Influence of the hole geometry on the flow distribution in ventricular catheters for hydrocephalus.

BACKGROUND: Hydrocephalus is a medical condition consisting of an abnormal accumulation of cerebrospinal fluid within the brain. A catheter is inserted in one of the brain ventricles and then connected to an external valve to drain the excess of cerebrospinal fluid. The main drawback of this technique is that, over time, the ventricular catheter ends up getting blocked by the cells and macromolecules present in the cerebrospinal fluid. A crucial factor influencing this obstruction is a non-uniform flow pattern through the catheter, since it facilitates adhesion of suspended particles to the walls. In this paper we focus on the effects that tilted holes as well as conical holes have on the flow distribution and shear stress. METHODS: We have carried out 3D computational simulations to study the effect of the hole geometry on the cerebrospinal fluid flow through ventricular catheters. All the simulations were done with the OpenFOAM® toolbox. In particular, three different groups of models were investigated by varying (i) the tilt angles of the holes, (ii) the inner and outer diameters of the holes, and (iii) the distances between the so-called hole segments. RESULTS: The replacement of cylindrical holes by conical holes was found to have a strong influence on the flow distribution and to lower slightly the shear stress. Tilted holes did not involve flow distribution changes when the hole segments are sufficiently separated, but the mean shear stress was certainly reduced. CONCLUSIONS: The authors present new results about the behavior of the fluid flow through ventricular catheters. These results complete earlier work on this topic by adding the influence of the hole geometry. The overall objective pursued by this research is to provide guidelines to improve existing commercially available ventricular catheters.

Parametric study of ventricular catheters for hydrocephalus.

BACKGROUND: To drain the excess of cerebrospinal fluid in a hydrocephalus patient, a catheter is inserted into one of the brain ventricles and then connected to a valve. This so-called ventricular catheter is a standard-size, flexible tubing with a number of holes placed symmetrically around several transversal sections or "drainage segments". Three-dimensional computational dynamics shows that most of the fluid volume flows through the drainage segment closest to the valve. This fact raises the likelihood that those holes and then the lumen get clogged by the cells and macromolecules present in the cerebrospinal fluid, provoking malfunction of the whole system. In order to better understand the flow pattern, we have carried out a parametric study via numerical models of ventricular catheters. METHODS: The parameters chosen are the number of drainage segments, the distances between them, the number and diameter of the holes on each segment, as well as their relative angular position. RESULTS: These parameters were found to have a direct consequence on the flow distribution and shear stress of the catheter. As a consequence, we formulate general principles for ventricular catheter design. CONCLUSIONS: These principles can help develop new catheters with homogeneous flow patterns, thus possibly extending their lifetime.

New designs of ventricular catheters for hydrocephalus by 3-D computational fluid dynamics.

INTRODUCTION: Based on a landmark study by Lin et al. of the two-dimensional flow in ventricular catheters (VCs) via computational fluid dynamics (CFD), we studied in a previous paper the three-dimensional flow patterns of five commercially available VC. We found that the drainage of the cerebrospinal fluid (CSF) mostly occurs through the catheter's most proximal holes. In this paper, we design five VC prototypes with equalized flow characteristics. METHODS: We study five prototypes of VC by means of CFD in three-dimensional (3-D) automated models and compare the fluid-mechanical results with our previous study of currently in use VC. The general procedure for the development of a CFD model calls for transforming the physical dimensions of the system to be studied into a virtual wire-frame model, which provides the coordinates for the virtual space of a CFD mesh. The incompressible Navier-Stokes equations, a system of strongly coupled, nonlinear, partial differential equations governing the motion of the flow field, are then solved numerically. RESULTS: By varying the number of drainage holes and the ratio hole/segment, we improved flow characteristics in five prototypes of VC. Models 1, 2, and 3 have a distal to proximal decreasing flow. Model 4 has an inverse flow to the previous ones, that is, a distal to proximal increasing flow, while model 5 has a constant flow over the segments. CONCLUSIONS: New catheter designs with variable hole diameter, number of holes, and ratio hole/segment along the catheter allow the fluid to enter the catheter more uniformly along its length, thus reducing the chance that the catheter becomes occluded.

Basic cerebrospinal fluid flow patterns in ventricular catheters prototypes.

OBJECT: A previous study by computational fluid dynamics (CFD) of the three-dimensional (3-D) flow in ventricular catheters (VC) disclosed that most of the total fluid mass flows through the catheter's most proximal holes in commercially available VC. The aim of the present study is to investigate basic flow patterns in VC prototypes. METHODS: The general procedure for the development of a CFD model calls for transforming the physical dimensions of the system to be studied into a virtual wire-frame model which provides the coordinates for the virtual space of a CFD mesh, in this case, a VC. The incompressible Navier-Stokes equations, a system of strongly coupled, nonlinear, partial differential conservation equations governing the motion of the flow field, are then solved numerically. New designs of VC, e.g., with novel hole configurations, can then be readily modeled, and the corresponding flow pattern computed in an automated way. Specially modified VCs were used for benchmark experimental testing. RESULTS: Three distinct types of flow pattern in prototype models of VC were obtained by varying specific parameters of the catheter design, like the number of holes in the drainage segments and the distance between them. Specifically, we show how to equalize and reverse the flow pattern through the different VC drainage segments by choosing appropriate parameters. CONCLUSIONS: The flow pattern in prototype catheters is determined by the number of holes, the hole diameter, the ratio hole/segment, and the distance between hole segments. The application of basic design principles of VC may help to develop new catheters with better flow circulation, thus reducing the possibility of becoming occluded.

Computational fluid dynamics of ventricular catheters used for the treatment of hydrocephalus: a 3D analysis.

INTRODUCTION: The most common treatment for hydrocephalus remains the ventriculoperitoneal shunt. Yet, the most frequent complication is ventricular catheter obstruction, which may account for 50-80 % of newly inserted shunts. Although many factors contribute to this, the main one is related to flow characteristics of the catheter within the hydrocephalic brain. A landmark study by Lin et al. addressed the problem of fluid characteristics in ventricular catheters using a two-dimensional simulation program of computational fluid dynamics (CFD). METHODS: The authors have studied five current commercially available ventricular catheter designs using CFD in three-dimensional automated designs. The general procedure for the development of a CFD model involves incorporating the physical dimensions of the system to be studied into a virtual wire-frame model. The shape and features of the actual physical model are transformed into coordinates for the virtual space of the computer and a CFD computational grid (mesh) is generated. The fluid properties and motion are calculated at each of these grid points. After grid generation, flow field boundary conditions are applied, and the fluid's thermodynamic and transport properties are included. At the end, a system of strongly coupled, nonlinear, partial differential conservation equations governing the motion of the flow field are numerically solved. This numerical solution describes the fluid motion and properties. RESULTS: The authors calculated that most of the total fluid mass flows into the catheter's most proximal holes. Fifty to 75 % flows into the two most proximal sets of inlets of current commercially available 12-32-hole catheters. Some flow uniformity was disclosed in Rivulet-type catheter. CONCLUSIONS: Most commercially available ventricular catheters have an abnormally increase flow distribution pattern. New catheter designs with variable hole diameters along the catheter tip will allow the fluid to enter the catheter more uniformly along its length, thereby reducing the probability of its becoming occluded.

Jazz, guitar, and neurosurgery: the Pat Martino case report.

OBJECTIVE: We present the case of a professional jazz guitarist with temporal lobe epilepsy secondary to an arteriovenous cerebral malformation. CASE DESCRIPTION: The patient underwent a left temporal lobectomy in 1980. After surgery, he presented with severe retrograde amnesia and complete loss of musical interest and capabilities. The patient's musical abilities recovered over time, and he regained his previous virtuoso status. In 2007, his medical history, neuropsychologic functions, and structural magnetic resonance imaging study were examined and revealed a remarkable degree of recovery of memory and musical abilities in the context of extensive temporal lobe resection. The neuropsychologic findings and neuroanatomic features of the magnetic resonance imaging study were analyzed to try to understand the high degree of recovery of both long-term memory and musical processing abilities in this musician. CONCLUSIONS: This case reveals the possibility of an unusual degree of cerebral plasticity and reorganization. Additionally, it emphasizes the question of musical virtuosity. This report shows that the musical capabilities of professional musicians, in specific cases, can completely recover even when much of the left temporal lobe has been removed.

Similar rewarding effects of testosterone in mice rated as short and long attack latency individuals.

An attempt was made to confirm and extend the findings of an earlier study on the rewarding properties of testosterone in male mice using conditioned place preference (CPP). Previous results had only partially demonstrated such an effect because the reinforcement depended on environmental cues such as the colour of the compartment. High individual variability was evident, suggesting that basal levels of aggressiveness may modulate such effects. Animals were pre-screened for aggressive behaviour and allocated to short and long attack latency (SAL and LAL) categories. Five days later the CPP procedure started. This involved pre-conditioning tests, conditioning and post-conditioning tests. SAL and LAL animals were treated with vehicle, 1 or 2 mg/kg of testosterone. During conditioning (on alternate days), a distinctive floor was paired four times with testosterone. On the intervening days animals were paired with a different floor with vehicle. CPP was clearly observed after testosterone treatment when the colour of the compartment was controlled in both SAL and LAL animals. These results provide additional support for the idea that testosterone and its derivatives have rewarding properties, which could explain processes of dependence.

Efectos de un estresor académico sobre las respuestas psicológica e inmune en jóvenes / Effects of an academic stressor on the psychological and immune response in the young males

El objetivo de este estudio es analizar la respuesta psicológica e inmune frente a una situación de estrés académico. A trece estudiantes que iban a realizar la prueba de Selectividad se les pasó una batería de tests psicológicos, autoinformes, y se les tomó muestras de sangre para determinar variables inmunológicas, trece días antes del examen y el día previo al mismo. Los resultados muestran un aumento significativo en ansiedad y disminuciones significativas en los recuentos de linfocitos totales, monocitos, linfocitos T CD8+ y células NK, no variando los linfocitos T CD4+ totales pero sí su porcentaje y la ratio CD4/CD8+ que aumentaron. Asimismo encontramos un efecto modulador de la ansiedad-rasgo, al observar diferencias significativas, entre altos y bajos en esta variable, en cl nivel de leucocitos, monocitos, neutrófilos y linfocitos CD8+; además, la interacción entre ansiedad-rasgo y la sesión resultó significativa para el porcentaje de linfocitos CD8+ y la ratio CD4/CD8+ (AU)

The aim of this study was to analyze the psychological and immune responses to an academic stress situation. In a pre-university examination, thirteen students had to answer a series of psychological tests, give self-reports and two samples were drawn to determine some immunological variables firstly, thirteen days before examination and then the previous day.The results show a significant increase of anxiety-state and significant decreases in the lymphocyte total re-count, monocytes, T CD8+ lymphocytes and NK cells. There was no total T CD4+ lymphocytes increase but therefore there was an increase in their percentage and the CD4+/CD8+ ratio. A modulator effect of the anxiety-trait was also found: there were significant differences between the highest and the lowest scores of this variable in the level of the leukocytes, monocytes, neutrophils and lymphocytes CD8+. Moreover, the interaction between anxiety-trait and the session turned out to be significant in the percentage of the lymphocytes CD8+ and the CD4+/CD8+ ratio (AU)