Modeling Of The Interaction Between Colon And Colonoscope During A Colonoscopy

Abstract

One of the main complications in completing a colonoscopy is that the colonoscope causes patient pain during the procedure. To reduce patient pain, small-caliber (SC) colonoscopes have been developed. To evaluate the efficacy of SC colonoscopes in reducing patient pain with that of traditional standard colonoscope (SDC), several randomized control trials (RCTs) were conducted and showed varying results, with some showed benefits whereas others did not. Among these RCTs, patient characteristics, including gender, age, and region were varied and further assumed to be responsible for the varied results. However, the influence of patient characteristics on the efficacy of SC colonoscopes in terms of reducing patient pain is still unclear due to many unavoidable disturbing factors in RCTs, including endoscopists’ skills, bowel preparation methods, and other new beneficial features of colonoscopes (passive bending and high force transmission shaft). Therefore, to explore the influence of gender, age, and region of patients on the efficacy of SC colonoscopes in terms of reducing patient pain, a numerical model could overcome the limitations of RCTs and provide such insight is developed in our work. As a first step, the structural differences of the human colon with respect to gender, age, and region were analyzed and summarized, which further functions as the basis of the development of colon models and their boundary conditions. As a result, three normalized colon segments were selected and modelled, including rectosigmoid junction (RCJ), rectum-splenic flexure (RSF), and transverse-hepatic flexure (THF) models. The colonoscope was modelled as a thin and flexible cylinder with a hemisphere tip. Three different diameters were applied to colonoscope models, including 9.2mm for ultrathin colonoscope (UTC), 11.3mm for pediatric colonoscope (PDC), and 12.8mm for standard colonoscope (SDC). UTC and PDC were classified as SC colonoscopes. In the stage of insertion simulation, a comparison between implicit and explicit finite element solution method was conducted, and then an explicit solver ANSYS-LSDYNA was selected to simulate the insertion process of colonoscopes in colon models. An uni-axial tension test was carried out to provide the experimental data of a porcine colon, and then an optimization procedure with the use of ANSYS and Optislang programs was performed to provide the necessary parameters of the constitutive material model of the colonic tissue. By comparing colon deformation during the insertion simulation, patient pain induced by colonoscopes were further predicted. The model developed in this research serves as a starting point in understanding the efficacy of SC colonoscopes in reducing patient pain considering the effects of patient characteristics, including gender, age, and region. This model may also provide scientific guidelines for the selection of patient specified colonoscope