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A Redaelli

Publications and source records attributed to A Redaelli.

30 records · Page 2Linked to original sources
PubMed1996

Computational analysis of the ductus venosus fluid dynamics based on Doppler measurements.

The simplified Bernoulli equation is currently used to evaluate pressure gradients on the basis of Doppler velocity measurements when direct pressure data require highly invasive procedures. Recently, this method was applied to the ductus venosus (DV) in order to estimate the fetal central venous pressure. The complex geometry- and consequently hemodynamics-of this fetal region suggests caution in automatically converting Doppler velocity measurements to pressure data. To investigate the reliability of the Bernoulli equation for this practice, we simulated the hemodynamics of the branching between the umbilical vein (UV) and the DV on the basis of ultrasonographic data from a normal fetus, using a simplified parametric 3D numerical model of a bent tube with varying cross section (UV) and a smaller trumpet-shaped branch (DV). A finite element formulation has been adopted to solve the governing Navier-Stokes equations. The results show that the simplified Bernoulli equation, despite of its simplicity, provides a good estimation of the pressure drop between the UV and the DV outlet section (with an error of about 0.25 mmHg, equal to 15%, compared with the model results). Nevertheless, attention must be paid to the velocity measurement sites, as discussed in this paper. In turn, the error becomes notable (2.8 mmHg, i.e., 34%) for high velocity values, thus suggesting that the error in evaluating the pressure drop with the simplified Bernoulli equation during fetal inspiratory movements may be substantial.

Blood Flow Velocity↗
PubMed1996

Computational evaluation of intraventricular pressure gradients based on a fluid-structure approach.

The dynamics of intraventricular blood flow, i.e. its rapid evolution, implies the rise of intraventricular pressure gradients (IPGs) characteristic of the inertia-driven events as experimentally observed by Pasipoularides (1987, 1990) and by Falsetti et al. (1986). The IPG time course is determined by the wall contraction which, in turn, depends on the load applied, namely the intraventricular pressure which is the sum of the aortic pressure (i.e., the systemic net response) and the IPG. Hence the IPGs account, at least in part, for the wall movement. These considerations suggest the necessity of a comprehensive analysis of the ventricular mechanics involving both ventricular wall mechanics and intraventricular fluid dynamics as each domain determines the boundary conditions of the other. This paper presents a computational approach to ventricular ejection mechanics based on a fluid-structure interaction calculation for the evaluation of the IPG time course. An axisymmetric model of the left ventricle is utilized. The intraventricular fluid is assumed to be Newtonian. The ventricle wall is thin and is composed of two sets of counter-rotating fibres which behave according to the modified version of Wong's sarcomere model proposed by Montevecchi and Pietrabissa and Pietrabissa et al. (1987, 1991). The full Navier-Stokes equations describing the fluid domain are solved using Galerkin's weighted residual approach in conjunction with finite element approximation (FIDAP). The wall displacement is solved using the multiplane quasi-Newton method proposed by Buzzi Ferraris and Tronconi (1985). The interaction procedure is performed by means of an external macro which compares the flow fields and the wall displacement and appropriately modifies the boundary conditions to reach the simultaneous and congruous convergence of the two problems. The results refer to a simulation of the ventricular ejection with a heart rate of 72 bpm. In this phase the ventricle ejects 61 cm3 (ejection fraction equal to 54 percent) and the ventricular pressure varies from 78 mmHg to 140 mmHg. The IPG show an oscillating behaviour with two major peaks at the beginning (11.09 mmHg) and at the end (4.32 mmHg) of the ejection phase, when the flow rate hardly changes, according to the experimental data. Furthermore the wall displacement, the wall stress and strain, the pressure and velocity fields are calculated and reported.

Blood Flow Velocity↗
PubMed1996

A new pulsatile blood pump for adult cardiopulmonary bypass: design criteria and preliminary fluid dynamic evaluation.

A new pulsatile pumping device for adult cardiopulmonary bypass has been designed. Its main characteristic consists in having a fully disposable pumping head, since polymeric materials have been adopted for the housing as well as for the built-in inlet and outlet valves. Furthermore, the valves show an innovative design, as they are ring-shaped and accomplish their task by virtue of their elastic deformability. The design phase of the pumping head and the first fluid dynamic evaluations have been performed by numerical methods. Particularly, a three-dimensional CAD model of the pumping head (in the current configuration) is presented in this paper. On the basis of this model, computational fluid dynamic analysis of the hydraulic behaviour has been performed for some components. The obtained results show complex velocity patterns in the pumping chamber during the filling phase as well as limited pressure gradients across the inlet valve.

Biocompatible Materials↗
PubMed1995

Repair of 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea-induced damage by mammalian cell extracts.

The repair of damage induced by the alkylating antitumor drug 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) was investigated using an in vitro excision repair system. Hamster cell extracts prepared from the parental CHO-9 cell line and the ERCC1 mutant 43-3B were both proficient in the repair of CCNU-induced damage. The in vitro repair of CCNU damage was faster than the repair of UV damage and plasmid substrates were rapidly and efficiently incised after incubation with either CHO-9 or 43-3B extracts. 7-Methylguanine (7-meG) and 3-methyladenine (3-meA) glycosylases were active to a similar extent in the CHO-9 and 43-3B extracts. The data indicate that most damage induced by CCNU is repaired via the ERCC1-independent base excision repair pathway, initiating with removal of chloroethylated and hydroxyethylated bases by N-glycosylases. Yet, the sensitive phenotype of 43-3B cells suggests that the ERCC1 gene product is required for the removal of a small subset of CCNU-induced lesions that are important for drug cytotoxicity.

Animals↗
PubMed1995

Preliminary design and optimization of an ECC blood pump by means of a parametric approach.

This study concerns the development of an analytical parametric model of a centrifugal disk pump. The advantage of this kind of approach is to have an adaptable tool as a first step for the design of a pump device. The method allows the evaluation of the velocity profiles and the shear stresses within the impeller disks in the flow domain along with the performance of the device in terms of torque, mechanical power, power loss, head-flow performance, pump efficiency, and hemolytic index. Some simplifying hypotheses are assumed: steady state condition, laminar flow, Newtonian and incompressible fluid. The radial velocity profiles are assumed to be uniform and the flow cross-sectional area is assumed to be constant along the radius. The influence of the housing and secondary flows caused by recirculation are neglected. To test the approach reliability, the model was used to simulate a pump with the following characteristics: an external and internal radius of 50 mm and 5 mm, respectively, and a channel height of 2.5-0.25 mm (h) from inlet to outlet section. The angular velocity omega was varied in the range 500-3,000 rpm. The flow rate has been varied from 1 to 5 L/min. The results show that when the flow rate is increased, head performances obtained using this pump model vary from 411 to 100 mm Hg, and its efficiency varies from 48 to 15%. A parallel simulation has been carried out by means of a Finite Element Method model with an angular velocity equal to 2,000 rpm.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Flow Velocity↗
PubMedDate not supplied

Mesh updating in fluid-structure interactions in biomechanics: an iterative method based on an uncoupled approach.

In this study, a computational uncoupled approach to fluid-structure interaction problems in biofluid mechanics is presented. It is based on the finite element method and is applied to study the local fluid dynamics in two specific situations: the left ventricular ejection phase and the motion of an isolated red blood cell along a small artery. Particularly, the focus is on the algorithms developed to deal with mesh updating, because both examined districts are characterized by geometrical deformations of the fluid domain edges. This is currently a challenging issue in the application of computational fluid dynamics techniques to living systems, especially to the cardiovascular system. Although the chosen approach uses a commercial computational fluid dynamics package for the solution of the fluid domain, original algorithms have been developed to perform the boundary displacement calculations correctly, as well as the corresponding mesh updating. Results are reported and compared with available data in the literature pertinent to the two studied problems.

Algorithms↗
PubMedDate not supplied

An assisted automated procedure for vessel geometry reconstruction and hemodynamic simulations from clinical imaging.

In this paper a method is described to obtain realistic 3-D geometric models of vascular districts from clinical tomographic 3-D images. The aim is the simulation of individual local hemodynamics by means of computational fluid-dynamics (CFD). As a test case, the method is applied to the carotid bifurcation. Attention is focused on the minimisation of the time demanding costs. The proposed procedure has been automated whenever possible and takes about 2h from the acquisition of the images to the attainment of the simulation results, a time lapse compatible with diagnostic exigency.

Aged↗
PubMedDate not supplied

[Laparoscopic versus conventional surgery in the treatment of colorectal diseases].

The aim of the study was to compare the results obtained with laparoscopic (LPS) and laparotomic (LPT) colorectal resection after our initial experience with the laparoscopic technique. Fifty-six patients were submitted to colorectal resection, 26 with the LPS and 30 with the LPT technique. Eighteen patients out of 26 in the LPS group and 22/30 in the LPT group had malignancies. All resections were performed with a curative intent. The mean operating time was 220 min in the LPS group and 208 min in the LPT group. Mean blood loss was 287 ml and 312 ml, respectively (blood transfusions were needed in 1/26 and in 7/30 patients). The rates of major complications were 9.5% and 5.7%, respectively. There was no mortality. The conversion rate for the LPS group was 19.2%. In the cancer patients, no significant difference was observed between the two groups as regards postoperative staging. The mean length of specimens and the mean distance of the tumours from the resection margins were adequate. The mean number of lymph nodes harvested was 11.8 in the LPS group as against 18.5 in the LPT group. No early recurrences were observed. Resumption of gastrointestinal function was faster in the LPS patients who underwent the surgical procedure under general anaesthesia associated with epidural anaesthesia/postoperative analgesia. In conclusion, these preliminary results indicate that laparoscopic colorectal surgery is feasible and that the resections in cancer patients appear to be oncologically adequate. Long-term follow-up is needed for reliable assessment of oncological outcomes.

Adenocarcinoma↗
PubMedDate not supplied

Proteins, nucleic acids and genetic codes.

On the basis of the previous article (Morchio and Traverso [1999]), we discuss the possible interactions between the first proteic fragments developed in the hydrophobic layer made of hydrocarbons, which would have covered the surface of the primitive seas, and the nitrogenous bases, particularly the pyrimidinic ones, which would have found in such hydrophobic layer favourable conditions to their prebiotic synthesis. These interactions would have presumably brought, on the basis of the physicochemical laws, at the moment the only ones at work, to the linkage of various bases and so to the construction of the first nucleic acid chains (most likely RNA). Interestingly enough this result would have been obtained by inserting two more bases between those hydrogen bound to the amino acids and this might have been the ground for the future "triplets". These interactions might have been particularly significant because of two important consequences: the birth of a rough genetic code and the starting of interactions of the co-operative type between bases and amino acids that would have made the growth of both proteic and nucleic acid fragments easier and faster. We conclude that the development of the genetic code was neither a "frozen accident" nor an occurrence directed by any information flow.

Genetic Code↗