BEE 4530 – 2024 Student Papers

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    Modeling Cryoballoon Ablation Techniques for Enhanced Efficacy in Atrial Fibrillation Management
    Jung, Erika; Ma, Isabella; Ma, Katelyn; Zhang, Rachel (2024-05-17)
    Atrial fibrillation is a common form of heart arrhythmia characterized by irregular heartbeat originating in the pulmonary veins (PV) of the heart. The cycle of electrical impulses controlling the beating of the heart is disturbed, leading to poor blood flow to the rest of the heart. In more persistent cases, surgical intervention is needed to isolate the disruptive electrical signals. Cryoballoon ablation (CBA) is a minimally invasive procedure where a catheter with a deflated balloon is inserted into a blood vessel and guided to the heart. Once in the pulmonary vein ostium (region where the pulmonary veins meet the atrium), the balloon is inflated and filled with freezing nitrous oxide to kill the myocardial tissue in contact, preventing the faulty electrical signals originating in the PV from reaching the heart [1]. This study seeks to give greater understanding on the distribution of temperatures within heterogeneous tissue and the effectiveness of the procedure in accordance with biological differences. Currently, there are no technologies that can give data on tissue temperature while the procedure is occurring. This causes a lack of predicting when the procedure is “complete,” that is, complete ablation with low chance of recurrence of atrial fibrillation in the patient [2]. Our model seeks to gain insight into the variation of temperatures in the tissue which is not possible in an in vivo procedure. Additionally, there is wide variety in vein thicknesses and geometries, which can affect efficacy and increase the risk of complications from the procedure. To improve patient outcomes, pre-procedure scans are recommended. Cardiac CT angiography (cCTA) is the most commonly used preoperative scan to get a 3D cardiac visualization for planning catheter placement [2]. With computer simulation software, the effect of various vein thicknesses on a safe and effective duration of pulmonary vein isolation (PVI) can be investigated. Modeling was done in COMSOL Multiphysics 6.0, a commercially available software, as a transient heat conduction problem with water to ice transitions in blood and myocardial tissue. Simplifications to the CBA procedure were made by adapting real anatomy into 2-D axisymmetric geometry and assuming a constant balloon surface temperature. For our analysis, we considered complete cell death at temperatures below -30°C, which is the critical temperature for myocardium tissue [3]. Our results indicate that the biological variance in thickness in the atrial vein does in fact change the needed length of procedure. Indeed, cryoballoon application times might be reduced in cases where a patient has relatively thin walls constituting the venous ostia. In the future, with improved imaging instruments capable of sub-millimeter resolutions, the preoperative cCTA scan should also include measurements to determine the specific thickness of their venoatrial junctions. Some limitations of our model include not being able to detect damage in surrounding nerves and esophagus and not accounting for differences in bioheat.
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    Computational Analysis of the Effects of Interatrial Shunt Diameter on Atrial Hemodynamics in Heart Failure (HFpEF) Patients
    Cai, Jeffery; Demiri, Endon; Gavin, Siena; Makuta, Hedges (2024-05-17)
    The purpose of this study is to investigate the effect of the diameter of an interatrial shunt on patients with heart failure with preserved ejection fraction (HFpEF). HFpEF is characterized by the stiffening of left ventricle heart cells, which results in higher left ventricular pressure and consequently causes a higher pressure in the left atrium as it attempts to force blood through the left ventricle. The study seeks to investigate the effect of placing a small shunt in the septum – the tissue that divides the left and right heart chambers – on reducing the left atrium, left ventricular, and pulmonary pressures that arise as a result of HFpEF. As the shunt diameter increases, more blood is allowed to flow from the left atrium to the right atrium, thereby reducing the pressure buildup in the left atrium at the cost of a rise in pressure in the right atrium. However, large-diameter shunts may be more invasive and cause future complications for the patient, especially by increasing the pulmonary-to-systemic flow rate ratio (Qp:Qs) to dangerously high levels. The goal of this study is to determine the largest possible shunt diameter to reduce the left atrium pressure of a typical HFpEF patient down to a healthy level without increasing Qp:Qs to dangerous levels. The heart atria are modeled by mapping the 3D heart atria into an idealized 2D model of the heart atria. Using the 3D-2D procedure and coupled equations found in Meindertsma, this paper investigates the effect of varying shunt diameter on the target pressures (left atrium, left ventricle, pulmonary system) and flow rate. [8]. Simulations show that increasing shunt diameters from 0 to 12 mm consistently dropped target pressures but increased the Qp:Qs. Using the same criterion as Kemmerling and Meindertsma suggest, our study found the 9 mm shunt to be the largest and most pressure-reducing shunt that still maintains a safe Qp:Qs ratio for patients [7, 8].
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    Kidney Transportation: Improving Success Rates of Transportation for Transplanting Organs
    O'Brien, Ariana; Patel, Rhianna; Rougeuz, Cody (2024-05-17)
    With only 4% of people with kidney failure receiving a transplant in the US due to miscommunication in the supply chain, delayed time spent in transportation, and damage during transportation, there is a substantial need to improve the transportation of the donation system. Using a finite element analysis, cooling during organ transportation can be modeled to fully understand heat transfer between the transportation system and the organ. Here, we used conductive heat transfer and melting physics in a 3D model of a transportation module designed for a kidney. The kidney is contained in an insulated environment with a frozen saline solution-based cooling mechanism to develop a novel understanding of the crucial parameters involved in temperature fluctuations and the time elapsed before the organ reaches a threshold temperature that makes it no longer viable for transplantation. We determined the optimized parameters for the transportation vessel and cooling mechanism while considering external environmental temperatures. Our findings suggest that using an insulating material made of polyurethane, with a cooling mechanism involving Easislush, starting at an initial temperature of -4℃, ensures the optimal conditions to keep a kidney viable for transplantation over 36 hours.
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    A Chilling Revelation: Investigating the Impact of Cooling Sleeves
    Allen, Sam; Friedman, Alexandra; Rogers, Lauren; Wong, Megan (2024-05-17)
    This paper investigates the combined effects of arm sleeves and water application as cooling strategies for marathon runners to regulate body temperature during races. The research addresses the hypothesis that a wet arm sleeve will be up to twice as effective at cooling a runner as the effects of natural sweating alone. In addition, the sleeve will decrease the temperature of the veins and increase the penetration depth of the cooler temperature muscles compared to a bare arm. Despite the common use of both running sleeves and water pouring in the running community, a comprehensive exploration of their combined impact on body temperature is absent from current research. Using a computational model of the cooling process, the study compares the heat flux through the arm in two distinct scenarios: a bare arm and a wet arm sleeve. The investigation seeks to explore the combined effects of these cooling methods, aiming to enhance understanding of optimal cooling strategies for marathon runners and contribute to advancements in running sleeve design and application for improved comfort and performance. The research employs a bioheat transfer equation to model heat transfer within the arm, considering factors such as conduction, convection, and metabolic heat generation. Additionally, the temperature profile inside major blood vessels of the arm is modeled to understand the impact of cooling strategies on blood temperature. Results indicate that the combination of a wet arm sleeve and water application results in a greater cooling effect compared to a bare arm. Temperature distribution graphs along the arm and contour slices of the arm’s cross-section demonstrate the effectiveness of the cooling sleeve in reducing arm temperature and potentially lowering core body temperature during exercise. Future steps include developing the geometry of our model further so that it incorporates more accurate layers of the arm, including but not limited to skin layers and fat. Additionally, we would like to incorporate evaporative cooling of porous media in the cooling sleeve. These steps will further refine our model and ensure robustness in capturing parameter variability affecting the cooling effect. This research provides valuable insights into optimizing cooling strategies for marathon runners, potentially enhancing performance and reducing the risk of overheating during races.
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    Will It Turn Over? Modeling the Turnover Process in Mirror Lake
    Newcomb, Isaac; Mushohwe, Moreblessing; Zamor, Maya (1999-05-17)
    One of the most important events to happen underwater is rarely modeled. This project examines the essential ecological process of lake turnover, a chemical and physical mixing process that evenly distributes nutrients, oxygen, and other dissolved chemicals in temperate lakes each spring and autumn [1]. The inquiry focuses on the autumn turnover process of Mirror Lake, a small temperate lake in the village of Lake Placid, NY, which failed to turn over from 2016 through 2018 due to road salt pollution [2]. We created a model of a successful turnover process, which field data shows occurred in autumn 2019 [3]. This model is intended to enable further research of the lake turnover process and what environmental factors might interfere with its success. The model may also be used to design interventions that support the natural turnover process while still maintaining winter safety for cars and pedestrians around the lake. Turnover is driven by a combination of natural convection (from temperature changes as seasons change) and wind-forced flow. At the beginning of autumn, the lake has stratified over the summer: there is a warm (less dense) layer on top, with a colder (denser) layer at the bottom, usually at around 4 °C (the temperature at which water is maximally dense). As autumn progresses, the air cools the surface water, which increases in density, sinks, and mixes with the lower layer [1]. Eventually the temperature distribution (and therefore the density distribution) becomes nearly uniform at 4 °C, allowing the wind to generate larger-scale flow patterns that mix the water more completely. We created this model in COMSOL, representing natural convection with transient fluid flow and heat transfer driven by density variation with temperature and surface wind. A 2D cross section at the deepest part of the lake was modeled using a half-lake geometry (represented by a quarter ellipse) with a symmetry condition. Air temperature data from the nearby Adirondack Regional Airport was used for the external temperature [4]. To reduce simulation time, we created models representing half the turnover process– from summer stratification to uniformity around 4 °C. After validating the results using measured data from the lake, we modeled a full-lake geometry (represented by a half ellipse) that simulated the entire autumn 2019 Mirror Lake turnover process spanning 30 days. Our final result was a 30-day simulation and animation of autumn turnover for Mirror Lake in 2019. The model shows the streamlines and temperature profiles across the duration of the process. We learned that the lake mixes to a uniform temperature, then cools down to 4 °C homogeneously. The lake then becomes stratified again, this time with cooler water on the top and warmer water at the bottom. For future models of turnover, we recommend that users incorporate salt concentration to observe its effects, use non-isothermal physics for accurate results, and include a point constraint of zero atmospheres gauge pressure at the center of the lake’s surface.
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    Heat Transfer in Intramedullary Rod in Tibia on Cold Day©
    Altamirano, Angela; Hidalgo, Amy; Rianda, Wade; Spirko, Anthea (2024-05-17)
    Many patients with orthopedic implants complain of pain associated with cold temperatures. This study aims to investigate how the temperature of the tissue in the lower leg is affected by the presence of a metal implant on a cold day. Two bioheat transfer models were made using eccentric cones and cylindrical solids to create our domain of interest, the region from the popliteal crease of the knee to the lateral malleolus at the ankle; the dimensions were based on average values for a 20 year old male, which was the demographic that most commonly received this implant [1]. The applicable parameters for modeling include heat conductivity, density, specific heat, and heat transfer coefficient. One model included a stainless steel rod placed in the medullary cavity of the tibia. The other model, which contains no implant, was used as a control. The models contain three boundary conditions: two thermal insulation boundaries at the top and bottom of the model, and a convective heat flux for the skin in contact with environmental air. The temperature profile of the lower leg was obtained in the model through a parasagittal cut plane evaluated 120 minutes after being exposed to an external temperature of 4.45°C. After running the model with a fine mesh (being the ideal mesh size) three points were taken just below the skin on the anterior side of the leg where thermoreceptors are located. The temperature vs. time graphs were evaluated at the three points between the two models, which found the temperature graph to be lower for the model with the implant. The temperature difference has a maximum of 0.33°C which, although slight, may stimulate the sensitive thermoreceptors that cause the perception of cool sensation. Sensitivity of the result to uncertainty was analyzed through varying the thermal conductivity of the rod’s stainless steel, convective heat transfer coefficient for the convective boundary condition, blood perfusion rates, and metabolic rates. The overall uncertainty of the cut-point temperature was found to be 4.68℃. Due to uncertainties in the blood flow, it is difficult to offer strong conclusions since this uncertainty is greater than the difference in temperatures with and without the implant. Our results do suggest, however, that the implant will not significantly affect the perception of cold sensation and that cold temperatures in the tissue surrounding the implant are unlikely to be the source of reported pain.
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    Collagen fixation in microfluidics: optimizing uniform flow using PDMS posts and contact line pinning
    James, Elijah; Shi, Aixin; Strauss, Pom; Townsend, Austin (2024-05-17)
    Microfluidic devices have been emphasized as a tool for effective preclinical models. Devices integrating biomodels (here, type I collagen) afford replication of cell or tissue physiology and have been particularly impactful when studying interstitial flow and chemo invasion. The current work uses computational models and simulation to optimize microfluidic device experimental efficacy and functional use, focusing on two particular platforms proposed by Li et al. (2018) and Tung et al. (2013). Both of these designs use collagen as a model tissue, and we aim to optimize collagen fixation in the experimental channel of these microfluidic devices. Specifically, we aim to analyze flow velocity profiles in a porous media for different methods of porous media fixation. The device is a 10 mm long channel with an inlet and outlet for pressure driven flow with a 1.2 mm experimental channel in the center perpendicular to the long channel. This experimental channel is filled with type I collagen, which is used to replicate human tissue. The porous media is fixed in this center channel, with an inlet fully developed flow boundary condition of 1 μm/s average velocity, outlet boundary condition of 0 Pa, no-slip boundary conditions along all channel walls, fluid dynamic viscosity of 0.731 mPa-s, and porous media permeability and porosity of 10-11 m2 and 0.9789, respectively. Flow velocity, spatial non-uniformity, and the total cross-sectional area accounted for by the fixation method were computed. Upon initial validation of our model, we found uniform flow is able to be maintained in the contact-line pinning design, allowing for fluid flow representative of physiological flow. We then optimized the geometry by introducing Polydimethylsiloxane (PDMS) posts to improve use, reduce the amount of collagen leaking out from the experimental channel, and prevent air bubble entrapment. We found that combining the contact-line pinning method with 2-3 PDMS posts of varying surface area from 10-30% of total cross sectional area produced the most optimal results. We provide a design that reduces the cross-sectional area of the PDMS post fixation method and maintains similar flow uniformity to the contact-line pinning method.