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The Airflow Characteristics in a 3D Airway Model Based on CT Images

Journal of Medical Biomechanics.2019;34(5):E453-E459. doi:10.16156/j.1004-7220.2019.05.01

Objective To discuss the mass transfer of low temperature gas in the lung bronchus, so as to provide a theoretical basis for the implementation of hypothermic ventilation cooling non-heart-beating donor (NHBD) lung program. Methods A real airway model was reconstructed based on human lung CT images, and the computational fluid dynamics (CFD) method was used to investigate the airflow characteristics inside the airway during reciprocating ventilation. The effect of ventilation frequency (0.5, 0.25, 0.125 Hz) on bronchial flow was also studied. Results The flow in the airway showed complex three-dimensional （3D） flow characteristics during reciprocating ventilation. The flow in different areas of the airway was different during inhaling and exhaling; the irregular bronchial geometry had an important effect on its internal flow; when the ventilation frequency decreased from 0.5 Hz to 0.125 Hz, the thickness of flow boundary layer would increase, and the mainstream velocity in different areas of the airway was enhanced to different degrees. Conclusions The real airway model based on CT 3D reconstruction was more accurate than the ideal circularity tube model in showing the bronchial flow. The research findings have an important guiding significance to optimize the hypothermic ventilation cooling NHBD lung technique.

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Characteristics of Airflow in Lower Respiratory Tract of ARDS Patients

Lijuan LIU ; Wenchao SUO

Journal of Medical Biomechanics.2019;34(5):E460-E467. doi:10.16156/j.1004-7220.2019.05.02

Objective To study the airflow characteristics in lower respiratory tract of acute respiratory distress syndrome (ARDS) patients with different degrees of respiratory distress by using computational fluid dynamics (CFD) technology. Methods Three-dimensional model of lower respiratory tract from a healthy subject was established based on CT image data. Standard k-ε turbulence model was used to simulate the airflow in lower respiratory tract, and the distribution characteristics of air velocity, airflow rate, air pressure and wall shear stress (WSS) in lower respiratory tract were analyzed. Results The function relationship between the pressure drop of airflow in lower respiratory tract and the respiratory intensity was fitted. The distribution characteristics of air velocity, air pressure and WSS in lower respiratory tract were obtained, and the airflow distributions in the lungs and the bronchi of each lobe were also obtained. Conclusions More detailed data of lower respiratory airflow field can be obtained by CFD simulation analysis, which provides the theoretical basis for clinical treatment of ARDS patients.

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Hemodynamic Analysis on Meglev Left Ventricular Assist Device of a New Generation

Di NIU ; Mingxin ZHU ; Haiquan FENG ; Kun WANG

Journal of Medical Biomechanics.2019;34(5):E468-E472. doi:10.16156/j.1004-7220.2019.05.03

Objective To reduce the thrombosis probability and hemolysis risk of the meglev left ventricular assist device (LVAD), so as to increase the efficiency of blood supply. Methods The influences of the pump outlet diameter, exit angle, fillet size between the outlet and the inner wall of the pump, as well as gap between the rotor and the shell on internal flow field of the pump were studied by using the computational fluid dynamics (CFD) method, so as to optimize the internal structure and improve the hydrodynamic performance of the pump. Results Compared with pump of the previous generation, the maximum wall shear stress (WSS) of the pump inner wall, the maximum WSS of the pump rotor, the area with WSS >200 Pa were reduced by 23.6%, 47.4%, 76.2%, respectively, while the outlet flow was increased by 14.4%. Conclusions For the meglev LVAD of the new generation, its internal blood flow tended to be smooth, and the hemodynamic performance of blood flow was improved comprehensively. The research findings provide references for optimization design of the meglev LVAD and related experimental researches in the future.

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In vitro Experiment and Numerical Simulation-Based Study on Transient Hemodynamic Characteristics upon Balloon Deflation in Coronary Interventional Operation

Jie LI ; Zhaofang YIN ; Fuyou LIANG

Journal of Medical Biomechanics.2019;34(5):E473-E480. doi:10.16156/j.1004-7220.2019.05.04

Objective To investigate the transient hemodynamic changes during balloon deflation in coronary interventional operation, so as to explore the potential influence of balloon deflation on the occurrence of post-operative no-reflow. Methods An in vitro experimental apparatus was built, in which a high-speed camera was used to take snapshots of balloon deformation and flow field (marked by dyed water) during balloon deflation. Subsequently, image processing techniques were employed to derive the parameters of balloon deformation and estimate the flow velocity downstream from the balloon. A computer model of the experimental apparatus was constructed, with the incorporation of the measured balloon deformation data, to simulate the balloon deflation process under various perfusion pressure and fluid conditions. Results The balloon exhibited a highly nonlinear deformation behavior during deflation. The measured and simulated flow velocities downstream from the balloon were in reasonable agreement, both manifesting a monotonic increase with post-deflation time and perfusion pressure. Numerical simulations further revealed that when the flow velocity downstream from the balloon approached the physiological value of blood flow velocity in the coronary artery, the flow velocity in the balloon-vessel gap and wall shear stress (WSS) reached up to 8-10 times and 60-70 times of their physiological values, respectively. Conclusions Balloon deflation led to a sharp acceleration of flow in balloon-vessel gap and a concomitant abnormal rise in WSS, which might promote the stripping of plaque or thrombus flakes. In view of the fact that the balloon deflation-induced rise in WSS was augmented by the increase in perfusion pressure, taking strategies such as lowering pre-operative blood pressure or implementing balloon deflation during diastole in coronary interventional operation might help to reduce the risk of no-reflow.

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Effects from Size Parameters of Minimally Invasive Vascular Clamp on Vascular Mechanical Properties

Weidong ZHANG ; Haipo CUI ; Chengli ONG ; Chengyong WANG ; Tao ZHANG ; Chunxiao ZHANG ; Qianli HENG

Journal of Medical Biomechanics.2019;34(5):E481-E485. doi:10.16156/j.1004-7220.2019.05.05

Objective To analyze the influence from size parameters of minimally invasive vascular clamp on mechanical properties of small arteries. Methods The finite element simulation analysis on the process of minimally invasive vascular clamp clamping small arteries was performed. The influence patterns of 5 different sawtooth spacing, sawtooth heights and sawtooth lengths on mechanical properties of small arteries were studied. Results Larger sawtooth spacing led to smaller maximum equivalent stress of the clamped artery. The maximum equivalent stress of the small artery was not linear with the sawtooth height of the vascular clamp. The maximum equivalent stress of the small artery was the smallest and the vascular injury was the minimal when the swatooth height was 75 μm. The sawtooth length of the vascular clamp had an important influence on mechanical properties of clamped small arteries. The maximum equivalent stress of the artery was proportional to the sawtooth length of the vascular clamp. Conclusions The size parameters of minimally invasive vascular clamp had an important influence on mechanical properties in the process of clamping small arteries. The research findings can provide guidance for the design of the minimally invasive vascular clamp.

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Biomechanical Characteristics of Internal Fixation Methods for Treating Thoracolumbar Burst Fractures

Zhe CHENG ; You HE ; Weiguo WANG ; Jianlong WANG

Journal of Medical Biomechanics.2019;34(5):E486-E492. doi:10.16156/j.1004-7220.2019.05.06

Objective To analyze the biomechanical characteristics of 3 different posterior internal fixation methods for treating thoracolumbar burst fracture by three-dimensional finite element (FE) method. Methods The FE fixation models of normal thoracolumbar, short-segment posterior fixation (SSPF), short-segment posterior fixation with intermediate screws at fractured level (SSPFI) and long-segment posterior fixation (LSPF) were established, respectively. The biomechanical characteristics of L1 centrum and the adjacent intervertebral disc under 6 kinds of motion states (spinal flexion, extension, lateral bending and axial rotation), in normal thoracolumbar model and 3 fixation models were compared by FE analysis. Results L1 centrum equivalent stress distributions in normal thoracolumbar model, SSPF model, SSPFI model, LSPF model were 31.63, 13.41, 110.35, 13.17 MPa, respectively. The maximum equivalent stress of adjacent intervertebral disc in normal thoracolumbar model was 3.84 MPa, which was located in L1-2 intervertebral disc; the maximum equivalent stress of adjacent intervertebral disc in 3 fixation models was 0.41, 0.36, 0.40 MPa, respectively, which was all located in T12-L1 intervertebral disc. Conclusions Fixation in short segment of the fractured vertebrae could lead to an increase of stress in the centrum. The stress of the adjacent intervertebral disc in 3 fixation models was smaller than that in normal spinal model.

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Finite Element Study of Lumbar Disc Herniation Loaded with Muscle Force

Hui LIU ; Guoquan HEN ; Xilin ZHANG ; Nan ZHOU ; Xiaowei YANG ; Wenjie HUANG ; Sihan ZHOU

Journal of Medical Biomechanics.2019;34(5):E493-E499. doi:10.16156/j.1004-7220.2019.05.07

Objective To investigate the effect of muscle function on structural stress in patient with lumbar disc herniation (LDH), by observing the stress changes in LDH lumbar-pelvis finite element model loaded with muscle force. Methods One normal healthy volunteer and one LDH patient were selected. Their CT data were collected to establish two corresponding normal and LDH lumbar-pelvis finite element models, and their gait data were also simultaneously collected to drive the AnyBody musculoskeletal model. The muscle force around the lumbar and pelvis as well as the hip-joint force were obtained as the loading condition. Self-loading of the normal and LDH model as well as the normal model loaded with LDH muscle forces were conducted seperately. Then the stress changes in L4 and L5 intervertebral discs and sacroiliac joints under two above loading conditions were compared. Results The stress curve of normal model loaded with LDH muscle force showed a unimodal stress curve, instead of a bimodal curve, and such trend of stress-time curve was as same as the trend of the LDH model during self-loading. But the stress difference in L4 and L5 intervertebral discs and sacroiliac joint of the normal model loaded with LDH muscle force was smaller than that in the LDH model during self-loading. Conclusions Abnormal muscle function of LDH could lead to abnormal joint stress of the intervertebral discs and sacroiliac joint. Structural imbalance itself could lead to stress imbalance, and muscle as a driving factor was an important cause of anomaly structural dynamic stress, thus leading to abnormal joint motion patterns. Therefore, attention should be paid to assessment of the imbalance of peripheral muscle function in clinical treatment of LDH.

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The Influence of Ligaments Surrounding Sacroiliac Joints on Stability of Sacroiliac Joints

Shaoqun ZHANG ; Ruxia REN ; Yili CHEN ; Ziyu FENG ; Yikai LI

Journal of Medical Biomechanics.2019;34(5):E500-E506. doi:10.16156/j.1004-7220.2019.05.08

Objective To analyze the influence of ligaments surrounding sacroiliac joints (SIJs) on stability of SIJs by finite element method. Methods The finite element lumbar spine-pelvis-femur model was established. Based on this normal model, all SIJ ligaments in both sides were removed in turn, to establish models without iliolumbar ligaments, sacroiliac anterior ligaments, sacroiliac posterior ligament, sacrotuberous ligaments, sacrospinous ligaments, sacroiliac interosseous ligaments, respectively. The models were used to simulate physiological motions of the spine. The range of motion (ROM) and average stress on the left and right SIJs were analyzed and compared with the normal models. Results Compared with the normal SIJ model, no significant differences in the ROM of bilateral SIJs were found in the models without sacrotuberous ligaments, sacrospinous ligaments and sacroiliac posterior ligaments; for the model without acroiliacinterosseous ligaments, there was no significant difference in the ROM of the left SIJs under spinal right rotation and ROM of the right SIJs under spinal extension, but the ROM of bilateral SIJs increased significantly under the other spinal physiological activities. Under the physiological activities of the spine, the average stress of the SIJ surface in the left and right sides of the model without acroiliacinterosseous ligaments significantly decreased. Conclusions Of all the sacroiliac ligaments, the sacroiliac interosseous ligaments showed the maximum influences on the stability of SIJs. The research findings are helpful to investigate the mechanism of SIJ subluxation and provide certain theoretical basis for clinical treatment of SIJ subluxation.

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Influences of Lateral Meniscus Posterior Root Tear with Different Suture Methods on Knee Biomechanics

Pengfei ZHANG ; Yansong QI ; Huricha BAO ; Yongxiang WANG ; Baogang WEI ; Bingxian MA ; Xiaohe LI ; Yongsheng XU

Journal of Medical Biomechanics.2019;34(5):E507-E513. doi:10.16156/j.1004-7220.2019.05.09

Objective To evaluate the biomechanical effects of lateral meniscus posterior root (LMPR) tears fixed at different suture positions, so as to investigate the optimal suture method for repairing LMPR tears. Methods Eight fresh cadaveric knees were used. Each knee was tested under 6 conditions: intact knee, ruptur of LMPR, suture of LMPR to the center point of root insertion, suture of LMPR posterior, interior and later 5 mm to the center point of root insertion, respectively. The peak contact pressure, the average contact pressure and contact area were evaluated using a Tek-scan sensor positioned between the meniscus and tibial plateau, under 1 kN compressive loading, at 0 degree knee extension. Results In the lateral compartment, the average contact pressure and peak pressure significantly increased under rupture of LMPR compared with the intact state (P<0.01), and the contact area decreased significantly (P<0.05). For LMPR tears fixed by four different suture methods, both the average pressure and peak contact pressure reduced, and the contact area increased. The average contact pressure, peak pressure and contact area were closer to the knee joint in the intact state when the suture positions of LMPR tears was posterior 5 mm to the center point of root insertion (P<0.05). In the medial compartment, there were no significant differences in contact pressure, peak contact pressure and contact area with the knee joint at 0 degree (P>0.05). Conclusions The average contact pressure, the peak contact pressure and the contact area between the lateral meniscus and the tibial plateau changed obviously due to the LMPR tears. When the suture position was 5 mm lateral to the center point of root insertion, similar biomechanical function with the intact knee could be obtained.

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Applicability of Foot-Ground Contact Model at Different Gait Speed

Yinghu PENG ; Zhenxian CHEN ; Jiayu HU ; Zhifeng ZHANG ; Zhongmin JIN ; Pingping WEI

Journal of Medical Biomechanics.2019;34(5):E514-E521. doi:10.16156/j.1004-7220.2019.05.10

Objective To establish the musculoskeletal multi-body dynamic foot-ground contact model and explore its applicability at different speed. Methods The gait data of the subjects at different speed were collected, and the foot-ground contact model was established based on the full body model from the musculoskeletal multibody dynamic software AnyBody. Then the calculated ground reaction forces (GRFs) and ground reaction moments (GRMs) at different speed (slow walking, normal walking, fast walking and jogging) were compared with the measurements from the force plates. Results The predicted GRFs and GRMs correlated well with the experimental measurements at slow, normal and fast speed (stride speed ranged from 0.69 to 1.68 m/s). The correlation coefficients between predicted and measured GRFs were greater than 0.875 and the correlation coefficients for GRMs were greater than 0.9. Conclusions The developed foot-ground contact model could simultaneously predict GRFs and GRMs with good accuracy, thus eliminating the dependency on force plates. The model could be applied to low-speed gait conditions, such as the elderly and pathological gait.

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