Transient Hemodynamic Characteristics Upon Balloon Deflation In Coronary Interventional Operation

The occurrence of no-reflow after coronary stent implantation is an important cause of surgical failure,which seriously affects the middle to long-term prognosis of patients.However,mechanisms underlying noreflow remain poorly understood.This thesis is devoted to exploring the mechanisms behind the no-reflow phenomenon from the perspective of biomechanics,mainly hemodynamics.For this purpose,we investigated the dynamic deformation of the outer wall of balloon and its impact on flow field(hemodynamic parameters of interest mainly included blood flow velocity and wall shear stress)in the near-balloon coronary artery segment during the deflation process of balloon so as to analyze the correlation between abnormal disturbances of flow field and the stripping of plaque/thrombus flakes and its potential influence on the risk of no-reflow.The results were expected to provide a theoretical basis for improving the strategy of coronary intervention or predicting operation-related risk.In this study,the following two methods were used to study hemodynamic problems related to balloon deflation: 1)construct an in vitro experimental device,in which a high-speed camera is used to record balloon deformation(in the air)and flow field(wather marked by dye)in the nearballoon region,followed by the utilization of image analysis techniques to extract balloon deformation parameters and estimate flow velocity downstream from the balloon.2)use ICEM software to create a computational mesh model of a coronary artery segment embedded with a balloon,and then use the fluid dynamics package Fluent to simulate the dynamic deformation of balloon through incorporating the measured ballon deformation data with a UDF-guided dynamic mesh technology and associated flow changes,with the obtained results being analyzed to evaluate the transient changes in hemodynamic parameters upon balloon deflation and their potential association with no-reflow.The in vitro balloon deformation experiment showed that the balloon exhibited significant nonlinear deformation characteristics during the deflation process,and the spatially non-uniform shrinking of the balloon wall caused the balloon to finally exhibit a ‘dumbbell shape'.The model-simulated flow velocities downstream from the balloon agreed well with the measured data,both of which showed that flow velocity increased with the increases of the time after the onset of balloon deflation and perfusion pressure.The numerical simulations further revealed that under the simulated physiological conditions,hemodynamic parameters in the ballon-vessel gap were significantly increased upon balloon deflation.For instance,when the downstream flow velocity was close to the physiological value of blood flow velocity in the coronary artery,flow velocity in the ballon-vessel gap and wall shear stress reached up to 8-10 times and 50-60 times of their physiological values,respectively.These results demonstrated that balloon deflation led to a marked acceleration of flow in the balloon-vessel gap and caused an abnormal increase in wall shear stress,which might increase the risk of plaque/thrombus stripping,eventually blocking the downstream microcirculation and inducing no-reflow.Given the fact that perfusion pressure is one of the key factors determining the degree of blood flow acceleration upon balloon deflation,selecting the diastolic phase for the timing of balloon deflation or performing pre-operative anti-hypertensive treatment for patients with hypertension may help to reduce the risk of noreflow related to coronary intervention operation.It should be noted that the work is limited to the study on a single type balloon under simplified conditions,without fully considering the complex in vivo environment,therefore,the reported results only have qualitative or semi-quantitative reference value.In future studies,it would be necessary to fully consider the combined structure of coronary artery,plaque,stent and balloon as well as patient-specific pathophysiological conditions so as to more reasonably assess the potential association between balloon deflation and no-reflow.