Photochromic Flow Visualization Technique Research Articles

Vena Cava Filter Performance Based on Hemodynamics and Reported Thrombosis and Pulmonary Embolism Patterns

Three inferior vena cava (IVC) filters of different designs were studied to identify the potential links between published clinical results for thrombosis and recurrent pulmonary embolism (PE) rates and in vitro hemodynamics patterns in the region of the filters. The filters studied were the Greenfield over-the-wire filter (Medi-tech/Boston Scientific, Watertown, Mass), TrapEase filter (Cordis Europa, Roden, the Netherlands), and Mobin-Uddin umbrella filter (Edwards Laboratories, Santa Ana, Calif). To assess hemodynamics, velocity contour maps were generated for each filter by using the in vitro photochromic flow visualization technique. Results were obtained for both the unoccluded and partially occluded states. Steady flow (R(e) = 600) was used to model physiologic conditions. To estimate the rates of IVC occlusion and recurrent PE, the authors analyzed published clinical studies spanning more than 30 years and a U.S. Food and Drug Administration database. For both the unoccluded and partially occluded Mobin-Uddin and TrapEase filters, regions of flow stagnation and/or recirculation and turbulence developed downstream of the filter. The Greenfield filter did not produce any prothrombotic flow patterns for either the unoccluded or partially occluded states. Results of published clinical studies supported the hemodynamic findings, with the TrapEase and Mobin-Uddin filters having high rates of IVC occlusion and recurrent PE compared with those of the Greenfield filter. Flow stagnation or recirculation and turbulence have been linked to thrombosis and thrombus and/or PE formation. Thus, the hemodynamic results from this study may help explain the relatively higher rates of filter thrombosis and PE for the Mobin-Uddin and TrapEase filters versus the Greenfield filter.

Hemodynamic Effects of Clot Entrapment in the TrapEase Inferior Vena Cava Filter

The TrapEase vena cava filter has a symmetric design. Emboli can be trapped in the outlet conical section (superior cone) or between the filter and vessel wall at the inlet end (inferior cone). The purpose of this in vitro study is to investigate the hemodynamic effects of clot entrapment by the TrapEase filter and to examine the possibility of flow-induced filter thrombosis. Velocity and wall shear stress maps were determined for steady flow with use of the photochromic flow visualization technique. Experiments were done for a filter without clot and for three other cases: an asymmetric clot in the inferior zone, a symmetric clot in the superior zone, and a filter with both zones partially occluded. Each simulated clot was 1500 mm(3) and the vessel diameter was 2 cm. The unoccluded filter did not significantly affect the flow field. However, for a partially occluded filter, flow stagnation/recirculation and turbulence developed downstream from the clot. The greatest effect was noted when the clot was against the vessel wall in the inferior trapping region. The tendency for clots to be trapped between the filter and the vessel wall in the inferior (inlet) region may play an important role in the performance of the TrapEase filter. A clot in this configuration will generate a large region of flow stagnation/recirculation that is considered to be prothrombotic. In addition, a significant amount of the filter wire will be embedded in this region, which may also promote thrombosis.

A multi-stage nitrogen laser for the photochromic flow visualization technique

A multi-stage nitrogen laser was developed in an attempt to enhance the potential of the photochromic tracer technique for complex flow analysis. With this system, either single or multiple low-divergence ultraviolet beams can be produced. The resulting photochromic traces are of comparable length but are substantially finer than either the tracers produced by a commercial nitrogen laser or those produced by an excimer laser. A significant advantage of these finer traces is that they were not smeared by high shear rates, as is seen with the traces produced by the other types of laser, and this will lead to more accurate analysis of complex flows.

Fluid motion investigation by the photochromic flow visualization technique

The development and application of the photochromic flow visualization method (PFV) in experimental hydrodynamics are described. Tracers in the form of colored lines with a lifetime of 20–300 s are created in a photochromic solution by pulse radiation for 10 −9 s. The displacement of the tracers in the flow is followed by a high-speed movie camera. The information given by the PFV method permits the flow pattern velocity distribution, localization of circulation, and stagnation zones as well as other characteristics of the flow to be found. Several applications are considered such as flows in channels with complicated shapes, flows behind prosthetic heart valves, and thermocapillary and thermogravitational convective flows in homogeneous and stratified liquids.

Laser Induced Photochromic Flow Visualization

The photochromic flow visualization technique has been utilized to study several different liquid flows. The technique utilizes radiachromic dyes that can be dissolved in a number of liquids. The resulting dye-solvent solutions remain colorless in the absence of ultraviolet radiation; however, the solutions turn dark blue when exposed to ultraviolet light. A nitrogen pulse laser has been constructed for use as source of ultraviolet radiation. When sharply focused, the emitted beam of ultraviolet light produces a very narrow, well defined line in a solvent-dye solution. The subsequent motion of the “activated trace” can then be recorded with high-speed photography. Digitization of the resulting movies allows one to quantify the flow field of interest. Several interesting flows have been studied using the photochromic flow visualization technique. This paper begins with a brief summary of several of these past studies. The remainder of the text concerns a set of experiments that were conducted to ascertain the rigidity of liquid-liquid interfaces. The experimental apparatus used to obtain high-speed movies will first be described. Next, the quantitative evaluation of these movies will be explained. Finally, typical results of the quantitative analysis will be presented.

Improved photochronic flow visualization technique

A photochromic flow visualization technique has been modified so as to allow the study of liquid-liquid interfaces. The technique utilizes two immiscible radiochromic dye solutions that remain colorless in the absence of ultraviolet radiation. The solutions turn dark blue when irradiated with ultraviolet light. A nitrogen pulse laser has been used to create distinct traces through the interface of a forming or ascending drop. Three distinct modes of operation are available for the study of drop interfaces. Activated traces can be formed one after another through the same location in the test column. Alternatively, the column can be raised or lowered relative to the laser, resulting in the formation of activated traces at preset intervals above or below previously formed traces. This technique provides a new tool for studying experimentally the behavior of liquid-liquid interfaces during drop formation and release. With the utilization of high-speed movies taken of traces activated through a growing drop, the shear stress on both sides of the liquid-liquid interface was calculated. It was found that a liquid-liquid interface can behave in a totally rigid manner, as predicted by some theoreticians.

Measurement of Velocity for Polymeric Fluids by a Photochromic Flow Visualization Technique: The Tubeless Siphon

A flow visualization technique based on photochromic dyes has been used for the study of polymeric fluids in a number of flow configurations. The technique is based on the activation of the dye by ultraviolet light. This photoactivation results in the apparition of dark marker lines in the midst of the fluid. High‐speed movies can then be digitized and allow us to compute velocities anywhere inside the flow field. The results presented here address more particularly the case of the tubeless siphon. We have measured the velocity profile inside its fluid column for a number of flow conditions, and observed unexpectedly large velocity gradients. Indeed, the axial velocity at the centerline was found to be much greater than the velocity of the free surface at the same axial location. An interesting feature of this flow field is that the velocity profile appears to be a linear function of the radial location over most of the cross‐section of the column.

Experimental study of the internal fluid dynamics of forming drops

AbstractA non‐disturbing photochromic flow visualization technique has been used to study fluid flow conditions within the vertical core region of organic liquid drops growing from a single nozzle in an equilibrated water phase. The indicator 1,3,3‐trimethylindolino‐6′‐nitrobenzopyrospiran (0.015%), which was dissolved in the dispersed phase produced extremely fine tracer lines in the drops when irradiated with UV light from a multipulse nitrogen laser. High speed cinephotographs of the observed time lines were used to estimate axial and radial velocity components by means of a numerical mass balance technique. By substitution in the Navier‐Stokes equations it is shown how the axial and radial pressure change distributions may be obtained from the velocity measurements.