Search

The effect of the dimensions of the thoracic cage on the resuscitation outcome of cardiopulmonary resuscitation (CPR) maneuvers has long been debated. In this study, the effect of changes in the rib cage dimensions on the achieved compression depth was investigated using finite element simulations. A total of 216 different rib cage geometry models were considered and, in each case, the result of applying different levels of compression force up to 600 N were simulated. The Haller Index of the rib cage is defined as the ratio of the transverse diameter and the antero‐posterior diameter. Our results suggest that, with a fixed level of compression force, performing CPR on rib cages having a low Haller Index and/or a larger height leads to compression depths below the average. Alternatively, if a target compression depth is set for CPR, in general a lower compression force would be required for individuals with higher Haller Index and/or lower chest height. In addition, present results indicate that wider chested individuals will experience lower stress levels on their ribs to achieve the required CPR target depth. Moreover, in the present study we propose predictive models, based on anthropometric parameters, for compression depth and rib stress during chest compressions. In particular, the model suggests that in future correlations of empirical CPR data the patients' Haller index and vertical (sagittal) cross‐area are the best parameters to be used as independent variables in a fit. [ABSTRACT FROM AUTHOR]

The biomechanical response of a human rib cage to cardiopulmonary resuscitation maneuvers was investigated by means of finite element simulations. We analyzed the effect of the location where the force was applied on the achieved compression depths and stress levels experienced by the breastbone and ribs. For compression locations on the breastbone, a caudal shift of the application area toward the breastbone tip resulted in a 17% reduction of the force required to achieve a target 5 cm compression depth. We found that the use of compression regions located on the costal cartilages would involve higher risk of rib fractures. [ABSTRACT FROM AUTHOR]

The alteration of blood flow around an OPTEASE inferior vena cava filter with one or two blood clots attached was investigated by means of computational fluid dynamics. We used a patient‐specific vein wall geometry, and we generated different clot models with shapes adapted to the filter and vein wall geometries. A total of eight geometries, with one or two clots and a total clot volume of 0.5 or 1 cm3, were considered. A non‐Newtonian model for blood viscosity was adopted and the possible development of turbulence was accounted for by means of a three‐equation model. Two blood flow rates were considered for each case, representative for rest and exercise conditions. In exercise conditions, flow unsteadiness and even turbulence was detected in some cases. Pressure and wall shear stress (WSS) distributions were modified in all cases. Clots attached to the filter downstream basket considerably increased averaged WSS values by up to almost 50%. In all the cases a flow recirculation region appeared downstream of the clot. The degree of flow stagnation in these regions, an indicator of propensity to thrombogenesis, was estimated in terms of mean residence times and mean blood viscosity. High levels of flow stagnation were detected in rest conditions in the wake of those clots that were placed upstream from the filter. Our results suggest that one downstream placed big clot, showing a higher tendency to induce flow instabilities and turbulence, might be more harmful than two small clots placed in tandem. [ABSTRACT FROM AUTHOR]

Quantum chemical calculations have been performed to study the photocycle of [Ru(bpy)3]2+, a complex that is extensively used as an electron donor in photocatalytic reactions. After the initial spin-allowed excitation from the nonmagnetic ground state to a singlet state of metal-to-ligand charge transfer character, the system undergoes a rapid intersystem crossing to a triplet state of equal character. The calculations indicate a lifetime of 10 fs, in good agreement with experimental estimates. Important factors for this extremely fast intersystem crossing are the large spin-orbit coupling and the large vibrational overlap of the states involved. Both MLCT states are delocalized over the three bipyridine ligands, but the delocalized electron can easily increase its degree of localization. The hopping parameters have been calculated and found to be large for the localization on two ligands and subsequently on one. The combination of localization and geometry relaxation creates a rather long-lived trapped triplet MLCT state with a calculated lifetime of 9 µs. The addition of methyl groups on the bipyridine ligands decreases the ligand field and consequently lowers the metal-centered triplet states. This could eventually lead to opening of a fast deactivation channel of the ³MLCT states to the initial nonmagnetic states via the triplet ligand field states as occurs in the corresponding Fe(II) complex. [ABSTRACT FROM AUTHOR]

Azo compounds are organic photochromic systems that have the possibility of switching between cis and trans isomers under irradiation. The different photochemical properties of these isomers make azo compounds into good light-triggered switches and their significantly different geometries make them very interesting as components in molecular engines or mechanical switches. For instance, azo ligands are used in coordination complexes to trigger photoresponsive properties. The light-induced trans-to-cis isomerization of phenylazopyridine (PAPy) plays a fundamental role in the room-temperature switchable spin crossover of Ni-porphyrin derivatives. In this work, we present a computational study developed at the SA-CASSCF/CASPT2 level (State Averaged Complete Active Space Self Consistent Field/CAS second order Perturbation Theory) to elucidate the mechanism, up to now unknown, of the cis-trans photoisomerization of 3-PAPy. We have analyzed the possible reaction pathways along its lowest excited states, generated by excitation of one or two electrons from the lone pairs of the N atoms of the azo group (nazoπ8 2 and nazo 2π8 2 states), from a π delocalized molecular orbital (ππ8 state), or from the lone pair of the N atom of the pyridine moiety (npyπ8 state). Our results show that the mechanism proceeds mainly along the rotation coordinate in both the nazoπ8 and ππ8 excited states, although the nazo 2π8 2 state can also be populated temporarily, while the npyπ8 does not intervene in the reaction. For rotationally constrained systems, accessible paths to reach the cis minimum along planar geometries have also been located, again on the nazoπ8 and ππ8 potential energy surfaces, while the nazo 2π8 2 and npyπ8 states are not involved in the reaction. The relative energies of the different paths differ from those found for azobenzene in a previous work, so our results predict some differences between the reactivities of both compounds. [ABSTRACT FROM AUTHOR]

Deep venous thrombosis (DVT) is a common disease. Large thrombi in venous vessels cause bad blood circulation and pain; and when a blood clot detaches from a vein wall, it causes an embolism whose consequences range from mild to fatal. Walking is recommended to DVT patients as a therapeutical complement. In this study the mechanical effects of walking on a specific patient of DVT were simulated by means of an unprecedented integration of 3 elements: a real geometry, a biomechanical model of body tissues, and a computational fluid dynamics study. A set of computed tomography images of a patient's leg with a thrombus in the popliteal vein was employed to reconstruct a geometry model. Then a biomechanical model was used to compute the new deformed geometry of the vein as a function of the fiber stretch level of the semimembranosus muscle. Finally, a computational fluid dynamics study was performed to compute the blood flow and the wall shear stress (WSS) at the vein and thrombus walls. Calculations showed that either a lengthening or shortening of the semimembranosus muscle led to a decrease of WSS levels up to 10 %. Notwithstanding, changes in blood viscosity properties or blood flow rate may easily have a greater impact in WSS. [ABSTRACT FROM AUTHOR]

Reversible, room-temperature light-induced spin-crossover has been reported in a Ni-porphyrin functionalized with a phenylazopyridine (PAPy) ligand (Venkataramani et at., Science, 2011, 331, 445). Upon light irradiation (500 nm), the azopyridine moiety induces a change in the N i (II) coordination sphere from square planar (n = 4) to square pyramid (n = 5), leading to a change in the total spin of the molecule from S = 0 to S = 1. The trans-cis isomerization in the azopyridine ligand has been proposed to trigger the spin-crossover effect. However, the radiation used to induce the HS state is about 135 nm red-shifted with respect to the radiation used for trans-cis isomerization of the N=N double bond in other compounds. To elucidate the light-induced spin-crossover mechanism of this Ni(ii) compound, a combined DFT/CASSCF/CASPT2 study has been performed to determine the most stable cis and trans conformers with n = 4 or n = 5, and to characterize the excitation that triggers the SCO process. π-π interactions between porphyrin and PAPy are shown to play an essential role in the spin crossover. [ABSTRACT FROM AUTHOR]

A common problem in the elaboration of models is determining the properties and characteristics (measures) of the physical behavior of in vivo tissues in the human body. Correct estimates must be made of the tissue's physical properties and its surroundings. We suggest a method to compute the constitutive modeling of venous tissue, for every specific patient, from clinically registered ultrasounds images. The vein is modeled as a hyperelastic, incompressible, thin-walled cylinder and the membrane stresses are computed using strain energy. The approach is based on a strain-energy function suggested by Holzapfel capturing the characteristic nonlinear anisotropic responses of femoral veins with its collagen fibers. [ABSTRACT FROM AUTHOR]

We are interested in studying the genesis of a very common pathology: the human inguinal hernia. How the human inguinal hernia appears is not definitively clear, but it is accepted that it is caused by a combination of mechanical and biochemical alterations, and that muscular simulation plays an important role in this. This study proposes a model to explain how some physical parameters affect the ability to simulate the region dynamically and how these parameters are involved in generating inguinal hernias. We are particularly interested in understanding the mechanical alterations in the inguinal region because little is known about them or how they behave dynamically. Our model corroborates the most important theories regarding the generation of inguinal hernias and is an initial approach to numerically evaluating this affection. [ABSTRACT FROM AUTHOR]

Abstract: Computational fluid dynamics was used to simulate the flow of blood within an inferior vena cava (IVC) geometry model that was reconstructed from computed tomography images obtained from a real patient. The main novelty of the present work is that we simulated the implantation of 4 different filter models in this realistic IVC geometry. We considered different blood flow rates in the range between Vin=20 and Vin=80 cm3/s, and all simulations were performed with both the Newtonian and a non‐Newtonian model for the blood viscosity. We compared the hemodynamics performance of the different filter models, and we paid a special attention to the total drag force, Fd, exerted by the blood flow on the filter surface. This force is the sum of 2 contributions: the viscous skin friction force, which was found to be roughly proportional to the filter surface area, and the pressure force, which depended on the particular filter geometry design. The Fd force is relevant because it must be balanced by the total force exerted by the filter hooks/struts on the IVC wall at the attachment locations. For the highest Vin value investigated, the variation in Fd among filters was from 116 to 308 dyne. We also showed how the present results can be extrapolated to obtain good estimates of the drag forces if the blood viscosity levels change, ie, if the patient with a filter implanted is treated with anticoagulant therapy. [ABSTRACT FROM AUTHOR]

Electronic structure calculations have been performed on four different Mn corrole and corrolazine complexes to clarify the role of the imide axial ligand on the relative stability of the different spin states and the stabilization of the high-valent Mn ion in these complexes. Multiconfigurational perturbation theory energy calculations on the DFT-optimized geometries show that all complexes have a singlet ground state except the complex with the strongest electron-withdrawing substituent on the imide axial ligand, which is found to have a triplet ground state. The analysis of the σ and π interaction between the metal and imide ligand shows that this spin crossover is caused by a subtle interplay of geometrical factors (Mn-N distance and coordination angle) and the electron-withdrawing character of the substituent on the imide, which reduces the electron donation to the metal center. The analysis of the multiconfigurational wave functions reveals that the formally Mn(V) ion is stabilized by an important electron transfer from both the equatorial corrole/corrolazine ligand and the axial imide. The macrocycle donates roughly half an electron, being somewhere between the closed-shell trianionic and the dianionic radical form. The imide ligand transfers 2.5 electrons to the metal center, resulting in an effective d-electron count close to five in all complexes.