Wentao Jiang

Numerical simulation on the effects of drug eluting stents at different Reynolds numbers on hemodynamic and drug concentration distribution

BackgroundThe changes of hemodynamics and drug concentration distribution caused by the implantation of drug eluting stents (DESs) in curved vessels have significant effects on In-Stent Restenosis.MethodsA 3D virtual stent with 90°curvature was modelled and the distribution of wall shear stress (WSS) and drug concentration in this model were numerically studied at Reynolds numbers of 200, 400, 600, 800.ResultsThe results showed that (1) the intensity of secondary flow at the 45° cross-section was stronger than that at the 90° cross-section; (2) As the Reynolds number increases, the WSS decreases. When the Reynolds number reaches 600, the low-WSS region only accounts for 3% of the total area. (3) The effects of Reynolds number on drug concentration in the vascular wall decreases in proportionally and then the blood velocity increased 4 times, the drug concentration in the vascular wall decreased by about 30%. (4) The size of the high drug concentration region is inversely proportional to the Reynolds number. As the blood velocity increases, the drug concentration in the DES decreases, especially at the outer bend.ConclusionsIt is beneficial for the patient to decrease vigorous activities and keep calm at the beginning of the stent implantation, because a substantial amount of the drug is released in the first two months of stent implantation, thus a calm status is conducive to drug release and absorption; Subsequently, appropriate exercise which increases the blood velocity is helpful in decreasing regions of low-WSS.

Studies on Foam Decay Trend and Influence of Temperature Jump on Foam Stability in Sclerotherapy

Objectives: This study investigated the influence of temperature jump and liquid–gas ratio on foam stability to derive the foam-decay law. Methods: The experimental group conditions were as follows: mutation temperatures (10°C, 16°C, 20°C, 23°C, 25°C, and 27°C to >37°C) and liquid–gas ratios (1:1, 1:2, 1:3, and 1:4). The control group conditions were as follows: temperatures (10°C, 16°C, 20°C, 23°C, 25°C and 27°C) and liquid–gas ratios (1:1, 1:2, 1:3, and 1:4). A homemade device manufactured using the Tessari DSS method was used to prepare the foam. The decay process was videotape recorded. In the drainage rate curve, the temperature rose, and the liquid–gas ratio varied from 1:1 to 1:4, causing faster decay. Results: In the entire process, the foam volume decreased with increasing drainage rate. The relationships were almost linear. Comparison of the experimental and control groups shows that the temperature jump results in a drainage time range of 1 to 15 seconds. The half-life ranges from 10 to 30 seconds. The maximum rate is 18.85%. Changes in the preparation temperature yields a drainage time range of 3 to 30 seconds. The half-life varies from 20 to 60 seconds. Conclusion: Decreasing the temperature jump range and liquid–gas ratio gradually enhances the foam stability. The foam decay time and drainage rate exhibit an exponential function distribution.

Hemodynamics study of a multilayer stent for the treatment of aneurysms

BackgroundThe changes of hemodynamics caused by the implantation of multilayer stent (MS) have significant effects for aneurysm sac.MethodsComparisons of 3D numerical models with/without a MS in an abdominal aortic aneurysm with a 90° branch vessel were numerically studied from the viewpoint of hemodynamics.ResultsThe results showed that: (1) The flow fields and Wall Shear Stress (WSS) are changed dramatically after MS implantation. The velocity of the blood flow in aneurysm sac decreases significantly and the regions of low-WSS increase. These help thrombus formation; (2) The pressure in aneurysm slightly decreases and keeps close to the normal level of blood pressure, however the risk of aneurysm enlargement or even rupture still exists; (3) The flux and the velocity in branch artery are reduced by about half after MS implantation. Due to the implantation of MS, the changes in the flow field causes the decrease of pressure/WSS in aneurysm sac and the blood flow in branch vessel.ConclusionsThe implantation of MS into abdominal artery results in more low-WSS regions inside aneurysm which induces thrombus formation. The pressure is reduced slightly means the risk of aneurysm rupture exists.

REVIEW: HEMODYNAMIC STUDIES FOR LOWER LIMB AMPUTATION AND REHABILITATION

No matter what the reason and level of amputation are, amputees will face many complex postoperative problems and potential complications. From the perioperative stage to lengthy rehabilitation process, patients need comprehensive and cautious therapies to help them rebuild their physical and mental health. Although there is some scattered information, the achievements of hemodynamic study for lower limb amputation and rehabilitation have not been systematically classified and summarized. The purpose of this review is to introduce and discuss the hemodynamic issues in preoperative diagnosis, surgical techniques and postoperative problems in the past two decades. Whether from clinical or biomechanical perspective, the investigations of the former two stages have been relatively mature and gained some clear outcomes, even if some conclusions are conflicting and controversial. While in terms of the postoperative problems, such as the common pressure ulcers, DTI and muscle atrophy, there is a lack of vascular or blood flow state studies specifically for lower residual limb. Therefore, the future research focus of hemodynamics for lower limb amputation should probably be the detailed investigations on the relationships between various blood flow parameters and certain common complications. Although hemodynamic research has made some achievements at this stage, it is believed that more advanced and reliable techniques are pending for further explorations and developments.

Developing transmission line equations of oxygen transport for predicting oxygen distribution in the arterial system

The oxygen content in the arterial system plays a significant role in determining the physiological status of a human body. Understanding the oxygen concentration distribution in the arterial system is beneficial for the prevention and intervention of vascular disease. However, the oxygen concentration in the arteries could not be noninvasively monitored in clinical research. Although the oxygen concentration distribution in a vessel could be obtained from a three-dimensional (3D) numerical simulation of blood flow coupled with oxygen transport, a 3D numerical simulation of the systemic arterial tree is complicated and requires considerable computational resources and time. However, the lumped parameter model of oxygen transport derived from transmission line equations of oxygen transport requires fewer computational resources and less time to numerically predict the oxygen concentration distribution in the systemic arterial tree. In this study, transmission line equations of oxygen transport are developed according to the theory of oxygen transport in the vessel, and fluid transmission line equations are used as the theoretical reference for the development. The transmission line equations of oxygen transport could also be regarded as the theoretical basis for developing lumped parameter models of other substances in blood.

Effect of Multiple Factors on Foam Stability in Foam Sclerotherapy

Foam sclerotherapy is a widely used treatment for varicose veins. However, complications caused by poor foam stability still remain. Most studies ignore multiple influencing factors and only study a single factor. Furthermore, a stable foam preparation using different preparation conditions has not been developed. This study aimed to explore the changing laws of foam stability under multifactorial conditions, and to determine the influence of various factors and optimal preparation conditions on the half-life of foam. A two-level orthogonal test was conducted using four factors (syringe size, surfactant, preparation temperature, and pump speed). Classifications were established as follows: syringe sizes, 2.5 mL and 5 mL; surfactant concentrations, 6% and 0%; preparation temperatures, 20 °C and 10 °C; and pump speeds, 250 mm/s and 125 mm/s, respectively. Eight experimental group (EG) multi-factor combinations were tested. Half-life and drainage time were recorded for analysis. The initial drainage time was within 200 s, but the difference between the groups was also about 200 s. The drainage rate curves of all EGs gradually increased over time. Conversely, the foam half-life extended by about 10 times for the four factors. In addition, the analyses revealed that the order of influence was surfactant >temperature >pump speed >syringe size. The most stable foam preparation was determined. Syringe size, surfactant, temperature, and pump speed had markedly observable influences on foam half-life. A combination of multiple factors can be used to prepare a more stable foam in clinical scenarios and to suitably superimpose favorable conditions to avoid unfavorable conditions.