ABSTRACT
Objective To investigate the effect of left ventricular assist device (LVAD) and aortic graft angle on hemodynamics of aortic valve. Methods Three models of aorta and aortic valve with 45°, 60° and 90° anastomosis angles between LVAD and aorta were constructed, and an in vitro pulsating table was built for in vitro experiments. Using particle image velocimetry (PIV) system, three moments in the cardiac cycle ( T1 systolic peak, T rapid closure, T3 diastolic peak), were selected to study the hemodynamic state of aortic valve. Results Velocity vector, vorticity and viscous shear stress were used to evaluate the effect of LVAD anastomosis angle on hemodynamics of aortic valve. During the period of rapid valve closure, with the increase of graft angle, the blood flow velocity near the valve wall, the average vorticity and the maximum viscous shear stress all increased. Conclusions When the graft angle is lower, the impact velocity of blood on the valve is smaller, and the shear force on the valve decreases, so that the valve is in a better hemodynamic environment. This study provides references for the selection of anastomotic angles in clinical operations.
ABSTRACT
Objective To investigate the airflow distribution mode in human upper respiratory tract model for understanding the characteristics of the airflow in human upper respiratory tract, and provide scientific basis for analyzing the diffusion, transition and deposition patterns of aerosol in human upper respiratory tract. Methods PIV（particle image velocimetry）technology was adopted to study flow fields of the real human upper respiratory tract model. The airflow state in oral cavity，pharynx and trachea was analyzed. Results The flow velocity was relatively high at the upper tongue coating and in the middle of the oral cavity; when the airflow reached the pharynx, the velocity was increased rapidly due to the reduction of sectional area; the maximum velocity (10.24 m/s) appeared in the glottis, and the velocity in the anterior wall was higher than that in the posterior wall of the trachea; as the airflow injected at the glottis, the velocity gradient was increased, and the vorticity was concentrated at the anterior and posterior wall of the glottis, resulting in a significantly higher vorticity value at anterior wall of the trachea than that at the posterior wall. Conclusions PIV technology is an effective way to investigate the airflow distribution mode in human upper respiratory tract, and it is of great importance for exploring the harm of toxic aerosol to human body and the therapeutic effect of inhalation drug aerosol, as well as for researching the pathogenesis of respiratory system.
ABSTRACT
Objective To investigate the hemodynamic factors in internal carotid arteries (ICA) with different shapes, and analyze the relationship between the arterial geometry and atherosclerotic stenosis to provide the hemodyanmic basis for the risk prediction and early diagnosis of ICA stenosis. Methods The flow field in the most two common types of ICAs, U and V-shaped ICA, were investigated by numerical simulation and particle image velocimetry (PIV) experiment under the condition of steady flow. Results At the upstream bend of ICA, the hemodynamic factors were monotonically associated with the curvature of the bend. As a result, the risk for stenosis here was smaller in the V-shaped ICA, as compared to U-shaped ICA. But at the downstream bend, such monotonic relationship didn’t exist due to the synergistic effect of the two bends. ConclusionsThe curvature of the artery is positively related to the risk for stenosis, but the synergistic effect of bends needs to be considered for studying arteries with the serial bends. The research on the synergistic effect may explain why the stenosis is frequently observed in arteries with multiple bends.
ABSTRACT
Objective To develop a measurement device and provide a platform for researching the characteristics of human upper respiratory tract flow field based on PIV (particle image velocimetry) technology with respect to the characteristics that human upper respiratory tract flow may form the vortex structure, flow shunt and secondary flow. Methods A transparent physical model of human upper respiratory tract was prepared based on the completely scanned medical images. By means of selecting appropriate air pressure system, combined with two-dimensional PIV system, a complete experimental apparatus was established. Based on the apparatus, preliminary experiment on air velocity in human upper respiratory tract flow field was conducted, and the experiment result was compared with the numerical simulation result. Results Under the steady breathing pattern at respiratory flow of 30 L/min, respiratory air flow measured by the experimental apparatus led to the formation of vortex structure in the front part of oral cavity. Air velocity was relatively higher both in the lower part of oral cavity near the upper tongue and in the middle part of oral cavity, while the velocity was relatively lower in the other parts of oral cavity. The results were in accordance with numerical simulation. Conclusions The experimental apparatus for human upper respiratory tract flow measurement based on PIV technology is practical and reliable, which can be applied in the measurement of airflow organization patterns and vorticity distributions in human upper respiratory tract, and realize the verification of numerical simulation results.
ABSTRACT
Objective To visualize the process of introcular flow caused by injection into the posterior chamber of the impermeable vitro eyeball with particle image velocimetry (PIV) technology, and calculate the flow fields at different moments, so as to investigate PIV experimental scheme for low-speed flow field measurement in the eye and provide basis for the in vivo measurement of aqueous humor flow under physiological status. Methods In an impermeable vitro eyeball, the introcular flow would be slow enough when the injection pump was driven at the rate of 0.2, 0.4, 0.6, 0.8, 1.0, 1.5 mL/min. Fluorescent particle solution, with a certain concentration and particle diameter of 10 μm, was injected into the posterior chamber of the vitro rabbit eye, and the sheet laser was projected to the medial frontal plane of the eye. Then clear particle images were captured by camera, and the velocity field was recorded and calculated by PIV system. Results The fluid into the posterior chamber first filled in the posterior chamber and the pupil, then passed the pupillary margin and flowed into the anterior chamber, which was consistent with the theoretical flow process of aqueous humor under physiological conditions. Based on analysis of the particle images, the velocity inside an impermeable eyeball was calculated at the magnitude of a few millimeters per second. Conclusions PIV method can be applied to low-speed flow field measurement, and the flow characteristics inside the eyeball can also be measured by PIV method, which contributes to the measurement of aqueous flow under both physical and pathological conditions, provides experimental verification for numerical simulations on aqueous humor field, and offers a new diagnostic and treatment perspective for shear force damage and destructions of corneal endothelial cells, the iris and lens under different flow fields.