title: Model-Based Comparison of the Normal and Fontan Circulatory Systems-Part II: Major Differences in Performance Characteristics.
abstract: BACKGROUND
  In the absence of an accessible chronic animal model of the Fontan circulation, computational modeling can provide insights into this unique circulatory arrangement, especially how differently it behaves from the normal mammalian circulation. Many groups have focused on refining a single element of the entire Fontan circulation-the total cavopulmonary connection (TCPC). Yet, only modest improvements in transplant-free survival have resulted. From an engineering perspective, optimizing the performance of a complex, multiparameter system requires an understanding of how the performance is affected by the full set of system parameters.
  
  
  METHODS
  We evaluated the hemodynamic impact of nine physiological perturbations in the two-year-old (yo) patient with hypoplastic left heart syndrome having a Fontan rearrangement (using our previously described lumped-parameter multicompartment model of both pulmonary and systemic circulations). In cases where comparison is appropriate, we evaluated the hemodynamic impact of analogous pathophysiologies in the normal two-year-olds. We operated the model in open-loop mode in order to expose the magnitude of the impact of uncompensated physiological perturbations.
  
  
  RESULTS
  Without the benefit of compensatory mechanisms, a valvar regurgitant fraction of 50% is sufficient to drop the cardiac index (CI) to 2.0 L/min/m(2) or less. Aortopulmonary collateral flow of 0.6 L/min (1.1 L/min/m(2)) or 0.5 L/min (0.9 L/min/m(2)), sufficient to raise the ratio of pulmonary flow to systemic flow (Qp/Qs) to no higher than 1.2 or 1.5 (fenestration present or absent, respectively), is the maximum which could be tolerated (CI = 2.0 L/min/m(2)) without the help of compensatory mechanisms. Ventricular end-diastolic elastance (stiffness) changes have dramatic effects on CI in a Fontan circulatory arrangement.
  
  
  CONCLUSIONS
  Several components of the Fontan circulation other than the TCPC actually have equal, or greater, impact on CI under certain conditions.
authors.affiliation: Division of Cardiology, Children's Hospital of Philadelphia, Philadelphia, PA, USA Department of Pediatrics, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA chinalvi@mail.med.upenn.edu.
authors.forename: Alvin J
authors.initials: AJ
authors.lastname: Chin
authors.affiliation: Division of Cardiology, Children's Hospital of Philadelphia, Philadelphia, PA, USA.
authors.forename: Raymond L
authors.initials: RL
authors.lastname: Watrous
mesh_terms: D002675:Child, Preschool; D003097:Collateral Circulation / Q000502:physiology; D003198:Computer Simulation; D018729:Fontan Procedure / Q000379:methods*; D006349:Heart Valve Diseases / Q000503:physiopathology; D006352:Heart Ventricles / Q000601:surgery; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D018636:Hypoplastic Left Heart Syndrome / Q000503:physiopathology* / Q000601:surgery; D008955:Models, Cardiovascular; D011651:Pulmonary Artery / Q000502:physiology / Q000601:surgery; D011668:Pulmonary Veno-Occlusive Disease / Q000503:physiopathology; D014655:Vascular Resistance / Q000502:physiology; D016276:Ventricular Function / Q000502:physiology*
keywords: Fontan; cardiovascular hemodynamics; computational modeling; hypoplastic left heart; lumped-parameter modeling; single ventricle