D019295:Computational Biology / Q000379:methods; D003198:Computer Simulation; D015444:Exercise / Q000502:physiology*; D018729:Fontan Procedure; D006801:Humans; D017711:Nonlinear Dynamics; D011673:Pulsatile Flow / Q000502:physiology*; D016276:Ventricular Function