The aim of the study is modelling and calculation of flows in human lungs which can be regarded as flows in an elastic tube system. By inhalation air will enter the lung, and this flow will create pressure gradients which may deform the lung-tubes which on their turn will influence the flow-pattern. This research will take as stepping stone an earlier research in which lung-tubes where modelled as rigid tubes.

The practical relevance of this project is that lungfunction tests for patients are mainly based on forced expiration. The outcome is strongly dependent on the elasticity of certain parts of the lungs (depending on the kind and the state of the disease). Also many pulmonary problems (varying from astma to emphysema) are governed by elasticity of (parts of) the lung. If insight is gained which parts of the lung under which circumstances collapse, this may lead to better ventilation and better suppletion of aerosol-medication. Also diagnosis of diseases and intrepretation of measured lungfunction will be improved. The study will take place in cooperation with the departments of lungfunction and neonatology of the Academic Medical Centre, University of Amsterdam. The study will be mainly theoretically with a numerical solution method. A part of the study may consist of an experimental setup for validation of the results obtained with the developed solution method. Normally the study will end with a PhD degree.

For more information, please contact

dr.ir. F.H.C. de Jongh, projectleader, telephone +31 53 489 1186 (e-mail f.h.c.dejongh@wb.utwente.nl)

prof.dr.ir. H.W.M. Hoeijmakers, promotor, telephone +31 53 489 4838 (e-mail h.w.m.hoeijmakers@wb.utwente.nl).

Project description

The aim of the project is to obtain qualitative and quantitative insight in the transport of gases in lungs of humans, whether healthy adults or prematurely-born babies, whether under conditions of natural respiration or of artificial ventilation. The approach taken is to develop a numerical simulation method employing realistic mathematical models of:

(1) the geometrical structure of the lungs, its surroundings and its mechanical characteristics, where the latter may also depend on the state of health of the lungs;

(2) the unsteady flow of air in spontaneously-breathing or ventilated lungs;

(3) the function of the alveoli, i.e. the extraction of oxygen from the inhaled air and the suppletion of carbon-dioxide to the exhaled air;

The utilisation lies in the potential to use the numerical simulation method, prior to clinical application, for:

(1) optimizing the ventilation frequency and other parameters of artificial ventilation under a wide variety of conditions (for conventional as well as high-frequency ventilation), e.g. to minimize lung damage in prematurely born babies;

(2) investigating the effect of malfunctioning parts of the lungs on the intake of oxygen and the washout of carbondioxide;

(3) studying the influence of diseases such as tachypneu, bradypneu, temperature, mucus, mucosal swelling, spasm of hypertrophied muscles in the bronchial wall on lungfunctions.

Structural models of lungs, a complex multiple-branching tube system, do already exist. The more or less standard model is the model of Weibel, which contains 23 generations of rigid, symmetrically branching, tubes. The dimensions of the tubes are derived from anatomical data obtained by pathologists. For the earlier developed one-dimensional flow analysis the basic element is a one-dimensional rigid tube with a cross-section and other characteristics relevant for the specific generation. Thus the longmodel consists of the assembly of the cross-sections of all the (equal) tubes of the generation at a given location. In the proposed project the structural model will be improved by including a local compliance of the tubes and the alveoli. Also an analysis generation-wise axi-symmetric flow model will be developed as the basic element for a more detailed analysis of the gas transport in the compliant lung. In order to develop rules for the basic elements for accounting for effects for transition from one generation to the next one the flow in a branching tube is considered with a three-dimensional flow (CFD) method. Also lung models with non-symmetric structure and non-uniform mechanical properties will be considered.

The flow in the lungs is rather complex, due to the wide range of length and velocity scales the transport mechanisms range from a flow dominated by convection and turbulence in the upper airways to a flow dominated by molecular diffusion in the alveoli. Also the role of surface tension in and the effect of surfactant on the stability of an alveolus or a cluster of alveoli will be investigated, specifically important for prematurely-born babies with surfactant deficiency and for older patients with the Adult Respiratory Distress Syndrome (ARDS). The flow modelling in the proposed project will take as stepping stone the work of de Jongh, who developed the one-dimensional model for the flow-mechanisms, transport processes and concentration distributions in the human lung within the framework of his PhD project.

Scientific relevance

The flow in the human pulmonary system has a strong interest in the medical sciences. The complexity of the flow and its many diverse aspects associated with the widely varying types of flow features encountered, the flexible and geometrically complex structure of the lungs and the complexity of the alveolar gas exchange process require a multi-disciplinary approach, necessitating the close cooperation of fluid dynamicists and medical experts. This project is based on the close cooperation between fluid dynamicists of the Section Fluid Mechanics of the University Twente and physicians of the Academic Medical Center of the University of Amsterdam, established during the PhD project of de Jongh. The proposed project will provide qualitative and quantitative insight in the way in which the transport of gases takes place in the lungs of humans, whether healthy adults or prematurely-born babies, whether under conditions of natural respiration or of artificial ventilation. The proposed project will increase the knowledge on the functioning of the physical processes that take place in the pulmonary system and their effect on the respiratory efficiency. The proposed project will decrease the need to employ empirical rules in applying ventilation. Furthermore, with the knowledge acquired in the project ventilation strategies can be developed for people with breathing problems, such as caused by accidental inhalation of toxic gases (by implementing the effect of these gases on the mechanical and geometrical properties of the airway system) to ensure optimal transport of oxygen to, and carbondioxide and toxic gases out of the lungs. If it proves possible to improve artificial ventilation such that a more efficient oxygenation and CO2 outwash is possible at lower peak pressures, this will prevent the occurrence of chronic lung disease (CLD). Prevention of CLD is very beneficial since the life-long treatment of each patient with CLD costs around 1 million guilders. Due to technical and medical achieve-ments and improvements an increasing number of prematurely-born babies survives, many more than in the past decades. The number of too-early born babies has also increased due to other reasons (e.g. women getting their first baby later in time, in-vitro fertilization sometimes resulting in more than one child per birth). This leads to a larger number of babies needing mechanical ventilation. The lower peak and mean pressures possible with optimized ventilation will result in less irreversible overdistention of the lungs, which will reduce the cost of medical care needed for breathing problems later in life.