Study On The Interaction Between Endoscopic Approach And Esophageal Tissue

Natural orifice transluminal endoscopic surgery(NOTES)and endoscopy are science and technology combining the most advanced and cutting-edge medical technology,imaging technology and engineering technology.For this kind of operation,doctors manipulate the surgical medical instruments to enter various body cavities such as abdominal cavity or chest cavity through the mouth,anus,and vagina to complete a series of examinations,including clamping,traction,suture and removal of tissues or organs with the help of real-time 2D images.At present,most minimally invasive surgical(MIS)instruments lack force sensing device and doctors cannot accurately perceive the contact,friction and extrusion between minimally invasive surgical instruments and human soft tissues,which may cause tissue damage due to excessive thrust or extrusion pressure during the process of entry of the instruments,and finally lead to various postoperative complications.As a result,exploring the interaction between endoscope and esophagus is necessary and urgent.It can promote the efficiency of natural orifice transluminal endoscopic surgery and improving the security of operation.The contact behaviors such as friction,extrusion and adhesion between the front-tip of endoscope and esophageal tissue during endoscopy and NOTES were studied by combining experimental research,theoretical modeling and numerical simulation in this paper.Firstly,by choosing porcine esophagus as the experiment sample,the macroscopic mechanical properties of esophagus in different physiological regions,different esophageal layers and different directions of esophageal tissue were analyzed;on this basis,the frictional behavior under different extrusion and moving speed as well as the different physiological regions and layers were studied to simulate the medical operations during endoscopy;besides,the frictional behavior in axial and circumferential direction under different extention rate were also studied due to the expansion and deformation behavior of esophagus during endoscopy.Secondly,nanoindentation behavior of esophageal mucosa tissues under different loading rates,deflection of cantilever and dwell time were studied at the microscopic scale using atomic force microscope.Finally,combining with CT data of specific patients with software of Abaqus,a contact interactional model between esophagus and ensoscope was established,which stimulating the interaction process of endoscope passing through human esophagus.The main conclusions were made as follows:The esophageal tissue presented large-deformation and visco-hyperelasticity and showed typically nonlinear stress-strain relationship when simulating the traction operation during gastroscopy.Due to the structural difference of esophageal tissue in different physiological regions and layers,the uniaxial tensile mechanical properties of esophagus showed obvious anisotropy.The fracture stress for axial muscular layer was bigger than circumferential muscular layer;the fracture stress under different esophageal layers and directions presented velocity-dependence.The tribological properties of esophageal tissues were related to the structure and mechanical property of physiological regions and layers.The coefficient of friction presented a typical "stick-slip" phenomenon during the sliding process of front-tip of endoscope on the inner surface of esophagus,the friction coefficient decreased with the increasing normal load and increased with the increasing sliding velocity.The thoracic esophagus presents the smallest friction coefficient during the sliding process relative to the cervical esophagus and abdominal esophagus.It can reduce the risk of tissue damage and frictional performance for cervical esophagus and abdominal esophagus were close.Owning to the fact that intact esophageal tissue had a strong resistance for deformation,it had a larger coefficient of friction compared with the single mucosal layer.The endoscope can cause the expansion and extrusion of digestive tract tissues in axial or circumferential directions during endoscopy.When the esophageal mucosa was stretched in different directions,the friction behavior between esophageal mucosa and endoscope presented an opposite trend.The friction coefficient and the corresponding energy dissipation decreased with the increasing circumferential extension rate and increased with the increasing axial extension rate of the esophageal mucosa.The differences of friction behavior between endoscope and esophageal mucosa in different direction were related to the esophageal mucosa structure and mechanical properties.In addition,with the increasing normal load on the surface of esophageal mucosa,the degree of surface rupture gradually increased.Lidocaine commonly used in diagnosis and treatment can effectively reduce the friction dissipation and injury of esophageal mucosa.The mechanical properties of esophageal mucosa at microscopic scale mainly included elastic modulus,plastic index and adhesion force.The elastic modulus of the mucosal layer showed a positive correlation with the increasing loading rate,and a negative correlation with the increasing cantilever deflection as well as dwell time.In these cases,the value of elastic modulus presented difference to several orders.The plasticity and adhesion force of esophageal mucosa increased with the increasing loading rate and decreased with the increasing deflection of cantilever;the tendency of plasticity and adhesion force under different dwell time was opposite.The surface of the esophageal mucosal tissue showed obvious heterogeneity at the microscopic scale,which affected the expression of microscopic mechanical properties.For the basic interfacial model between endoscope and esophagus,the numerical simulation results were made as follows: with the increasing amplitude,coefficient of friction and decreasing esophageal inner diameter,the total force due to friction force(CFSM),friction dissipation energy(FD)and strain energy(SE)presented positive correlation.The length of the overlapping part between esophageal tissue and endoscope had no obvious significance for above indexes.The location of maximum Mises stress of the whole model under different conditions were mainly concentrated in the initial contact position between esophageal tissue and endoscope.For the patient-specific model between endoscope and esophageal tissue,when the endoscope passed through the narrow esophageal region,the radius of the narrow esophagus was the leading factor of the maximum Mises stress.With the increasing coefficient of friction and amplitude,the CFSM,FD,SE and maximum Mises stress of the abdominal and thoracic esophagus increased correspondingly.With the increasing coefficient of friction,the stress value of endoscope impacting on the thoracic esophageal wall also increased.