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Ionic mechanisms underlying atrial fibrillation (AF) generation and propagation are unclear. In this study, we investigate the dependence of AF related properties to changes in human atrial ion channel characteristics by systematically conducting a sensitivity analysis. Cell and tissue simulations are performed using the Maleckar action potential computational model for control and AF remodeling conditions,...
To compute extracellular potentials from transmembrane potentials an elliptic boundary-value problem must be solved. This must be done at a spatial resolution of 0.2 mm or better to avoid artefacts in the form of large spikes before and after major deflections. For macroscopic heart models, this leads to very large linear systems. Artefacts in low-resolution solutions are related to the restriction...
In this paper, we propose the substitution of the original, non-pulsatile cardiac sub-model of the Guyton model by an elastance-based pulsatile model of the heart, including interventricular interaction through the septum. Parameters of this cardiac model were identified by comparing the simulations obtained from the original Guyton model with those obtained from the proposed integrated, pulsatile...
It is well-known that visually-induced motion sickness (VIMS) is caused by image motion. Therefore it is important to clarify the relationship between image motion and the change in discomfort level. However, it is difficult to know the quick change in the level of discomfort during watching actual video image. The authors have proposed a method of interpolation for the subjective score, which has...
The study aimed to determine the potential of pulse wave velocity measurements to reflect changes in compliant cerebral arteries/arterioles in head injured patients. The approach utilizes the electrocardiogram and intracranial pressure signals to measure the wave transit time between heart and cranial cavity. Thirty five clinical records of nineteen head injured patients, with different levels of...
The aim of this study was to investigate sex and age related differences in drug induced QT prolongation by dofetilide under reduced repolarization reserve in simulated ventricular cells. Left ventricular endocardial action potentials were simulated using a modified Luo Rudy model. Sex, age and regional differences in currents ICaL, IKr, IKs, and Ito were incorporated into the model by modifying the...
The Pulse Transit Time (PTT) is generally assumed to be a good surrogate measure to comfortably track blood pressure (BP) and blood pressure changes. This paper investigates PTT variations for healthy young subjects during a sequence of short-term physical exercises. PTT was measured by two different methodologies having different measurement accuracies as well as underlying assumptions: the total...
In this paper we introduce a new theoretical formulation for the description of the blood flow in the circulatory system. Starting from a linearized version of the Navier-Stokes equations, the Green's function of the propagation problem is computed in a rational form. As a consequence, the input-output transfer function relating the upstream and downstream pressure and blood flow is written in a rational...
In this work we present a new electromechanical cardiac myocyte model tailored to reproduce the electrical and force generating activities of human ventricular myocytes. The model was created by coupling two existing models: the ten Tusscher electrophysiology model and the Rice myofilament mechanics model. The parameters of the new model were adjusted in order to replicate the available experimental...
Implantation of sensors to measure hemodynamic parameters such as pulsatile pump flow and differential pressure (head) in an implantable rotary pump (IRBP) requires regular in situ calibration due to measurement drift. In addition, risks associated with sensor failure and thrombus formation makes the long-term implantation in patients problematic. In our laboratory, two stable and novel dynamical...
Modern control theory allows the representation of cardiac dynamics in the state-space, describing the operation of the vascular systems in terms of the cushioning effect of the arterial wall facing compliance changes. In this paper we use state equations to modeling the effect of the compliance variations on the arterial wall. The characteristics of the dynamics and of the calculated parameters of...
The Dominant T-wave (DTW) offers an overall view of the venticular repolarization as it reflects the first-order derivative of the transmembrane potential of the myocytes during repolarization (TMPR). DTW can be estimated from the analysis of surface T-waves, which are modeled as a linear combination of DTW and its derivatives. Usually, the contribute of the DTW dominates but, when dispersion of the...
In this work, the effect of high heart rate on the LDL transport in arteries is examined using the finite element method. The velocity profile is pulsatile, while the tachycardia case is assumed to have 40% increased flow rate and 25% increased velocity than the normal case. The Navier-Stokes equations are used to model the blood flow and LDL transfer is modeled using the convection-diffusion equation...
This paper reports two attempts at estimating the magnitude of atrial flutter amplitude modulation caused by atrial motion during heart contraction. The first approach consists in analyzing the ECG of a patient in flutter with atrioventricular block and an implanted pacemaker. These conditions facilitate QRST cancellation, even in the presence of time-varying flutter wave amplitude. The second approach...
This paper presents a method to identify the cardiovascular baroreflex parameters that are useful for probing homeostatic stability. The work is built upon a physiology-based model of the closed-loop cardiovascular and baroreflex feedback system describing the regulation of heart rate and blood pressure. Parametric sensitivity analysis is conducted on the model to classify the model parameters into...
The role that sarcoplasmic reticulum (SR) luminal Ca2+ concentration plays in regulating ryanodine receptors (RyRs) is considered to be very important in process of cardiac excitation-contraction coupling. Here we developed a multi-scale mathematical model by coupling a two-dimensional spatio-temporal Ca2+ reaction-diffusion model with an action potential model of the ventricular myocyte. The simulation...
Doppler echocardiography remains the most extended clinical modality for the evaluation of left ventricular (LV) function. Current Doppler ultrasound methods, however, are limited to the representation of a single flow velocity component. We thus developed a novel technique to construct 2D time-resolved (2D+t) LV velocity fields from conventional transthoracic clinical acquisitions. Combining color-Doppler...
Lumped parameter differential equation models are a common approach to modeling the cardiovascular system. However, there are highly non-linear valve dynamics inherent in these models which makes parameter identification difficult. Standard methods for parameter identification rely on gradient descent, which can often converge to wrong solutions, particularly as the number of parameters increases...
Applications of mathematical and physical analog models of total artificial heart (TAH) play a significant role in simulating human cardiovascular system. Instead of a hydraulic model, an inexpensive, compact and simple electrical circuit consisting of resistances, capacitances, inductances and diodes has been constructed, using parametric values that are transformed from hydraulic models. Results...
A cardiovascular model for blood pressure control system is developed in this paper. This model is used to simulate hypertensive patients in order to design control systems for regulation of blood pressure. The stability of the model is also investigated. The model can accurately represent human arterial blood pressure and therefore, the control system designed and simulated based on the model can...
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