Giacomo Benedetto - Academia.edu (original) (raw)

Papers by Giacomo Benedetto

Research paper thumbnail of Biomechanics of actin filaments: a computational multi-level study

Journal of biomechanics

The actin microfilament (F-actin) is a structural and functional component of the cell cytoskelet... more The actin microfilament (F-actin) is a structural and functional component of the cell cytoskeleton. Notwithstanding the primary role it plays for the mechanics of the cell, the mechanical behaviour of F-actin is still not totally explored. In particular, the relationship between the mechanics of F-actin and its molecular architecture is not completely understood. In this study, the mechanical properties of F-actin were related to the molecular topology of its building monomers (G-actin) by employing a computational multi-level approach. F-actins with lengths up to 500 nm were modelled and characterized, using a combination of equilibrium molecular dynamics (MD) simulations and normal mode analysis (NMA). MD simulations were performed to analyze the molecular rearrangements of G-actin in physiological conditions; NMA was applied to compute the macroscopic properties of F-actin from its vibrational modes of motion. Results from this multi-level approach showed that bending stiffness,...

Research paper thumbnail of Sports, dietary habits, self-perception and BMI in a sample of young Italian athletes

Sport Sciences for …, 2011

The concept of health closely associates absence of disease and a state of overall well-being (ph... more The concept of health closely associates absence of disease and a state of overall well-being (physical, mental, social). This state can be achieved by a healthy dietary habit and by engagement in physical activity. Despite this, children and teenagers are ...

Research paper thumbnail of Biomechanics of actin filaments: A computational multi-level study

Journal of Biomechanics, 2011

The actin microfilament (F-actin) is a structural and functional component of the cell cytoskelet... more The actin microfilament (F-actin) is a structural and functional component of the cell cytoskeleton. Notwithstanding the primary role it plays for the mechanics of the cell, the mechanical behaviour of F-actin is still not totally explored. In particular, the relationship between the mechanics of F-actin and its molecular architecture is not completely understood. In this study, the mechanical properties of F-actin were related to the molecular topology of its building monomers (G-actin) by employing a computational multi-level approach. F-actins with lengths up to 500 nm were modelled and characterized, using a combination of equilibrium molecular dynamics (MD) simulations and normal mode analysis (NMA). MD simulations were performed to analyze the molecular rearrangements of G-actin in physiological conditions; NMA was applied to compute the macroscopic properties of F-actin from its vibrational modes of motion. Results from this multi-level approach showed that bending stiffness,...

Research paper thumbnail of A parametric model of cannula to investigate hemolysis by using CFD

Proceedings of the 22nd Annual International Conference of the IEEE Engineering in Medicine and Biology Society (Cat. No.00CH37143), 2000

Abstract Extracorporeal circulation and more recently ventricular assistance are used in cardiova... more Abstract Extracorporeal circulation and more recently ventricular assistance are used in cardiovascular surgery helping the success of complex intervention; however hemolytic problems are provided by the use of a great amount of external surfaces and the scheme ...

Research paper thumbnail of An agent-based system model to support cardiac tissue engineering: preliminary results

Research paper thumbnail of Sports, dietary habits, self-perception and BMI in a sample of young Italian athletes

Sport Sciences for Health, 2011

The concept of health closely associates absence of disease and a state of overall well-being (ph... more The concept of health closely associates absence of disease and a state of overall well-being (physical, mental, social). This state can be achieved by a healthy dietary habit and by engagement in physical activity. Despite this, children and teenagers are increasingly becoming overweight and obese. The aim of this study was to evaluate whether different exercise habits, dietary habits and self perceptions could influence anthropometric characteristics, in particular the body mass index (BMI), in selected participants in high-level sport aged between 10 and 18 years. An anonymous questionnaire consisting of 20 multiple choice questions was submitted to 1,096 participants (757 males and 339 females) undergoing the preparticipation physical examination that is necessary before taking part in high-level sport in Italy. A descriptive analysis was developed based on relative frequencies because of the qualitative nature of most of the questions with the aim of determining the influence on BMI of: each type of sport; training hours; training hours and type of sport; individual diet (carbohydrates and proteins); habit with regard to breakfast; hours of training and diet; and psychological motivations for eating. Only the combined action of a proper dietary habit and an adequate number of training hours resulted in a radical shift towards an optimal BMI. Moreover, a "negative" psychological motivation for eating possibly influenced the distribution of BMI even in athletes who followed a correct dietary and training lifestyle.

Research paper thumbnail of Temporal segmentation and multiple-source analysis of short-latency median nerve SEPs

Journal of Medical Engineering & Technology, 1995

Short-latency (10-50 ms) median nerve somatosensory evoked potentials (SEPs) from four normal sub... more Short-latency (10-50 ms) median nerve somatosensory evoked potentials (SEPs) from four normal subjects were analysed by means of temporal segmentation techniques and source derivation methods. In each case the responses were recorded using 32 electrodes. Dipolar optimization was carried out with a time-varying technique, using three different approaches: regional source estimation, spherical source estimation (one radial and one tangential component), and multiple dipolar approach. This was to assess the relative influence on the dipolar solution of the different optimization techniques. The effect of the different number of channels in the estimation procedures has been also investigated. The methods of optimization are crucial, particularly for the orientation of P22. In all cases the source location estimated with the 32-electrode montage was shifted towards the centre of the spheres.

Research paper thumbnail of Biomechanics of actin filaments: A computational multi-level study

Journal of Biomechanics, 2011

The actin microfilament (F-actin) is a structural and functional component of the cell cytoskelet... more The actin microfilament (F-actin) is a structural and functional component of the cell cytoskeleton. Notwithstanding the primary role it plays for the mechanics of the cell, the mechanical behaviour of F-actin is still not totally explored. In particular, the relationship between the mechanics of F-actin and its molecular architecture is not completely understood. In this study, the mechanical properties of F-actin were related to the molecular topology of its building monomers (G-actin) by employing a computational multi-level approach. F-actins with lengths up to 500 nm were modelled and characterized, using a combination of equilibrium molecular dynamics (MD) simulations and normal mode analysis (NMA). MD simulations were performed to analyze the molecular rearrangements of G-actin in physiological conditions; NMA was applied to compute the macroscopic properties of F-actin from its vibrational modes of motion. Results from this multi-level approach showed that bending stiffness, bending modulus and persistence length are independent from the length of F-actin. On the contrary, the orientations and motions of selected groups of residues of G-actin play a primary role in determining the filament flexibility. In conclusion, this study (i) demonstrated that a combined computational approach of MD and NMA allows to investigate the biomechanics of F-actin taking into account the molecular topology of the filament (i.e., the molecular conformations of G-actin) and (ii) that this can be done using only crystallographic G-actin, without the need of introducing experimental parameters nor of reducing the number of residues.

Research paper thumbnail of Computational model of the fluid dynamics of a cannula inserted in a vessel: incidence of the presence of side holes in blood flow

Journal of Biomechanics, 2002

Vascular access methods, performed by the insertion of cannulae into vessels, may disturb the phy... more Vascular access methods, performed by the insertion of cannulae into vessels, may disturb the physiological flow of blood, giving rise to non-physiological pressure variations and shear stresses. To date, the hydrodynamic behaviour of the cannulae has been evaluated comparing their pressure loss-flow rate relationships, as obtained from in vitro experiments using a monodimensional approach; this methodology neither furnish information about the local fluid dynamics nor the established flow field in specific clinical work conditions. Since the shear stress is a critical factor in the design of artificial circulatory devices, more knowledge should be necessary about the local values assumed by the haemodynamic parameters during cannulation. An alternative way to investigate the fluid dynamic as accurately as possible is given by numeric studies. A 3D model of cannula concentrically placed in a rigid wall vessel is presented, with the finite element methodology used to numerically simulate the steady-state flow field in two different venous cannulation case studies, with two cannulae having a central hole and two or four side holes, respectively, with the same boundary conditions. Lower velocity and shear stress peak values have been computed for the model with four side holes upstream of the central hole, in the region of the cannula where the inlet flows meet and towards cannula's outlet, due to the increased flow symmetry and inlet area with respect to the model with two side holes. Starting from the investigation of different cannula designs, numerically assessing the local fluid dynamics, indications can be drawn to support both the design phase and the device optimal clinical use, in order to limit risks of biomechanical origin. Thus the presence of four side holes implied, as a consequence of the greater inlet area and of the increased symmetry, a less disturbed blood flow, together with reduced shear stress values. Furthermore, results show that the numerical simulations furnished useful informations on the interaction between vessel and cannula, e.g. on the fluid dynamics establishing in the free luminal space left, in the vessel, by the inserted cannula.

Research paper thumbnail of Temporal segmentation and multiple-source analysis of short-latency median nerve SEPs

Journal of Medical Engineering & Technology, 1995

Short-latency (10-50 ms) median nerve somatosensory evoked potentials (SEPs) from four normal sub... more Short-latency (10-50 ms) median nerve somatosensory evoked potentials (SEPs) from four normal subjects were analysed by means of temporal segmentation techniques and source derivation methods. In each case the responses were recorded using 32 electrodes. Dipolar optimization was carried out with a time-varying technique, using three different approaches: regional source estimation, spherical source estimation (one radial and one tangential component), and multiple dipolar approach. This was to assess the relative influence on the dipolar solution of the different optimization techniques. The effect of the different number of channels in the estimation procedures has been also investigated. The methods of optimization are crucial, particularly for the orientation of P22. In all cases the source location estimated with the 32-electrode montage was shifted towards the centre of the spheres.

Research paper thumbnail of Dynamics of blood electrolytes in repeated hyper- and/or hypoglycaemic events in patients with type 1 diabetes

Diabetologia, 2011

Aims/hypothesis Electrolyte disturbances are well-known consequences of the diabetic pathology. H... more Aims/hypothesis Electrolyte disturbances are well-known consequences of the diabetic pathology. However, less is known about the cumulative effects of repeated changes in glycaemia, a characteristic of diabetes, on the electrolyte balance. We therefore investigated the ionic profiles of patients with type 1 diabetes during consecutive hyper-and/or hypoglycaemic events using the glucose clamp. Methods In protocol 1, two successive hyperglycaemic excursions to 18 mmol/l were induced; in protocol 2, a hypoglycaemic excursion (2.5 mmol/l) was followed by a hyperglycaemic excursion (12 mmol/l) and another hypoglycaemic episode (3.0 mmol/l). Results Blood osmolarity increased during hyperglycaemia and was unaffected by hypoglycaemia. Hyperglycaemia induced decreases in plasma Na + Cl − and Ca 2+ concentrations and increases in K + concentrations. These changes were faithfully reproduced during a second hyperglycaemia. Hypoglycaemia provoked rapid and rapidly reversible increases in Na + , Cl − and Ca 2+. In sharp contrast, K + levels displayed a rapid and substantial fall from which they did not fully recover even 2 h after the re-establishment of euglycaemia. A second hypoglycaemia caused an additional fall. Conclusions/interpretation Repeated hyperglycaemia events do not lead to any cumulative effects on blood electrolytes. However, repeated hypoglycaemias are cumulative with respect to K + levels due to a very slow recovery following hypoglycaemia. These results suggest that recurring hypoglycaemic events may lead to progressively lower K + levels despite rapid re-establishment of euglycaemia. This warrants close monitoring of plasma K + levels combined with continuous glucose monitoring particularly in patients under intensive insulin therapy who are subject to repeated hypoglycaemic episodes.

Research paper thumbnail of Identification of a model of non-esterified fatty acids dynamics through genetic algorithms: The case of women with a history of gestational diabetes

Computers in Biology and Medicine, 2011

Elevation in non-esterified fatty acids (NEFA) has been shown to modulate insulin secretion and i... more Elevation in non-esterified fatty acids (NEFA) has been shown to modulate insulin secretion and it is considered as a risk factor for the development of type 2 diabetes. Here we present a method that complements a mathematical model of NEFA kinetics with genetic algorithms for model identification. The complemented strategy allowed to assess parameters of NEFA kinetics and to get insight into their relationship with insulin during oral glucose tolerance tests in women with former gestational diabetes: (i) providing a reliable estimation of the model parameters, (ii) assuring the usability of the model, and (iii) promoting and facilitating its application in a clinical context.

Research paper thumbnail of A parametric model of cannula to investigate hemolysis by using CFD

… in Medicine and …, 2000

Extracorporeal circulation and more recently ventricular assistance are used in cardiovascular su... more Extracorporeal circulation and more recently ventricular assistance are used in cardiovascular surgery helping the success of complex intervention; however hemolytic problems are provided by the use of a great amount of external surfaces and the scheme ...

Research paper thumbnail of Computational model of the fluid dynamics of a cannula inserted in a vessel: incidence of the presence of side holes in blood flow

Journal of …, 2002

Vascular access methods, performed by the insertion of cannulae into vessels, may disturb the phy... more Vascular access methods, performed by the insertion of cannulae into vessels, may disturb the physiological flow of blood, giving rise to non-physiological pressure variations and shear stresses. To date, the hydrodynamic behaviour of the cannulae has been evaluated ...

Research paper thumbnail of A novel formulation for blood trauma prediction by a modified power-law mathematical model

Biomechanics and Modeling in Mechanobiology, 2005

With the increasing use of artificial organs, blood damage has been raising ever more clinical co... more With the increasing use of artificial organs, blood damage has been raising ever more clinical concern. Blood trauma is in fact a major complication resulting from the implantation of medical devices and the use of life support apparatuses. Red blood cells damage predictive models furnish critical information on both the design and the evaluation of artificial organs, because their correct usage and implementation are thought to provide clear and rational guidance for the improvement of safety and efficacy. The currently adopted power-law shear-induced haemolysis prediction model lacks sensitivity with respect to the cumulative effect of previously applied stress magnitudes. An alternative model is proposed where a mechanical quantity was defined, able to describe the blood damage sustained by red cells under unsteady stress conditions, taking into account the load history. The proposed formulation predicted the same trend as the available experimental data. The obtained results have to be considered a preliminary validation of the basic hypothesis of this modified red blood cell damage prediction model. To date, the necessity to design further experiments to validate the proposed damage function clashes with the limitations inherent to current systems to get the time-varying shear stress completely under control.

Research paper thumbnail of The Power-law Mathematical Model for Blood Damage Prediction: Analytical Developments and Physical Inconsistencies

Artificial Organs, 2004

Blood trauma caused by medical devices is a major concern. Complications following the implantati... more Blood trauma caused by medical devices is a major concern. Complications following the implantation/ application of devices such as prosthetic heart valves, cannulae, blood pumps, tubing, and throttles lead to sublethal and lethal damage to platelets and erythrocytes. This damage is provided by the alterations in fluid dynamics, providing a mechanical load on the blood corpuscle's membrane by means of the shear stress. An appropriate quantification of the shear-induced hemolysis of artificial organs is thought to be useful in the design and development of such devices in order to minimize device-induced blood trauma. To date, a power-law mathematical relationship using the time of exposure of a blood corpuscle to a certain mechanical load and the shear stress itself (derived under the peculiar condition of uniform shear stress) has served as a basic model for the estimation of the damage to blood, investigated by means of numerical and/or experimental

Research paper thumbnail of Predicting the Metabolic Condition After Gestational Diabetes Mellitus from Oral Glucose Tolerance Test Curves Shape

Annals of Biomedical Engineering, 2014

ABSTRACT The objective of this feasibility study is to predict the metabolic condition in women w... more ABSTRACT The objective of this feasibility study is to predict the metabolic condition in women with a history of gestational diabetes mellitus (GDM) from the shape of oral glucose tolerance test (OGTT) data. The rationale for this approach is that the evolution to a metabolic condition could be traceable in the shape of OGTT curves. 3-h OGTT data of 136 women with follow up, for a total of 401 OGTTs were analyzed. Subjects were classified as having normal (NGT) or non-normal glucose tolerance (NON-NGT), according to the American Diabetes Association criteria. The measured glucose, insulin, C-peptide data and combination of them were used to build up NGT and NON-NGT reference curves. Similarity between reference and individual OGTT-based curves was calculated using the Kullback-Leibler divergence. Our findings suggest that the shape of OGTT curves (1) contains information on the evolution to disease and (2) could be a reliable indicator to predict with high sensitivity (75%) and high specificity (69%) the metabolic condition of women with a history of GDM. In the future, the proposed shape-based prediction could be easily translated to the clinical practice, because it does not require the intervention of an operator specifically trained, thus facilitating its application in a clinical setting and ultimately empowering risk estimation, by improving/complementing the information which is currently adopted for risk stratification after pregnancy with GDM.

Research paper thumbnail of Identification of a model of non-esterified fatty acids dynamics through genetic algorithms: The case of women with a history of gestational diabetes

Computers in Biology and Medicine, 2011

Elevation in non-esterified fatty acids (NEFA) has been shown to modulate insulin secretion and i... more Elevation in non-esterified fatty acids (NEFA) has been shown to modulate insulin secretion and it is considered as a risk factor for the development of type 2 diabetes. Here we present a method that complements a mathematical model of NEFA kinetics with genetic algorithms for model identification. The complemented strategy allowed to assess parameters of NEFA kinetics and to get insight into their relationship with insulin during oral glucose tolerance tests in women with former gestational diabetes: (i) providing a reliable estimation of the model parameters, (ii) assuring the usability of the model, and (iii) promoting and facilitating its application in a clinical context.

Research paper thumbnail of Biomechanics of actin filaments: a computational multi-level study

Journal of biomechanics

The actin microfilament (F-actin) is a structural and functional component of the cell cytoskelet... more The actin microfilament (F-actin) is a structural and functional component of the cell cytoskeleton. Notwithstanding the primary role it plays for the mechanics of the cell, the mechanical behaviour of F-actin is still not totally explored. In particular, the relationship between the mechanics of F-actin and its molecular architecture is not completely understood. In this study, the mechanical properties of F-actin were related to the molecular topology of its building monomers (G-actin) by employing a computational multi-level approach. F-actins with lengths up to 500 nm were modelled and characterized, using a combination of equilibrium molecular dynamics (MD) simulations and normal mode analysis (NMA). MD simulations were performed to analyze the molecular rearrangements of G-actin in physiological conditions; NMA was applied to compute the macroscopic properties of F-actin from its vibrational modes of motion. Results from this multi-level approach showed that bending stiffness,...

Research paper thumbnail of Sports, dietary habits, self-perception and BMI in a sample of young Italian athletes

Sport Sciences for …, 2011

The concept of health closely associates absence of disease and a state of overall well-being (ph... more The concept of health closely associates absence of disease and a state of overall well-being (physical, mental, social). This state can be achieved by a healthy dietary habit and by engagement in physical activity. Despite this, children and teenagers are ...

Research paper thumbnail of Biomechanics of actin filaments: A computational multi-level study

Journal of Biomechanics, 2011

The actin microfilament (F-actin) is a structural and functional component of the cell cytoskelet... more The actin microfilament (F-actin) is a structural and functional component of the cell cytoskeleton. Notwithstanding the primary role it plays for the mechanics of the cell, the mechanical behaviour of F-actin is still not totally explored. In particular, the relationship between the mechanics of F-actin and its molecular architecture is not completely understood. In this study, the mechanical properties of F-actin were related to the molecular topology of its building monomers (G-actin) by employing a computational multi-level approach. F-actins with lengths up to 500 nm were modelled and characterized, using a combination of equilibrium molecular dynamics (MD) simulations and normal mode analysis (NMA). MD simulations were performed to analyze the molecular rearrangements of G-actin in physiological conditions; NMA was applied to compute the macroscopic properties of F-actin from its vibrational modes of motion. Results from this multi-level approach showed that bending stiffness,...

Research paper thumbnail of A parametric model of cannula to investigate hemolysis by using CFD

Proceedings of the 22nd Annual International Conference of the IEEE Engineering in Medicine and Biology Society (Cat. No.00CH37143), 2000

Abstract Extracorporeal circulation and more recently ventricular assistance are used in cardiova... more Abstract Extracorporeal circulation and more recently ventricular assistance are used in cardiovascular surgery helping the success of complex intervention; however hemolytic problems are provided by the use of a great amount of external surfaces and the scheme ...

Research paper thumbnail of An agent-based system model to support cardiac tissue engineering: preliminary results

Research paper thumbnail of Sports, dietary habits, self-perception and BMI in a sample of young Italian athletes

Sport Sciences for Health, 2011

The concept of health closely associates absence of disease and a state of overall well-being (ph... more The concept of health closely associates absence of disease and a state of overall well-being (physical, mental, social). This state can be achieved by a healthy dietary habit and by engagement in physical activity. Despite this, children and teenagers are increasingly becoming overweight and obese. The aim of this study was to evaluate whether different exercise habits, dietary habits and self perceptions could influence anthropometric characteristics, in particular the body mass index (BMI), in selected participants in high-level sport aged between 10 and 18 years. An anonymous questionnaire consisting of 20 multiple choice questions was submitted to 1,096 participants (757 males and 339 females) undergoing the preparticipation physical examination that is necessary before taking part in high-level sport in Italy. A descriptive analysis was developed based on relative frequencies because of the qualitative nature of most of the questions with the aim of determining the influence on BMI of: each type of sport; training hours; training hours and type of sport; individual diet (carbohydrates and proteins); habit with regard to breakfast; hours of training and diet; and psychological motivations for eating. Only the combined action of a proper dietary habit and an adequate number of training hours resulted in a radical shift towards an optimal BMI. Moreover, a "negative" psychological motivation for eating possibly influenced the distribution of BMI even in athletes who followed a correct dietary and training lifestyle.

Research paper thumbnail of Temporal segmentation and multiple-source analysis of short-latency median nerve SEPs

Journal of Medical Engineering & Technology, 1995

Short-latency (10-50 ms) median nerve somatosensory evoked potentials (SEPs) from four normal sub... more Short-latency (10-50 ms) median nerve somatosensory evoked potentials (SEPs) from four normal subjects were analysed by means of temporal segmentation techniques and source derivation methods. In each case the responses were recorded using 32 electrodes. Dipolar optimization was carried out with a time-varying technique, using three different approaches: regional source estimation, spherical source estimation (one radial and one tangential component), and multiple dipolar approach. This was to assess the relative influence on the dipolar solution of the different optimization techniques. The effect of the different number of channels in the estimation procedures has been also investigated. The methods of optimization are crucial, particularly for the orientation of P22. In all cases the source location estimated with the 32-electrode montage was shifted towards the centre of the spheres.

Research paper thumbnail of Biomechanics of actin filaments: A computational multi-level study

Journal of Biomechanics, 2011

The actin microfilament (F-actin) is a structural and functional component of the cell cytoskelet... more The actin microfilament (F-actin) is a structural and functional component of the cell cytoskeleton. Notwithstanding the primary role it plays for the mechanics of the cell, the mechanical behaviour of F-actin is still not totally explored. In particular, the relationship between the mechanics of F-actin and its molecular architecture is not completely understood. In this study, the mechanical properties of F-actin were related to the molecular topology of its building monomers (G-actin) by employing a computational multi-level approach. F-actins with lengths up to 500 nm were modelled and characterized, using a combination of equilibrium molecular dynamics (MD) simulations and normal mode analysis (NMA). MD simulations were performed to analyze the molecular rearrangements of G-actin in physiological conditions; NMA was applied to compute the macroscopic properties of F-actin from its vibrational modes of motion. Results from this multi-level approach showed that bending stiffness, bending modulus and persistence length are independent from the length of F-actin. On the contrary, the orientations and motions of selected groups of residues of G-actin play a primary role in determining the filament flexibility. In conclusion, this study (i) demonstrated that a combined computational approach of MD and NMA allows to investigate the biomechanics of F-actin taking into account the molecular topology of the filament (i.e., the molecular conformations of G-actin) and (ii) that this can be done using only crystallographic G-actin, without the need of introducing experimental parameters nor of reducing the number of residues.

Research paper thumbnail of Computational model of the fluid dynamics of a cannula inserted in a vessel: incidence of the presence of side holes in blood flow

Journal of Biomechanics, 2002

Vascular access methods, performed by the insertion of cannulae into vessels, may disturb the phy... more Vascular access methods, performed by the insertion of cannulae into vessels, may disturb the physiological flow of blood, giving rise to non-physiological pressure variations and shear stresses. To date, the hydrodynamic behaviour of the cannulae has been evaluated comparing their pressure loss-flow rate relationships, as obtained from in vitro experiments using a monodimensional approach; this methodology neither furnish information about the local fluid dynamics nor the established flow field in specific clinical work conditions. Since the shear stress is a critical factor in the design of artificial circulatory devices, more knowledge should be necessary about the local values assumed by the haemodynamic parameters during cannulation. An alternative way to investigate the fluid dynamic as accurately as possible is given by numeric studies. A 3D model of cannula concentrically placed in a rigid wall vessel is presented, with the finite element methodology used to numerically simulate the steady-state flow field in two different venous cannulation case studies, with two cannulae having a central hole and two or four side holes, respectively, with the same boundary conditions. Lower velocity and shear stress peak values have been computed for the model with four side holes upstream of the central hole, in the region of the cannula where the inlet flows meet and towards cannula's outlet, due to the increased flow symmetry and inlet area with respect to the model with two side holes. Starting from the investigation of different cannula designs, numerically assessing the local fluid dynamics, indications can be drawn to support both the design phase and the device optimal clinical use, in order to limit risks of biomechanical origin. Thus the presence of four side holes implied, as a consequence of the greater inlet area and of the increased symmetry, a less disturbed blood flow, together with reduced shear stress values. Furthermore, results show that the numerical simulations furnished useful informations on the interaction between vessel and cannula, e.g. on the fluid dynamics establishing in the free luminal space left, in the vessel, by the inserted cannula.

Research paper thumbnail of Temporal segmentation and multiple-source analysis of short-latency median nerve SEPs

Journal of Medical Engineering & Technology, 1995

Short-latency (10-50 ms) median nerve somatosensory evoked potentials (SEPs) from four normal sub... more Short-latency (10-50 ms) median nerve somatosensory evoked potentials (SEPs) from four normal subjects were analysed by means of temporal segmentation techniques and source derivation methods. In each case the responses were recorded using 32 electrodes. Dipolar optimization was carried out with a time-varying technique, using three different approaches: regional source estimation, spherical source estimation (one radial and one tangential component), and multiple dipolar approach. This was to assess the relative influence on the dipolar solution of the different optimization techniques. The effect of the different number of channels in the estimation procedures has been also investigated. The methods of optimization are crucial, particularly for the orientation of P22. In all cases the source location estimated with the 32-electrode montage was shifted towards the centre of the spheres.

Research paper thumbnail of Dynamics of blood electrolytes in repeated hyper- and/or hypoglycaemic events in patients with type 1 diabetes

Diabetologia, 2011

Aims/hypothesis Electrolyte disturbances are well-known consequences of the diabetic pathology. H... more Aims/hypothesis Electrolyte disturbances are well-known consequences of the diabetic pathology. However, less is known about the cumulative effects of repeated changes in glycaemia, a characteristic of diabetes, on the electrolyte balance. We therefore investigated the ionic profiles of patients with type 1 diabetes during consecutive hyper-and/or hypoglycaemic events using the glucose clamp. Methods In protocol 1, two successive hyperglycaemic excursions to 18 mmol/l were induced; in protocol 2, a hypoglycaemic excursion (2.5 mmol/l) was followed by a hyperglycaemic excursion (12 mmol/l) and another hypoglycaemic episode (3.0 mmol/l). Results Blood osmolarity increased during hyperglycaemia and was unaffected by hypoglycaemia. Hyperglycaemia induced decreases in plasma Na + Cl − and Ca 2+ concentrations and increases in K + concentrations. These changes were faithfully reproduced during a second hyperglycaemia. Hypoglycaemia provoked rapid and rapidly reversible increases in Na + , Cl − and Ca 2+. In sharp contrast, K + levels displayed a rapid and substantial fall from which they did not fully recover even 2 h after the re-establishment of euglycaemia. A second hypoglycaemia caused an additional fall. Conclusions/interpretation Repeated hyperglycaemia events do not lead to any cumulative effects on blood electrolytes. However, repeated hypoglycaemias are cumulative with respect to K + levels due to a very slow recovery following hypoglycaemia. These results suggest that recurring hypoglycaemic events may lead to progressively lower K + levels despite rapid re-establishment of euglycaemia. This warrants close monitoring of plasma K + levels combined with continuous glucose monitoring particularly in patients under intensive insulin therapy who are subject to repeated hypoglycaemic episodes.

Research paper thumbnail of Identification of a model of non-esterified fatty acids dynamics through genetic algorithms: The case of women with a history of gestational diabetes

Computers in Biology and Medicine, 2011

Elevation in non-esterified fatty acids (NEFA) has been shown to modulate insulin secretion and i... more Elevation in non-esterified fatty acids (NEFA) has been shown to modulate insulin secretion and it is considered as a risk factor for the development of type 2 diabetes. Here we present a method that complements a mathematical model of NEFA kinetics with genetic algorithms for model identification. The complemented strategy allowed to assess parameters of NEFA kinetics and to get insight into their relationship with insulin during oral glucose tolerance tests in women with former gestational diabetes: (i) providing a reliable estimation of the model parameters, (ii) assuring the usability of the model, and (iii) promoting and facilitating its application in a clinical context.

Research paper thumbnail of A parametric model of cannula to investigate hemolysis by using CFD

… in Medicine and …, 2000

Extracorporeal circulation and more recently ventricular assistance are used in cardiovascular su... more Extracorporeal circulation and more recently ventricular assistance are used in cardiovascular surgery helping the success of complex intervention; however hemolytic problems are provided by the use of a great amount of external surfaces and the scheme ...

Research paper thumbnail of Computational model of the fluid dynamics of a cannula inserted in a vessel: incidence of the presence of side holes in blood flow

Journal of …, 2002

Vascular access methods, performed by the insertion of cannulae into vessels, may disturb the phy... more Vascular access methods, performed by the insertion of cannulae into vessels, may disturb the physiological flow of blood, giving rise to non-physiological pressure variations and shear stresses. To date, the hydrodynamic behaviour of the cannulae has been evaluated ...

Research paper thumbnail of A novel formulation for blood trauma prediction by a modified power-law mathematical model

Biomechanics and Modeling in Mechanobiology, 2005

With the increasing use of artificial organs, blood damage has been raising ever more clinical co... more With the increasing use of artificial organs, blood damage has been raising ever more clinical concern. Blood trauma is in fact a major complication resulting from the implantation of medical devices and the use of life support apparatuses. Red blood cells damage predictive models furnish critical information on both the design and the evaluation of artificial organs, because their correct usage and implementation are thought to provide clear and rational guidance for the improvement of safety and efficacy. The currently adopted power-law shear-induced haemolysis prediction model lacks sensitivity with respect to the cumulative effect of previously applied stress magnitudes. An alternative model is proposed where a mechanical quantity was defined, able to describe the blood damage sustained by red cells under unsteady stress conditions, taking into account the load history. The proposed formulation predicted the same trend as the available experimental data. The obtained results have to be considered a preliminary validation of the basic hypothesis of this modified red blood cell damage prediction model. To date, the necessity to design further experiments to validate the proposed damage function clashes with the limitations inherent to current systems to get the time-varying shear stress completely under control.

Research paper thumbnail of The Power-law Mathematical Model for Blood Damage Prediction: Analytical Developments and Physical Inconsistencies

Artificial Organs, 2004

Blood trauma caused by medical devices is a major concern. Complications following the implantati... more Blood trauma caused by medical devices is a major concern. Complications following the implantation/ application of devices such as prosthetic heart valves, cannulae, blood pumps, tubing, and throttles lead to sublethal and lethal damage to platelets and erythrocytes. This damage is provided by the alterations in fluid dynamics, providing a mechanical load on the blood corpuscle's membrane by means of the shear stress. An appropriate quantification of the shear-induced hemolysis of artificial organs is thought to be useful in the design and development of such devices in order to minimize device-induced blood trauma. To date, a power-law mathematical relationship using the time of exposure of a blood corpuscle to a certain mechanical load and the shear stress itself (derived under the peculiar condition of uniform shear stress) has served as a basic model for the estimation of the damage to blood, investigated by means of numerical and/or experimental

Research paper thumbnail of Predicting the Metabolic Condition After Gestational Diabetes Mellitus from Oral Glucose Tolerance Test Curves Shape

Annals of Biomedical Engineering, 2014

ABSTRACT The objective of this feasibility study is to predict the metabolic condition in women w... more ABSTRACT The objective of this feasibility study is to predict the metabolic condition in women with a history of gestational diabetes mellitus (GDM) from the shape of oral glucose tolerance test (OGTT) data. The rationale for this approach is that the evolution to a metabolic condition could be traceable in the shape of OGTT curves. 3-h OGTT data of 136 women with follow up, for a total of 401 OGTTs were analyzed. Subjects were classified as having normal (NGT) or non-normal glucose tolerance (NON-NGT), according to the American Diabetes Association criteria. The measured glucose, insulin, C-peptide data and combination of them were used to build up NGT and NON-NGT reference curves. Similarity between reference and individual OGTT-based curves was calculated using the Kullback-Leibler divergence. Our findings suggest that the shape of OGTT curves (1) contains information on the evolution to disease and (2) could be a reliable indicator to predict with high sensitivity (75%) and high specificity (69%) the metabolic condition of women with a history of GDM. In the future, the proposed shape-based prediction could be easily translated to the clinical practice, because it does not require the intervention of an operator specifically trained, thus facilitating its application in a clinical setting and ultimately empowering risk estimation, by improving/complementing the information which is currently adopted for risk stratification after pregnancy with GDM.

Research paper thumbnail of Identification of a model of non-esterified fatty acids dynamics through genetic algorithms: The case of women with a history of gestational diabetes

Computers in Biology and Medicine, 2011

Elevation in non-esterified fatty acids (NEFA) has been shown to modulate insulin secretion and i... more Elevation in non-esterified fatty acids (NEFA) has been shown to modulate insulin secretion and it is considered as a risk factor for the development of type 2 diabetes. Here we present a method that complements a mathematical model of NEFA kinetics with genetic algorithms for model identification. The complemented strategy allowed to assess parameters of NEFA kinetics and to get insight into their relationship with insulin during oral glucose tolerance tests in women with former gestational diabetes: (i) providing a reliable estimation of the model parameters, (ii) assuring the usability of the model, and (iii) promoting and facilitating its application in a clinical context.