- Email: [email protected]
Characterization of expiratory aerosol deposition patterns in human airway bifurcations
J. Aerosol Sci, Vol. 30, Suppl, 1, pp. $725--$726, 1999 © 1999 Published by Elsevier Science Ltd. All fights reserved Printed in Great Britain 0021-8502/99/$ - see front matter
Pergamon
CHARACTERIZATION OF EXPIRATORY AEROSOL DEPOSITION PATTERNS IN HUMAN AIRWAY BIFURCATIONS
A. Nagy, Cs. Hegedfs, P. Vtrtes, E. Ling, M. L6rinc, P.P. Szab6 KFKI Atomic Energy Research Institute, P OBox 49, H-1525 Budapest 114, Hungary KEYWORDS Expiratory aerosol deposition, Numerical modeling, Human airways, Enhancement factors INTRODUCTION Aerosol deposition studies have demonstrated that deposition patterns of inhaled aerosols within airway bifurcations are strongly inhomogeneous even during exhalation (Kim et al. 1989, Balhshhzy and Hofmann 1993b, 1994). Although a complete breathing cycle consists of an inspiration and an expiration phase, deposition studies usually examine only the effects of inhalation. Most of the deposition models are analytical descriptions and analytical approaches cannot describe the local inhomogeneities of deposition within airway bifurcations (Hofmann and Balhshhzy 1991). In the present study, we compute local deposition patterns in airway bifurcations upon expiration by the numerical model of Balhsh~tzy and Hofmann 1993a, Bal~tsh~y 1994, Heistracher et al. 1995, 1996a,b. To quantify the inhomogeneities of predicted deposition patterns, we scan the whole surface of the bifurcation with a pre-speeified surface area element, patch, and determine the local relative to the average deposition densities (enhancement factors). Bal~tshhzy et ai. 1999 computed the maxima and distributions of enhancement factors on inspiratory particle deposition patterns. Here, we apply their model for expiration conditions in the upper human airways at different particle sizes, patch sizes and flow rates. Since the prevalent philosophy of inhalation risk assessment is based upon the assumption of a uniform particle deposition pattern, the introduction of the deposition enhancement factors within airway bifurcations will provide a more accurate dose and risk estimation. MODEL In the present study, the geometry, the airflow field and the expiratory deposition patterns were computed with the numerical approach of Balhsh~izy et al. 1996, Hofmann et al. 1995, 1996a,b. In this model, geometry of a bifurcation may have idealized or physiologically realistic shape. The air velocity field is determined by the FIRE® (AVL, Graz, Austria) finite volume fluid dynamics code. Particle trajectories are simulated with Monte Carlo techniques, applying simultaneously all the four characteristic deposition mechanisms: inertial impaction, gravitational sedimentation, Brownian diffusion and interception. The local deposition patterns within the bifurcation model is then determined by the intersections of the simulated particle trajectories with the surrounding wall surfaces. For the quantification of local inhomogeneities of deposition patterns, we have computed the ratio of local to average deposition densities (enhancement factors) by scanning along the whole surface of the bifurcation with a pre-specified surface area element (Baihsh~y and Hofmann 1999). The dimensions and shape of this unit surface element can be specified depending on the biological effect under consideration. Here, we analyze the maxima and the corresponding distributions of enhancement factors upon expiration in the upper human airways (airway generations 3-4, Weibel's Model-A 1963) with various sizes of surface elements, patches, (0.1 mm x 0.1 mm - - 3 mm x 3ram) at different flow rates (10 l/min, 60 i/min) at physiologically realistic bifurcation geometry for a wide range of particle sizes (1 nm - - 10 lain) at parabolic and at uniform inlet flow profiles.
$725
$726
Abstracts of the 1999EuropeanAerosol Conference
RESULTS The computed air velocity fields and particle trajectories demonstrate the significant role of secondary flows for particle deposition during expiration. The enhanced deposition areas, ,,hot spots", are formed primarily at the top and bottom sides of the parent airway and not at the carinal ridge or inner sides of the daughter branches as in the case of inspiration. The length and width of the hot spots depend on the particle, flow and geometry parameters e.g. at large particles the enhanced deposition areas are much more intense than for ultraflne sizes, or at parabolic inlet flow profile the hot spots are much more elongated than at uniform inlet flow conditions. The computed local deposition enhancement factors exhibit strong local inhomogeneities for all particle sizes (except the case of nanoparticles at very low flow rates) considered here. The maximum value of the enhancement factors in a bifurcation strongly increases by decreasing the patch size, representing the high degree of inhomogeneity in the upper human airways during expiration. d = 0.01/am
d = 7~m
.*
•
-...*
•
e,.~.
•
..
•
-
.
.
i
i%
~
"~ "'"
•
• •°
I"--"""""" 'q=34% ""--"-
"
°"b
n = 19%
Figure 1. Expiratory deposition patterns of 7 ~tm and 0.01 lxrn aerosol particles in an asymmetric airway bifurcation, branching angles are 20 and 40 degree, linear dimensions correspond to generations 3-4 (Weibel's Model-A, 1963) at 30 l/min tracheal minute volume and parabolic inlet flow profile. Both the flow rates and the numbers of selected particles are equal at the inlets of the two daughter branches, rl is the deposition efficiency, the main plane of the bifurcation is horizontal. ACKNOWLEDGEMENT This research was supported by: OMFB-01790/98 Contract, Hungarian-Austrian T6T Contract: A-8/98, Hungarian OTKA T 030571 Project, and CEC Contract No. FI4P-CT95-0026. REFERENCES Bal~h/tzy, I. and Hofmann, W. (1993a)J Aerosol Sci. 24: 745-772. Balhshhzy, I. and Hofmann, W. (1993b) J. Aerosol Sci. 24: 773-786. Bal~h,h_~y,I, (1994) d. Comput Phys. 110:11-22. Bal~Mzy, I. and Hofmann, W. (1994) In: Inhaled Particles VII, Ann. occup. Hyg. 38:S 1,47-53. Bai~sh,qzy, I., Heistracher, T. and Hofmann, W. (1996) J. AerosolMed. 9: 287-301. Bal~hhzy, I., Hofmann, W. and Heistraeher, T. (1999)d. Aerosol Sci. 30:185-203. Heistraeher, T., Bai~h~-y, I. and Hofmann, W. (1995) J. AerosolSci. 26:Sl.615-616. Heistracher, T., Hofmann, W. and Bal~sh~y, I. (1996a)3;. Aerosol Sci. 27:S 1.603-604. Heistraeher, T., Hofmann, W. and Bal~shhzy,I. (1996b) Sympos. on Rad. Prot. in Neighbouring Countries in Central Europe, Portoroz, Slovenia,Sept. 4-7, 1995, Proceedings 74-76. Ed.: D. Glavic-Cindro. Hofmann, W. and Bal~hiizy, I. (1991)Radiat. Prot. Dosim. 38:57-63. Hofmarm, W., Bai~sh,qzy,I. and Koblinger, L. (1995) J. Aerosol Sci. 26:1161-1168. Hofmann, W., Balashazy, I., Heistracher, T. and Koblinger, L. (1996a) Aerosol Sci. Technol. 25:305-327. Hofmann, W., Heistracher, T. and Bal/tsMzy, I. (1996b) Environ. International 22:S 1.935-940. Kim, C.S., Iglesias, A.J. and Garcia, L. (1989)3;. AerosolMed 2: 15-27. Weibel, E.R. (1963)Morphometry of the Human Lung. Springer Verlag, Berlin.
Pergamon
CHARACTERIZATION OF EXPIRATORY AEROSOL DEPOSITION PATTERNS IN HUMAN AIRWAY BIFURCATIONS
A. Nagy, Cs. Hegedfs, P. Vtrtes, E. Ling, M. L6rinc, P.P. Szab6 KFKI Atomic Energy Research Institute, P OBox 49, H-1525 Budapest 114, Hungary KEYWORDS Expiratory aerosol deposition, Numerical modeling, Human airways, Enhancement factors INTRODUCTION Aerosol deposition studies have demonstrated that deposition patterns of inhaled aerosols within airway bifurcations are strongly inhomogeneous even during exhalation (Kim et al. 1989, Balhshhzy and Hofmann 1993b, 1994). Although a complete breathing cycle consists of an inspiration and an expiration phase, deposition studies usually examine only the effects of inhalation. Most of the deposition models are analytical descriptions and analytical approaches cannot describe the local inhomogeneities of deposition within airway bifurcations (Hofmann and Balhshhzy 1991). In the present study, we compute local deposition patterns in airway bifurcations upon expiration by the numerical model of Balhsh~tzy and Hofmann 1993a, Bal~tsh~y 1994, Heistracher et al. 1995, 1996a,b. To quantify the inhomogeneities of predicted deposition patterns, we scan the whole surface of the bifurcation with a pre-speeified surface area element, patch, and determine the local relative to the average deposition densities (enhancement factors). Bal~tshhzy et ai. 1999 computed the maxima and distributions of enhancement factors on inspiratory particle deposition patterns. Here, we apply their model for expiration conditions in the upper human airways at different particle sizes, patch sizes and flow rates. Since the prevalent philosophy of inhalation risk assessment is based upon the assumption of a uniform particle deposition pattern, the introduction of the deposition enhancement factors within airway bifurcations will provide a more accurate dose and risk estimation. MODEL In the present study, the geometry, the airflow field and the expiratory deposition patterns were computed with the numerical approach of Balhsh~izy et al. 1996, Hofmann et al. 1995, 1996a,b. In this model, geometry of a bifurcation may have idealized or physiologically realistic shape. The air velocity field is determined by the FIRE® (AVL, Graz, Austria) finite volume fluid dynamics code. Particle trajectories are simulated with Monte Carlo techniques, applying simultaneously all the four characteristic deposition mechanisms: inertial impaction, gravitational sedimentation, Brownian diffusion and interception. The local deposition patterns within the bifurcation model is then determined by the intersections of the simulated particle trajectories with the surrounding wall surfaces. For the quantification of local inhomogeneities of deposition patterns, we have computed the ratio of local to average deposition densities (enhancement factors) by scanning along the whole surface of the bifurcation with a pre-specified surface area element (Baihsh~y and Hofmann 1999). The dimensions and shape of this unit surface element can be specified depending on the biological effect under consideration. Here, we analyze the maxima and the corresponding distributions of enhancement factors upon expiration in the upper human airways (airway generations 3-4, Weibel's Model-A 1963) with various sizes of surface elements, patches, (0.1 mm x 0.1 mm - - 3 mm x 3ram) at different flow rates (10 l/min, 60 i/min) at physiologically realistic bifurcation geometry for a wide range of particle sizes (1 nm - - 10 lain) at parabolic and at uniform inlet flow profiles.
$725
$726
Abstracts of the 1999EuropeanAerosol Conference
RESULTS The computed air velocity fields and particle trajectories demonstrate the significant role of secondary flows for particle deposition during expiration. The enhanced deposition areas, ,,hot spots", are formed primarily at the top and bottom sides of the parent airway and not at the carinal ridge or inner sides of the daughter branches as in the case of inspiration. The length and width of the hot spots depend on the particle, flow and geometry parameters e.g. at large particles the enhanced deposition areas are much more intense than for ultraflne sizes, or at parabolic inlet flow profile the hot spots are much more elongated than at uniform inlet flow conditions. The computed local deposition enhancement factors exhibit strong local inhomogeneities for all particle sizes (except the case of nanoparticles at very low flow rates) considered here. The maximum value of the enhancement factors in a bifurcation strongly increases by decreasing the patch size, representing the high degree of inhomogeneity in the upper human airways during expiration. d = 0.01/am
d = 7~m
.*
•
-...*
•
e,.~.
•
..
•
-
.
.
i
i%
~
"~ "'"
•
• •°
I"--"""""" 'q=34% ""--"-
"
°"b
n = 19%
Figure 1. Expiratory deposition patterns of 7 ~tm and 0.01 lxrn aerosol particles in an asymmetric airway bifurcation, branching angles are 20 and 40 degree, linear dimensions correspond to generations 3-4 (Weibel's Model-A, 1963) at 30 l/min tracheal minute volume and parabolic inlet flow profile. Both the flow rates and the numbers of selected particles are equal at the inlets of the two daughter branches, rl is the deposition efficiency, the main plane of the bifurcation is horizontal. ACKNOWLEDGEMENT This research was supported by: OMFB-01790/98 Contract, Hungarian-Austrian T6T Contract: A-8/98, Hungarian OTKA T 030571 Project, and CEC Contract No. FI4P-CT95-0026. REFERENCES Bal~h/tzy, I. and Hofmann, W. (1993a)J Aerosol Sci. 24: 745-772. Balhshhzy, I. and Hofmann, W. (1993b) J. Aerosol Sci. 24: 773-786. Bal~h,h_~y,I, (1994) d. Comput Phys. 110:11-22. Bal~Mzy, I. and Hofmann, W. (1994) In: Inhaled Particles VII, Ann. occup. Hyg. 38:S 1,47-53. Bai~sh,qzy, I., Heistracher, T. and Hofmann, W. (1996) J. AerosolMed. 9: 287-301. Bal~hhzy, I., Hofmann, W. and Heistraeher, T. (1999)d. Aerosol Sci. 30:185-203. Heistraeher, T., Bai~h~-y, I. and Hofmann, W. (1995) J. AerosolSci. 26:Sl.615-616. Heistracher, T., Hofmann, W. and Bal~sh~y, I. (1996a)3;. Aerosol Sci. 27:S 1.603-604. Heistraeher, T., Hofmann, W. and Bal~shhzy,I. (1996b) Sympos. on Rad. Prot. in Neighbouring Countries in Central Europe, Portoroz, Slovenia,Sept. 4-7, 1995, Proceedings 74-76. Ed.: D. Glavic-Cindro. Hofmann, W. and Bal~hiizy, I. (1991)Radiat. Prot. Dosim. 38:57-63. Hofmarm, W., Bai~sh,qzy,I. and Koblinger, L. (1995) J. Aerosol Sci. 26:1161-1168. Hofmann, W., Balashazy, I., Heistracher, T. and Koblinger, L. (1996a) Aerosol Sci. Technol. 25:305-327. Hofmann, W., Heistracher, T. and Bal/tsMzy, I. (1996b) Environ. International 22:S 1.935-940. Kim, C.S., Iglesias, A.J. and Garcia, L. (1989)3;. AerosolMed 2: 15-27. Weibel, E.R. (1963)Morphometry of the Human Lung. Springer Verlag, Berlin.