Very Late Patent Foramen Ovale Occluder Device Structural Dysfunction and Thrombosis.

Mechanical dysfunction of patent foramen ovale (PFO) closure device is extremely rare. We present a 58-year-old male patient who had multiple episodes of ischemic strokes 3 years after PFO closure, which was related to PFO device mechanical dysfunction and thrombosis. He was successfully treated with surgical intervention.

Effects of interfacial molecular mobility on thermal boundary conductance at solid-liquid interface.

The effects of interfacial molecular mobility on the thermal boundary conductance (TBC) across graphene-water and graphene-perfluorohexane interfaces were investigated using non-equilibrium molecular dynamics simulations. The molecular mobility was varied by equilibrating nanoconfined water and perfluorohexane at different temperatures. The long-chain molecules of perfluorohexane exhibited a prominent layered structure, indicating a low molecular mobility, over a wide temperature range between 200 and 450 K. Alternatively, water increased its mobility at high temperatures, resulting in an enhanced molecular diffusion that significantly contributed to the interfacial thermal transport, in addition to the increasing vibrational carrier population at high temperatures. Furthermore, the TBC across the graphene-water interface exhibited a quadratic relationship with the rise in temperature, whereas for the graphene-perfluorohexane interface, a linear relationship was observed. The high rate of diffusion in interfacial water facilitated additional low-frequency modes, and a spectral decomposition of the TBC also indicated an enhancement in the same frequency range. Thus, the enhanced spectral transmission and higher molecular mobility of water with respect to perfluorohexane explained the difference in the thermal transport across the interfaces considered herein.

Angiographically Patent Saphenous Vein Graft to Left Anterior Descending Artery at 51 Years Post-Coronary Artery Bypass Grafting.

We describe an unusual case of an angiographically patent saphenous vein graft to the left anterior descending artery at 51 years post coronary artery bypass grafting surgery in a patient who presents with exertional dyspnea and only relatively recent tobacco-smoking cessation. Factors associated with improved saphenous vein graft patency include the target vessel used for grafting, good distal run-off, and the use of optimal medical therapy alongside aggressive cardiovascular risk-factor modification.

Nous rapportons le cas inhabituel d'un greffon de veine saphène perméable à l'angiographie, greffé à l'artère interventriculaire antérieure 51 ans auparavant après un pontage aorto-coronarien, chez une patiente présentant une dyspnée à l'effort et ayant arrêté de fumer assez récemment. Parmi les facteurs associés à une meilleure perméabilité du greffon de veine saphène, citons le vaisseau cible utilisé pour la greffe, la bonne qualité du lit d'aval et l'utilisation d'un traitement médical optimal associé à une prise en charge énergique des facteurs de risque cardiovasculaire.

Effects of Electrostatic Interactions on Kapitza Resistance in Hexagonal Boron Nitride-Water Interfaces.

Electrostatic interactions in nanoscale systems can influence the heat transfer mechanism and interfacial properties. This study uses molecular dynamics simulations to investigate the impact of various electrostatic interactions on the Kapitza resistance (Rk) on a hexagonal boron nitride-water system. The Kapitza resistance at hexagonal boron nitride nanotube (hBNNT)-water interface reduces with an increase in diameter of the nanotube due to more aggregation of water molecules per unit surface area. An increase in the partial charges on boron and nitride caused the reduction in Rk. With the increase in partial charge, a better hydrogen bonding between hBNNT and water was observed, whereas the structure and order of the water molecules remain the same. Nevertheless, the addition of NaCl salt into water does not have any influence on interfacial thermal transport. Rk remains unchanged with electrolyte concentration because the cumulative Coulombic interaction between the ions and the hBNNT is significantly less when compared with water molecules. Furthermore, the effect of electric field strength on interfacial heat transfer is also investigated by providing uniform positive and negative surface charges on the outermost hBN layers. Rk is nearly independent of the practical range of applied electric fields and decreases with an increasing electric field for extreme field strengths until the electrofreezing phenomenon occurs. The ordering of water molecules toward the charged surface leads to an increase in the layering effect, causing the reduction in Rk in the presence of an electric field.

Hydrodynamic slip of alkali chloride solutions in uncharged graphene nanochannels.

Using non-equilibrium molecular dynamics simulations, we demonstrate the effect of concentration and alkali cation types (K+, Na+, and Li+) on the hydrodynamic slip of aqueous alkali chloride solutions in an uncharged graphene nanochannel. We modeled the graphene-electrolyte interactions using the potential of Williams et al. [J. Phys. Chem. Lett. 8, 703 (2017)], which uses optimized graphene-ion Lennard-Jones interaction parameters to effectively account for surface and solvent polarizability effects on the adsorption of ions in an aqueous solution to a graphene surface. In our study, the hydrodynamic slip exhibits a decreasing trend for alkali chloride solutions with increasing salt concentration. The NaCl solution shows the highest reduction in the slip length followed by KCl and LiCl solutions, and the reduction in the slip length is very much dependent on the salt type. We also compared the slip length with that calculated using a standard unoptimized interatomic potential obtained from the Lorentz-Berthelot mixing rule for the ion-carbon interactions, which is not adjusted to account for the surface and solvent polarizability at the graphene surface. In contrast to the optimized model, the slip length of alkali chloride solutions in the unoptimized model shows only a nominal change with salt concentration and is also independent of the nature of salts. Our study shows that adoption of the computationally inexpensive optimized potential of Williams et al. for the graphene-ion interactions has a significant influence on the calculation of slip lengths for electrolyte solutions in graphene-based nanofluidic devices.

Nanoconfinement Effects on the Kapitza Resistance at Water-CNT Interfaces.

The Kapitza resistance (Rk) at the water-carbon nanotube (CNT) interface, with water on the inside of the nanotube, was investigated using molecular dynamics simulations. We propose a new equilibrium molecular dynamics (EMD) method, also valid in the weak flow regime, to determine the Kapitza resistance in a cylindrical nanoconfinement system where nonequilibrium molecular dynamics (NEMD) methods are not suitable. The proposed method is independent of the correlation time compared to Green-Kubo-based methods, which only work in short correlation time intervals. Rk between the CNT and the confined water strongly depends on the diameter of the nanotube and is found to decrease with an increase in the CNT diameter, the opposite to what is reported in the literature when water is on the outside of the nanotube. Rk is furthermore found to converge to the planar graphene surface value as the number of water molecules per unit surface area approaches the value in the graphene surface and a higher overlap of the vibrational spectrum. A slight increase in Rk with the addition of the number of CNT walls was observed, whereas the chirality and flow do not have any impact.

Kapitza resistance at water-graphene interfaces.

Heat transfer across fluid-solid interfaces in nanoconfinement has received significant attention due to its relevance in nanoscale systems. In this study, we investigate the Kapitza resistance at the water-graphene interface with the help of classical molecular dynamics simulation techniques in conjunction with our recently proposed equilibrium molecular dynamics (EMD) method [S. Alosious et al., J. Chem. Phys. 151, 194502 (2019)]. The size effect of the Kapitza resistance on different factors such as the number of graphene layers, the cross-sectional area, and the width of the water block was studied. The Kapitza resistance decreases slightly with an increase in the number of layers, while the influence of the cross-sectional area and the width of the water block is negligible. The variation in the Kapitza resistance as a function of the number of graphene layers is attributed to the large phonon mean free path along the graphene cross-plane. An optimum water-graphene system, which is independent of size effects, was selected, and the same was used to determine the Kapitza resistance using the predicted EMD method. The values obtained from both the EMD and the non-equilibrium molecular dynamics (NEMD) methods were compared for different potentials and water models, and the results are shown to be in good agreement. Our method allows us to compute the Kapitza resistance using EMD simulations, which obviates the need to create a large temperature gradient required for the NEMD method.

Thermal conductivity of graphene under biaxial strain: an analysis of spectral phonon properties.

Thermal transport in graphene is strongly influenced by strain. We investigate the influence of biaxial tensile strain on the thermal conductivity of zigzag and armchair graphene (AG and ZG) using non-equilibrium molecular dynamics simulations (NEMD). We observe that the thermal conductivity is significantly reduced under strain with a maximum reduction obtained at equi-biaxial strain. It is interesting to note that the high lateral to longitudinal strain ratios reduce the negative impact of strain on the thermal conductivity of AG and ZG. The in-plane acoustic modes are found to be the major heat carriers in unstrained graphene but are severely softened due to strain, and hence, their contribution to the conductivity drops down significantly. Strain alleviates the out-of-plane fluctuations in graphene and the group velocity of the out-of-plane acoustic mode (ZA) increases due to the linearisation of its dispersion relation. These factors result in the dominance of ZA mode in the thermal transport of strained graphene. Significant increase in the size dependence of the thermal conductivity of strained graphene is observed, which is attributed to the long-wavelength ZA phonons. The discrepancies between the results of BTE studies and NEMD are also discussed. This study suggests that biaxial strain can be an effective method to tune the thermal transport in graphene. Our findings can lead to better phonon engineering of graphene for various nanoscale applications.

Efficiency of Electropumping in Nanochannels.

Electropumping has been shown to be an effective means of inducing a net positive flow in fluids confined within planar nanochannels and carbon nanotubes. In this Letter, we investigate the efficiency of electropumping relative to Couette and Poiseuille flows. We apply a spatially uniform rotating electric field to a fluid confined in a functionalized nanochannel that couples the water's permanent dipole moment resulting in a net positive flow. We then induce a net positive flow in nanochannels for Couette and Poiseuille flows, matching volume flow rates to allow a direct comparison of average power dissipation per unit volume between all flow types. We show that while electropumping is less efficient than Couette flow, it is 4 orders of magnitude more efficient than Poiseuille flow. This suggests that, rather than being a mere novelty, electropumping is a far more energetically efficient means of transporting water compared to conventional pressure driven pumping.

A Novel Hybrid Approach to Iatrogenic Circumflex Artery Injury After Mitral Repair.

Iatrogenic coronary injury after mitral repair is related to blind annuloplasty suture ligation or kinking of the circumflex artery (CxA) and can present with early ST segment changes, malignant ventricular arrhythmias, and segmental wall motion abnormalities. Corrective treatment is imperative to avoid myocardial infarction and can include removal of the annuloplasty ring or CxA bypass. We present a novel hybrid approach for the rapid diagnosis and management of iatrogenic CxA injury after mitral repair.

Prediction of Kapitza resistance at fluid-solid interfaces.

Understanding the interfacial heat transfer and thermal resistance at an interface between two dissimilar materials is of great importance in the development of nanoscale systems. This paper introduces a new and reliable linear response method for calculating the interfacial thermal resistance or Kapitza resistance in fluid-solid interfaces with the use of equilibrium molecular dynamics (EMD) simulations. The theoretical predictions are validated against classical molecular dynamics (MD) simulations. MD simulations are carried out in a Lennard-Jones (L-J) system with fluid confined between two solid slabs. Different types of interfaces are tested by varying the fluid-solid interactions (wetting coefficient) at the interface. It is observed that the Kapitza length decreases monotonically with an increasing wetting coefficient as expected. The theory is further validated by simulating under different conditions such as channel width, density, and temperature. Our method allows us to directly determine the Kapitza length from EMD simulations by considering the temperature fluctuation and heat flux fluctuations at the interface. The predicted Kapitza length shows an excellent agreement with the results obtained from both EMD and non-equilibrium MD simulations.

Inducing a Net Positive Flow of Water in Functionalized Concentric Carbon Nanotubes Using Rotating Electric Fields.

Electropumping has shown great potential as an effective means of inducing a net positive flow of water in confined channels. In this paper we present the first nonequilibrium molecular dynamics study and continuum based numerical solutions that demonstrate an effective net positive flow between concentric carbon nanotubes (CNT) using electropumping. We apply a spatially uniform rotating electric field that couples to the water's permanent dipole moment. Taking advantage of the coupling between the spin angular momentum and the linear momentum we break the symmetry of the channel radius by functionalizing the inner CNT's outer surface with carboxyl groups to induce a net positive flow. We also show that our results for concentric nanotubes are consistent with our previous work where we demonstrated that an increase in functionalization beyond an optimal point in a single walled carbon nanotube resulted in a decrease in positive net flow. We then numerically solve the coupled hydrodynamic momentum equations to show that the nonequilibrium molecular dynamics results are consistent with the continuum theory.

Rotational Diffusion of Proteins in Nanochannels.

The rotational diffusion coefficient is an essential parameter in determining the mechanistic features of biomolecules in both crowded and confined environments. Understanding the influence of nanoconfinement on rotational diffusion is vital in conceptualizing dynamics of biomolecules (such as proteins) in nanopores. The control of the translational movement of biomolecules is practiced widely in nanopore experiments. However, the restrictions on the translational movement may affect other dynamic properties such as rotational diffusion. In this paper, we use a coarse-grained molecular dynamics approach to study the rotational dynamics of a sample protein under the influence of cylindrical nanopore confinement. Our simulation reveals a 2-fold reduction in magnitude from the bulk rotational diffusion coefficient value as the confinement radius reaches double the size of protein's hydrodynamic radius. However, the changes in the rotational diffusion coefficient are relatively small compared to the changes in the translational diffusion coefficient. Interestingly, the rotational anisotropy also varies considerably when pore radii approach protein dimensions. Our simulations point out that the confinement effects cause the breakdown of small angular displacement theory when the pore radius is close to the protein hydrodynamic radius.

Effect of Hydrogen Bonds on the Dielectric Properties of Interfacial Water.

The dielectric constant for water is reduced under confinement. Although this phenomenon is well known, the underlying physical mechanism for the reduction is still in debate. In this work, we investigate the effect of the orientation of hydrogen bonds on the dielectric properties of confined water using molecular dynamics simulations. We find a reduced rotational diffusion coefficient for water molecules close to the solid surface. The reduced rotational diffusion arises due to the hindered rotation away from the plane parallel to the channel walls. The suppressed rotation in turn affects the orientational polarization of water, leading to a low value for the dielectric constant at the interface. We attribute the constrained out-of-plane rotation to originate from a higher density of planar hydrogen bonds formed by the interfacial water molecules.

Preparing the Next Generation of Code Blue Leaders Through Simulation: What's Missing?

INTRODUCTION: Despite the increasing reliance on simulation to train residents as code blue leaders, the perceived role and effectiveness of code blue simulations from the learners' perspective have not been explored. A code blue Simulation Program (CBSP), developed based on evidence-based simulation principles, was implemented at our institution. We explored the role of simulation in code blue training and the differences between real and simulated code blues from the learner perspective. METHODS: Using a thematic analysis approach and a purposeful sampling strategy, residents who participated in the CBSP were invited to participate in one of the three focus groups. Data were collected through small group discussions guided by semistructured interviews. The interviews were audio-recorded and transcribed. Interview transcripts were coded to assess underlying themes. RESULTS: Thematic analysis revealed that participants believed that the CBSP enhanced preparedness by capturing aspects of real codes (eg, inclusion of precode scenarios with awake patients, lack of readily available information) and facilitating automatization of code blue processes. Despite efforts to develop a high-fidelity simulation, participants noted that they experienced more anxiety, observed more chaos in the environment, and encountered different communication challenges in real codes. CONCLUSIONS: The CBSP enhanced resident preparedness to serve as code blue leaders. Learners highlighted that they valued the CBSP; however, differences remain between simulated and real codes that could be addressed to enhance the fidelity of future simulations.

Reason and Timing for Conversion to Sternotomy in Robotic-Assisted Coronary Artery Bypass Grafting and Patient Outcomes.

OBJECTIVE: Conversion to sternotomy is a primary bailout method for robotically assisted coronary artery bypass grafting procedures. The aims of this study were to identify the primary reasons for conversion from robotically assisted coronary artery bypass grafting to sternotomy and to evaluate the in-hospital outcomes in such patients. METHODS: Prospectively collected data from February 2004 to April 2017 were reviewed for 72 patients (56 men; mean age = 63.8 years) who required conversion to sternotomy during a robotically assisted coronary artery bypass grafting procedure with planned endoscopic left internal thoracic artery harvest and anastomosis to the left anterior descending on the beating heart. RESULTS: The overall rate of conversion was 12.4% (72/581). Conversions occurred either during attempted endoscopic left internal thoracic artery harvest (31.9%), during endoscopic left anterior descending isolation (40.3%), during manual isolation and anastomosis of the left anterior descending (19.4%), or after anastomosis due to unsatisfactory flow (8.3%). Overall, the most common reason for conversion was an intramyocardial left anterior descending (43.1%). The median stay in the intensive care unit was 1 day (range = 0-20) and the median hospital length of stay was 5 days (range = 3-43). In-hospital complications included new atrial fibrillation (16.7%), need for blood transfusion (20.8%), mediastinitis (4.2%), postoperative myocardial infarction (2.8%), exploration for bleeding (2.8%), and 1 in-hospital death. CONCLUSIONS: The reasons for conversion were primarily related to anatomical factors that created difficulties for endoscopic left internal thoracic artery harvesting and left anterior descending identification. Patients who required conversion to sternotomy from robotically assisted coronary artery bypass grafting demonstrated acceptable outcomes and low complication rates.

Prediction of fluid slip in cylindrical nanopores using equilibrium molecular simulations.

We introduce an analytical method to predict the slip length (L s) in cylindrical nanopores using equilibrium molecular dynamics (EMD) simulations, following the approach proposed by Sokhan and Quirke for planar channels [39]. Using this approach, we determined the slip length of water in carbon nanotubes (CNTs) of various diameters. The slip length predicted from our method shows excellent agreement with the results obtained from nonequilibrium molecular dynamics (NEMD) simulations. The data show a monotonically decreasing slip length with an increasing nanotube diameter. The proposed EMD method can be used to precisely estimate slip length in high slip cylindrical systems, whereas, L s calculated from NEMD is highly sensitive to the velocity profile and may cause large statistical errors due to large velocity slip at the channel surface. We also demonstrated the validity of the EMD method in a BNNT-water system, where the slip length is very small compared to that in a CNT pore of similar diameter. The developed method enables us to calculate the interfacial friction coefficient directly from EMD simulations, while friction can be estimated using NEMD by performing simulations at various external driving forces, thereby increasing the overall computational time. The EMD analysis revealed a curvature dependence in the friction coefficient, which induces the slip length dependency on the tube diameter. Conversely, in flat graphene nanopores, both L s and friction coefficient show no strong dependency on the channel width.

Is There a Role for Diagonal Coronary Artery Stenting in Patients Undergoing Robotic Coronary Artery Bypass Graft Surgery?

BACKGROUND: The efficacy of diagonal coronary artery stenting in patients undergoing robotic left internal thoracic artery-to-left anterior descending (LITA-to-LAD) anastomosis is not well defined. The objective of this study was to assess graft and stent patency in a single-stage hybrid revascularization with LITA-to-LAD anastomosis and PCI to a diagonal coronary artery. METHODS: From 2004 to 2014, a total of 25 patients consented to robotic-assisted LITA harvesting and a small left anterior thoracotomy for off-pump coronary artery bypass anastomosis onto the LAD along with concomitant PCI to the diagonal coronary artery. PCI to the diagonal coronary artery was performed in the same fluoroscopy-equipped hybrid operating room. RESULTS: Patients were on average 66 ± 11 years with 32% female. Pre-operative characteristics of these patients included 8% with a grade 3 or 4 left ventricle, 16% with a recent MI, and 92% with CCS III/IV symptoms. There were no death, one patient required an intra-aortic balloon pump, and one patient required re-operation for bleeding. The average ICU stay was 1.1 ± 0.53 days, and the average hospital stay was 4.6 ± 2.4 days. Fitzgibbon Grade A LITA-to-LAD patency at 6-month follow-up was 100%. As well, at 6-month follow-up the DES to the diagonal coronary artery had a patency rate of 96%. CONCLUSIONS: Single-stage hybrid revascularization strategy for bifurcating lesions of the LAD and diagonal coronary arteries with LITA-to-LAD anastomosis and PCI to a diagonal coronary artery appears to have acceptable clinical results with excellent 6-month angiographic patency results.

Translational mobilities of proteins in nanochannels: A coarse-grained molecular dynamics study.

We investigated the translation of a protein through model nanopores using coarse-grained (CG) nonequilibrium molecular dynamics (NEMD) simulations and compared the mobilities with those obtained from previous coarse-grained equilibrium molecular dynamics model. We considered the effects of nanopore confinement and external force on the translation of streptavidin through nanopores of dimensions representative of experiments. As the nanopore radius approaches the protein hydrodynamic radius, r_{h}/r_{p}→1 (where r_{h} is the hydrodynamic radius of protein and r_{p} is the pore radius), the translation times are observed to increase by two orders of magnitude. The translation times are found to be in good agreement with the one-dimensional biased diffusion model. The results presented in this paper provide useful insights on nanopore designs intended to control the motion of biomolecules.

Water desalination using graphene nanopores: influence of the water models used in simulations.

Molecular dynamics simulations are widely employed to analyze water and ion permeation through nanoporous membranes for reverse osmosis applications. In such simulations, water models play an important role in accurately reproducing the properties of water. We investigated the water and ion transport across a hydroxyl (OH) functionalized graphene nanopore using six water models: SPC, SPC/E, SPC/Fw, TIP3P, TIP4P, and TIP4P/2005. The water flux thus obtained varied up to 84% between the models. The water and ion flux showed a correlation with the bulk transport properties of the models such as the diffusion coefficient and shear viscosity. We found that the hydrogen-bond lifetime, resulting from the partial charges of the model, influenced the flux. Our results are useful in the selection of a water model for computer simulations of desalination using nanomembranes. Our findings also suggest that lowering the hydrogen-bond lifetime and enhancing the rate of diffusion of water would lead to enhanced water/ion flux.