Use of multi-lumen catheters to preserve injected stem cell viability and injectant dispersion.

Infusion catheters, when used with balloons, are susceptible to compression of the catheter lumen. A consequence is that shear stress is increased in the fluid that passes through the lumen. When the injected fluid contains viable cells, hemolysis of the cells can result. This study investigates the effect of a new injection catheter design which is intended to resist the deleterious effect of balloon compression on cell viability for various flowrates, balloon pressures, and fluid viscosity values. Two types of catheters were employed for the study; a standard single-lumen device and a newly designed multi-lumen alternate. Experimental and numerical simulations show that for a single-lumen injection catheter, balloon pressures in excess of 7-8atm have the potential for causing hemolysis for flows of approximately 1-4ml/min. The critical balloon pressure is dependent on the viscosity of the cell-carrying fluid and the injectant flowrate. Higher injection rates and viscosities lead to lower threshold balloon pressures. The results show a sharp rise in cell death when pressures rose above approximately 7atm. On the other hand, the multi-lumen design was shown to resist hemolysis for all tested and simulated balloon pressures and flowrates up to 10ml/min. Experimental results confirmed the numerical findings that hemolysis-causing shear stress was not found with the multi-lumen, up to 12atm. This study indicates that a pressure-resistant multi-lumen catheter better preserves cell viability compared to the standard.

Particle Trajectories and Agglomeration/Accumulation in Branching Arteries subjected to Orbital Atherectomy.

BACKGROUND: The transport of particles in surrogate and actual arterial geometries has been investigated synergistically by experimentation and numerical simulation. The motivating application for this work is orbital atherectomy which spawns a particle cloud in the process of debulking plaque from arterial walls. METHODS: Paired simulations and experiments were performed to prove the capability of the simulation model to predict both fluid and particle motions in branched arterial geometries. The verified model was then employed to predict the pattern of fluid flow in an actual multi-branched arterial geometry, including the flowrates passing through each of the individual branches. These predictions are in very good agreement with experimental data. Focus was then shifted to the issues of particle agglomeration within the flowing fluid and particle accumulation on the vessel walls. Once again, a synergistic approach was used. Flow visualization was employed to track the particle motions and to identify possible particle agglomeration within the fluid. RESULTS AND CONCLUSIONS: Accumulation of particles on walls was identified by measuring size distributions of effluent and residue within the artery. Scanning Electron Microscopy (SEM) evaluation showed evidence of a size-based sorting as the particles passed through vessels. It was found that plaque-facsimile particles resisted particle-particle agglomeration. They also did not accumulate to the wall of the facsimile artery. In addition, simulations showed that if particle-wall accumulation were to occur, it would be limited to very small regions in the artery branches.

Optimal techniques with the Diamondback 360° System achieve effective results for the treatment of peripheral arterial disease.

The Diamondback 360® Orbital PAD System (DB360) is a novel orbital atherectomy system for the treatment of calcified lower extremity lesions associated with peripheral arterial disease (PAD). This percutaneous, endovascular system incorporates the use of centrifugal force and differential sanding to modify plaque morphologies. The mechanism of differential sanding discriminates between compliant arterial tissue and diseased fibro-calcific or calcific plaque. An eccentrically mounted diamond-coated crown orbits at high speeds and removes a thin layer of calcific plaque with each pass of the crown. The crown creates a more concentric, smooth vessel lumen with increased diameter, increased lesion compliance and improved blood flow while protecting the vessel media. As a result, the risk for post-procedure thrombus formation and potential for restenosis may be reduced. The risk of intra-procedural events (slow flow, hemolysis, spasm and pain) may be reduced due to the design of this orbital sanding system along with proper technique. Extensive benchtop, in vivo, and clinical testing has confirmed these results and is presented within this paper. In addition, guidelines for selecting the most appropriate crown size and type (solid versus classic) and step-by-step procedural technique and pharmacology information are presented. The DB360 System provides a safe, efficacious, and cost-effective endovascular method for PAD treatment. Careful understanding of procedural methods, use of pharmacological drugs, and understanding of device operation contributes to improved treatment success.

Heat flow from rechargeable neuromodulation systems into surrounding media.

A synergistic investigation involving both experiment and numerical simulation was performed in vitro to determine the heat flow from rechargeable neuromodulation systems into surrounding media. Each system consists of an implant and an external recharging antenna, and the heat flows of each of these components were determined separately. Three systems, each produced by a different medical device firm, were evaluated. The evaluated products included those from Medtronic Inc. (MDT), ANS (a St. Jude Company), and the Boston Scientific Company (BSC, formerly Advanced Bionics). To ensure statistical significance, three nominally identical samples of each of the three systems were included in the study. Furthermore, for each sample of each system, replicate evaluations were performed for both the implant and the antenna. It was found that for both components of MDT, substantially lower rates of heat flow were produced compared with those for ANS and BSC. With regard to the latter systems, the higher rates of heat flow were not consistently ordered for the implant and for the antenna. In general, replicate data runs for each system and each component were in satisfactory agreement. The different samples of the MDT system showed only minor deviations with regard to heat flow. The deviations among the different samples of both ANS and BSC were larger than those evidenced for MDT.

Numerical simulation of a BPH thermal therapy--a case study involving TUMT.

The use of numerical simulation as a means to predict the outcome of transurethral microwave thermotherapy (TUMT) is set forth in detail. The simulation was carried out as a case study of a specific TUMT procedure. The selection of the case study was based on the availability of extensive medical records which documented an extraordinary application of TUMT. Predictions were made of the time-varying temperature patterns within the prostate, the bladder, the sphincter, the pelvic floor, and the fat and connective tissue which envelop these organs. These temperature patterns provided the basis of maps which highlighted those locations where necrosis occurred. An injury integral was used to predict the extent of the necrotic tissue produced by the therapy. It was found that, for the specific case being considered, necrosis occurred not only within the prostate but also extended to the neck of the bladder and to the fatty tissue. A special feature of the simulation was the accounting of the liquid-to-vapor phase change of the interstitial water. The vapor generated by the phase change is believed to significantly enlarge the region of necrosis. By the same token, the vapor pressure is expected to cause motion of the high-temperature liquid to deep-tissue regions. The damage predicted by the numerical simulation was compared, in detail, with post-operative medical examinations and found to be corroborated.

Numerical simulation of the urine flow in a stented ureter.

When a stent is implanted in a blocked ureter, the urine passing from the kidney to the bladder must traverse a very complicated flow path. That path consists of two parallel passages, one of which is the bore of the stent and the other is the annular space between the external surface of the stent and the inner wall of the ureter. The flow path is further complicated by the presence of numerous pass-through holes that are deployed along the length of the stent. These holes allow urine to pass between the annulus and the bore. Further complexity in the pattern of the urine flow occurs because the coiled "pig tails," which hold the stent in place, contain multiple ports for fluid ingress and egress. The fluid flow in a stented ureter has been quantitatively analyzed here for the first time using numerical simulation. The numerical solutions obtained here fully reveal the details of the urine flow throughout the entire stented ureter. It was found that in the absence of blockages, most of the pass-through holes are inactive. Furthermore, only the port in each coiled pig tail that is nearest the stent proper is actively involved in the urine flow. Only in the presence of blockages, which may occur due to encrustation or biofouling, are the numerous pass-through holes activated. The numerical simulations are able to track the urine flow through the pass-through holes as well as adjacent to the blockages. The simulations are also able to provide highly accurate results for the kidney-to-bladder urine flow rate. The simulation method presented here constitutes a powerful new tool for rational design of ureteral stents in the future.