Assessment of valve implantation in the descending aorta as an alternative for aortic regurgitation patients not treatable with conventional procedures.

BACKGROUND: Aortic Regurgitation (AR) produces the entrance of an abnormal amount of blood in the left ventricle. This disease is responsible for high morbidity and mortality worldwide and may be caused by an aortic valve dysfunction. Surgical and transcatheter aortic valve replacement (TAVR) are the current options for treating AR. They have replaced older procedures such as Hufnagel's one. However, some physicians have reconsidered this procedure as a less aggressive alternative for patients not eligible for surgical or TAVR. Although Hufnagel suggested a 75% regurgitation reduction when a valve is placed in the descending aorta, a quantification of this value has not been reported. METHODS: In this paper, CFD/FSI numerical simulation is conducted on an idealized geometry. We quantify the effect of placing a bileaflet mechanical heart valve in the descending aorta on a moderate-severe AR case. A three-element Windkessel model is employed to prescribe pressure outlet boundary conditions. We calculate the resulting flow rates and pressures at the aorta and first-generation vessels. Moreover, we evaluate several indices to assess the improvement due to the valve introduction. RESULTS AND CONCLUSIONS: Regurgitation fraction (RF) is reduced from 37.5% (without valve) to 18.0% (with valve) in a single cardiac cycle. This reduction clearly shows the remarkable efficacy of the rescued technique. It will further ameliorate the left ventricle function in the long-term. Moreover, the calculations show that the implantation in that location introduces fewer incompatibilities' risks than a conventional one. The proposed methodology can be extended to any particular conditions (pressure waveforms/geometry) and is designed to assess usual clinical parameters employed by physicians.

Analytical model for managing hypotony after implantation surgery of a glaucoma drainage device.

The main aim of glaucoma treatment is to reduce the intraocular pressure (IOP). One of the most common surgical treatments of glaucoma is the implantation of a glaucoma drainage device to drain the aqueous humor from the anterior chamber to a filtration bleb, where the aqueous humor is absorbed. In some cases, the excess of drainage causes ocular hypotony, which constitutes a sight-threatening complication. To prevent hypotony after this intervention, surgeons frequently introduce a suture into the device tube, which increases the hydraulic resistance of the tube and, therefore, the IOP. This study aims to provide an analytical model to correct hypotony following implantation surgery of a glaucoma drainage device, which may help glaucoma surgeons decide on hypotony treatment. The results indicate that the IOP after implanting a cylindrical tube around 300 µm in diameter is essentially the same as that built up in the filtering bleb and can hardly be controlled by introducing a straight suture unless the suture diameter is slightly lower than that of the tube. On the contrary, when the tube diameter is smaller than, for example, 100 µm, significant reductions of the IOP can be obtained by introducing a thin suture into the tube.

Construction of a hybrid lung model by combining a real geometry of the upper airways and an idealized geometry of the lower airways.

BACKGROUND AND OBJECTIVE: Health care costs represent a substantial an increasing percentage of global expenditures. One key component is treatment of respiratory diseases, which account for one in twelve deaths in Europe. Computational simulations of lung airflow have potential to provide considerable cost reduction and improved outcomes. Such simulations require accurate in silico modeling of the lung airway. The geometry of the lung is extremely complex and for this reason very simple morphologies have primarily been used to date. The objective of this work is to develop an effective methodology for the creation of hybrid pulmonary geometries combining patient-specific models obtained from CT images and idealized pulmonary models, for the purpose of carrying out experimental and numerical studies on aerosol/particle transport and deposition in inhaled drug delivery. METHODS: For the construction of the hybrid numerical model, lung images obtained from computed tomography were exported to the DICOM format to be treated with a commercial software to build the patient-specific part of the model. At the distal terminus of each airway of this portion of the model, an idealization of a single airway path is connected, extending to the sixteenth generation. Because these two parts have different endings, it is necessary to create an intermediate solid to link them together. Physically realistic treatment of truncated airway boundaries in the model was accomplished by mapping of the flow velocity distribution from corresponding conducting airway segments. RESULTS: The model was verified using two sets of simulations, steady inspiration/expiration and transient simulation of forced spirometry. The results showed that the hybrid model is capable of providing a realistic description of air flow dynamics in the lung while substantially reducing computational costs relative to models of the full airway tree. CONCLUSIONS: The model development outlined here represents an important step toward computational simulation of lung dynamics for patient-specific applications. Further research work may consist of investigating specific diseases, such as chronic bronchitis and pulmonary emphysema, as well as the study of the deposition of pollutants or drugs in the airways.

Influence of an iris-fixed phakic intraocular lens on the transport of nutrients by the aqueous humor.

We study numerically the influence of an iris-fixed phakic intraocular lens (PIOL) on the transport of nutrients by the aqueous humor across a realistic model of the human eye. The Boussinesq equations are solved to calculate the velocity field both in the anterior and posterior chambers. The transport of the nutrient is modeled as that of a passive scalar convected by that velocity field and diffused by the concentration gradient. The nutrient is assumed to be adsorbed at the non-vascularized tissues, i.e., the crystalline lens and cornea endothelium. The adsorption rates at the crystalline and cornea endothelium are supposed to be proportional to the nutrient concentration there. The comparison between the results obtained with and without the PIOL allows us to quantify the influence of this device on the nutrient supply from the aqueous humor. The amount of nutrient adsorbed onto the crystalline is hardly affected by the presence of the PIOL in the anterior chamber, even though there is an iridotomy in this case. When the PIOL is implanted, the flux adsorbed onto the cornea endothelium increases up to around 32% for the highest value of the adsorption coefficient, and hardly varies for the other values of this parameter. This counterintuitive effect is explained by the efficient role played by the iridotomy in evacuating the nutrient from the posterior to the anterior chamber. Based on these results, one can estimate the variation of glucose available in the cornea endothelium after implanting the PIOL, and discuss potential effects on the cell metabolism. These simulations can be regarded as a first attempt to shed light on the mechanisms responsible for the supply of oxygen and glucose to eye avascular structures like the cornea endothelium and crystalline.

Numerical analysis of the pressure drop across highly-eccentric coronary stenoses: application to the calculation of the fractional flow reserve.

BACKGROUND: Fractional flow reverse (FFR) is the gold standard assessment of the hemodynamic significance of coronary stenoses. However, it requires the catheterization of the coronary artery to determine the pressure waveforms proximal and distal to the stenosis. On the contrary, computational fluid dynamics enables the calculation of the FFR value from relatively non-invasive computed tomography angiography (CTA). METHODS: We analyze the flow across idealized highly-eccentric coronary stenoses by solving the Navier-Stokes equations. We examine the influence of several aspects (approximations) of the simulation method on the calculation of the FFR value. We study the effects on the FFR value of errors made in the segmentation of clinical images. For this purpose, we compare the FFR value for the nominal geometry with that calculated for other shapes that slightly deviate from that geometry. This analysis is conducted for a range of stenosis severities and different inlet velocity and pressure waveforms. RESULTS AND CONCLUSIONS: The errors made in assuming a uniform velocity profile in front of the stenosis, as well as those due to the Newtonian and laminar approximations, are negligible for stenosis severities leading to FFR values around the threshold 0.8. The limited resolution of the stenosis geometry reconstruction is the major source of error when predicting the FFR value. Both systematic errors in the contour detection of just 1-pixel size in the CTA images and a low-quality representation of the stenosis surface (coarse faceted geometry) may yield wrong outcomes of the FFR assessment for an important set of eccentric stenoses. On the contrary, the spatial resolution of images acquired with optical coherence tomography may be sufficient to ensure accurate predictions for the FFR value.

Simulation of the human airways using virtual topology tools and meshing optimization.

A method is proposed to improve the quality of the three-dimensional airway geometric models using a commercial software, checking the number of elements, meshing time, and aspect ratio and skewness parameters. The use of real and virtual topologies combined with patch-conforming and patch-independent meshing algorithms results in four different models being the best solution the combination of virtual topology and patch-independent algorithm, due to an excellent aspect ratio and skewness of the elements, and minimum meshing time. The result is a reduction in the computational time required for both meshing and simulation due to a smaller number of cells. The use of virtual topologies combined with patch-independent meshing algorithms could be extended in bioengineering because the geometries handling is similar to this case. The method is applied to a healthy person using their computed tomography images. The resulting numerical models are able to simulate correctly a forced spirometry.

Numerical and experimental analysis of the transitional flow across a real stenosis.

In this paper, we present a numerical study of the pulsatile transitional flow crossing a severe real stenosis located right in front of the bifurcation between the right subclavian and right common carotid arteries. The simulation allows one to determine relevant features of this subject-specific flow, such as the pressure waves in the right subclavian and right common carotid arteries. We explain the subclavian steal syndrome suffered by the patient in terms of the drastic pressure drop in the right subclavian artery. This pressure drop is caused by both the diverging part of the analyzed stenosis and the reverse flow in the bifurcation induced by another stenosis in the right internal carotid artery.

Hipergranulación periestomal / Peristomal hypergranulation

Las enfermedades cutáneas son comunes en pacientes con estoma. Incluyen desde reacciones irritativas a dermatitis alérgica de contacto, infecciones,alteraciones relacionadas con una enfermedad intestinal y enfermedades cutáneas previas como la psoriasis.Describimos el caso de un paciente conhipergranulación de la colostomía, causada posiblemente por la irritación (AU)

Skin disorders are common in stoma patients. These range from irritant reactions to allergic contact dermatitis, infections, disorders related to boweldisease and pre-existing. A patient with a hypergranulation by colostomy is reported (AU)