Doel van het onderzoek is het modelleren en berekenen van stromingen in elastische buizen. Door ademhalingsbewegingen zal er lucht in de longen stromen, waardoor drukgradiënten worden opgewekt en de longbuizen vervormen, hetgeen zijn weerslag heeft op de stroming in de longbuizen. Het onderzoek is een voortzetting van eerder onderzoek waarin longen werden gemodelleerd als een star buizenstelsel.

De praktische relevantie van dit onderzoek is dat longfunctie-onderzoek bij patiënten zich in de praktijk hoofdzakelijk richt op maximale ademhalingsoefeningen (geforceerde uitademingen) waarbij de te meten grootheden sterk afhankelijk zijn van de elasticiteit van bepaalde delen van de long. Ook de verschijnselen die optreden bij veel ziektebeelden, variërend van astma tot emfyseem, worden bepaald door de mate van elasticiteit van bepaalde longdelen. Het inzichtelijk/berekenbaar maken van welke longdelen bij welke geforceerde ademhalingsoefeningen vervormen/inklappen, kan leiden tot het verbeteren van zowel de beademing van patiënten als de toediening van medicijnen in aërosol-vorm, de diagnostisering van longziektes en een diepergaande interpretatie van longfunctiemetingen. Het onderzoek zal plaatsvinden in samenwerking met de afdelingen longfunctie en neonatologie van het Academisch Medisch Centrum Amsterdam (AMC). Het onderzoek zal hoofdzakelijk theoretisch/numeriek van aard zijn en kan eventueel voor een deel bestaan uit het uitvoeren van metingen met een experimentele proefopstelling, dit ter validatie van de resultaten van de te ontwikkelen rekenmethode. In principe wordt het onderzoek in vier jaar met een promotie afgesloten. Vacaturenummer 98/078.

Informatie Voor nadere inlichtingen kunt u contact opnemen met:

dr.ir. F.H.C. de Jongh, projectleider, telefoon (053) 489 1186 (e-mail f.h.c.dejongh@wb.utwente.nl)

prof.dr.ir. H.W.M. Hoeijmakers, promotor, telefoon (053) 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.