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Transport and deposition of uniform respirable fibres in a physical lung model
J. Aerosol Sci., Vol. 22, Suppl, 1, pp. $859-$862, 1991.
0021-8502/91 $3.00+0.00 Pergamon Press plc
Printed in Great Britain,
T R A N S P O R T AND DEPOSITION OF U N I F O R M RESPIRABLE FIBRES IN A PHYSICAL LUNG MODEL Jan Marijnlssen, Angela Zeckendorf, Saul Lemkowitz and Henk Bibo Faculty of Chemical Engineering, Sections Particle Technology and Chemical Risk Management, Delft University of Technology, P.O. Box 5045, 2600 GA Delft, the Netherlands
Abstract In view of the health hazards of asbestos fibres, Industry Is searching for safe fibrous materials as substitutes. A question remains regarding the health hazards of fibrous materials in general. To examine this a physical model representing the lung yet still flexible In use has been constructed. It consists of separate parts with true lung geometry and has a conductive Inner surface. Also a device to create a high relative humidity of the air is Included. The system has been tested with latex spheres and proves to work properly. A deposition hot spot was found at the carlna. Initial tests with monodlsperse nylon fibres have been performed.
Keywords Fiber deposition; fiber transport; lung model; monodlsperse fibers.
Introduction Due to health hazards, asbestos fibres are being substituted by other fibrous materials. A question remains, however, concerning the health hazards of fibrous materials In general.
Aim of the research The basic aim is modelling the fundamental aerodynamic behaviour of fibres, as a function of physical and chemical properties, In the human respiratory system. Such properties Include: dimensions, density, surface properties (hydrophilic, etc.), charge, etc. After this Is achieved, biological research, to be done elsewhere, will determine the physlopathologlcal response to fibres of the dimensions tested. To study fibre behaviour In general, monodisperse fibres In the micron range must be available. The lack of such fibres has handicapped research In this area for many years. Marljnlssen et al (1989) and Buwalda et al (1990) were one of the first to achieve production of uniform fibres in the micron range. Now that such fibres are available, studying the behavlour of these fibres In a physical lung model can begin in earnest. This paper describes the design and construction of such a model and some preliminary results.
The lung model Present mathematical particle deposition models as well as physical ones have been developed largely for describing deposition of spherical particles. Furthermore, most research groups which did develop mathematical models specifically for fibre behaviour did not perform measurements themselves, but made use of experiments performed by other research groups using physical models. In addition, experiments with these physical deposition models were often carded out with poorly defined fibres. S859
$860
J. MARIJNISSEN et al.
Characteristic for the present study Is the use of a combination of theory together with experiments with a physical lung model. This model Is based on that of Yeh and Schum (1980). Improvements consist of the use of transparent materials (glass), a transparent, electrically conducting inner coating of the model segments, and the use of air with a high relative humidity. These last two modifications serve to better simulate the conditions existing in the human lung. Additionally, and very importantly, highly monodlsperse fibres are used. The system developed is shown schematically in fig. 1.
AIR [ d=luent )
I I I I
x \\ I
I
1 I I I I
J L
1
J E3
E
-1
11 AIR ( pr=mary )
Fig. 1. Schematic representation of measurement system.
1. Flow control valve. 2. Absolute filter (for particles > 0.2 micron). 3. Flow meter (rotameter). 4. Aerosol generator. 5. Drying chamber. 6. Charge neutralizer (Kr 85). 7. Air humidifier. 8. Plenum chamber (for flow stabilization). 9. Sampling probe (Isokinetlc). 10. Lung model. 11. Laser panicle counter (LPC) for particles > 0.3 micron; data to computer. 12. Computer. 13. Vacuum pump. A photograph of a modelled lung segment including generation 3 is presented In fig. 2.
Experiments The system was first tested with spherical latex particles of 1 micron. These were dispersed with a aerosol generator (DeVilblss Class Nebulizer No. 40 for Aerosol Therapy) with a volumetric flow rate of 6.5 liter/min. The aerosol generator contained a 0.01 wt-% suspension of latex particles in water. Conditions were: T=20 ° C., P=atmospheric; volumetric flow rate (in one direction) = 50 liter/mln (moderate physical activity); relative humidity in model = 78%. Particle concentrations entering and leaving the lung model were measured using an LPC (laser particle counter; TSI, model 3753). Deposition In the model was observed using a long range microscope. Constant model input concentrations of ca. 120 partlcles/cm 3 were measured with the LPC. A deposition hot spot was clearly found at the carina. On the basis of these results experiments were begun using fibres.
Transport and deposition of fibres in lungs
$861
Fig. 2. Model of lung segment Including generation 3.
Fig. 3. Fibres, cut to 20 micron length. Diameter = 1.2 micron (separated by means of sedimentation). Highly monodisperse nylon fibres (Fig. 3) were prepared (MarlJnissen et al. 1989; Buwalda et al., 1990). These were suspended at 0.01 wt-% In an acetone-water solution and dispersed using an aerosol generator (as above, at the same conditions). The fibres used were of three lengths: ca. 5, 10 and 20 micron; diameter In all cases was ca. 1 micron. Dispersion in air was achieved, but with a much lower efficiency than with the latex mlcrospheres. Particle deposition was followed using a long range microscope. Initial results suggest behavlour roughly similar to that of spherical particles, I.e., a deposition hot spot at the cadna.
$862
J. MARIJNISSEN et al.
Future work Another type of aerosol generator Is necessary for achieving dispersion of these fibres In air, e.g., a fluid bed. Furthermore, a better method than a long range microscope for visualizing particle deposition Is probably necessary. Fibre optics Will be tried. Particle orientation In the air stream Is Important for modelling. Possible measurement methods are being studied. References /
Buwalda, J.R.F., J.CM. Marijnissen, M Bilius, S.M. Lemkowlt]. and B.H. Bibo (1990). The Production of Well-Defined Fibres in the Micron and Submlcron Range for inhalation Experiments. S. Masuda and K. Takahashi (editors), Proceedings of the 3rd International Aerosol Conference, 24-27 September 1990, Kyoto, Japan, Pergamon Press, Volume II, 1238-1241. Marijnissen, J.C.M., J.R.G. Buwalda, M. van Pinxteren, S.M Lemkowit.z and B.H. Blbo (1989). Production of Well-defined Organic Fibres for Inhalation Experiments J. Aerosol ScL, 20('8~, 1285-1288. Yeh, H.C., and G.M. Schum (1980). Models of human lung airways and their application to Inhaled particle deposition. Bull. Math. Biol., 42, 461-480.
0021-8502/91 $3.00+0.00 Pergamon Press plc
Printed in Great Britain,
T R A N S P O R T AND DEPOSITION OF U N I F O R M RESPIRABLE FIBRES IN A PHYSICAL LUNG MODEL Jan Marijnlssen, Angela Zeckendorf, Saul Lemkowitz and Henk Bibo Faculty of Chemical Engineering, Sections Particle Technology and Chemical Risk Management, Delft University of Technology, P.O. Box 5045, 2600 GA Delft, the Netherlands
Abstract In view of the health hazards of asbestos fibres, Industry Is searching for safe fibrous materials as substitutes. A question remains regarding the health hazards of fibrous materials in general. To examine this a physical model representing the lung yet still flexible In use has been constructed. It consists of separate parts with true lung geometry and has a conductive Inner surface. Also a device to create a high relative humidity of the air is Included. The system has been tested with latex spheres and proves to work properly. A deposition hot spot was found at the carlna. Initial tests with monodlsperse nylon fibres have been performed.
Keywords Fiber deposition; fiber transport; lung model; monodlsperse fibers.
Introduction Due to health hazards, asbestos fibres are being substituted by other fibrous materials. A question remains, however, concerning the health hazards of fibrous materials In general.
Aim of the research The basic aim is modelling the fundamental aerodynamic behaviour of fibres, as a function of physical and chemical properties, In the human respiratory system. Such properties Include: dimensions, density, surface properties (hydrophilic, etc.), charge, etc. After this Is achieved, biological research, to be done elsewhere, will determine the physlopathologlcal response to fibres of the dimensions tested. To study fibre behaviour In general, monodisperse fibres In the micron range must be available. The lack of such fibres has handicapped research In this area for many years. Marljnlssen et al (1989) and Buwalda et al (1990) were one of the first to achieve production of uniform fibres in the micron range. Now that such fibres are available, studying the behavlour of these fibres In a physical lung model can begin in earnest. This paper describes the design and construction of such a model and some preliminary results.
The lung model Present mathematical particle deposition models as well as physical ones have been developed largely for describing deposition of spherical particles. Furthermore, most research groups which did develop mathematical models specifically for fibre behaviour did not perform measurements themselves, but made use of experiments performed by other research groups using physical models. In addition, experiments with these physical deposition models were often carded out with poorly defined fibres. S859
$860
J. MARIJNISSEN et al.
Characteristic for the present study Is the use of a combination of theory together with experiments with a physical lung model. This model Is based on that of Yeh and Schum (1980). Improvements consist of the use of transparent materials (glass), a transparent, electrically conducting inner coating of the model segments, and the use of air with a high relative humidity. These last two modifications serve to better simulate the conditions existing in the human lung. Additionally, and very importantly, highly monodlsperse fibres are used. The system developed is shown schematically in fig. 1.
AIR [ d=luent )
I I I I
x \\ I
I
1 I I I I
J L
1
J E3
E
-1
11 AIR ( pr=mary )
Fig. 1. Schematic representation of measurement system.
1. Flow control valve. 2. Absolute filter (for particles > 0.2 micron). 3. Flow meter (rotameter). 4. Aerosol generator. 5. Drying chamber. 6. Charge neutralizer (Kr 85). 7. Air humidifier. 8. Plenum chamber (for flow stabilization). 9. Sampling probe (Isokinetlc). 10. Lung model. 11. Laser panicle counter (LPC) for particles > 0.3 micron; data to computer. 12. Computer. 13. Vacuum pump. A photograph of a modelled lung segment including generation 3 is presented In fig. 2.
Experiments The system was first tested with spherical latex particles of 1 micron. These were dispersed with a aerosol generator (DeVilblss Class Nebulizer No. 40 for Aerosol Therapy) with a volumetric flow rate of 6.5 liter/min. The aerosol generator contained a 0.01 wt-% suspension of latex particles in water. Conditions were: T=20 ° C., P=atmospheric; volumetric flow rate (in one direction) = 50 liter/mln (moderate physical activity); relative humidity in model = 78%. Particle concentrations entering and leaving the lung model were measured using an LPC (laser particle counter; TSI, model 3753). Deposition In the model was observed using a long range microscope. Constant model input concentrations of ca. 120 partlcles/cm 3 were measured with the LPC. A deposition hot spot was clearly found at the carina. On the basis of these results experiments were begun using fibres.
Transport and deposition of fibres in lungs
$861
Fig. 2. Model of lung segment Including generation 3.
Fig. 3. Fibres, cut to 20 micron length. Diameter = 1.2 micron (separated by means of sedimentation). Highly monodisperse nylon fibres (Fig. 3) were prepared (MarlJnissen et al. 1989; Buwalda et al., 1990). These were suspended at 0.01 wt-% In an acetone-water solution and dispersed using an aerosol generator (as above, at the same conditions). The fibres used were of three lengths: ca. 5, 10 and 20 micron; diameter In all cases was ca. 1 micron. Dispersion in air was achieved, but with a much lower efficiency than with the latex mlcrospheres. Particle deposition was followed using a long range microscope. Initial results suggest behavlour roughly similar to that of spherical particles, I.e., a deposition hot spot at the cadna.
$862
J. MARIJNISSEN et al.
Future work Another type of aerosol generator Is necessary for achieving dispersion of these fibres In air, e.g., a fluid bed. Furthermore, a better method than a long range microscope for visualizing particle deposition Is probably necessary. Fibre optics Will be tried. Particle orientation In the air stream Is Important for modelling. Possible measurement methods are being studied. References /
Buwalda, J.R.F., J.CM. Marijnissen, M Bilius, S.M. Lemkowlt]. and B.H. Bibo (1990). The Production of Well-Defined Fibres in the Micron and Submlcron Range for inhalation Experiments. S. Masuda and K. Takahashi (editors), Proceedings of the 3rd International Aerosol Conference, 24-27 September 1990, Kyoto, Japan, Pergamon Press, Volume II, 1238-1241. Marijnissen, J.C.M., J.R.G. Buwalda, M. van Pinxteren, S.M Lemkowit.z and B.H. Blbo (1989). Production of Well-defined Organic Fibres for Inhalation Experiments J. Aerosol ScL, 20('8~, 1285-1288. Yeh, H.C., and G.M. Schum (1980). Models of human lung airways and their application to Inhaled particle deposition. Bull. Math. Biol., 42, 461-480.