Biomedical subjects

F Boschetti

Publications and source records attributed to F Boschetti.

6 recordsLinked to original sources

PubMed1998

Factors affecting the respiratory ratio during cardiopulmonary by-pass.

Despite the wide use of hypothermic cardiopulmonary bypass (CPB) during open heart surgery there is little information about the patient metabolism. In particular no complete studies addressed the assessment of the respiratory ratio (RR) during CPB at different core temperatures. Therefore a clinical study was performed in order to evaluate the oxygen consumption (VO2) and carbon dioxide production (VCO2) in adult patients with valvular or coronary heart disease undergoing CPB. Twenty-five patients (16 male, 9 female) aged between 26 and 76 (54.2+/-12.4 mean +/- SD) were the subjects of this study. Measurements (102) were taken at various perfusion flow rates (from 1.6 to 2.9 L/min(-1) x m(-2)) and temperatures (from 24 to 37 degrees C). Arterial and mixed venous gas analyses were performed and O2 and CO2 concentrations were calculated, including the carbamate contribute. We calculated VO2, VCO2 and then RR from artero-venous differences in O2 and CO2 contents. Both VO2 and VCO2 showed a positive linear correlation with temperature (r = 0.82 and r = 0.59 respectively) and with blood flow rate (r = 0.61 and r = 0.29 respectively). The mean RR was 0.78+/-0.28 and more than 84% of RR values fell in the range 0.5-1.2. No significant correlation between RR and temperature and blood flow rate was observed. VCO2 and RR showed a positive linear correlation with the gas to blood flow rate ratio (r = 0.37 and r = 0.49 respectively).

Adult↗

PubMed1997

The assignment of velocity profiles in finite element simulations of pulsatile flow in arteries.

In this paper we present a new method for the assignment of pulsatile velocity profiles as input boundary conditions in finite element models of arteries. The method is based on the implementation of the analytical solution for developed pulsatile flow in a rigid straight tube. The analytical solution provides the fluid dynamics of the region upstream from the fluid domain to be investigated by means of the finite element approach. In standard fluid dynamics finite element applications, the inlet developed velocity profiles are achieved assuming velocity boundary conditions to be easily implementable-such as flat or parabolic velocity profiles-applied to a straight tube of appropriate length. The tube is attached to the inflow section of the original fluid domain so that the flow can develop fully. The comparison between the analytical solution and the traditional numerical approach indicates that the analytical solution has some advantages over the numerical one. Moreover, the results suggest that subroutine employment allows a consistent reduction in solving time especially for complex fluid dynamic model, and significantly decreases the storage and memory requirements for computations.

Algorithms↗

PubMed1997

A semiautomatic procedure for edge detection of in vivo pulmonary microvessels and interstitial space.

OBJECTIVE: To develop an algorithm to detect the edges between lung tissue, perivascular interstitium, and microvessel using digital processing of in vivo microscopic images of lung surface. METHODS: A numerical technique was developed to identify three different regions (namely, pulmonary microvessel, perivascular interstitium, and lung tissue) based on their corresponding gray level distributions. We present a theoretical demonstration of the method and a semiautomatic procedure that, once the edges are detected, determines microvascular diameters and perivascular interstitium thickness. RESULTS: Microvessel diameters and perivascular interstitium thickness were calculated for precapillary arteriolar branching (40 to 140 microns) and saved in an ASCII file. CONCLUSIONS: We proved that the maximum value of the moving variance is useful to detect the edge between two adjacent regions whose gray level distributions satisfy the condition: magnitude of sigma Y2 - sigma X2 < or = (mu X - mu Y)2, where mu X, mu Y, sigma X2, sigma Y2 are the statistical moments of the two regions X and Y. Moreover, when the regions have similar means, the above conditions is not met, but the edge between them can be detected by the maximum of the moving variance error.

Algorithms↗

PubMed1997

Virtual extracorporeal circulation process.

Virtual instruments for an extracorporeal circulation (ECC) process were developed to simulate the reactions of a patient to different artificial perfusion conditions. The computer simulation of the patient takes into account the hydraulic, volume, thermal and biochemical phenomena and their interaction with the devices involved in ECC (cannulae dimensions, oxygenator and filter types, pulsatile or continuous pump and thermal exchangers). On the basis of the patient's initialisation data (height, weight, Ht) and perfusion variables (pump flow rate, water temperature, gas flow rate and composition) imposed by the operator, the virtual ECC monitors simulated arterial and venous pressure tracings in real time, along with arterial and venous flow rate tracings, urine production tracing and temperature levels. Oxyhemoglobin arterial and venous blood saturation together with other related variables (pO2, pCO2, pH, HCO3 are also monitored. A drug model which allows the simulation of the effect of vasodilator and diuretic drugs is also implemented. Alarms are provided in order to check which variables (pressure, saturation, pH, urine flow) are out of the expected ranges during the ECC simulation. Consequently the possibility of modifying the control parameters of the virtual devices of the ECC in run-time mode offers an interaction mode between the operator and the virtual environment.

Blood Gas Analysis↗

PubMed1993

Biomechanical factors in abdominal aortic aneurysm rupture.

Hitherto the size of abdominal aortic aneurysms (AAA) has been considered the most important factor in determining the risk of rupture. For this reason most interest has been devoted to physical, echographic and tomographic analyses of the shape of AAA. However, it is known that rupture can also occur in small AAA. Other factors must be considered to have an important role in the natural history of aneurysms. The aim of this study was to characterise the mechanical stress in the wall of an AAA due to pressure in the presence of atherosclerosis, intraluminal thrombus and anatomical restraints. The Finite Elements Method (FEM) was used to determine wall stress distribution. Due to the simplicity of the AAA structure an axisymmetric model has been built. The results of the structural analysis confirms that maximum stress increases with diameter. These effects may be reduced by the presence of intraluminal thrombus, which in the models reduces maximum stress by up to 30%; however this is not the case for dissecting thrombus. On the other hand atherosclerotic plaques cause stress concentration and a significant increase in maximum wall stress. The risk of rupture can increase by about 200%. Finally the investigation shows the FEM is a versatile tool for studying the mechanics of vascular structures. It enables the influence of various parameters on wall stress to be quantified in diagnostic settings, and so could be useful for predicting the rupture of AAA, although at present such predictions are limited by data leakage and by the approximations used in the model.

Aged↗

PubMedDate not supplied

Hemodynamic effects of attachment modes and device design of a thoracic artificial lung.

A thoracic artificial lung (TAL) was designed to treat respiratory insufficiency, acting as a temporary assist device in acute cases or as a bridge to transplant in chronic cases. We developed a computational model of the pulmonary circulatory system with the TAL inserted. The model was employed to investigate the effects of parameter values and flow distributions on power generated by the right ventricle, pulsatility in the pulmonary system, inlet flow to the left atrium, and input impedance. The ratio of right ventricle (RV) power to cardiac output ranges between 0.05 and 0.10 W/(L/min) from implantation configurations of low impedance to those of high impedance, with a control value of 0.04 W/(L/min). Addition of an inlet compliance to the TAL reduces right heart power (RHP) and impedance. A compliant TAL housing reduces flow pulsatility in the fiber bundle, thus affecting oxygen transfer rates. An elevated bundle resistance reduces flow pulsatility in the bundle, but at the expense of increased right heart power. The hybrid implantation mode, with inflow to the TAL from the proximal pulmonary artery (PA), outflow branches to the distal PA and the left atrium (LA), a band around the PA between the two anastomoses, and a band around the outlet graft to the LA, is the best compromise between hemodynamic performance and preservation of some portion of the nonpulmonary functions of the natural lungs.

Artificial Organs↗