Curt G. DeGroff

Artificial Neural Network–Based Method of Screening Heart Murmurs in Children

Background—Early recognition of heart disease is an important goal in pediatrics. Efforts in developing an inexpensive screening device that can assist in the differentiation between innocent and pathological heart murmurs have met with limited success. Artificial neural networks (ANNs) are valuable tools used in complex pattern recognition and classification tasks. The aim of the present study was to train an ANN to distinguish between innocent and pathological murmurs effectively. Methods and Results—Using an electronic stethoscope, heart sounds were recorded from 69 patients (37 pathological and 32 innocent murmurs). Sound samples were processed using digital signal analysis and fed into a custom ANN. With optimal settings, sensitivities and specificities of 100% were obtained on the data collected with the ANN classification system developed. For future unknowns, our results suggest the generalization would improve with better representation of all classes in the training data. Conclusion—We demonstrated that ANNs show significant potential in their use as an accurate diagnostic tool for the classification of heart sound data into innocent and pathological classes. This technology offers great promise for the development of a device for high-volume screening of children for heart disease.

Analysis of the Effect of Flow Rate on the Doppler Continuity Equation for Stenotic Orifice Area Calculations A Numerical Study

BACKGROUND Flow-rate dependencies of the Doppler continuity equation are addressed in this study. METHODS AND RESULTS By use of computational fluid dynamic (CFD) software with turbulence modeling, three-dimensional axisymmetric models of round stenotic orifices were created. Flow simulations were run for various orifice area sizes (0.785, 1.13, 1.76, and 3.14 cm2) and flow rates (0.37 to 25.0 L/min). Reynolds numbers ranged from 100 to 8000. Once adequate convergence was obtained with each simulation, the location of the vena contracta was determined. For each run, maximum and average velocities across the cross section of the vena contracta were tabulated and vena contracta cross-sectional area (effective orifice area) determined. The difference between the maximum velocity and the average velocity at the vena contracta was smallest at high-flow states, with more of a difference at low-flow states. At lower-flow states, the velocity vector profile at the vena contracta was parabolic, whereas at high-flow states, the profile became more flattened. Also, the effective orifice area (vena contracta cross-sectional area) varied with flow rate. At moderate-flow states, the effective orifice area reached a minimum and expanded at low- and high-flow states, remaining relatively constant at high-flow states. CONCLUSIONS We have shown that significant differences exist between the maximum velocity and the average velocity at the vena contracta at low flow rates. A likely explanation for this is that viscous effects cause lower velocities at the edges of the vena contracta at low flow rates, resulting in a parabolic profile. At higher-flow states, inertial forces overcome viscous drag, causing a flatter profile. Effective orifice area itself varies with flow rate as well, with the smallest areas seen at moderate-flow states. These flow-dependent factors lead to flow rate-dependent errors in the Doppler continuity equation. Our results have strong relevance to clinical measurements of stenotic valve areas by use of the Doppler continuity equation under varying cardiac output conditions.

Influence of Connection Geometry and SVC-IVC Flow Rate Ratio on Flow Structures within the Total Cavopulmonary Connection: A Numerical Study

The total cavopulmonary connection (TCPC) is a palliative cardiothoracic surgical procedure used in patients with one functioning ventricle that excludes the heart from the systemic venous to pulmonary artery pathway. Blood in the superior and inferior vena cavae (SVC, IVC) is diverted directly to the pulmonary arteries. Since only one ventricle is left in the circulation, minimizing pressure drop by optimizing connection geometry becomes crucial. Although there have been numerical and in-vitro studies documenting the effect of connection geometry on overall pressure drop, there is little published data examining the effect of SVC-IVC flow rate ratio on detailed fluid mechanical structures within the various connection geometries. We present here results from a numerical study of the TCPC connection, configured with various connections and SVC:IVC flow ratios. The role of major flow parameters: shear stress, secondary flow, recirculation regions, flow stagnation regions, and flow separation, was examined. Results show a complex interplay among connection geometry, flow rate ratio and the types and effects of the various flow parameters described above. Significant changes in flow structures affected local distribution of pressure, which in turn changed overall pressure drop. Likewise, changes in local flow structure also produced changes in maximum shear stress values; this may have consequences for platelet activation and thrombus formation in the clinical situation. This study sheds light on the local flow structures created by the various connections andflow configurations and as such, provides an additional step toward understanding the detailed fluid mechanical behavior of the more complex physiological configurations seen clinically.

Comparison of In Vitro Velocity Measurements in a Scaled Total Cavopulmonary Connection with Computational Predictions

AbstractMinimizing pressure drop through the total cavopulmonary surgical connection (TCPC), where the superior and inferior vena cavae (SVC), (IVC) are connected directly to the right and left pulmonary arteries, is an important clinical consideration. Computational fluid dynamics (CFD) models have been used to examine the impact of connection configuration on TCPC pressure drop. However, few studies have validated CFD results with experimental data. This study compares flow field measurements on two different TCPC models at varying SVC:IVC flow rate ratios using CFD and digital particle image velocimetry (DPIV). Although the primary flow fields generated by CFD and DPIV methods were similar for the majority of flow conditions, three key differences were found: (1) the CFD model did not reproduce the 3D complexity of flow interactions in the no-offset model with 50:50 flow ratio; (2)in vitro results showed consistently higher secondary flow components within the pulmonary artery segments, especially for the no-offset model; (3) recirculation areas for the 1/2 diameter offset model were consistently higher forin vitro versus CFD results. We conclude that this numerical model is a reasonable means of studying TCPC flow, although modifications need to be addressed to ensure that numerical results reproduce secondary flow characteristics.

Utility of Three-Dimensional Ultrasound Doppler Flow Reconstruction of the Proximal Jet to Quantify Effective Orifice Area: In Vitro Steady and Pulsatile Flow Studies

We examined the utility of three-dimensional (3D) reconstruction of two-dimensional color Doppler images of the proximal jet to quantify the effective area of an orifice in an in vitro model. Steady and pulsatile flows were directed through various orifices; orifice vena contracta areas were quantified with laser flow visualization, thus providing gold standard effective orifice areas. Three-dimensional areas followed vena contracta areas well, although variations in color Doppler gain and 3D gray levels for thresholding produced significant changes in reconstructed images. These variations were minimized by using minimum color gain and 50% gray level threshold. At these settings, 3D areas still overestimated vena contracta areas by approximately 25% because of the poor lateral resolution of the color Doppler system, which caused bleeding of the flow signal past the edges of the proximal jet. Nevertheless, 3D flow images provided a superior format for qualitative and quantitative appreciation of proximal jet shape and dimensions.

Flow in the Early Embryonic Human Heart: A Numerical Study

Computational fluid dynamic (CFD) experimentation provides a unique medium for detailed examination of flow through complex embryonic heart structures. The purpose of this investigation was to demonstrate that streaming blood flow patterns exist in the early embryonic heart and that fluid surface stresses change significantly with anomalous alterations in fetal heart lumen shape. Stages 10 and 11 early human embryo hearts were digitized as calibrated two-dimensional (2D) cross-sectional sequential images. A 3D surface was constructed from the stacking of these 2D images. CFD flow solutions were obtained (steady and pulsatile flow). Particle traces were placed in the inlet and outlet portions of these two stages. Sections of the embryonic heart were artificially reshaped. CFD flow solutions were obtained and surface stress changes analyzed. Streaming was shown to exist, with particles released on one or the other side of the cardiac lumen tending not to cross over and mix with particles released from the opposite side of the cardiac lumen. Shear stress changes (stage 10) occur in the altered lumens. Streaming exists in steady and pulsatile flow scenarios in the embryonic heart models. There are differences in local shear stress distributions with surface shape anomalies of the fetal heart lumen. These observations may help shed light on the potential role of fluid dynamic factors in determining patterns of abnormal heart development.

Minimal Sedation Second Dose Strategy With Intranasal Midazolam in an Outpatient Pediatric Echocardiographic Setting

BACKGROUND Anxiety and movement in children during transthoracic echocardiography (TTE) can compromise study quality and reliability. Minimal sedation is often required. Intranasal midazolam (INM), used in various procedures, is an excellent sedative. Optimal INM dosing strategies for uncooperative children undergoing TTE are largely unknown, including second-dose INM strategies, introduced to maximize the potential for successful sedation and minimize risk. The purpose of this retrospective review was to evaluate the effectiveness of a second-dose INM minimal sedation strategy recently adopted at the Childrens Hospital of Pittsburgh. METHODS The strategy incorporates a second dose of INM if needed (10-15 minutes after the first dose) to obtain the desired level of anxiolysis. The effectiveness of this strategy was assessed in 100 consecutive patients (age range, 1-59 months). RESULTS There were no reported complications, minimal untoward side reactions, and no delays in discharge. Eighty patients attained satisfactory minimal sedation levels. CONCLUSION A second-dose INM strategy was effective in achieving satisfactory minimal sedation in children undergoing TTE. The results of this study also suggest that only a small proportion of patients would benefit from a one-dose INM strategy.