Keiichi Itatani

Computational Hemodynamic Analysis in Congenital Heart Disease: Simulation of the Norwood Procedure

Hypoplastic left heart syndrome (HLHS) is a congenital heart disease which should be treated at neonate. Even now, its operation is one of the greatest challenges. However, currently there are no quantitative standards to evaluate and predict the outcome of the therapy. In this study, computational fluid dynamics (CFD) was used to estimate the performance of first stage HLHS surgery, the Norwood operation. An image data transfer system was developed to convert clinical images into three-dimensional geometry. To confirm software applicability, a validation process was carried out to eliminate any influence of numerical procedures. The velocities derived from echocardiography measurements were used as boundary conditions, and pressure waves measured by a cardiac catheter simultaneous with an electrocardiogram (ECG) were employed to validate the results of CFD simulation. Calculated results were congruent with the in vivo measurement results. The blood flow circulations were successfully simulated and the distribution of blood flow in each vessel was estimated. Time-varying energy losses (EL), local pressure and wall shear stress (WSS) were analyzed to estimate clinical treatment. The results indicated that pulsatile simulation is essential in quantitative evaluation. Computational hemodynamics may be applied in the surgical optimization for the treatment of HLHS.

Intraventricular Flow Velocity Vector Visualization Based on the Continuity Equation and Measurements of Vorticity and Wall Shear Stress

We have developed a system to estimate velocity vector fields inside the cardiac ventricle by echocardiography and to evaluate several flow dynamical parameters to assess the pathophysiology of cardiovascular diseases. A two-dimensional continuity equation was applied to color Doppler data using speckle tracking data as boundary conditions, and the velocity component perpendicular to the echo beam line was obtained. We determined the optimal smoothing method of the color Doppler data, and the 8-pixel standard deviation of the Gaussian filter provided vorticity without nonphysiological stripe shape noise. We also determined the weight function at the bilateral boundaries given by the speckle tracking data of the ventricle or vascular wall motion, and the weight function linear to the distance from the boundary provided accurate flow velocities not only inside the vortex flow but also around near-wall regions on the basis of the results of the validation of a digital phantom of a pipe flow model.

Influence of surgical arch reconstruction methods on single ventricle workload in the Norwood procedure

OBJECTIVE The study objective was to evaluate various types of Norwood arch reconstruction methods and to show the factors that affect the cardiac workload of the single ventricle. The Norwood procedure is one of the most challenging congenital heart surgeries. Several aortic arch reconstruction techniques have been reported to avoid recoarctation, ensure coronary perfusion, and improve long-term outcomes. Inside the arch, complicated turbulent flow is generated; however, little is known about the cause of the disadvantageous inefficient flow and the surgical techniques to avoid it. METHODS We created patient-specific computational hemodynamic models of 9 patients who underwent different types of arch reconstruction methods. Four patients had aortic atresia, and 5 patients had aortic stenosis. Flow profiles were defined by echocardiography data corrected with body surface area. Turbulent pulsatile flow was analyzed with the finite volume method. Flow energy loss was calculated to estimate cardiac workload, and wall shear stress was calculated to estimate vessel wall stiffness increase. RESULTS Recoarctation and acute arch angles increased wall shear stress and energy loss. In the patients with aortic atresia, a longitudinal incision toward the descending aorta was effective in creating a smooth arch angle. In the patients with aortic stenosis, arch repair with the Damus-Kaye-Stansel procedure in a single anastomotic site was effective in creating sufficient anastomosis space and a smooth arch angle. CONCLUSIONS Creation of a large anastomotic space and a smooth aortic arch angle reduced wall shear stress and energy loss, and should improve long-term cardiac performance after the Norwood procedure.

Mechanical and thermal properties of silicon-carbide composites fabricated with short Tyranno® Si-Zr-C-O fibre

Silicon carbide (SiC) composites reinforced with 10–50 mass% (10.5–51.2 vol%) of short Tyranno® Si-Zr-C-O fibre (average length ∼0.5 mm) and 0–10 mol% of Al4C3as a sintering aid were fabricated using the hot-pressing technique. Firstly, the effect of Si-Zr-C-O fibre addition on the relative density (bulk density/true density) of the SiC composite hot-pressed at 1800 °C for 30 min was examined by fixing the amount of Al4C3to be 5 mol%. Although the relative density was reduced to 87.4% for 10 mass% of Si-Zr-C-O addition, further increases in the amount of Si-Zr-C-O fibre increased density to a maximum of 92.8% at 40 mass% of fibre addition. Secondly, the effect of varying the amount of Al4C3addition on the relative density was examined by fixing the amount of Si-Zr-C-O fibre to be 40 mass%. The optimum amount of Al4C3addition for the fabrication of dense SiC composite was found to be 5 mol%. The fracture toughness of the hot-pressed SiC composites with 20–40 mass% of Si-Zr-C-O fibre addition (amount of Al4C3: 5 mol%) was 3.2–3.4 MPa · m1/2and approximately 1.5 times higher than that (2.39 MPa · m1/2) of the hot-pressed SiC composite with no Si-Zr-C-O fibre addition. SEM observation showed evidence of Si-Zr-C-O fibre debonding and pull-out at the fracture surfaces. The hot-pressed SiC composite with 5 mol% of Al4C3and 40 mass% of Si-Zr-C-O fibre additions showed excellent heat-resistance at 1300 °C in air due to the formation of a SiO2layer at and near exposed surfaces.

The lower limit of the pulmonary artery index for the extracardiac Fontan circulation

OBJECTIVE In the era of the staged Fontan operation, small pulmonary artery index (<250 mm(2)/m(2)) has not affected the early or midterm results. The lower limit of pulmonary artery index, however, has not yet been determined. We created numeric models of the Fontan circulation to investigate the lower limit of the pulmonary artery size. METHODS The extracardiac Fontan geometries with pulmonary artery index, ranging from 50 to 200 mm(2)/m(2) with every 10-mm(2)/m(2) increase, were created from the postoperative angiographic data of 17 patients. The superior and inferior vena caval flow rates at rest and on 2 exercise levels (0.5 and 1.0 W/kg) were given by magnetic resonance imaging flow studies. Respiration-driven transient flow analysis was performed with a finite element solver. Energy loss and mean inferior vena caval pressure were obtained from the results. RESULTS Energy loss and mean inferior vena caval pressure were prominently increased in small pulmonary artery index models, especially during exercise. The pulmonary artery indices sufficient for mean inferior vena caval pressure less than 17 mm Hg were 80 mm(2)/m(2) at rest, 100 mm(2)/m(2) during 0.5-W/kg exercise, and 110 mm(2)/m(2) during 1.0-W/kg exercise. With the increase of pulmonary arterial resistance, mean inferior vena caval pressure increased, but the flow pattern did not change. CONCLUSIONS A small pulmonary artery causes a high pressure gradient and a high energy loss. The lower limit of pulmonary artery index, considering the exercise tolerance, was 110 mm(2)/m(2).

An approach of computational hemodynamics for cardiovascular flow simulation

Computational fluid dynamics (CFD) is one of available methods to quantitatively evaluate the treatments of cardiovascular disease. However, currently, applications of this technology to cardiac surgery are few due to the complexity of performing physiological simulation. Here, we used CFD to study the outcome of the Norwood surgical procedure for palliating hypoplastic left heart syndrome in a 33-month-old child. The Reynolds number for post-surgical flow calculated at the peak of systole was about 4000, consistent with turbulent flow. During diastole, by contrast, the flow reduced to low speed, suggesting the strong transition flow from systole to diastole. Therefore, to improve the simulation of transitional flow, we determined that time step intervals of 10−5 second were best in using the k–e turbulence model. We also develop a new boundary condition to simulate blood pressure wave reflection from peripheral vessels in order to physiologically capture pressure recovery and correctly obtained flow through each arch-branch and flow pattern in the coronary. Then we computed time-varying energy losses, local pressure, and wall shear stress at the anastomosis to evaluate the surgical outcome. The results suggest the time step and boundary conditions that take account of pressure wave reflection improve simulation of cardiovascular flow.Copyright

Image-based computational hemodynamics of distal aortic arch recoarctation following the Norwood procedure

Currently, few applications of computational hemodynamics predict outcomes after palliative surgery for congenital heart defects such as hypolastic left heart syndrome in infants. Here, we report on three-dimensional imaging methods for modeling recoarctation that commonly occurs in the distal aortic arch following the Norwood procedure. We used computer-aided design to simulate seven stages of increasing stenosis, analyze the resulting hemodynamics, and visualize the impairment of blood flow. A disproportionate drop in pressure occurred when stenosis reached 20% of the cross-sectional area of the descending aorta. The corresponding decrease in blood flow in the descending aorta was relatively small, however. Accordingly our findings suggest a reasonable approach to this phenomenon is watchful waiting rather than immediate surgical intervention. Such patient-specific predictions appear to be valuable for minimizing the risks of corrective surgery. These methods also may be applied to procedures for alleviating other congenital heart defects.

The effectiveness of prestorage leukocyte-reduced red blood cell transfusion on perioperative inflammatory response with a miniaturized biocompatible bypass system

OBJECTIVE Since 2007, the Japanese Red Cross Blood Center has provided prestorage leukocyte-reduced red blood cell concentrates in which the leukocytes were reduced soon after collection. We have established a miniaturized bypass system (140 mL) to reduce the perioperative inflammatory responses. This study was designed to reveal the effectiveness of leukocyte-reduced red blood cell concentrate transfusion on perioperative inflammatory responses in pediatric cardiac surgery. METHODS Between May 2006 and June 2008, 50 consecutive patients weighing less than 5 kg who underwent a surgical procedure with red blood cell concentrate transfusion using a miniaturized bypass system were reviewed retrospectively. Twenty-five patients before 2007 received stored red blood cell concentrate in which leukocytes were reduced with a filter just before transfusion (group A). After 2007, 25 patients received the prestorage leukocyte-reduced red blood cell concentrate transfusion (group B). The postoperative peak C-reactive protein level, peak white blood cell count, peak neutrophil count, percentage body weight gain, inotrope score, plasma lactate concentration, postoperative mechanical ventilation time, and length of intensive care unit stay were compared as the perioperative inflammatory response and morbidity for both groups. RESULTS There were no significant differences in peak white blood cell count, peak neutrophil count, percentage body weight gain, and inotrope score between the groups. The peak C-reactive protein level in group A was significantly greater than that in group B (6.7 +/- 4.7 vs 4.2 +/- 3.6 mg/dL, P < .05). The lactate concentration at 12 and 24 hours after surgical intervention in group A was significantly greater than that in group B (3.1 +/- 2.5 vs 1.9 +/- 1.1 mmol/L [P < .05] and 2.2 +/- 0.2 vs 1.4 +/- 0.2 mmol/L [P < .05], respectively). The postoperative mechanical ventilation time and intensive care unit stay in group A were significantly greater than those in group B (5.9 +/- 7.4 vs 2.1 +/- 2.0 days [P < .05] and 9.8 +/- 7.9 vs 5.0 +/- 2.1 days [P < 0.05], respectively). Multivariate analyses showed that the leukocyte-reduced red blood cell concentrate transfusion reduced the peak C-reactive protein level (in milligrams per deciliter; coefficient, -2.95; 95% confidence interval [CI], -4.66 to -0.93; P = .003), postoperative mechanical ventilation time (in days; coefficient, -3.41; 95% CI, -6.07 to -0.74; P = .013), and intensive care unit stay (in days; coefficient, -4.51; 95% CI, -7.37 to -1.64; P = .003). CONCLUSIONS Our study revealed that in neonates and small infants, compared with transfusions with stored red blood cell concentrate, transfusion of leukocyte-reduced red blood cell concentrates was associated with reduced perioperative inflammatory responses and improved clinical outcomes.

Grain size-sensitive viscoelastic relaxation and seismic properties of polycrystalline MgO

Torsional forced-oscillation experiments on a suite of synthetic MgO polycrystals, of high-purity and average grain sizes of 1–100 µm, reveal strongly viscoelastic behavior at temperatures of 800–1300°C and periods between 1 and 1000 s. The measured shear modulus and associated strain energy dissipation both display monotonic variations with oscillation period, temperature, and grain size. The data for the specimens of intermediate grain size have been fitted to a generalized Burgers creep function model that is also broadly consistent with the results for the most coarse-grained specimen. The mild grain size sensitivity for the relaxation time τL, defining the lower end of the anelastic absorption band, is consistent with the onset of elastically accommodated grain boundary sliding. The upper end of the anelastic absorption band, evident in the highest-temperature data for one specimen only, is associated with the Maxwell relaxation time τM marking the transition toward viscous behavior, conventionally ascribed a stronger grain size sensitivity. Similarly pronounced viscoelastic behavior was observed in complementary torsional microcreep tests, which confirm that the nonelastic strains are mainly recoverable, i.e., anelastic. With an estimated activation volume for the viscoelastic relaxation, the experimentally constrained Burgers model has been extrapolated to the conditions of pressure and temperature prevailing in the Earths uppermost lower mantle. For a plausible grain size of 10 mm, the predicted dissipation Q−1 ranges from ~10−3 to ~10−2 for periods of 3–3000 s. Broad consistency with seismological observations suggests that the lower mantle ferropericlase phase might account for much of its observed attenuation.

The effectiveness of high-flow regional cerebral perfusion in Norwood stage I palliation §

OBJECTIVE Regional cerebral perfusion (RCP) has been shown to provide cerebral circulatory support during Norwood procedure. In our institution, high-flow RCP (HFRCP) from the right innominate artery has been induced to keep sufficient cerebral and somatic oxygen delivery via collateral vessels. We studied the effectiveness of HFRCP to regional cerebral and somatic tissue oxygenation in Norwood stage I palliation. METHODS Seventeen patients, who underwent the Norwood procedure, were separated into two groups: group C (n=6) using low-flow RCP and group H (n=11) using HFRCP (mean flow: 54 vs 92mlkg(-1)min(-1), P<0.0001). The mean duration of RCP was 64±10min (range, 49-86min) under the moderate hypothermia. Chlorpromazine (3.0mgkg(-1)) was given to group H patients before and during RCP to increase RCP flow. The mean radial arterial pressure was kept <50mmHg during RCP. To clarify the effectiveness of HFRCP for cerebral and somatic tissue oxygenation, cerebral regional oxygen saturation (rSO(2)) and systemic venous oxygenation (SvO(2)) during RCP were compared between the two groups. Changes in the lactate level before and after RCP, and changes in the blood urea nitrogen (BUN), creatinine, lactate dehydrogenase (LDH), and creatinine kinase (CK) levels before and after surgery, were also compared between the groups. RESULTS Mean rSO(2) was 82.9±9.0% in group H and 65.9±10.7% in group C (P<0.05). Mean SvO(2) during RCP was 98.2±4.3% in group H and 85.4±9.7% in group C (P<0.01). During RCP, lactate concentration significantly increased in group C compared with that in group H (P<0.001). After surgery, the LDH and CK levels significantly increased in group C compared with that in group H (P<0.05). CONCLUSIONS Our study revealed that HFRCP preserved sufficient cerebral and somatic tissue oxygenation during the Norwood procedure. The reduction of vascular resistance of collateral vessels increased both cerebral and somatic blood flow, resulting in improved tissue oxygen delivery.