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Biomedical subjects

R Fumero

Publications and source records attributed to R Fumero.

At least 19 recordsLinked to original sources
PubMed2001

In vitro steady-flow analysis of systemic-to-pulmonary shunt haemodynamics.

A modified Blalock-Taussig shunt is a connection created between the systemic and pulmonary arterial circulations to improve pulmonary perfusion in children with congenital heart diseases. Survival of these patients is critically dependent on blood flow distribution between the pulmonary and systemic circulations which in turn depends upon the flow resistance of the shunt. Previously, we investigated the pressure-flow relationship in rigid shunts with a computational approach. to estimate the pulmonary blood flow rate on the basis of the in vivo measured pressure drop. The present study aims at evaluating, in vitro how the anastomotic distensibility and restrictions due to suture presence affect the shunt pressure-flow relationship. Two actual Gore-Tex shunts (3 and 4 mm diameters) were sutured to compliant conduits by a surgeon and tested at different steady flow rates (0.25-11 min(-1)) and pulmonary pressures (3-34 mmHg). Corresponding computational models were also created to investigate the role of the anastomotic restrictions due to sutures. In vitro experiments showed that pulmonary artery pressure affects the pressure-flow relationship of the anastomoses. particularly at the distal site. However, this occurrence scarcely influences the total shunt pressure drop. Comparisons between in vitro and computational models without anastomotic restrictions show that the latter underestimates the in vitro pressure drops at any flow rate. The addition of the anastomotic restrictions (31 and 47% of the original area of 3 and 4 mm shunts, respectively) to the computational models reduces the gap, especially at high shunt flow rate and high pulmonary pressure.

Anastomosis, Surgical↗
PubMed2001

Modeling of the Norwood circulation: effects of shunt size, vascular resistances, and heart rate.

Hypoplastic left heart syndrome is the most common lethal cardiac malformation of the newborn. Its treatment, apart from heart transplantation, is the Norwood operation. The initial procedure for this staged repair consists of reconstructing a circulation where a single outlet from the heart provides systemic perfusion and an interpositioning shunt contributes blood flow to the lungs. To better understand this unique physiology, a computational model of the Norwood circulation was constructed on the basis of compartmental analysis. Influences of shunt diameter, systemic and pulmonary vascular resistance, and heart rate on the cardiovascular dynamics and oxygenation were studied. Simulations showed that 1) larger shunts diverted an increased proportion of cardiac output to the lungs, away from systemic perfusion, resulting in poorer O2 delivery, 2) systemic vascular resistance exerted more effect on hemodynamics than pulmonary vascular resistance, 3) systemic arterial oxygenation was minimally influenced by heart rate changes, 4) there was a better correlation between venous O2 saturation and O2 delivery than between arterial O2 saturation and O2 delivery, and 5) a pulmonary-to-systemic blood flow ratio of 1 resulted in optimal O2 delivery in all physiological states and shunt sizes.

Computer Simulation↗
PubMed2000

Use of mathematical model to predict hemodynamics in cavopulmonary anastomosis with persistent forward flow.

BACKGROUND: The bidirectional cavopulmonary anastomosis with additional pulmonary blood flow is used as a staged procedure or a definitive palliation of univentricular hearts. In this paper the flow competition occurring between the caval and the pulmonary flows is investigated. The hemodynamics in the superior vena cava and the blood flow distribution into the lungs, as well as the systemic arterial oxygen availability, are correlated with the severity of the right ventricle outflow tract obstruction and the pulmonary arteriolar resistance. MATERIALS AND METHODS: Computer models of the pre- and postoperative hemodynamics of univentricular hearts were developed. The effects of increasing severity of the right ventricle outflow tract obstruction, with a pulmonary arteriolar resistance ranging from 0.8 to 7.9 nonindexed Woods units, were simulated. RESULTS: The study indicates that the presence of an additional pulmonary blood flow from the native pulmonary artery may be beneficial. Since an excessive additional blood flow may cause central venous hypertension, its optimal value should be chosen according to the value of pulmonary arteriolar resistance. The model was utilized to simulate four clinical cases. CONCLUSIONS: The simulations show that the model can predict the postoperative hemodynamics and could therefore be usefully applied to predict quantitatively the effect of the native pulmonary blood flow following bidirectional cavopulmonary anastomosis.

Anastomosis, Surgical↗
PubMed2000

Computational model of the fluid dynamics in systemic-to-pulmonary shunts.

A systemic-to-pulmonary shunt is a connection created between the systemic and pulmonary arterial circulations in order to improve pulmonary perfusion in children with congenital heart diseases. Knowledge of the relationship between pressure and flow in this new, surgically created, cardiovascular district may be helpful in the clinical management of these patients, whose survival is critically dependent on the blood flow distribution between the pulmonary and systemic circulations. In this study a group of three-dimensional computational models of the shunt have been investigated under steady-state and pulsatile conditions by means of a finite element analysis. The model is used to quantify the effects of shunt diameter (D), curvature, angle, and pulsatility on the pressure-flow (DeltaP-Q) relationship of the shunt. Size of the shunt is the main regulator of pressure-flow relationship. Innominate arterial diameter and angles of insertion have less influence. Curvature of the shunt results in lower pressure drops. Inertial effects can be neglected. The following simplified formulae are derived: DeltaP=(0. 097Q+0.521Q(2))/D(4) and DeltaP=(0.096Q+0.393Q(2))/D(4) for the different shunt geometries investigated (straight and curved shunts, respectively).

Blood Circulation↗
PubMed2000

Calculating blood flow from Doppler measurements in the systemic-to-pulmonary artery shunt after the Norwood operation: a method based on computational fluid dynamics.

Hypoplastic left heart syndrome is currently the most lethal cardiac malformation of the newborn infant. Survival following a Norwood operation depends on the balance between systemic and pulmonary blood flow, which is highly dependent on the fluid dynamics through the interposition shunt between the two circulations. We used computational fluid dynamic (CFD) models to determine the velocity profile in a systemic-to-pulmonary artery shunt and suggested a simplified method of calculating the blood flow in the shunt based on Doppler measurements. CFD models of systemic-to-pulmonary shunts based on the finite element method were studied. The size of the shunt has been varied from 3 to 5 mm. Velocity profiles at proximal and distal positions were evaluated and correlations between maximum and mean spatial velocity were found. Twenty-one Doppler measurements in the proximal and distal part of the shunt were obtained from six patients with hypoplastic left heart syndrome. Combining Doppler velocities and CFD velocity profiles, blood flow rate in the shunt was calculated. Flow rate evaluated from aortic Doppler and oxygen saturation measurements were performed for comparison. Results showed that proximal shunt Doppler velocities were always greater than the correspondent distal ones (ratio equal to 1.15 +/- 0.11). CFD models showed a similar behaviour (ratio equal to 1.21 +/- 0.03). CFD models gave a V(mean)/V(max) ratio of 0. 480 at the proximal junction and of 0.579 at the distal one. The agreement between the flow evaluated in the proximal and distal areas of the shunt was good (0.576 +/- 0.150 vs. 0.610 +/- 0.166 l/min). Comparison of these data with saturation data and aortic Doppler measurements correlate less well (0.593 +/- 0.156 vs. 1.023 +/- 0.493 l/min). A formula easily to quantify shunt flow rate is proposed. This could be used to evaluate the effects of different therapeutic and pharmacological manoeuvres in this unique circulation.

Anastomosis, Surgical↗
PubMed2000

The pumping oxygenator: design criteria and first in vitro results.

A new project is presented, the pumping oxygenator, functionally integrating pulsatile pumping and blood oxygenation in a single device. Solid, semipermeable silicone membranes allow gas exchange and simultaneously transfer energy from pressurized gas to blood thanks to their distensibility and to inlet and outlet 1-way valves. Two small-sized (1 m2 exchange surface area) prototypes were designed, constructed, hydraulically characterized, and subjected to gas transfer evaluation tests. Blood flow rates (Q(b)) up to 1,250 ml/min were obtained with 30 mm Hg static preload and 130 mm Hg afterload with 0.7 m upstream and 2.1 m downstream 3/8 inch pipes. Physiological oxygen transfer (VO2 = 5 ml/dl, ml of transferred O2/dl of treated blood) was delivered at Q(b) < 900 ml/min, about 4 ml/dl at Q(b) = 1,250 ml/min. VO2 also was significantly increased by increasing percent systolic time. CO2 transfer decreased regularly with increasing Q(b) from VCO2 = 4.8 ml/dl at Q(b) = 400 ml/min to VCO 2 = 2.1 ml/dl at Q(b) = 1,250 ml/min. The results confirm the possibility of integrating oxygenation and pulsatile pumping. The pumping oxygenator represents a promising project deserving further improvements.

Blood Flow Velocity↗
PubMed2000

Scaling approach to study the changes through the gestation of human fetal cardiac and circulatory behaviors.

During human gestation, fetal body size increases considerably and important transformations occur to hemodynamics of the cardiovascular system of the fetus. Vascular compliances and resistances as well as the cardiac function show important changes. In order to investigate these modifications, a mathematical approach based on scaling techniques was developed. Vascular and cardiac parameters of the human fetus were related by allometric equations to the anatomical dimensions of vessels that, in turn, depend on the fetal body weight and the gestational age. A scaling factor (b) was identified for each parameter under study: vascular resistances and flow inertances decrease with gestational age (b= -0.33 for flow inertances) whereas vascular compliances remarkably increase (b= 1.33). Scaling factors were also adopted for the fetal cardiac parameters, according to experimental data on the development of fetal myocardium. Parameter values calculated for each week of the last trimester of the fetal gestation, were tested using a mathematical lumped parameter model, previously developed for a human fetus near the term of the gestation. The validation of the scaling method adopted for the parameters was performed by comparing the results of the simulations with a group of data obtained by Doppler velocimetry at different stages of fetal normal gestation. The adopted allometric equations were appropriate in describing the development of the human fetal circulatory system. The ductus venosus, the ductus arteriosus, and the foramen ovale, that conclude their function at the birth moment, as well as the lungs and the brain, do not follow the general growth rate and require different scaling factors.

Biomedical Engineering↗
PubMed1999

The hemodynamic effects of double-orifice valve repair for mitral regurgitation: a 3D computational model.

OBJECTIVES: A 3D computational model has been implemented for the evaluation of the hemodynamics of the double orifice repair. Critical issues for surgical decision making and echo-Doppler evaluation of the results of the procedure are investigated. METHODS: A parametric 3D computational model of the double-orifice mitral valve based on the finite elements model has been constructed from clinical data. Nine different geometries were investigated, corresponding to three total inflow areas (1.5, 2.25 and 3 cm2) and to three orifice configurations (two equal orifices, two orifices of different areas, i.e. one twice as much the other one, and a single orifice). The simulations were performed in transit; the fluid was initially quiescent and was accelerated to the maximum flow rate with a cubic function. For each case, some characteristic values of velocity and pressure were determined: velocities were calculated downstream of each orifice, at the centre of it (Vcen1, Vcen2). The maximum velocity was also determined for each orifice (Vmax1, Vmax2). Maximum pressure drops (deltap(max)) across the valve were compared with the estimations (deltap(Bernoulli)) based on the Bernoulli formula (4 V2). RESULTS: In each simulation, no notable difference was observed between Vcen1 and Vcen2, and between Vmax1 and Vmax2, regardless of the valve configuration. Maximum velocity and deltap(max) were related to the total orifice area and were not influenced by the orifice configuration. Deltap(Bernoulli) calculated with Vmax was well correlated with the deltap(max) obtained throughout the simulations (y = 0.9126x + 0.3464, r = 0.996); on the contrary the pressure drops estimated using Vcen underestimated (y = 0.6757x + 0.3073, r = 0.999) the actual pressure drops. CONCLUSIONS: The hemodynamic behaviour of a double orifice mitral valve does not differ from that of a physiological valve of same total area: pressure drops and flow velocity across the valve are not influenced by the configuration of the valve. Echo Doppler estimation of the maximum velocities is a reliable method for the calculation of pressure gradients across the repaired valve.

Blood Flow Velocity↗
PubMed1999

Computational fluid dynamic simulations of cavopulmonary connections with an extracardiac lateral conduit.

Complex congenital heart defects due to the absence of a ventricular chamber can often be treated by the Fontan surgical procedure. The objective of this work was to quantify the haemodynamics in the Fontan operation (cavopulmonary connection) with extracardiac lateral conduit. Four different models based on the finite element method were constructed with different lengths of inferior anastomosis (range 18-25 mm) and inclinations of the conduit (33 and 47.5 degrees). Mass conservation and Navier-Stokes equations were solved by means of the FIDAP code, based on the finite element method. The left-to-right pulmonary flow ratio and percentage inferior caval blood to the left lung were the highest with the smallest anastomosis and highest inclination: 1.35 and 83.26%, respectively. Dissipated power percentage was higher with the largest anastomosis than with the smallest (19.4 vs 15.8%). It was concluded that, when performing a total cavopulmonary connection, an extracardiac lateral conduit: (i) diverts more flow to the left lung, and (ii) shows higher energy losses when compared with a connection with intra-atrial tunnel. This study could be useful to evaluate the incidence of pulmonary arteriovenous malformations.

Arteriovenous Shunt, Surgical↗
PubMed1999

Computational fluid dynamic and magnetic resonance analyses of flow distribution between the lungs after total cavopulmonary connection.

Total cavopulmonary connection is a surgical procedure adopted to treat complex congenital malformations of the right heart. It consists basically in a connection of both venae cavae directly to the right pulmonary artery. In this paper a three-dimensional model of this connection is presented, which is based on in vivo measurements performed by means of magnetic resonance. The model was developed by means of computational fluid dynamics techniques, namely the finite element method. The aim of this study was to verify the capability of such a model to predict the distribution of the blood flow into the pulmonary arteries, by comparison with in vivo velocity measurements. Different simulations were performed on a single clinical case to test the sensitivity of the model to different boundary conditions, in terms of inlet velocity profiles as well as outlet pressure levels. Results showed that the flow distribution between the lungs is slightly affected by the shape of inlet velocity profiles, whereas it is influenced by different pressure levels to a greater extent.

Adolescent↗
PubMed1998

Blood flow through the ductus venosus in human fetus: calculation using Doppler velocimetry and computational findings.

The present study was performed to assess a new method to calculate the blood flow rate through the ductus venosus (DV) in normal human fetuses using available echo-Doppler data. Color Doppler sonographic unit was used to study DV flow in 26 normal fetuses between 20 and 36 wk of gestation. Maximal velocity flow tracings and vessel diameters were obtained at the isthmic and the outlet portion of the DV. Time-averaged velocities in the DV were measured from the recorded tracings. The velocity distribution in the two investigated cross-sectional areas of the DV was evaluated by means of computational model simulations and the velocity shape coefficients h(in) and h(out), (i.e., the ratios between the maximal and mean spatial velocities) were calculated as a function of vessel geometry. These values allowed us to convert maximal Doppler velocities into mean spatial velocities for each fetus. Blood flow rate was evaluated both at the isthmus and at the outlet of the vessel by means of two formulae based on the ultrasonographic measures and the results of the computational model. The value of the DV blood flow rate was calculated as the average between the results provided by the two formulae. The velocity distributions both at the isthmus (h(in) = 0.677 +/- 0.040) and the outlet (h(out) = 0.374 +/- 0.072) of the ductus are skewed toward the inner wall. Ductus geometry, i.e., the isthmic/outlet diameter ratio, affects the shape of the velocity profiles in the vessel, particularly that at the outlet. The coefficients of variation for repeated measurements of the ductal diameters were 9.5 +/- 7.7% and 6.7 +/- 4.9% at the isthmus and the outlet, respectively. The two formulae gave values statistically identical for the time-average blood flow rate (36.3 +/- 22.1 vs. 39.4 +/- 24.0 mL/min; R = 0.946, p = NS). The mean percent difference between the results of the two formulae was 7.1%. Thus, in human fetuses, the use of the two formulae based on both Doppler data and computational model simulations makes it possible to calculate the ductal flow rate. When the difference between the calculations of the two formulae exceeds the 30% of their average value, it is convenient to adopt the flow rate value calculated at the isthmus instead of the average of the two measures. The measurements at the outlet of the ductus were more difficult to obtain, and the spatial velocity profile at the outlet depends more on the DV anatomy.

Blood Flow Velocity↗
PubMed1998

Biomechanics of abdominal aortic aneurysm in the presence of endoluminal thrombus: experimental characterisation and structural static computational analysis.

OBJECTIVES: To evaluate the role played by biomechanical and geometrical parameters of endoluminal thrombus and of aortic wall on abdominal aortic aneurysm (AAA) behaviour. MATERIALS AND METHODS: Tensile tests on 21 AAA thrombus specimens from six patients undergoing AAA repair and numerical evaluation of aneurysmal aortic wall stress and strain distribution. Parameters of the analysis were lumen eccentricity, thrombus Young's Modulus and the aortic wall constitutive equation. RESULTS: There was a linear stress/strain for all the thrombus specimens. The numerical analyses show the mechanical behaviour of AAA as a function of lumen eccentricity and biomechanical parameters. CONCLUSIONS: Well organised thrombus reduces the effect of the pressure load on the aneurysmal aortic wall.

Aged↗
PubMed1998

Dilatation of the ductus venosus in human fetuses: ultrasonographic evidence and mathematical modeling.

Autonomic regulation of blood flow through the fetal ductus venosus has been suggested, but the existence of a sphincter at the ductal entrance in human fetuses has yet to be established. In this paper two cases of apparent ductus venosus dilatation in two growth-restricted human fetuses are reported. Prolonged ultrasonographic analysis (45 min) showed rapid and substantial changes (>80%) of ductal diameters. Pulsed Doppler analysis was used to investigate flow velocity in the ductus venosus and umbilical vein for both normal and dilated conditions. Dilated conditions caused manifest modifications of velocity tracings. Systolic peak velocity in the ductus did not change visibly, whereas velocity at the atrial contraction showed evident reduction; consequently, pulsatility indexes increased. Furthermore, the umbilical vein presented flow velocity pulsations. The mean blood flow rate through the ductus seemed to increase substantially (>70%) for high dilatation. To investigate these findings further, we performed simulations of ductal dilatation by means of a lumped-parameter mathematical model of the human fetal circulation. Model results agreed with clinical evidence and confirmed the relationship between ductal dilatation and the observed velocity alterations. Simulated systolic peak velocity slightly increased for small dilatation (<30%), whereas atrial velocity was reduced when the ductus dilated. Furthermore, the model indicated that umbilical venous pressure decreases for increasing dilatation, whereas no change occurs in the central venous pressure. The present results seem to indicate the presence of active dilatation of the ductus venosus in human fetuses.

Female↗
PubMed1998

Optimisation of a stentless valve prosthesis based on an analytic parametric model of the aortic valve.

An analytical mathematical model of a stentless aortic valve has been implemented. The valve is characterised by a trileaflet geometry, cylindrical leaflets; the aortic root is schematised by a conical surface which includes the leaflet attachments. The model is defined through six geometric parameters: the base radius, the valve height, the commissure radius, the leaflet radial, circumferential and attachment line lengths. Five performance indexes have been used to optimise the valve geometry, namely: the systolic area, the leaflet circumferential stress in diastole, the leaflet bending strain in systole and two bending angles related to the rotation of the leaflets from the diastolic to the systolic configuration. The sensitivity analysis is carried out which can identify the influence of each geometric parameter on the performance indexes adopted for the optimum valve design. The analysis of the results provides the geometric configuration which optimises the overall function of the valve throughout the cardiac cycle.

Aortic Valve↗
PubMed1997

Assessment of the influence of the compliant aortic root on aortic valve mechanics by means of a geometrical model.

In recent years several researchers have suggested that the changes in the geometry and angular dimensions of the aortic root which occur during the cardiac cycle are functional to the optimisation of aortic valve function, both in terms of diminishing leaflet stresses and of fluid-dynamic behaviour. The paper presents an analytical parametric model of the aortic valve which includes the aortic root movement. The indexes used to evaluate the valve behaviour are the circumferential membrane stress and the stress at the free edge of the leaflet, the index of bending strain, the bending of the leaflet at the line attachment in the radial and circumferential directions and the shape of the conduit formed by the leaflets during systole. In order to evaluate the role of geometric changes in valve performance, two control cases were considered, with different reference geometric configuration, where the movement of the aortic root was ignored. The results obtained appear consistent with physiological data, especially with regard to the late diastolic phase and the early ejection phase, and put in evidence the role of the aortic root movement in the improvement of valve behaviour.

Aorta↗
PubMed1997

Mathematical modelling of the human foetal cardiovascular system based on Doppler ultrasound data.

A lumped parameter model of the human foetal circulation primarily based on blood velocity data derived from the Doppler analysis was developed in this study. It consists of two major parts, the heart and the foetal vascular circulation. The heart model accounts for both ventricular and atrial contractility. The circulation was divided into 19 compliant vascular compartments in order to describe all of the clinically monitored sites. The model parameters refer to the final gestation period and were derived either from literature on foetal sheep circulation or from anatomical dimension monitoring of the human foetus. No control mechanism is incorporated into the model. The model was validated by comparing several index values of simulated velocity curves to those of the experimental Doppler waveforms. The mean and maximum percentual errors in the estimation of the experimental results by the model are 7.7% and 20.1%, respectively. Velocity and pressure tracings of the foetal circulation were investigated, as well as regional blood flow rate distribution.

Cardiovascular Physiological Phenomena↗
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↗