Research progress on cardiovascular hemodynamic assessment based on computational fluid dynamics / 中国胸心血管外科临床杂志

@#Hemodynamics plays a vital role in the development and progression of cardiovascular diseases, and is closely associated with changes in morphology and function. Reliable detection of hemodynamic changes is essential to improve treatment strategies and enhance patient prognosis. The combination of computational fluid dynamics with cardiovascular imaging technology has extended the accessibility of hemodynamics. This review provides a comprehensive summary of recent developments in the application of computational fluid dynamics for cardiovascular hemodynamic assessment and a succinct discussion for potential future development.

Effect of nasal swell body on nasal airflow and Artemisia pollen deposition / 临床耳鼻咽喉头颈外科杂志

Objective:The nasal swell body（NSB） consists of the nasal septal cartilage, nasal bone, and swollen soft tissue, all of which are visible during endoscopic and imaging examinations. Although the function of the NSB remains uncertain, there is evidence to suggest that it plays a vital role in regulating nasal airflow and filtering inhaled air. Based on anatomical and histological evidence, it is hypothesized that the NSB is indispensable in these processes. This study aims to investigate the impact of NSB on nasal aerodynamics and the deposition of allergen particles under physiological conditions. Methods:The three-dimensional （3D） nasal models were reconstructed from computed tomography （CT） scans of the paranasal sinus and nasal cavity in 30 healthy adult volunteers from Northwest China, providing basis for the construction of models without NSB following virtual NSB-removal surgery. To analyze the distribution of airflow in the nasal cavity, nasal resistance, heating and humidification efficiency, and pollen particle deposition rate at various anatomical sites, we employed the computed fluid dynamics（CFD） method for numerical simulation and quantitative analysis. In addition, we created fully transparent segmented nasal cavity models through 3D printing, which were used to conduct bionic experiments to measure nasal resistance and allergen particle deposition. Results:①The average width and length of the NSB in healthy adults in Northwest China were （12.85±1.74） mm and （28.30±1.92） mm, respectively. ②After NSB removal, there was no significant change in total nasal resistance, and cross-sectional airflow velocity remained essentially unaltered except for a decrease in topical airflow velocity in the NSB plane. ③There was no discernible difference in the nasal heating and humidification function following the removal of the NSB; ④After NSB removal, the deposition fraction（DF） of Artemisia pollen in the nasal septum decreased, and the DFs post-and pre-NSB removal were（22.79±6.61）% vs （30.70±12.27）%, respectively; the DF in the lower airway increased, and the DFs post-and pre-NSB removal were（24.12±6.59）% vs （17.00±5.57）%, respectively. Conclusion:This study is the first to explore the effects of NSB on nasal airflow, heating and humidification, and allergen particle deposition in a healthy population. After NSB removal from the healthy nasal cavities: ①nasal airflow distribution was mildly altered while nasal resistance showed no significantly changed; ②nasal heating and humidification were not significantly changed; ③the nasal septum's ability to filter out Artemisia pollen was diminished, which could lead to increased deposition of Artemisia pollen in the lower airway.

A simulating method for dripping process of Ginkgo biloba leaf dripping pills based on computational fluid dynamics technology / 药学学报

A simulating method for dripping process of Ginkgo biloba leaf dripping pills based on computational fluid dynamics was constructed. Ginkgo biloba leaf dripping pills was explored as the experimental subject to simulate the dripping process based on FLOW-3D software. The dripping process was simulated through the derivation of the governing equations, the selection of the models, and simulation parameters. Firstly, the droplet morphologies and drop speeds under different liquid viscosity were simulated. It was found that with the increase of the liquid viscosity, the drop speed decreased and the difficulty of droplet preparation gradually increased. The simulation results were consistent with the experiment results. Secondly, the droplet morphologies at different drop speeds were investigated and verified by experiments. It was found that the simulation results had a good correlation with the experiment results. The results shown that the viscosity of the liquid was the critical material attribute, and the drop speed was the critical process parameter, according to the droplet morphology. The establishment of the simulation method can deepen the understanding of the dripping process and provide a reference for the selection of raw materials and process parameters.

Virus aerosol transmission, dispersion, and infection probability simulation: A case study in subway carriages / 环境与职业医学

Background Subways are typical congregate settings and may facilitate aerosol transmission of viruses. However, quantified transmission probability estimates are lacking. Purpose To model spread and diffusion of respiratory aerosols in subways by simulation and calculation of infection probabilities. Methods The internal environment of carriages of Shanghai Metro Line 10 was used to establish a study scene. The movement of tiny particles was simulated using the turbulent model. Trend analysis of infection probabilities and viral quantum doses was conducted in a closed subway carriage scene by a quantum emission-infection probability model. Results Under a typical twelve-vent air conditioning configuration, respiratory droplet aerosols within a subway carriage dispersed rapidly throughout various regions due to airflow, with limited short-term diffusion to other carriages. Concurrently, owing to the uncertainty of airflow patterns, the airflow might circulate and converge within carriages, causing delayed outward dispersion or hindered dispersion of droplet aerosols upon entry into these zones. Passengers boarding the carriage could exacerbate the formation of these zones. When the air conditioning system functioned adequately (air exchange rate=23.21 h−1), the probability of a virus carrier transmitting the virus to other passengers within the same carriage via aerosol transmission was approximately 3.8%. However, in the event of air conditioning system failure (air exchange rate=0.5 h−1), this probability escalated dramatically to 30%. Furthermore, a super-spreader (with virus spreading exceeding 90% of the average) elevated the infection probability to 14.9%. Additionally, due to the complexity of turbulence within the carriage, if local diffusion occurred in 1/2 zones of a carriage, the anticipated infection probability would increase to 8.9%, or during the morning or evening rush hours leading to elevated aerosol concentrations, the infection probability would rise to 4.7%. The subway transmission probability for common coronaviruses diminished to as low as 0.9%. Conclusion Combined computational fluid dynamics and infection probability analysis reveals that in the prevalent twelve-vent air conditioning configurations, despite being a major transportation hub with substantial spatial-temporal overlap, the internal space of subway carriages exhibits a certain level of resistance to virus aerosol transmission owing to built-in ventilation capabilities. However, turbulence and passenger positioning may lead to localized hovering of droplet aerosols, thereby increase the risk of virus transmission. Furthermore, super-spreaders, poor operational status of built-in air conditioning system, and high passenger volume at morning or evening peak hours exert profound effects on virus transmission and infection probability.

Simulation analysis on the distribution characteristics and movement rules of particulate matter in a convenience store / 中国职业医学

Objective: The spatial distribution model of particulate matter based on time change in a specific place was established to analyze the spatial and temporal distribution characteristics and movement of particulate matter. Methods: A convenience store was selected as the research subject. The micro-climate and particle number concentration (PNC) of the site were detected, and numerical simulation was carried out by computational fluid dynamics (CFD) simulation method. Based on the discrete phase model, the temporal and spatial distribution characteristics and movement rules of simulated particles were analyzed. Results: The wind speed at the entrance of the convenience store was low and almost unchanged during the detection, while the wind speeds outside and inside outlets were high and changed sharply. The PNC of particle size of 0.02-1.00 μm was higher than that of particle size >1.00 μm (all P<0.05). The PNC with particle size of 0.02-1.00 μm from high to low were checkout counter, entrance, outer outlet and inner outlet (all P<0.05). The PNC of the checkout counter and entrance varies greatly, while the PNC of the outer outlet and inner outlet was relatively steady. The CFD simulation results showed that particles exhaled by individuals near the entrance of the checkout counter of the convenience store could be expelled outdoors more quickly with the influence of airflow. However, particles exhaled by individuals in the middle of the shelves remained suspended indoors for a longer period of time compared to those near the checkout counter. Particles emitted from the air conditioning outlet diffuse throughout the entire store and reach a steady state in 300 seconds. Conclusion: The particulate matter in the convenience store was mainly small particle with the size less than 1.00 μm. The residence time, downward trend and number of suspended particulates of human exhaled particles were related to air flow. The particulates escaped from the air conditioner could quickly spread to almost the entire convenience store.

Application of Biomechanical Stress from Coronary Computed Tomography Angiography in Coronary Plaque Assessment and Prediction of Adverse Cardiovascular Events / 医用生物力学

Long-term exposure to risk factors will lead to coronary atherosclerosis, which will lead to the formation and progression of coronary plaque. Early identification of high-risk plaque characteristics will help prevent plaque rupture or erosion, thus avoiding the occurrence of acute cardiovascular events. Biomechanical stress plays an important role in progression and rupture of atherosclerotic plaques. In recent years, non-invasive coronary computed tomography angiography (CCTA) computational fluid dynamics (CFD) modeling has made it possible to acquire the corresponding biomechanical stress parameters. These coronary biomechanical stress parameters, especially wall shear stress (WSS), will aid in the development of a more accurate clinical model for predicting plaque progression and major adverse cardiovascular events ( MACE ). In this review, the biomechanical stress and the role of WSS from CCTA in atherosclerosis were introduced, and the researches on the relationship between biomechanical stress from CCTA and coronary artery diseases were discussed.

Hemodynamic Effects of Banding Width on Pulmonary Artery / 医用生物力学

Objective To investigate the effects of banding width on hemodynamic characteristics of pulmonary artery (PA) by constructing pulmonary artery banding (PAB) models with different widths. Methods Based on clinical practice, with the same banding position and degree, computer-aided design (CAD) was utilized to reconstruct three-dimensional PAB models with different banding widths (2, 3, 4, 5 mm). Hemodynamic characteristics of the models with different banding widths, including pressure, streamlines, energy loss, energy efficiency and blood flow distribution ratio, were compared and analyzed through computational fluid dynamics (CFD). Results The pressure of PA decreased significantly, while the change of banding width had no significant effects on the pressure drop level at banding position. With the increase of banding width, the energy loss decreased, and the energy efficiency showed an upward trend. The blood flow of the left PA raised, and the ratio of blood flow distribution between the left PA and right PA increased, with the maximum reaching up to 2.28 : 1. Conclusions The increase of banding width can reduce the energy loss of PA and improve the energy efficiency of blood flow, but it will lead to the imbalance of blood flow distributions between the left and right lungs. Both the balance of blood flow distribution and the energy loss should be considered in choice for banding width of PAB. The virtual design of PAB surgery based on CAD and CFD will assist individualized banding width selection in future.

Computational Study of Fenestration and Parallel Grafts Used in Aortic Arch Lesion / 医用生物力学

Objective To explore hemodynamics of the aortic arch and supraarch vessels after thoracic endovascular aortic repair with fenestration and parallel grafts techniques, and compare the differences of these techniques. Methods Four patients with aortic arch lesions whose supraarch vessels were reconstructed by different surgical techniques (fenestration, chimney and periscope) were studied, and three-dimensional (3D) geometric models were established based on postoperative image data. The physiological flow obtained from two dimensional (2D) phase contrast magnetic resonance imaging were imposed on the ascending aorta inlet and the supraarch vessels outlets. The pressure waveform of 3-element Windkessel model was imposed on the descending aorta outlet. Through computational fluid dynamics ( CFD ) simulations, the hemodynamic parameters were obtained, including the pressure of supraarch vessels, the velocity vector of the stent inlet, and the relative residence time. Results The pressure change of the periscope stent was the largest, followed by the fenestration stent, and the pressure change of the chimney stent was the smallest. The velocity of the fenestration and periscope stent inlet was uneven, which might form vortex. The velocity of the chimney stent inlet was even. The high relative residence time concentrated in distal end of the fenestration stent outer wall, the ‘gutter’ part, and the place where the chimney and periscope stent adhered to the vessel wall. Conclusions The pressure difference between the inner and outer walls of the fenestration and periscope stent was high, so it was recommended to use the balloon-expandable stent. The pressure difference between the inner and outer walls of the chimney stent was low, so it was recommended to use the self-expanding stent. The predicted location of thrombosis was consistent with the clinical follow-up data, so it may be used for surgical planning and risk assessment of interventional treatment of aortic arch lesions.

Positive Pressure and Negative Pressure Irrigation Dynamics with Different Needle Designs Using Computational Fluid Dynamics

@#This study aimed to investigate the irrigation dynamics of the positive pressure side-vented (SV) needle, EndoVac (micropores) needle and modified apical negative pressure (mANP) open-ended needle using computational fluid dynamics (CFD). A simulation of a prepared root canal (conical frustum) of 15 mm length with an apical diameter of 0.40 mm following Protaper F4 apical preparation was created using three-dimensional (3D) CAD software. The 3D simulated needle of SV 30G needle, EndoVac with micropores needle and mANP, 30G flat open-ended needle were also created. The irrigation dynamics were evaluated through transient CFD simulations. In addition, the irrigation dynamics of mANP at 0.2 mm, 0.5 mm, and 1.0 mm short from the working length were also assessed. The EndoVac and mANP showed negative apical static pressure and streamline patterns able to reach the apical region, thus indicating negligible extrusion. Meanwhile, SV showed positive apical static pressure and almost nonexistent streamlines beyond the needle tip. The SV showed the highest wall shear stress (WSS) magnitude of 1030Pa whereas Endovac (161 Pa) and mANP1 (258 Pa). However, SV revealed lower average WSS (10 Pa) compared to mANP1 (13 Pa) and mANP2 (11 Pa). This is due to SV developed a localised maximum WSS opposite the open vent area only therefore, uneven distribution of WSS. The EndoVac system developed a localised maximum WSS in the pair of micropores furthest away from the apical. CFD analysis of the EndoVac, mANP and SV showed different technique approach, needle design and needle depths insertion affect the irrigation dynamics pattern and magnitude.

Current research status and application prospect of numerical simulation in traditional Chinese medicine drying / 中国中药杂志

With the rapid development of computer technology, numerical simulation has gradually become an important method to study drying process and improve drying equipment. Using computer to simulate the drying process of traditional Chinese medicine(TCM) is characterized by intuitiveness, scientificity, and low cost, which serves as an auxiliary means for technical innovation in TCM drying. This paper summarizes the theories of different drying methods and the research status of numerical simulation in drying, introduces the modeling methods and software of numerical simulation, and expounds the significance of numerical simulation modeling in shortening the research and development cycle, improving drying equipment, and optimizing drying parameters. However, the current numerical simulation method for drying process has problems, such as low accuracy, lack of quantitative indicators for the control of simulation results on the process, and insufficient in-depth research on the mechanism of drug quality changes. Furthermore, this paper put forward the application prospect of numerical simulation in TCM drying, providing reference for the further study of numerical simulation in this field.

Reconstruction and Flow Field Analysis of Human Airway Based on Reverse Engineering / 医用生物力学

Objective In view of the situation that tracheal atrophy causes the overall airway size to become smaller in the elderly, effects of the airway wall surface on reconstruction of a narrow airway and the airflow field under different respiratory conditions were investigated. Methods A three-dimensional (3D) model of human airway was established by using Mimics, and flow field in the airway was simulated by computational fluid dynamics (CFD) method. The inner wall pressure and the distribution of airflow were analyzed and compared under different breathing states. Results Under different respiratory states, the pressure of endotracheal wall was relatively uniform in the endotracheal wall, but decreased significantly in air inlet of the bronchial stenosis segment, and reached negative pressure near the narrowest area. The airflow velocity decreased from the center of the pipe to the boundary layer, and the velocity reached the maximum at the narrow area. Vortex was generated when airflow passed through the narrow area, and the larger the inlet flow velocity was, the larger the positive pressure and negative pressure were, the more obvious the pressure drop at the narrow area was, and the more obvious the vortex phenomenon was. Conclusions The constriction of the airway stenosis area caused by negative pressure will lead to the patient’s dyspnea, and the eddy current will cause the airway wall to be affected by the aerodynamic shear stress and may damage the airway wall mucosa. Therefore, understanding of the pressure distribution and velocity distribution in the narrow airway can provide references for clinical diagnosis and treatment of such diseased airways.

Numerical Simulation of Thrombus Formation after Artery Bypass Grafting with Distal-End Side-to-Side Anastomosis / 医用生物力学

Objective To study the difference in thrombus formation at distal end of the graft with two different treatments.Methods For coronary artery bypass grafting with distal-end side-to-side anastomosis (DESSA), two models with or without distal end trimming of the graft were established. Using the blood substance transport and diffusion model considering biochemical reactions, combined with hemodynamics parameters of shear rate, fluid residence time, and platelet distribution, the possibility of thrombus formation was evaluated. Numerical simulation method was used to investigate thrombus growth in coronary artery bypass grafting with DESSA.ResultsFor the model without distal end trimming of the graft, the thrombus was first formed on inner wall at distal end of the graft, and then grew inward until the thrombus occupied most of the graft region at distal end, which indicated that thrombus formation was in a stable state, and the volume of the thrombus didn’t change, the final volume of the thrombus was 15.05 mm3. For the model with distal end trimming of the graft, the final volume of the thrombus was 7.35 mm3, which was 51.2% smaller than that of the model without distal end trimming of the graft. Thrombus was formed on inner wall of the graft above the anastomosis for the model with distal end trimming of the graft, and the wall thickness was about 0.16 mm, which was 10.65% of the graft radius (1.50 mm). In the above two procedures, multiple vortices (blood flow velocity less than 10 mm/s) were formed in distal region of the graft, which further promoted thrombus formation at distal end of the graft. The area of thrombus formation obtained from numerical simulation was consistent with clinical investigation.Conclusions For clinical coronary artery bypass grafting with DESSA, the volume of the generated thrombus can be reduced for the model with distal end trimming of the graft. However, the effect of thrombus formation on inner wall of the graft above the anastomosis on coronary artery bypass grafting needs further study.

Spray Drying in Research of Traditional Chinese Medicine Powders： A Review / 中国实验方剂学杂志

After more than 100 years of development， spray drying technology has become more mature and widely used， and it is of great importance in the field of traditional Chinese medicine （TCM）. TCM powders prepared by spray drying is the raw material of dispensing granules， and the powder properties have an important influence on subsequent molding process and product quality. As a new form of TCM， dispensing granules have been included in the management category of TCM decoction pieces， indicating a broader application market， and a consensus has also been reached on the importance of TCM powder research. Based on this， the author summarized the application progress of spray drying in the study of TCM powders， including the factors affecting spray drying process， such as liquid properties， process parameters and equipment factors， as well as the application of computational fluid dynamics （CFD） and thermodynamic model in spray drying process simulation. Moreover， some commonly used pharmaceutical excipients for the modification of TCM powders were also introduced such as maltodextrin， microcrystalline cellulose and povidone. In addition， spray drying technology can also be used as a preparation technology for new drug delivery systems such as microcapsules and solid dispersions. Through the summary of this paper， the author suggests that the future research direction of spray drying of TCM can be carried out from the aspects of application rule of the coprocessing auxiliary materials based on the "unification of medicines and excipients"， the "structure-property" relationship of spray-dried powders and the application of computer simulation and design， so as to further enrich the application of spray drying in the field of TCM powders.

Hemodynamic Study on the Relationship Between Collateral Circulation Caused by Iliac Vein Compression and Deep Venous Thrombosis / 医用生物力学

Objective To explore the relationship between the establishment of collateral circulation caused by iliac vein compression syndrom(IVCS) and the deep venous thrombosis (DVT). Methods Different types of ideal collateral circulation models and IVCS patient-specific models were numerically simulated using computational fluid dynamics (CFD) in combination with the blood stasis model. The relationship between blood retention and collateral types and cross-sectional area was studied, and the relationship with thrombosis was explored. Results Wall shear stress (WSS) at the distal end part of each ideal model was 0.3 Pa. After four cardiac cycles, the residual blood stayed at the stenosis and the distal end part for the lumbar ascending and pelvic type models, the old blood volume fraction (OBVF) varied with collateral cross-sectional areas, ranging from 5%-90% and 70%-80%, respectively. The OBVF of the coexistence model was above 80%. The WSS at the distal end part of the patient-specific model was 0.9 Pa, and the OBVF at the distal end part was 51.5%. Conclusions The stenosis and the distal end part are most prone to blood stasis, and closely related with DVT. The larger the collateral cross-sectional area, the more serious the blood stagnation. Blood stagnation of the coexistence model is higher compared with the model with lumbar ascending type and pelvic type.

Computational fluid dynamics analysis of influence of different pipe structures on gas mixing uniformity / 中国辐射卫生

Objective Tostudy the influence of pipe structures on the mixing uniformity of airborne effluents from nuclear power plant chimneys. Methods We used the computational fluid dynamics (CFD) method to simulate the velocity distribution and gas mixing in long straight pipes (I type) with square section and circular section, 90° single-bend pipes (L type) with square section and circular section, and 90° double-bend pipes (S type and U type) with square section and circular section. Results For the long straight pipe, due to the lack of flow disturbance caused by structural changes, the mixing effect was not good; when the pipe section was circular, it might take mixing distance 20 times the hydraulic diameter to achieve the uniformity index required by the relevant standard; for the square pipe, the distance might be longer. In the single bend pipe with square section, the velocity uniformity was improved more greatly after the bend, and the tracer gas met the mixing uniformity at a shorter distance (11 times the hydraulic diameter), as compared with the single bend pipe with circular section. For the S-type double-bend pipe, the tracer gas appeared uniformly mixed after a distance 6 times the hydraulic diameter in the square pipe, and 7 times the hydraulic diameter in the circular pipe. For the U-type double-bend pipe, the gas in the square pipe also achieved uniform mixing ata shorter distance downstream, and the airflow showed greater disturbance when passing through the bend. Conclusion The CFD method can make an accurate prediction for the change patterns of gas mixing uniformity in pipes with different structures, and can partially replace physical experiments to study the factors affecting the mixing uniformity of airborne effluents from the chimney of nuclear power plants.

Rational design of a 500 m3 fermenter for erythromycin production by Saccharopolyspora erythraea / 生物工程学报

Erythromycin is a macrolide antibiotic produced by Saccharopolyspora erythraea. Its yield is greatly affected by the fermentation conditions and the bioreactor configurations. In this study, a novel scale-up method for erythromycin fermentation was developed based on computational fluid dynamics (CFD) and time constant analysis. Firstly, the dissolved oxygen (DO) was determined as a key parameter according to the physiological properties of S. erythraea cultivated in a 50 L bioreactor. It was found that the time constant of oxygen supply (tmt) in a 500 m3 bioreactor should be less than 6.25 s in order to satisfy the organism's oxygen uptake rate (OUR). Subsequently, a 500 m3 bioreactor was designed using the time constant method combined with empirical correlations. The impeller combination with one BDT8 impeller at bottom and two MSX4 impellers at upper part was determined, and then validated by numerical simulation. The results indicated that the tmt of the bioreactor (< 6.25 s) and the fluid properties, including gas hold-up, shear stress and fluid vector, met the requirements of erythromycin fermentation. Finally, the industrial production of erythromycin in the 500 m3 showed the design method was applicable in large scale fermentation.

Hemodynamic Analysis on Proximal End of the Aortic Dissection with Different Rupture Shapes / 医用生物力学

Objective To explore hemodynamic performance of the aortic dissection after lesions, so as to provide a more scientific basis for patient treatment. Methods Based on computed tomography angiography (CTA) image data from a patient with complex Stanford B-type aortic dissection, the personalized aortic dissection models with different rupture shapes (H-type, O-type, and V-type) at proximal end of the aortic dissection were established. Combined with computational fluid dynamics (CFD) and morphological analysis method, distributions of the velocity at rupture section, the blood flow, the wall pressure and the wall shear stress (WSS) were analyzed. Results The flow velocity, the highest pressure difference and the WSS proportion at entrance of the H-shaped rupture showed larger hemodynamic parameters than those of the other two types. The risk of dissection rupture for type H was the largest, while type V was in the middle, and type O was the smallest. Conclusions This study provides an effective reference for further numerical analysis the cases and formulation of treatment plans.

Effects of Athlete’s Posture on Aerodynamic Characteristics During Flight in Ski Jumping / 医用生物力学

Objective To investigate the effects of athlete’s posture (including bending angle of upper body and angle between body and skis) on aerodynamic characteristics during flight in ski jumping. Methods The athlete and skis were regarded as a multi-body system. By using partially averaged Navier-Stokes (PANS) turbulence model and numerical simulation of computational fluid dynamics (CFD), the aerodynamic characteristics during flight under different postures were predicted. The calculation conditions for bending angle of upper body were 10°, 14°, 18°, 22° and 26°, and the calculation conditions of angle between body and skis were 8°, 12°, 16°, 20° and 24°. Results As the bending angle of upper body increased, the lift force and drag force of the multi-body system, the athlete and skis, and the pitch moment of skis all showed a monotonously decreasing trend, but the ratio of total lift force to total drag force increased first and then decreased. Meanwhile, the pitch moment of the multi-body system decreased first and then increased, and the pitch moment of athlete increased slightly and then decreased. As the angle between body and skis increased, the lift force and drag force of the multi-body system and skis increased first, then decreased and then increased, but the ratio of total lift force to total drag force decreased first, then increased and then decreased. Meanwhile, the lift force, drag force and pitch moment of the athlete increased monotonously, and the pitch moment of the multi-body system and the skis increased first and then decreased. The effect of bending angle of upper body on aerodynamic characteristics during flight in ski jumping was generally significantly larger than that of angle between body and skis. Conclusions The optimal range for bending angle of upper body is 14°-18°, and the optimal range of angle between body and skis is 16°-20°. The influence mechanism for bending angle of upper body and angle between body and skis on aerodynamic characteristics during flight in ski jumping can provide effective auxiliary support for on-the-spot prediction and decisionmaking,

Influences of Renal Artery Stenosis Morphology on its Hemodynamics / 医用生物力学

Objective To investigate the hemodynamic effects of morphological parameters on renal artery stenosis （RAS）, so as to provide theoretical references for clinical practice. Methods The idealized models of RAS were established, then the hemodynamic effects from morphological parameters of stenosis including its area, symmetry, length and shape on renal artery was explored using computational fluid dynamics （CFD） method. Results The renal perfusion, pressure drop and wall shear stress (WSS) distributions in renal artery were significantly correlated with area stenosis (AS). When the stenosis area increased from 50% to 70%, all hemodynamic parameters changed significantly. In addition, an asymmetrical stenosis resulted in a significant increase of abnormally high WSS and length of recirculation flow in renal artery, but the change of stenosis length or shape only led to marginal changes in hemodynamics. Conclusions Although AS is still the most significant factor to influence hemodynamics in RAS, other morphological parameters, especially asymmetric stenosis, cannot be neglected. Therefore, it is suggested that clinical treatment plans should be a comprehensive evaluation based on these morphological parameters.

Evaluating the effect of midpalatal corticotomy-assisted rapid maxillary expansion on the upper airway in young adults using computational fluid dynamics / 浙江大学学报（英文版）（B辑：生物医学和生物技术）

Midpalatal corticotomy-assisted rapid maxillary expansion (MCRME) is a minimally invasive treatment of maxillary transverse deficiency (MTD) in young adults. However, the effect of MCRME on respiratory function still needs to be determined. In this study, we evaluated the changes in maxillary morphology and the upper airway following MCRME using computational fluid dynamics (CFD). Twenty patients with MTD (8 males, 12 females; mean age 20.55 years) had cone-beam computed tomography (CBCT) images taken before and after MCRME. The CBCT data were used to construct a three-dimensional (3D) upper airway model. The upper airway flow characteristics were simulated using CFD, and measurements were made based on the CBCT images and CFD. The results showed that the widths of the palatal bone and nasal cavity, and the intermolar width were increased significantly after MCRME. The volume of the nasal cavity and nasopharynx increased significantly, while there were no obvious changes in the volumes of the oropharynx and hypopharynx. CFD simulation of the upper airway showed that the pressure drop and maximum velocity of the upper airway decreased significantly after treatment. Our results suggest that in these young adults with MTD, increasing the maxillary width, upper airway volume, and quantity of airflow by MCRME substantially improved upper airway ventilation.