Central Artery Hemodynamics in Angiotensin II-Induced Hypertension and Effects of Anesthesia.

Systemic hypertension is a strong risk factor for cardiovascular, neurovascular, and renovascular diseases. Central artery stiffness is both an initiator and indicator of hypertension, thus revealing a critical relationship between the wall mechanics and hemodynamics. Mice have emerged as a critical animal model for studying effects of hypertension and much has been learned. Regardless of the specific mouse model, data on changes in cardiac function and hemodynamics are necessarily measured under anesthesia. Here, we present a new experimental-computational workflow to estimate awake cardiovascular conditions from anesthetized data, which was then used to quantify effects of chronic angiotensin II-induced hypertension relative to normotension in wild-type mice. We found that isoflurane anesthesia had a greater impact on depressing hemodynamics in angiotensin II-infused mice than in controls, which led to unexpected results when comparing anesthetized results between the two groups of mice. Through comparison of the awake simulations, however, in vivo relevant effects of angiotensin II-infusion on global and regional vascular structure, properties, and hemodynamics were found to be qualitatively consistent with expectations. Specifically, we found an increased in vivo vascular stiffness in the descending thoracic aorta and suprarenal abdominal aorta, leading to increases in pulse pressure in the distal aorta. These insights allow characterization of the impact of regionally varying vascular remodeling on hemodynamics and mouse-to-mouse variations due to induced hypertension.

Comparative Passivation of Si(100) by H2 and D2 Atmospheres under Simultaneous Xe+ Bombardment: An X-ray Photoelectron Spectroscopy Analysis.

This study presents a comparison of H2 and D2 passivation on Si(100) under simultaneous Xe+ ion bombardment. The impact of Xe+ ions causes significant damage to the substrate surface, leading to an increase in H2 (D2) retention as Si-H (Si-D) bonds. The ion bombardment conditions are precisely controlled using a Kaufman ion gun. The atomic concentrations on the surface of the sample were investigated by quasi-in situ X-ray photoelectron spectroscopy. A simple methodology is employed to estimate the H (D) chemical concentration and the cover ratio of the sample, with regard to the oxygen concentration through residual water chemisorption present in the vacuum vessel. Differences in passivation are expected when using H2 or D2 atmospheres because their retained scission energies and physisorption properties differ. The results indicate an increase of the sticking coefficient for D2 and H2 under the ion bombardment. It is also found that the flux of H2 (D2) impinging on the surface contributes to play an important role in the whole process. Finally, a model is proposed to describe the phenomenon of the passivation of Si under Xe+ ion bombardment in the presence of H2 (D2).

Cerebrovascular super-resolution 4D Flow MRI - Sequential combination of resolution enhancement by deep learning and physics-informed image processing to non-invasively quantify intracranial velocity, flow, and relative pressure.

The development of cerebrovascular disease is tightly coupled to regional changes in intracranial flow and relative pressure. Image-based assessment using phase contrast magnetic resonance imaging has particular promise for non-invasive full-field mapping of cerebrovascular hemodynamics. However, estimations are complicated by the narrow and tortuous intracranial vasculature, with accurate image-based quantification directly dependent on sufficient spatial resolution. Further, extended scan times are required for high-resolution acquisitions, and most clinical acquisitions are performed at comparably low resolution (>1 mm) where biases have been observed with regard to the quantification of both flow and relative pressure. The aim of our study was to develop an approach for quantitative intracranial super-resolution 4D Flow MRI, with effective resolution enhancement achieved by a dedicated deep residual network, and with accurate quantification of functional relative pressures achieved by subsequent physics-informed image processing. To achieve this, our two-step approach was trained and validated in a patient-specific in-silico cohort, showing good accuracy in estimating velocity (relative error: 15.0 ± 0.1%, mean absolute error (MAE): 0.07 ± 0.06 m/s, and cosine similarity: 0.99 ± 0.06 at peak velocity) and flow (relative error: 6.6 ± 4.7%, root mean square error (RMSE): 0.56 mL/s at peak flow), and with the coupled physics-informed image analysis allowing for maintained recovery of functional relative pressure throughout the circle of Willis (relative error: 11.0 ± 7.3%, RMSE: 0.3 ± 0.2 mmHg). Furthermore, the quantitative super-resolution approach is applied to an in-vivo volunteer cohort, effectively generating intracranial flow images at <0.5 mm resolution and showing reduced low-resolution bias in relative pressure estimation. Our work thus presents a promising two-step approach to non-invasively quantify cerebrovascular hemodynamics, being applicable to dedicated clinical cohorts in the future.

A Computational Study of Dynamic Obstruction in Type B Aortic Dissection.

A serious complication in aortic dissection is dynamic obstruction of the true lumen (TL). Dynamic obstruction results in malperfusion, a blockage of blood flow to a vital organ. Clinical data reveal that increases in central blood pressure promote dynamic obstruction. However, the mechanisms by which high pressures result in TL collapse are underexplored and poorly understood. Here, we developed a computational model to investigate biomechanical and hemodynamical factors involved in Dynamic obstruction. We hypothesize that relatively small pressure gradient between TL and false lumen (FL) are sufficient to displace the flap and induce obstruction. An idealized fluid-structure interaction model of type B aortic dissection was created. Simulations were performed under mean cardiac output while inducing dynamic changes in blood pressure by altering FL outflow resistance. As FL resistance increased, central aortic pressure increased from 95.7 to 115.3 mmHg. Concurrent with blood pressure increase, flap motion was observed, resulting in TL collapse, consistent with clinical findings. The maximum pressure gradient between TL and FL over the course of the dynamic obstruction was 4.5 mmHg, consistent with our hypothesis. Furthermore, the final stage of dynamic obstruction was very sudden in nature, occurring over a short time (<1 s) in our simulation, consistent with the clinical understanding of this dramatic event. Simulations also revealed sudden drops in flow and pressure in the TL in response to the flap motion, consistent with first stages of malperfusion. To our knowledge, this study represents the first computational analysis of potential mechanisms driving dynamic obstruction in aortic dissection.

Fatty acids and recurrence of major depressive disorder: combined analysis of two Dutch clinical cohorts.

OBJECTIVE: Omega-3 (n-3) and omega-6 (n-6) polyunsaturated fatty acid (PUFA) alterations in patients with major depressive disorder (MDD) have been shown to persist after remission. Whether these alterations are risk factors for MDD recurrence remains unknown. Here, we examined whether fatty acids predict time until MDD recurrence in remitted MDD patients. METHODS: Data were used from remitted MDD patients of the Netherlands Study of Depression and Anxiety (n = 356) and the Depression Evaluation Longitudinal Therapy Assessment studies (n = 118). Associations of FAs with time until MDD recurrence up to 8-year follow-up were analyzed using Cox regression analyses. Study-specific estimates were pooled using mega- and meta-analysis techniques. RESULTS: 27.5% (NESDA) and 56.8% (DELTA) participants had an MDD recurrence. Pooled results showed that no FA was significantly associated with time until MDD recurrence (n-3 PUFAs: hazard ratio (HR) = 1.17, 95% confidence interval (CI) = 0.98-1.41, P = 0.082; n-6 PUFAs: HR = 1.08, 95% CI = 0.84-1.38, P = 0.55). CONCLUSION: In remitted MDD patients, circulating PUFAs were not associated with prospective risk of MDD recurrence. Consequently, circulating PUFAs are unlikely to reflect a vulnerability marker for recurrence, so correcting n-3 PUFA 'deficits' through supplementation does not seem a promising option to prevent MDD recurrence.

Decreased functional connectivity of the insula within the salience network as an indicator for prospective insufficient response to antidepressants.

Insufficient response to treatment is the main cause of prolonged suffering from major depressive disorder (MDD). Early identification of insufficient response could result in faster and more targeted treatment strategies to reduce suffering. We therefore explored whether baseline alterations within and between resting state functional connectivity networks could serve as markers of insufficient response to antidepressant treatment in two years of follow-up. We selected MDD patients (N = 17) from the NEtherlands Study of Depression and Anxiety (NESDA), who received ≥ two antidepressants, indicative for insufficient response, during the two year follow-up, a group of MDD patients who received only one antidepressant (N = 32) and a healthy control group (N = 19) matched on clinical characteristics and demographics. An independent component analysis (ICA) of baseline resting-state scans was conducted after which functional connectivity within the components was compared between groups. We observed lower connectivity of the right insula within the salience network in the group with ≥ two antidepressants compared to the group with one antidepressant. No difference in connectivity was found between the patient groups and healthy control group. Given the suggested role of the right insula in switching between task-positive mode (activation during attention-demanding tasks) and task-negative mode (activation during the absence of any task), we explored whether right insula activation differed during switching between these two modes. We observed that in the ≥2 antidepressant group, the right insula was less active compared to the group with one antidepressant, when switching from task-positive to task-negative mode than the other way around. These findings imply that lower right insula connectivity within the salience network may serve as an indicator for prospective insufficient response to antidepressants. This result, supplemented by the diminished insula activation when switching between task and rest related networks, could indicate an underlying mechanism that, if not sufficiently targeted by current antidepressants, could lead to insufficient response. When replicated, these findings may contribute to the identification of biomarkers for early detection of insufficient response.

Cortisol, dehydroepiandrosterone sulfate, fatty acids, and their relation in recurrent depression.

BACKGROUND: Alterations in hypothalamic-pituitary-adrenal (HPA)-axis activity, fatty acid metabolism, and their relation have been associated with (recurrent) major depressive disorder (MDD), although conflicting findings exist. AIMS: To determine whether alterations in HPA-axis activity and fatty acids in recurrent MDD remain during remission (i.e. reflect a potential trait factor). Furthermore, to test the association between HPA-axis activity and fatty acids in patients versus controls. METHODS: We cross-sectionally compared 73 remitted unmedicated recurrent MDD patients with 46 matched never-depressed controls. Measurements included salivary cortisol and dehydroepiandrosterone sulfate (DHEAS) (awakening, evening, and after sad mood induction) and erythrocyte fatty acid parameters: (I) three main fatty acids [omega-3 docosahexaenoic acid (DHA), and the omega-3 eicosapentaenoic acid/omega-6 arachidonic acid (EPA/AA)-ratio], and (II) structural fatty acid indices [chain length, unsaturation and peroxidation]. RESULTS: Patients showed higher cortisol awakening responses (p = 0.006) and lower evening cortisol/DHEAS ratios (p = 0.044) compared to matched controls. Fatty acids did not differ between patients and controls, but HPA-axis indicators were significantly associated with fatty acid parameters in both groups (0.001 ≤ p ≤ 0.043). Patients and controls significantly differed in the relations between awakening DHEAS or cortisol/DHEAS ratios and fatty acid parameters, including unsaturation and peroxidation indices (0.001≤ p ≤ 0.034). Significance remained after correction for confounders. CONCLUSIONS: Our results further support alterations in HPA-axis activity, i.e. a lower baseline, but higher responsiveness of awakening cortisol, in remitted medication-free recurrent MDD patients. Furthermore, the relationship between HPA-axis and fatty acids showed significant differences in recurrent MDD patients versus controls. Prospective research is needed to determine the predictive value of this relationship for MDD recurrence.

On the phonon dissipation contribution to nanoscale friction by direct contact.

The friction phenomenon is a ubiquitous manifestation of nature. Models considering phononic, electronic, magnetic, and electrostatic interactions are invoked to explain the fundamental forces involved in the friction phenomenon. In order to establish the incidence of the phonon prompting at the nanoscale friction by direct contact, we study a diamond spherical dome sliding on carbon thin films containing different amount of deuterium and hydrogen. The friction coefficient decreases by substituting hydrogen by deuterium atoms. This result is consistent with an energy dissipation vibration local mechanism from a disordered distribution of bond terminators.

Extensibility and Distensibility of the Thoracic Aorta in Patients with Aneurysm.

OBJECTIVES: Reference values of aortic deformation during the cardiac cycle can be valuable for the pre-operative planning of thoracic endovascular aortic repair (TEVAR) and for facilitating computational fluid dynamics. This study aimed to quantify normal aortic extensibility (longitudinal extension) and distensibility (radial expansion), as well as pulsatile strain, in a group of 10 (>60 years) individuals with abdominal or thoracic aortic aneurysms. METHODS: ECG gated CT images of the thoracic aorta were reconstructed into virtual 3D models of aortic geometry. The centre lumen line length of the thoracic aorta and three longitudinal segments, and the aortic diameter and luminal areas of four radial intersections were extracted with a dedicated software script to calculate extensibility, longitudinal strain, distensibility, and circumferential area strain. RESULTS: Mean extensibility and longitudinal strain of the entire thoracic aorta were 3.5 [1.3-6.8] × 10-3 N-1, and 2.7 [1.0-4.5]%, respectively. Extensibility and longitudinal strain were most pronounced in the ascending aorta (20.6 [5.7-36.2] × 10-3 N-1 and 15.9 [6.6-31.9]%) and smallest in the descending aorta (4.4 [1.6-12.3] × 10-3 N-1 and 2.2 [0.7-4.7]%). Mean distensibility and circumferential area strain were most pronounced at the sinotubular junction (1.7 [0.5-2.9] × 10-3 mmHg-1 and 11.3 [3.3-18.5]%, respectively). Distensibility varied between 0.9 [0.3-2.5] × 10-3 mmHg-1 and 1.2 [0.3-3.3] × 10-3 mmHg-1 at the intersections in the aortic arch and descending aorta. CONCLUSIONS: Pulsatile deformations in both longitudinal and circumferential directions are considerable throughout the thoracic aorta. These findings may have implications for pre-operative TEVAR planning and highlight the need for devices that can mimic the significant aortic longitudinal and circumferential strains.

Computational Study of Anatomical Risk Factors in Idealized Models of Type B Aortic Dissection.

OBJECTIVE/BACKGROUND: Several risk factors have been identified in type B aortic dissection (TBAD), namely tear size, location, patency and number, and false lumen (FL) location. However, the individual impact of each of these factors is poorly understood. The impact of these factors was investigated using computational fluid dynamics (CFD). METHODS: Fourteen idealized models of chronic TBAD were created of different shapes (straight vs. curved vessels), different number of proximal and distal tears, tear size (4, 10, and 20 mm diameter) and shape (circular or elliptical), FL location (inner or outer arch), treated (stented), and untreated. All models had identical length, relative size of true lumen (TL) and FL, and inlet (flow) and outlet (pressure) boundary conditions. Using validated CFD tools, inlet mean pressure (MP), pulse pressure (PP), TL and FL pressures, velocities, and flows were computed for each model. RESULTS: AD increased PP and MP relative to undissected aorta. Curvature did not change pressure and flow ratio between TL and FL. Inner curvature FL showed slightly larger pressures and tear velocities. Larger tears decreased hemodynamic differences between TL and FL. The combination of proximal and distal tear size determines the overall hemodynamics: larger proximal tears increased FL PP by up to 76%. Conversely, larger distal tears decreased FL PP and MP. Large proximal and distal tears decreased tear velocity (by up to 65%) and increased FL flow (up to 12 times). Proximal tear stenting resulted in a 54% reduction of PP. Conversely, distal occlusion tear increased FL PP and MP by 144% and 7%, respectively. CONCLUSION: Unfavorable hemodynamic conditions such as larger FL pressure occur when distal tear is small or absent, proximal tears are large, and FL is at the inner curvature, in agreement with previous clinical studies. CFD analysis is a powerful tool to understand the interplay between anatomy and hemodynamics in TBAD.

Identification of the Chemical Bonding Prompting Adhesion of a-C:H Thin Films on Ferrous Alloy Intermediated by a SiCx:H Buffer Layer.

Amorphous carbon (a-C) and several related materials (DLCs) may have ultralow friction coefficients that can be used for saving-energy applications. However, poor chemical bonding of a-C/DLC films on metallic alloys is expected, due to the stability of carbon-carbon bonds. Silicon-based intermediate layers are employed to enhance the adherence of a-C:H films on ferrous alloys, although the role of such buffer layers is not yet fully understood in chemical terms. The chemical bonding of a-C:H thin films on ferrous alloy intermediated by a nanometric SiCx:H buffer layer was analyzed by X-ray photoelectron spectroscopy (XPS). The chemical profile was inspected by glow discharge optical emission spectroscopy (GDOES), and the chemical structure was evaluated by Raman and Fourier transform infrared spectroscopy techniques. The nature of adhesion is discussed by analyzing the chemical bonding at the interfaces of the a-C:H/SiCx:H/ferrous alloy sandwich structure. The adhesion phenomenon is ascribed to specifically chemical bonding character at the buffer layer. Whereas carbon-carbon (C-C) and carbon-silicon (C-Si) bonds are formed at the outermost interface, the innermost interface is constituted mainly by silicon-iron (Si-Fe) bonds. The oxygen presence degrades the adhesion up to totally delaminate the a-C:H thin films. The SiCx:H deposition temperature determines the type of chemical bonding and the amount of oxygen contained in the buffer layer.

Male reproductive system and antioxidants in oxidative stress induced by hypobaric hypoxia.

In Chile, due to the intensive activity developed in confining areas of the Andes Mountains ranging in altitude over 4000 asl, there has been an increasing intermittent movement of human resources to high altitude conditions. This unusual condition, defined as hypobaric hypoxia, affects notoriously in any living organism and there shows a series of physiological responses. Studies performed in rats under chronic hypobaric hypoxia and intermittent hypobaric hypoxia have registered changes in testicular morphology together with loss of spermatogenic cells in all stages of spermatogenic cycle. Furthermore, recent tests reinforced the existence of an oxidative metabolism in epididymis of rats subjected to hypobaric hypoxia due to the increase in the regulator enzyme expression of reactive oxygen species (ROS), This increase in the production of ROS induced a rise in apoptosis at germinal cell level, leading to a state of hypo-spermatogenesis that may jeopardise masculine fertility. Therefore, the eventual development of oxidative stress in spermatogenic cells and consequently the spermatozoids of workers subjected to high altitude, either chronic or intermittent, turns out to be critical when it poses as an imminent risk to the viability and quality of the reproductive cells of workers subjected to intermittent hypobaric hypoxia.

Quantification of regional differences in aortic stiffness in the aging human.

There has been a growing awareness over the past decade that stiffening of the aorta, and its attendant effects on hemodynamics, is both an indicator and initiator of diverse cardiovascular, neurovascular, and renovascular diseases. Although different clinical metrics of arterial stiffness have been proposed and found useful in particular situations, there remains a need to understand better the complex interactions between evolving aortic stiffness and the hemodynamics. Computational fluid-solid-interaction (FSI) models are amongst the most promising means to understand such interactions for one can parametrically examine effects of regional variations in material properties and arterial geometry on local and systemic blood pressure and flow. Such models will not only increase our understanding, they will also serve as important steps towards the development of fluid-solid-growth (FSG) models that can further examine interactions between the evolving wall mechanics and hemodynamics that lead to arterial adaptations or disease progression over long periods. In this paper, we present a consistent quantification and comparison of regional nonlinear biaxial mechanical properties of the human aorta based on 19 data sets available in the literature and we calculate associated values of linearized stiffness over the cardiac cycle that are useful for initial large-scale FSI and FSG simulations. It is shown, however, that there is considerable variability amongst the available data and consequently that there is a pressing need for more standardized biaxial testing of the human aorta to collect data as a function of both location and age, particularly for young healthy individuals who serve as essential controls.

Blueberries prevent the effect of intermittent hypobaric hypoxia in rat epididymis.

Intermittent hypobaric hypoxia (IHH) induced a decrease in sperm count and oxidative damage in epididymis. We have previously demonstrated that a blueberry-enriched polyphenol extract (BB-4) reduced the adverse effects of oxidative stress in rat testis under hypobaric hypoxia. The aim of this study was to evaluate whether BB-4 could reverse oxidative stress in epididymis. To evaluate the protective role of BB-4 in epididymis, male rats were exposed to IHH. Lipid peroxidation, (LPO) expression and activity of glutathione reductase (GR) were evaluated. Our results showed a reduction in LPO and a decrease in GR activity in rat epididymis exposed to IHH. These results suggest that BB-4 can prevent the effects of IHH in rat epididymis.

Bacterial consortium for copper extraction from sulphide ore consisting mainly of chalcopyrite.

The mining industry is looking forward for bacterial consortia for economic extraction of copper from low-grade ores. The main objective was to determine an optimal bacterial consortium from several bacterial strains to obtain copper from the leach of chalcopyrite. The major native bacterial species involved in the bioleaching of sulphide ore (Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Leptospirillum ferrooxidans and Leptospirillum ferriphilum) were isolated and the assays were performed with individual bacteria and in combination with At. thiooxidans. In conclusion, it was found that the consortium integrated by At. ferrooxidans and At. thiooxidans removed 70% of copper in 35 days from the selected ore, showing significant differences with the other consortia, which removed only 35% of copper in 35 days. To validate the assays was done an escalation in columns, where the bacterial consortium achieved a higher percentage of copper extraction regarding to control.

Medical students' knowledge and attitudes toward organ donation: results of a Dutch survey.

BACKGROUND: In the Netherlands, as in many other countries, a paucity of research exists on the attitudes and intentions of medical students toward organ donation. These students are of interest for the effect that increasing medical knowledge might have on the willingness to register as a donor. OBJECTIVE: To examine which factors determine medical students' willingness to register as donors. METHODS: We conducted a cross-sectional survey among medical students at the University of Amsterdam. Our questionnaire included questions on actual donor registration, motives, knowledge, and attitudes toward donation. To assess which factors were related to self-reported donor registration status, we conducted multivariate logistic regression analyses. RESULTS: We received 506 questionnaires (response rate at least 84%). The majority of respondents (80%) intended to donate organs, while 59% were registered. Self-reported medical knowledge and positive attitudes on donation were independently associated with registering as a donor. A rising study year was associated with registering as a donor; this could be explained by increasing medical knowledge and changing attitudes. CONCLUSION: The results of our study suggest that willingness to register as a donor increases with a rising level of knowledge on organ donation up to some minimal level.

Sequential identification of boundary support parameters in a fluid-structure vascular model using patient image data.

Viscoelastic support has been previously established as a valuable modeling ingredient to represent the effect of surrounding tissues and organs in a fluid-structure vascular model. In this paper, we propose a complete methodological chain for the identification of the corresponding boundary support parameters, using patient image data. We consider distance maps of model to image contours as the discrepancy driving the data assimilation approach, which then relies on a combination of (1) state estimation based on the so-called SDF filtering method, designed within the realm of Luenberger observers and well adapted to handling measurements provided by image sequences, and (2) parameter estimation based on a reduced-order UKF filtering method which has no need for tangent operator computations and features natural parallelism to a high degree. Implementation issues are discussed, and we show that the resulting computational effectiveness of the complete estimation chain is comparable to that of a direct simulation. Furthermore, we demonstrate the use of this framework in a realistic application case involving hemodynamics in the thoracic aorta. The estimation of the boundary support parameters proves successful, in particular in that direct modeling simulations based on the estimated parameters are more accurate than with a previous manual expert calibration. This paves the way for complete patient-specific fluid-structure vascular modeling in which all types of available measurements could be used to estimate additional uncertain parameters of biophysical and clinical relevance.

Bacterial consortium for copper extraction from sulphide ore consisting mainly of chalcopyrite

The mining industry is looking forward for bacterial consortia for economic extraction of copper from low-grade ores. The main objective was to determine an optimal bacterial consortium from several bacterial strains to obtain copper from the leach of chalcopyrite. The major native bacterial species involved in the bioleaching of sulphide ore (Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Leptospirillum ferrooxidans and Leptospirillum ferriphilum) were isolated and the assays were performed with individual bacteria and in combination with At. thiooxidans. In conclusion, it was found that the consortium integrated by At. ferrooxidans and At. thiooxidans removed 70% of copper in 35 days from the selected ore, showing significant differences with the other consortia, which removed only 35% of copper in 35 days. To validate the assays was done an escalation in columns, where the bacterial consortium achieved a higher percentage of copper extraction regarding to control.

External tissue support and fluid-structure simulation in blood flows.

The objective of this work is to address the formulation of an adequate model of the external tissue environment when studying a portion of the arterial tree with fluid-structure interaction. Whereas much work has already been accomplished concerning flow and pressure boundary conditions associated with truncations in the fluid domain, very few studies take into account the tissues surrounding the region of interest to derive adequate boundary conditions for the solid domain. In this paper, we propose to model the effect of external tissues by introducing viscoelastic support conditions along the artery wall, with two-possibly distributed-parameters that can be adjusted to mimic the response of various physiological tissues. In order to illustrate the versatility and effectiveness of our approach, we apply this strategy to perform patient-specific modeling of thoracic aortae based on clinical data, in two different cases and using a distinct fluid-structure interaction methodology for each, namely an Arbitrary Lagrangian-Eulerian (ALE) approach with prescribed inlet motion in the first case and the coupled momentum method in the second case. In both cases, the resulting simulations are quantitatively assessed by detailed comparisons with dynamic image sequences, and the model results are shown to be in very good adequacy with the data.

Patient-specific modeling of blood flow and pressure in human coronary arteries.

Coronary flow is different from the flow in other parts of the arterial system because it is influenced by the contraction and relaxation of the heart. To model coronary flow realistically, the compressive force of the heart acting on the coronary vessels needs to be included. In this study, we developed a method that predicts coronary flow and pressure of three-dimensional epicardial coronary arteries by considering models of the heart and arterial system and the interactions between the two models. For each coronary outlet, a lumped parameter coronary vascular bed model was assigned to represent the impedance of the downstream coronary vascular networks absent in the computational domain. The intramyocardial pressure was represented with either the left or right ventricular pressure depending on the location of the coronary arteries. The left and right ventricular pressure were solved from the lumped parameter heart models coupled to a closed loop system comprising a three-dimensional model of the aorta, three-element Windkessel models of the rest of the systemic circulation and the pulmonary circulation, and lumped parameter models for the left and right sides of the heart. The computed coronary flow and pressure and the aortic flow and pressure waveforms were realistic as compared to literature data.