As crucial factors in blood clot formation, shear stress distribution and low flow zones are assessed in different central venous catheter tip designs by using a combined numeric and experimental approach. Computational Fluid Dynamics was validated with Particle Image Velocimetry by comparing simulated and measured velocities and shear strains in three designs of the blood withdrawing arterial lumen: cylindrical and with tip (1) cut straight, (2) cut at an angle, or (3) cut straight with a sleeve entrance. After validation, four additional designs were studied: (4) with two side holes and tip cut straight or (5) at an angle, (6) concentric lumens, and (7) Ash Split-based. In these seven designs, shear stress (SS), blood residence time (RT), and Platelet Lysis Index, which combines the influence of shear stress magnitude and exposure time, were simulated. Concentric catheter was discarded due to highly elevated SS. Ash Split-based design had elevated RT values in the distal tip zone as major inflow occurs through the most proximal side holes, but this is compensated by low average SS. A straight-cut tip and possibly two side holes are preferred when aiming at minimal SS and RT. These data may lead to more patent catheters.
The number of candidates waiting for a heart valve replacement rises yearly. Even though there is a trend toward implantation of biological valves or reconstruction, the prosthetic heart valves (PHVs) are still commonly used for implantation or as a part of cardiac assist devices in many countries worldwide. However, the hemodynamic consequences of these valves are still not completely understood. Unfortunately, these devices currently do not perform sufficiently on a long-term basis and may lead to several complications, many of them are related to fluid mechanical aspects. A novel method, stereoscopic high-speed particle image velocimetry, was applied to quantify all three velocity components behind a PHV in detailed time domain. In this study, we compared clinically used bileaflet aortic prosthetic (ATS) valve and monoleaflet prototype of tilting disk PHV. The absolute velocities calculated out of two and three velocity components were compared to each other to estimate the overall difference in the desired region of interest. The most significant discrepancies between the two- and three-component absolute velocities were found at the regions of Valsalva sinuses and in a major jet stream of monoleaflet PHV.
Prosthetic heart valves (PHVs) have been used to replace diseased native valves for more than five decades. Among these, mechanical PHVs are the most frequently implanted. Unfortunately, these devices still do not achieve ideal behavior and lead to many complications, many of which are related to fluid mechanics. The fluid dynamics of mechanical PHVs are particularly complex and the fine-scale characteristics of such flows call for very accurate experimental techniques. Adequate temporal resolution can be reached by applying time-resolved PIV, a high-resolution dynamic technique which is able to capture detailed chronological changes in the velocity field. The aim of this experimental study is to investigate the evolution of the flow field in a detailed time domain of a commercial bileaflet PHV in a mock-loop mimicking unsteady conditions, by means of time-resolved 2D Particle Image Velocimetry (PIV). The investigated flow field corresponded to the region immediately downstream of the valve plane. Spatial resolution as in “standard” PIV analysis of prosthetic valve fluid dynamics was used. The combination of a Nd:YLF high-repetition-rate double-cavity laser with a high frame rate CMOS camera allowed a detailed, highly temporally resolved acquisition (up to 10000 fps depending on the resolution) of the flow downstream of the PHV. Features that were observed include the non-homogeneity and unsteadiness of the phenomenon and the presence of large-scale vortices within the field, especially in the wake of the valve leaflets. Furthermore, we observed that highly temporally cycle-resolved analysis allowed the different behaviors exhibited by the bileaflet valve at closure to be captured in different acquired cardiac cycles. By accurately capturing hemodynamically relevant time scales of motion, time-resolved PIV characterization can realistically be expected to help designers in improving PHV performance and in furnishing comprehensive validation with experimental data on fluid dynamics numeric modelling.
The aim of this study was to validate the 2D computational fluid dynamics (CFD) results of a moving heart valve based on a fluid-structure interaction (FSI) algorithm with experimental measurements. Firstly, a pulsatile laminar flow through a monoleaflet valve model with a stiff leaflet was visualized by means of Particle Image Velocimetry (PIV). The inflow data sets were applied to a CFD simulation including blood-leaflet interaction. The measurement section with a fixed leaflet was enclosed into a standard mock loop in series with a Harvard Apparatus Pulsatile Blood Pump, a compliance chamber and a reservoir. Standard 2D PIV measurements were made at a frequency of 60 bpm. Average velocity magnitude results of 36 phase-locked measurements were evaluated at every 10° of the pump cycle. For the CFD flow simulation, a commercially available package from Fluent Inc. was used in combination with in-house developed FSI code based on the Arbitrary Lagrangian-Eulerian (ALE) method. Then the CFD code was applied to the leaflet to quantify the shear stress on it. Generally, the CFD results are in agreement with the PIV evaluated data in major flow regions, thereby validating the FSI simulation of a monoleaflet valve with a flexible leaflet. The applicability of the new CFD code for quantifying the shear stress on a flexible leaflet is thus demonstrated. (Int J Artif Organs 2007; 30: 640–8)
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