4,587 research outputs found
Theoretical open-loop model of respiratory mechanics in the extremely preterm infant
Non-invasive ventilation is increasingly used for respiratory support in
preterm infants, and is associated with a lower risk of chronic lung disease.
However, this mode is often not successful in the extremely preterm infant in
part due to their markedly increased chest wall compliance that does not
provide enough structure against which the forces of inhalation can generate
sufficient pressure. To address the continued challenge of studying treatments
in this fragile population, we developed a nonlinear lumped-parameter model of
respiratory system mechanics of the extremely preterm infant that incorporates
nonlinear lung and chest wall compliances and lung volume parameters tuned to
this population. In particular we developed a novel empirical representation of
progressive volume loss based on compensatory alveolar pressure increase
resulting from collapsed alveoli. The model demonstrates increased rate of
volume loss related to high chest wall compliance, and simulates laryngeal
braking for elevation of end-expiratory lung volume and constant positive
airway pressure (CPAP). The model predicts that low chest wall compliance
(chest stiffening) in addition to laryngeal braking and CPAP enhance breathing
and delay lung volume loss. These results motivate future data collection
strategies and investigation into treatments for chest wall stiffening.Comment: 22 pages, 5 figure
Absolute electrical impedance tomography (aEIT) guided ventilation therapy in critical care patients: simulations and future trends
Thoracic electrical impedance tomography (EIT) is a noninvasive, radiation-free monitoring technique whose aim is to reconstruct a cross-sectional image of the internal spatial distribution of conductivity from electrical measurements made by injecting small alternating currents via an electrode array placed on the surface of the thorax. The purpose of this paper is to discuss the fundamentals of EIT and demonstrate the principles of mechanical ventilation, lung recruitment, and EIT imaging on a comprehensive physiological model, which combines a model of respiratory mechanics, a model of the human lung absolute resistivity as a function of air content, and a 2-D finite-element mesh of the thorax to simulate EIT image reconstruction during mechanical ventilation. The overall model gives a good understanding of respiratory physiology and EIT monitoring techniques in mechanically ventilated patients. The model proposed here was able to reproduce consistent images of ventilation distribution in simulated acutely injured and collapsed lung conditions. A new advisory system architecture integrating a previously developed data-driven physiological model for continuous and noninvasive predictions of blood gas parameters with the regional lung function data/information generated from absolute EIT (aEIT) is proposed for monitoring and ventilator therapy management of critical care patients
A poroelastic model coupled to a fluid network with applications in lung modelling
Here we develop a lung ventilation model, based a continuum poroelastic
representation of lung parenchyma and a 0D airway tree flow model. For the
poroelastic approximation we design and implement a lowest order stabilised
finite element method. This component is strongly coupled to the 0D airway tree
model. The framework is applied to a realistic lung anatomical model derived
from computed tomography data and an artificially generated airway tree to
model the conducting airway region. Numerical simulations produce
physiologically realistic solutions, and demonstrate the effect of airway
constriction and reduced tissue elasticity on ventilation, tissue stress and
alveolar pressure distribution. The key advantage of the model is the ability
to provide insight into the mutual dependence between ventilation and
deformation. This is essential when studying lung diseases, such as chronic
obstructive pulmonary disease and pulmonary fibrosis. Thus the model can be
used to form a better understanding of integrated lung mechanics in both the
healthy and diseased states
Mathematical modelling of a human external respiratory system
A closed system of algebraic and common differential equations solved by computer is investigated. It includes equations which describe the activity pattern of the respiratory center, the phrenic nerve, the thrust produced by the diaphragm as a function of the lung volume and discharge frequency of the phrenic nerve, as well as certain relations of the lung stretch receptors and chemoreceptors on various lung and blood characteristics, equations for lung biomechanics, pulmonary blood flow, alveolar gas exchange and capillary blood composition equations to determine various air and blood flow and gas exchange parameters, and various gas mixing and arterial and venous blood composition equations, to determine other blood, air and gas mixing characteristics. Data are presented by means of graphs and tables, and some advantages of this model over others are demonstrated by test results
Lung Circulation Modeling: Status and Prospect
Mathematical modeling has been used to interpret anatomical and physiological data obtained from metabolic and hemodynamic studies aimed at investigating structure-function relationships in the vasculature of the lung, and how these relationships are affected by lung injury and disease. The indicator dilution method was used to study the activity of redox processes within the lung. A steady-state model of the data was constructed and used to show that pulmonary endothelial cells may play an important role in reducing redox active compounds and that those reduction rates can be altered with oxidative stress induced by exposure to high oxygen environments. In addition, a morphometric model of the pulmonary vasculature was described and used to detect, describe,and predict changes in vascular morphology that occur in response to chronic exposure to low-oxygen environments, a common model of pulmonary hypertension. Finally, the model was used to construct simulated circulatory networks designed to aid in evaluation of competing hypotheses regarding the relative contribution of various morphological and biomechanical changes observed with hypoxia. These examples illustrate the role of mathematical modeling in the integration of the emerging metabolic, hemodynamic, and morphometric databases
Fluid-structure interaction in lower airways of CT-based lung geometries
In this study, the deformability of airway walls is taken into account to study airflow patterns
and airway wall stresses in the first generations of lower airways in a real lung geometry. The
lung geometry is based on CT-scans that are obtained from in-vivo experiments on humans. A
partitioned fluid-structure interaction (FSI) approach, realized within a parallel in-house finite
element code, is employed. It is designed for the robust and eficient simulation of the interaction
of transient incompressible Newtonian flows and (geometrically) nonlinear airway wall behavior.
Arbitrary Lagrangian Eulerian (ALE)-based stabilized tetrahedral finite elements are used for the fluid and Lagrangian-based 7-parametric mixed/hybrid shell elements are used for the airway walls using unstructured meshes due to the complexity of the geometry. Air flow patterns as well as airway wall stresses in the bronchial tree are studied for a number of different scenarios. Thereby, both models for healthy and diseased lungs are taken into account and both normal breathing and mechanical ventilation scenarios are studied
Optimal Determination of Respiratory Airflow Patterns Using a Nonlinear Multicompartment Model for a Lung Mechanics System
We develop optimal respiratory airflow patterns using a nonlinear multicompartment model for a lung mechanics system. Specifically, we use classical calculus of variations minimization techniques to derive an optimal airflow pattern for inspiratory and expiratory breathing cycles. The physiological interpretation of the optimality criteria used involves the minimization of work of breathing and lung volume acceleration for the inspiratory phase, and the minimization of the elastic potential energy and rapid airflow rate changes for the expiratory phase. Finally, we numerically integrate the resulting nonlinear two-point boundary value problems to determine the optimal airflow patterns over the inspiratory and expiratory breathing cycles
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