A Simulation Study Of Respiratory Mechanics And Computational Fluid Dynamics In Patients With Mechanical Ventilation Under General Anesthesia

PART ? Clinical Study of the Effects of Prolonged Gynecological Laparoscopic Surgery on Respiratory Dynamics and Dead Space/Tidal Volume RatioBackground: Laparoscopic operations have become longer and more complex and applied to a broader patient population in the last decades,prolonged gynecological laparoscopic surgeries require prolonged pneumoperitoneum and Trendelenburg position,which can influence respiratory dynamics and other measurements of pulmonary function,we investigated the differences between volume-controlled ventilation(VCV)and pressure-controlled ventilation(PCV)and tried to determine the more efficient ventilation mode during prolonged pneumoperitoneum in gynecological laparoscopy[12].Methods: Twenty-six patients scheduled for laparoscopic radical hysterectomy combined with or without laparoscopic pelvic lymphadenectomy were randomly allocated to be ventilated by either VCV or PCV,measurements of respiratory and hemodynamic dynamics were obtained after induction of anesthesia,at 10,30,60,and 120 min after establishing pneumoperitoneum,and at 10 min after return to supine lithotomy position and removal of carbon dioxide[12].Results: Patients under PCV ventilation had a similar increase of dead space/tidal volume ratio,but had a lower Ppeak increase compared with those under VCV ventilation,the critical value of duration of pneumoperitoneum was predicted to be 355 min under VCV ventilation,corresponding to the risk of Ppeak higher than 40 cm H2O[12].Conclusions: Both VCV and PCV can be safely applied to prolonged gynecological laparoscopic surgery,however,PCV may become the better choice of ventilation after ruling out of other reasons for Ppeak increasing[12].PART ? Three-Dimensional Reconstruction of Airway Model Based on MRI and MimicsBackground: In this study,we intend to reconstruct the three-dimensional model of airway based on MRI images and Mimics software.The DICOM format image obtained by MRI scan is of high quality and regularity.It can be viewed in the Mimics software with sagittal,coronal and cross section.This study is based on the following three-dimensional reconstruction.Methods: A healthy middle-aged male volunteer was selected for the head,neck and thorax MRI scan,and the acquired DICOM images were imported into the Mimics software.The three-dimensional model of the airway was constructed by using the tools of airway segmentation and dynamic region growth.The STL file derived by Mimics software is imported into the Geomagic Studio software for modification,and then the 3-matic tool is used to divide the modified airways model into volume mesh.Results: Based on the MRI image data,we successfully reconstructed the three-dimensional model of the airway,and carried out the division of volume mesh.This model can also display the effect of the virtual bronchoscopy.Conclusions: This study simplifies the modeling process and reduces human error by using the 3D reconstruction tool and manual adjustment of the software.The three-dimensional finite element model of tracheobronchial tube is constructed by using Geomagic Studio software and 3-matic software,which lays a foundation for the subsequent computational fluid mechanics research.Therefore,it is feasible for MRI images to reconstruct three-dimensional models of airways.PART ? Virtual Prediction of Mechanical Ventilation Airway Based on MRI and CFD SimulationBackground: Mechanical ventilation is an indispensable tool for life support of critically ill patients and maintenance of breathing during general anesthesia.It may also cause ventilator-induced lung injury(VILI)while providing effective respiratory supportive treatment.The CFD technique was used to simulate the airflow in the respiratory system under different conditions,and to calculate wall pressure and wall shear stress,which could provide a way to explain the initial mechanism of VILI.This study intends to reconstruct the three-dimensional airway model based on MRI images,calculate with CFD software,perform dynamic analysis of air flow inside the airway undergoing mechanical ventilation,and verify the calculation results with the experiment and our previous study.Thus,the role of CFD simulation in the assessment of the airway undergoing mechanical ventilation and the value of virtual prediction will be demonstrated.The possible mechanism of VILI would be also discussed.Methods: ANSYS CFX software was used to carry out CFD simulation and dynamic analysis of airflow in the airway of mechanical ventilation.Results: We applied the inlet boundary conditions of different flow velocity to the CFD simulation,and analyzed the velocity distribution,the wall pressure distribution,the change of the streamline and the change of the wall shear stress.Conclusions: The airway flow velocity,wall pressure,wall shear stress,and vortex have a close relationship with the inlet velocity and airway structure.When local velocity,wall pressure and wall shear stress change,local inflammatory response may occur,which may lead to VILI.