70 research outputs found
Computational fluid dynamics in the evaluation of hemodynamic performance of cavopulmonary connections after the Norwood procedure for hypoplastic left heart syndrome
No full textAbstractObjectiveComputational fluid dynamics have been used to study the hemodynamic performance of surgical operations, resulting in improved design. Efficient designs with minimal energy losses are especially important for cavopulmonary connections. The purpose of this study was to compare hydraulic performance between the hemi-Fontan and bidirectional Glenn procedures, as well as the various types of completion Fontan operations.MethodsThree-dimensional models were constructed of typical hemi-Fontan and bidirectional Glenn operations according to anatomic data derived from magnetic resonance scans, angiocardiograms, and echocardiograms. Boundary conditions were imposed, and fluid dynamics were calculated from a mathematic code. Power losses, flow distribution to each lung, and pressures were measured at three predetermined levels of pulmonary arteriolar resistance. Models of the lateral tunnel, total cavopulmonary connection, and extracardiac conduit completion Fontan operations were constructed, and power losses, total flow distribution, vena caval and pulmonary arterial pressures, and flow distribution of inferior vena caval return were calculated.ResultsThe hemi-Fontan and bidirectional Glenn procedures performed nearly identically, with similar power losses and nearly equal flow distributions to each lung at all levels of pulmonary arteriolar resistance. However, the lateral tunnel Fontan procedure as performed after the hemi-Fontan operation had lower power losses (6.9 mW, pulmonary arteriolar resistance 3 units) than the total cavopulmonary connection (40.5 mW) or the extracardiac conduit (42.9 mW), although the inclusion of an enlargement patch toward the right in the total cavopulmonary connection was effective in reducing the difference (10.0 mW). Inferior vena caval flow to the right lung was 52% for the lateral tunnel, compared with 19%, 30%, 19%, and 15% for the total cavopulmonary connection, total cavopulmonary connection with right-sided enlargement patch, extracardiac conduit, and extracardiac conduit with a bevel to the left lung, respectively.ConclusionsAccording to these methods, the hemi-Fontan and bidirectional Glenn procedures performed equally well, but important differences in energy losses and flow distribution were found after the completion Fontan procedures. The superior hydraulic performance of the lateral tunnel Fontan operation after the hemi-Fontan procedure relative to any other method may be due to closer to optimal caval offset achieved in the surgical reconstruction
Magnetic Resonance Imaging and Computed Tomography in the Diagnosis of Congenital Heart Defects
No full text
Sub-diaphragmatic venous hemodynamics in the Fontan circulation
No full textObjective: We investigated the subdiaphragmatic venous physiology in
patients subjected to the Fontan operation to understand some of the early
and late problems of this circulation.
Methods: Flows were evaluated by Doppler ultrasonography in the subhepatic
inferior vena cava, hepatic vein, and portal vein during respiratory
monitoring and with a tilt table. Twenty control subjects (group A) and 56
patients who had the Fontan operation, 27 in functional class I (group B) and
29 in class III or IV (group C), were studied. Inspiratory/expiratory flow
ratio was calculated to reflect respiratory effects, and upright/supine flow
ratio was calculated to assess gravity effects. Inferior vena caval, hepatic
venous, and wedged hepatic venous pressures were measured during
catheterization in 21 control subjects and 25 Fontan patients. The difference
between wedged and hepatic venous pressures represents the transhepatic
venous pressure gradient.
Results: Fontan hepatic venous flow depended more on inspiration than control,
but without difference between groups B and C (inspiratory/expiratory
flow ratios: 1.7, 2.9, and 2.9, respectively; P < .02). Normal portal venous
flow was higher in expiration; this effect was lost in group B and reversed in
group C (inspiratory/expiratory flow ratios: 0.8, 1.0, and 1.3; P < .0005).
Gravity reduced portal venous flow in groups A and B, but progression to
functional class III or IV (group C) exacerbated this effect (upright/supine
flow ratios: 0.8, 0.7, and 0.5; P < .01). Inferior vena caval, hepatic venous,
and wedged hepatic venous pressures (in millimeters of mercury) in the
Fontan groups were all elevated compared with the control group (inferior
vena cava, 14.4 ± 4.4 vs 5.9 ± 2.3; hepatic vein, 14.7 ± 4.5 vs 5.9 ± 1.9;
wedged hepatic vein, 14.7 ± 4.0 vs 8.3 ± 2.6; P < .0001). However, transhepatic
venous pressure gradient in the Fontan group was lower than in the
control group (0.5 ± 0.5 vs 2.4 ± 2.0; P < .001). Univariate analysis of inferior
vena caval pressure and transhepatic venous pressure gradient showed
significant inverse correlation (r = 0.6, P < .002).
Conclusions: In patients who are in functionally poorer condition after the
Fontan operation, portal venous flow loses normal expiratory augmentation
and adverse gravity influence is enhanced. These suboptimal flow dynamics,
coupled with higher splanchnic venous pressures and lower transhepatic venous pressure gradients, suggest that hepatic sinusoids are congested, acting
as “open tubes.” Transhepatic gradient loss is incrementally worse with
higher caval pressures. These observations may be responsible for late gastrointestinal
problems in patients who have had the Fontan operation
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