1,721,500 research outputs found
Human atrial cell models to analyse haemodialysis-related effects on cardiac electrophysiology: Work in progress
Full text linkDuring haemodialysis (HD) sessions, patients undergo alterations in the extracellular environment, mostly concerning plasma electrolyte concentrations, pH, and volume, together with a modification of sympathovagal balance. All these changes affect cardiac electrophysiology, possibly leading to an increased arrhythmic risk. Computational modeling may help to investigate the impact of HD-related changes on atrial electrophysiology. However, many different human atrial action potential (AP) models are currently available, all validated only with the standard electrolyte concentrations used in experiments. Therefore, they may respond in different ways to the same environmental changes. After an overview on how the computational approach has been used in the past to investigate the effect of HD therapy on cardiac electrophysiology, the aim of this work has been to assess the current state of the art in human atrial AP models, with respect to the HD context. All the published human atrial AP models have been considered and tested for electrolytes, volume changes, and different acetylcholine concentrations. Most of them proved to be reliable for single modifications, but all of them showed some drawbacks. Therefore, there is room for a new human atrial AP model, hopefully able to physiologically reproduce all the HD-related effects. At the moment, work is still in progress in this specific field
The virtual sinoatrial node: What did computational models tell us about cardiac pacemaking?
No full textSince its discovery, the sinoatrial node (SAN) has represented a fascinating and complex matter of research. Despite over a century of discoveries, a full comprehension of pacemaking has still to be achieved. Experiments often produced conflicting evidence that was used either in support or against alternative theories, originating intense debates. In this context, mathematical descriptions of the phenomena underlying the heartbeat have grown in importance in the last decades since they helped in gaining insights where experimental evaluation could not reach. This review presents the most updated SAN computational models and discusses their contribution to our understanding of cardiac pacemaking. Electrophysiological, structural and pathological aspects - as well as the autonomic control over the SAN - are taken into consideration to reach a holistic view of SAN activity
Quantification of Local Calcium Releases Contribution to Diastolic Depolarization in a 3D Model of Single Rabbit Sinoatrial Node Cell
No full textPerformance limits of time synchronization in wireless sensor networks
No full textWe propose a new approach to evaluate the ultimate performance limit of time synchronization in wireless sensor networks based on the estimation theory. In particular the lower bound on the variance of the average synchronization error in a fully connected network is derived by taking into account the statistical characterization of the message delivering time. ©2008 IEEE
Optical and Electrical Characterization of Biocompatible Polymeric Lines for Hemodialysis Applications
Full text linkDuring hemodialysis (HD), blood is circulated through an extracorporeal tubing system (bloodline) made of medical-grade polymeric material. Sensors of various types that do not come into contact with blood (optical, electromagnetic, etc.) are applied directly across the bloodline for clinical purposes and for therapy customization. Thus, a detailed knowledge of the bloodline’s physical properties is useful for the development of next-generation HD sensors. In this work, we performed a novel comparative analysis of the materials used by the manufacturers of the bloodlines. We focused on signals and characterization techniques matching those of the abovementioned sensors; consequently, this is an application-specific study of the optical and electrical characterization of bloodline material. Such properties are analyzed and compared for bloodlines from seven different manufacturers by optical absorbance spectroscopy and electrical impedance spectroscopy (EIS). Absorbance spectrum measurements are carried out in the VIS-NIR range. Absorbance spectra are pre-processed and data from both types of analyses are normalized with respect to sample thickness. Optical analysis shows that all bloodlines except one have similarly shaped spectra with slight quantitative differences. In all optical spectra, we find a decreasing trend of specific absorption from 0.14 mm−1 at 400 nm to 0.06 mm−1 at 1000 nm, with an absorption peak at 915 nm. In one case, a large absorption peak centered at ≃600 nm is found. Electrical analysis shows that all bloodlines have the electrical properties of a constant-phase element (CPE), with statistically significant differences in parameters’ values. Estimation of electrical CPE parameters for all bloodline returns a range of 0.942–0.957 for parameter n and a range of 12.41–16.64 for parameter Q0’. In conclusion, we find that, although some statistically significant differences are present, bloodlines from a representative group of manufacturers share similar electrical and optical properties. Therefore, contactless sensing devices developed for HD will work on different bloodlines if a simple recalibration is performed
Preliminary findings on left atrial appendage occlusion simulations applying different endocardial devices
Full text linkAtrial fibrillation (AF) is one of the most investigated arrhythmias since it is
associated with a five-fold increase in the risk of strokes. Left atrium dilation
and unbalanced and irregular contraction caused by AF favour blood stasis
and, consequently, stroke risk. The left atrial appendage (LAA) is the site of the
highest clots formation, increasing the incidence of stroke in AF population. For
many years oral anticoagulation therapy has been the most used AF treatment
option available to decrease stroke risk. Unfortunately, several contraindications
including bleeding risk increase, interference with other drugs and with multiorgan
functioning, might outweigh its remarkable benefits on thromboembolic events.
For these reasons, in recent years, other approaches have been designed, including
LAA percutaneous closure. Unfortunately, nowadays, LAA occlusion (LAAO) is
restricted to small subgroups of patients and require a certain level of expertise
and training to successfully complete the procedure without complications. The
most critical clinical problems associated with LAAO are represented by peridevice
leaks and device related thrombus (DRT). The anatomical variability of the
LAA plays a key role in the choice of the correct LAA occlusion device and in its
correct positioning with respect to the LAA ostium during the implant. In this
scenario, computational fluid dynamics (CFD) simulations could have a crucial
role in improving LAAO intervention. The aim of this study was to simulate the fluid
dynamics effects of LAAO in AF patients to predict hemodynamic changes due
to the occlusion. LAAO was simulated by applying two different types of closure
devices based on the plug and the pacifier principles on 3D LA anatomical models
derived from real clinical data in five AF patients. CFD simulations were performed
on the left atrium model before and after the LAAO intervention with each device.
Blood velocity, particle washout and endothelial damage were computed to
quantify flow pattern changes after the occlusion in relation to the thrombogenic
risk. Our preliminary results confirmed an improved blood washout after the
simulated implants and the capability of foreseeing thrombogenic risk based on
endothelial damage and maximum blood velocities in different scenarios. This
tool may help to identify effective device configurations in limiting stroke risk for
patient-specific LA morphologies
A New Method for Continuous Relative Blood Volume and Plasma Sodium Concentration Estimation during Hemodialysis
No full textNon-invasive sensing and reliable estimation of physiological parameters are important features of hemodialysis machines, especially for therapy customization (biofeedback). In this work, we present a new method for joint estimation of two important hemodialysis-related physiological parameters: relative blood volume and plasma sodium concentration. Methods: Our method makes use of a non-invasive sensor setup and of a mathematical estimator. The estimator, based on the Kalman filter, allows to merge data from multiple sensors, newly-designed as well as on-board, with modeling knowledge about the hemodialysis process. The system was validated on in-vitro hemodialysis sessions using bovine blood. Results: The estimation error we obtained (0.97±0.73% on relative blood volume and 0.47±0.19 mM on plasmatic sodium) proved to be comparable with that of reference data for both parameters: the system is sufficiently accurate to be relevant in a clinical context. Conclusion: Our system has the potential to provide accurate and important information on the state of a patient undergoing hemodialysis, while only low-cost modifications to the existing on-board sensors are required. Significance: Through improved knowledge of blood parameters during hemodialysis, our method will allow better patient monitoring and therapy customization in hemodialysis
Non-Invasive Estimation of Plasma Sodium Concentration During Hemodialysis via Capacitively-Coupled Electrical Impedance Spectroscopy
Full text linkThis paper presents a compact, low-cost, and non-invasive system for real-time estimation of plasma sodium concentration ([Na]Pl) during a hemodialysis (HD) session with state-of-the-art accuracy. It is based on electrical impedance spectroscopy (EIS) performed with a capacitively-coupled impedance sensing cell and a high-frequency measurement device, both custom-built. The EIS data are processed to infer the resistance of the liquid inside the cell, which is used together with an optical hemoglobin sensor to estimate the [Na]Pl. Validation of the EIS was performed by estimating the conductivity of blood-mimicking fluid (BMF). The complete method was validated using whole bovine blood, comparing the results to those obtained with standard instruments. The system was able to estimate the [Na]Pl with sufficient accuracy (RMS error of 3.0 mol/m3 with respect to reference data) to provide clinically useful information. The proof-of-concept hardware can be converted to a cheap an
Finite-element modeling of time-dependent sodium exchange across the hollow fiber of a hemodialyzer by coupling with a blood pool model
No full textINTRODUCTION:
Hollow fiber models describe the exchange of solutes between blood and dialysate across the membrane of a single fiber of the hemodialysis filter (hemodialyzer). This work aims to develop a new approach to simulate the solute exchange in a hollow fiber in a dynamic and realistic way. Sodium was chosen as our solute of interest due to its importance in hemodialysis as an osmotic regulator.
METHODS:
A 2-dimensional (2D) hollow fiber model based on the finite element method (FEM) is coupled to a simple blood pool model to dynamically update the concentration of the solute entering the dialyzer. The resulting coupled model maintains the geometrical detail of the 2D fiber representation and gains a dynamic, blood-side inlet solute concentration. In vitro dialysis sessions were carried out for model validation, by implementing a combination of blood volume loss and/or sodium concentration steps. Plasmatic sodium concentration was recorded by blood gas sampling. Dialysate inlet and outlet conductivities were continuously recorded.
RESULTS:
Simulated plasmatic sodium concentration was compared with data from the blood gas samples. A mean error of 1.76 ± 1.03 mM was found for the complete dataset, along with a 3.87 mM maximum error. The simulated outlet dialysate sodium concentration was compared with the recorded outlet dialysate conductivity: a very high correlation was found on the whole dataset (R2 = 0.992).
CONCLUSIONS:
Coupling our FEM hollow fiber model to a simple blood pool model proved to be an effective approach for dynamical analysis of the properties of the hemodialyzer
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