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BackgroundThe novel coronavirus disease 2019 (COVID-19) undermines the benefits of cancer screening. To date, no study has identified specific infection control methods. We aimed to provide practical methods for COVID-19 risk reduction during breast cancer screening mammography (MMG) by examining an overview of potential contamination routes of aerosols and possible risks for patients and health care providers.MethodsComputational fluid dynamics (CFD) simulations were conducted for airflow and aerosol dispersion in a 3D virtual model of a mobile MMG laboratory room. This model was constructed based on the actual mobile screening MMG bus ‘Cosmos’ in the Chiba Foundation for Health Promotion & Disease Prevention. Examiner and patient geometries were obtained by scanning an actual human using a 3D Scanner. Contamination of the room was evaluated by counting the numbers of suspended and deposited aerosols.ResultsWe applied the CFD simulation model to the exhalation of small or large aerosols from a patient and examiner in the MMG laboratory. Only 14.5% and 54.5% of large and small aerosols, respectively, were discharged out of the room with two doors open. In contrast, the proportion of large and small aerosols discharged out of the room increased to 96.6% and 97.9%, respectively, with the addition of forced gentle wind by the blower fan. This simulation was verified by a mist aerosol experiment conducted in the mobile MMG laboratory.ConclusionAdding forced ventilation to a MMG laboratory with two doors open may enable risk reduction dramatically. This could be applied to other clinical situations.

Initiation, growth, and rupture of cerebral aneurysms are caused by hemodynamic factors. It is extensively accepted that the cerebral aneurysm wall is assumed to be rigid using computational fluid dynamics (CFD). Furthermore, fluid-structure interactions have been recently applied for simulation of an elastic cerebral aneurysm model. Herein, we examined cerebral aneurysm hemodynamics in a realistic moving boundary deformation model based on 4-dimensional computed tomographic angiography (4D-CTA) obtained by high time-resolution using numerical simulation. The aneurysm of the realistic moving deformation model based on 4D-CTA at each phase was constructed. The effect of small wall deformation on hemodynamic characteristics might be interested. So, four hemodynamic factors (wall shear stress, wall shear stress divergence, oscillatory shear index and residual residence time) were determined from the numerical simulation, and their behaviors were assessed in the basilar bifurcation aneurysm.

The mortality and morbidity rate due to the severe effect of intracranial aneurysm (IA) is increasing, which has driven research trend on aneurysm rupture risk. By understanding the nature and causes of the aneurysm rupture, preventive measures could be taken in avoiding rupture besides recommending proper treatments such as endovascular coiling. However, the presence of flow recirculation causes the aneurysm wall to degenerate and weakened. The weakened wall is due to the haemodynamic factors such as velocity, wall shear stress (WSS), time average WSS (TAWSS), OSI and RRT, which were analysed in this study. In the present study, the flow model simulated a human patient-specific aneurysm at the apex of the bifurcation in the middle cerebral artery (MCA) in the transient state. Experimental results of full-scale models were collected on a median, side plane to study the flow behaviour and validation to the numerical simulation settings, which resulted in good agreement with only 8% difference. The simulation results obtained showed several interesting findings. The jet flow into the aneurysm led to complex vortex formation due to impinging flow behaviour within the aneurysm dome. Additionally, the area that recorded low velocity was at 30% of low TAWSS with only 1% of OSI that was more than 0.3, while the OSI critical value and 0.27% area exceeded RRT threshold, which caused the large oscillating blood flow direction and activated the atherosclerosis progression. These results suggest that the jet flow into the dome may cause further damage to the wall of the MCA aneurysm, which will help in providing an insight towards completing a guidance system assessment of rupture risk for medical practitioners in future work.

Thermoacoustic engines use waste heat available at a higher temperature to produce mechanical energy in the form of waves. The purpose of this study is to visualize the fluid behavior downstream of the stack of a thermoacoustic engine by applying numerical analysis and to explore the effect of vortex shedding on the temperature field. The self-sustained oscillation is reproduced by two-dimensional numerical analysis using the compressible solver of OpenFOAM, and the vorticity field and temperature field were visualized. The vortex downstream of the stack changed from symmetric to asymmetric near the peak of the flow velocity. Changes in the vortex structure by the unsteady flow caused irregular and non-uniform temperature field. It is found that the vortex significantly affects the heat transfer between the heat exchanger and the fluid.

Background Constipation is frequently observed in patients with chronic kidney disease (CKD). Lactulose is expected to improve the intestinal environment by stimulating bowel movements as a disaccharide laxative and prebiotic. We studied the effect of lactulose on renal function in adenine-induced CKD rats and monitored uremic toxins and gut microbiota. Methods Wistar/ST male rats (10-week-old) were fed 0.75% adenine-containing diet for 3 weeks to induce CKD. Then, they were divided into three groups and fed as follows: control, normal diet; and 3.0- and 7.5-Lac, 3.0% and 7.5% lactulose-containing diets, respectively, for 4 weeks. Normal diet group was fed normal diet for 7 weeks. The rats were observed for parameters including renal function, uremic toxins, and gut microbiota. Results The control group showed significantly higher serum creatinine (sCr) and blood urea nitrogen (BUN) 3 weeks after adenine feeding than at baseline, with a 8.5-fold increase in serum indoxyl sulfate (IS). After switching to 4 weeks of normal diet following adenine feeding, the sCr and BUN in control group remained high with a further increase in serum IS. In addition, tubulointerstitial fibrosis area was increased in control group. On the other hand, 3.0- and 7.5-Lac groups improved sCr and BUN levels, and suppressed tubulointerstitial fibrosis, suggesting preventing of CKD progression by lactulose. Lac groups also lowered level of serum IS and proportions of gut microbiota producing IS precursor. Conclusion Lactulose modifies gut microbiota and ameliorates CKD progression by suppressing uremic toxin production.

The behavior of wall shear stress (WSS) was previously reported in a deformable aneurysm model using fluid-structure interactions. However, these findings have not been validated. In the present study, we examined the effect of elasticity (i.e., deformation) on wall shear stress inside a cerebral aneurysm at the apex of a bifurcation using particle image velocimetry in vitro. The flow model simulated a human patient-specific aneurysm at the apex of the bifurcation of the middle cerebral artery. Flow characteristics by wall elasticity were examined for both elastic and non-deformable aneurysm models with pulsatile blood flow. The absolute temporally- and spatially-averaged WSS along the bleb wall was smaller in the elastic model than that in the non-deformable model. This small WSS may be related to attenuation of the WSS. Further, the WSS gradient had a finite value near the stagnation point of the aneurysm dome. Finally, the WSS gradient near the stagnation point was slightly smaller in the elastic model than that in the non-deformable model. These data suggest that elasticity of the aneurysm wall can affect the progression and rupture of aneurysms via hemodynamic stress.

The mechanisms underlying the growth and rupture of aneurysms are poorly understood. Although the wall shear stress (WSS) in elastic aneurysm models is examined using fluid-structure interaction (FSI) simulations, it has not been sufficiently validated using experimental modalities, such as particle image velocimetry (PIV) or phase contrast magnetic resonance imaging (PC-MRI). In this study, we investigated pulsatile flow in an elastic, image-based, patient-specific cerebral aneurysm model using PIV. The phantom model was carefully fabricated using a specialized technique by silicone elastomer. We explored the hemodynamics of the WSS and the kinetic energy cascade (KEC) in the elastic model compared with a rigid model, at the apex of the bifurcation of the middle cerebral artery (MCA) in vitro. The effects of elasticity on the WSS, WSS gradient (WSSG), and tensile strength of the aneurysm wall were also investigated, in addition to the effect of wall elasticity on the KEC compared to a rigid wall. Although the WSSG around the stagnation point had a large positive value, there was no difference between the two models. In particular, wall elasticity suppressed the WSS magnitude around the stagnation point and attenuated the KEC (i.e., the flow fluctuation). Future studies examining KEC frequency and WSS characteristics in a phantom model should consider assessing elasticity.

The nasal airway is an extremely complex structure, therefore grid generation for numerical prediction of airflow in the nasal cavity is time-consuming. This paper describes the development of a voxel-based model with a Cartesian structured grid, which is characterized by robust and automatic grid generation, and the simulation of the airflow and air-conditioning in an individual human nasal airway. Computed tomography images of a healthy adult nose were used to reconstruct a virtual three-dimensional model of the nasal airway. Simulations of quiet restful inspiratory flow were then performed using a Neumann boundary condition for the energy equation to adequately resolve the flow and heat transfer. General agreements of airflow patterns, which were a high-speed jet posterior to the nasal valve and recirculating flow that occupied the anterior part of the upper cavity, and temperature distributions of the airflow and septum wall were confirmed by comparing in-vivo measurements with numerical simulation results.

We visualized the flow patterns in an alveolated duct model with breathing-like expanding and contracting wall motions using particle image velocimetry, and then, we investigated the effect of acinar deformation on the flow patterns. We reconstructed a compliant, scaled-up model of an alveolated duct from synchrotron microcomputed tomography images of a mammalian lung. The alveolated duct did not include any bifurcation, and its entire surface was covered with alveoli. We embedded the alveolated duct in a sealed container that was filled with fluid. We oscillated the fluid in the duct and container simultaneously and independently to control the flow and duct volume. We examined the flow patterns in alveoli, with the Reynolds number (Re) at 0.03 or 0.22 and the acinar volume change at 0%, 20%, or 80%. At the same Re, the heterogeneous deformation induced different inspiration and expiration flow patterns, and the recirculating regions in alveoli changed during respiratory cycle. During a larger acinar deformation at Re = 0.03, the flow patterns tended to change from recirculating flow to radial flow during inspiration and vice versa during expiration. Additionally, the alveolar geometric characteristics, particularly the angle between the alveolar duct and mouth, affected these differences in flow patterns. At Re = 0.22, recirculating flow patterns tended to form during inspiration and expiration, regardless of the magnitude of the acinar deformation. Our in vitro experiments suggest that the alveolated flows with nonself-similar and heterogeneous wall motions may promote particle mixing and deposition.

ATP9A is localized to phosphatidylserine-positive early and recycling endosomes, but not late endosomes, in HeLa cells. ATP9A plays a crucial role in recycling of transferrin and glucose transporter 1 from endosomes to the plasma membrane., Type IV P-type ATPases (P4-ATPases) are phospholipid flippases that translocate phospholipids from the exoplasmic (or luminal) to the cytoplasmic leaflet of lipid bilayers. In Saccharomyces cerevisiae, P4-ATPases are localized to specific subcellular compartments and play roles in compartment-mediated membrane trafficking; however, roles of mammalian P4-ATPases in membrane trafficking are poorly understood. We previously reported that ATP9A, one of 14 human P4-ATPases, is localized to endosomal compartments and the Golgi complex. In this study, we found that ATP9A is localized to phosphatidylserine (PS)-positive early and recycling endosomes, but not late endosomes, in HeLa cells. Depletion of ATP9A delayed the recycling of transferrin from endosomes to the plasma membrane, although it did not affect the morphology of endosomal structures. Moreover, depletion of ATP9A caused accumulation of glucose transporter 1 in endosomes, probably by inhibiting their recycling. By contrast, depletion of ATP9A affected neither the early/late endosomal transport and degradation of epidermal growth factor (EGF) nor the transport of Shiga toxin B fragment from early/recycling endosomes to the Golgi complex. Therefore ATP9A plays a crucial role in recycling from endosomes to the plasma membrane.

This paper describes the simulation of airflow in human nasal airways using voxel-based modeling characterized by robust, automatic, and objective grid generation. Computed tomography scans of a healthy adult nose are used to reconstruct 3D virtual models of the nasal airways. Voxel-based simulations of restful inspiratory flow are then performed using various mesh sizes to determine the level of granularity required to adequately resolve the airflow. For meshes with close voxel spacings, the model successfully reconstructs the nasal structure and predicts the overall pressure drop through the nasal cavity.

A T-junction is a fundamental fluid element prevalent in pipe networks of water supplies and power plants. In the present study, a double T-junction was investigated for flow instability and fluid vibration. Both axi-aligned and skewed double T-junctions are examined from viewpoint of flow instability. With single-phase flow in an open-ended double T-junction, fluid vibration is induced in both side branches because of a high shear rate with a point of inflection. The frequency of vibration in the downstream branch is higher than that in the upstream branch. Except for the upstream branch in the skewed double T-junction, the frequency is higher than that in a single T-junction. The fluid vibrations are closely associated with the fluid interference created by the presence of the two side branches.

The effect of a simple bare-metal stent on suppression of wall shear stress inside a spherical intracranial aneurysm model was experimentally investigated by two dimensional particle image velocimetry in vitro . The flow model simulated an intracranial aneurysm induced both at the side wall and at the apex of bifurcation between the anterior cerebral artery and the anterior communicating artery. Wall shear stress was investigated using both stented and non-stented models to assess the simple bare metal stent characteristics. The flow behavior inside the stented aneurysm sac was unusual and wall shear stress was much smaller inside the aneurysm sac. For both models, the maximum and the temporal and spatial averaged wall shear stress in the stented model is reduced by at least 50 % from those in the non-stented model. Stent placement effectively suppresses the temporal and spatial variations, and the magnitude of wall shear stress. Consequently, there is an effective possibility that would retard the progress of cerebral aneurysms by even simple stent.

The location and concentration of particle deposition of pollen by filtration in the human nasal cavity were visualized in a transparent silicone nasal airway model using laser-induced fluorescence (LIF) to clarify the relationship between flow and particle deposition. The model was created from a water-soluble plaster mold fabricated by a 3D printer based on X-ray computed tomography images. The working fluid was air and the tracer particles as a substitute for cedar pollen were lycopodium powder doped with fluorescent dye (Rhodamine 6G). After particle deposition, the nasal airway model was filled with an aqueous solution of glycerin that had the same refractive index as silicone. Then, LIF was applied to illuminate the deposited particles with a YAG laser sheet. Results revealed that particle deposition in the right and left cavities was highly heterogeneous and was related to the complex flow structure in the nasal cavities. .

The present paper deals with the longitudinal heat transportation by an oscillatory flow in a curved tube heat transportation pipe. The velocity and temperature fields during oscillatory water flow in a curved tube with inner diameter of 10 mm were numerically simulated using the commercial software FLUENT. To clarify the effect of the curvature on heat transportation, the ratio of the tube radius to the curvature radius was varied from 0.0125 to 0.075, and oscillatory flow frequency was varied from 0.1 to 2.0 Hz. The effective thermal diffusivity exhibited a peak at a curvature ratio around 0.05–0.07 and reached a value 12 times higher than that of a straight tube. It was also found that the dispersion of fluid particles due to secondary flow caused the enhancement of heat transportation.

Mass transport phenomena in airways, including dispersion, may be influenced by the complicated three-dimensional (3D) branching geometry, which undergoes expansion and contraction during the respiratory cycle. In this study, we investigated the effects of this expansion and contraction on gas dispersion in multi-branching airways using computational fluid dynamics. A 3D multi-branching airway model was constructed based on mammalian computed tomography images, with diameters ranging from 1.25 mm in the parent tube to 0.35 mm in the daughter tube. We examined the dispersion of oxygen in the airway when subject to oscillatory flow while the airway expanded and contracted sinusoidally with time. After several respiratory cycles, the oxygen fraction was higher in the airway-motion model than in the rigid model, and it increased as the volume expansion factor increased. Furthermore, the oxygen fraction increased as the breathing frequency was increased for the airway model undergoing wall motion. Transport simulation of passive tracer particles showed that, although the particles were dispersed around the initial position in the rigid model, many particles were anchored around the carina and dispersed widely in the airway-motion model. These results indicate that steady streaming and unsteady flow behavior due to airway branches and expanding and contracting motion may enhance gas dispersion in multi-branching airways.

We visualized pulmonary acini in the core regions of the mouse lung in situ using synchrotron refraction-enhanced computed tomography (CT) and evaluated their kinematics during quasi-static inflation. This CT system (with a cube voxel of 2.8 μm) allows excellent visualization of not just the conducting airways, but also the alveolar ducts and sacs, and tracking of the acinar shape and its deformation during inflation. The kinematics of individual alveoli and alveolar clusters with a group of terminal alveoli is influenced not only by the connecting alveolar duct and alveoli, but also by the neighboring structures. Acinar volume was not a linear function of lung volume. The alveolar duct diameter changed dramatically during inflation at low pressures and remained relatively constant above an airway pressure of ∼8 cmH2O during inflation. The ratio of acinar surface area to acinar volume indicates that acinar distension during low-pressure inflation differed from that during inflation over a higher pressure range; in particular, acinar deformation was accordion-like during low-pressure inflation. These results indicated that the alveoli and duct expand differently as total acinar volume increases and that the alveolar duct may expand predominantly during low-pressure inflation. Our findings suggest that acinar deformation in the core regions of the lung is complex and heterogeneous.

For laminar flow in the side branch of a T-junction, periodic fluid vibrations occur with the Strouhal number independent of characteristic flow conditions. As the mechanics is unknown, an experiment was performed to establish the underlying cause in high-shear-rate flow. The fluid vibration appears along both the shearing separation layer and the boundary between two vortices immediately downstream of the side branch, where the shear rates are several orders larger than those further downstream. This vibration is caused by flow instability induced in two types of high-shear-rate flow confirming that is a universal phenomenon associated with the geometry of the T-junction.

Background Many numerical studies have been published with respect to about flow structures around cerebral aneurysm assuming to be rigid. Furthermore, there is little experimental research concerning aneurysm with elastic wall. Wall shear stress in elastic wall comparing with rigid wall should be clarified in experimental approach and verified in CFD. Objective We have experimentally realized elastic aneurysm model accompanying with wall deformation. Wall shear stress was examined for both rigid and elastic aneurysm models in pulsatile flow. Methods Effect of elasticity on wall shear stress inside aneurysm induced at the apex of anterior cerebral artery was experimentally examined by particle image velocimetry in vitro. In order to adjust the wall deformation, the pressure adjustment chamber was specially equipped outside the aneurysm wall. Results Effect of elasticity on wall shear stress was noticed on the comparison with that of rigidity. Wall elasticity reduced the peak magnitude, the spatial and temporal averaged wall shear stress comparing with those of wall rigidity experimentally. These reductions were endorsed by fluid-structure interaction simulation. Conclusion Elastic wall comparing with rigid wall would reduce the peak magnitude, the spatial and temporal averaged wall shear stress acting on vascular wall.

Computational fluid dynamics (CFD) simulation was carried out for an oscillatory flow in an expanding and contracting model of small airways, and the effects of airway geometry and rhythmic breathing motion on the kinematic irreversibility of oscillatory flow were revealed. A 3D realistic model of multi-branching small airways was reconstructed from X-ray CT images of a mouse, which were obtained by the high-resolution synchrotron radiation CT system of SPring-8. Airway diameters range from 360 μm in the primary branch to 55 μm in the distal branch. The airway model was expanded and contracted in a sinusoidal volume change with time such that the geometry remains self-similar throughout a period. The Fluent software package was used for calculation of the fluid particle trajectory in the airway model. The dispersion of the fluid particle was evaluated in terms of the variance of the marked minute particles in the axial direction. The results show that the axial dispersion is enhanced by the expanding and contracting motion of the airways. It was also found that the augmentation of steady streaming is responsible for enhanced dispersion of fluid particles.

Turbulence in the oscillatory flow in realistic model human central airways was measured by particle image velocimetry (PIV) to reveal the nature of turbulence in a lung. The transparent silicone model of multi-branching airways was fabricated from X-ray CT images by rapid prototyping. The multi-branching airways comprise trachea, and right and left bronchi, with airway diameters ranging from 14 to 2 mm, respectively. Experiments were performed for a Reynolds number from 1200 to 2200 and a Womersley number from 1.9 to 2.3 in the trachea. Results showed that spatial and temporal variations of turbulent intensity strongly depends on the airway geometry and on the phase of oscillatory flow, and that expiratory flow generates strong turbulence which explosively occurs in the entire cross-section especially in the right bronchi, whereas inspiratory flow generates relatively weak turbulence near the airway wall.

The WHO classifications of tumors are the global standards of tumor diagnosis. In spite of the detailed descriptions of the histopathological features of tumors in the classifications, tumors may be difficult to diagnose or the diagnosis can be improper. One of the reasons is that the diagnostic criteria have indeterminacy. In this article, we clarify this indeterminacy and discuss the diagnostic problems associated with indeterminacy. Indeterminacy of the histopathological features is classified according to the following three points: specificity, constancy, and exclusiveness. We consider an oblique (ambiguous description), variable (not always present), or duplicative feature as an indeterminate feature. Under indeterminacy, pathologists make their diagnosis on the basis of their experience and heuristic reasoning, which can lead to improper diagnosis. Not only the histopathological features, but also the diagnostic criterion, will have indeterminacy, which may be the direct influence of the indeterminacy of the features. Also, it is possible for there to be too many combinations of findings that satisfy a criterion, preventing an exhaustive description. The diagnostic criteria of the WHO classification have indeterminacy. Users should therefore verify their diagnosis. Further efforts by WHO editors to improve the diagnostic criteria also are desirable.