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REVIEW
Age-dependence and intersubject variability of tracheobronchial particle clearance
1
Division of Physics and Biophysics Department of Material Science and Physics University of Salzburg Hellbrunner Strasse 34 A-5020 Salzburg Austria
Pneumon 2011;24(1):77-85
KEYWORDS
ABSTRACT
Background:
The detailed study of tracheobronchial clearance of inhaled particles represents one of the basic research questions in lung medicine. The clearance efficiency varies in different age groups and between males and females.The differences can be partly clarified by the application of a well validated theoretical approach. This study applied a relevant model to children (1 year, 5 years, 10 years), juveniles (15 years), and adults of different ages (18, 21, 25, 34, 50, and 60 years) and to both sexes.
Methods:
The mathematical model used for clearance simulation is based on the concept of a stochastic lung structure and considers both early fast mucociliary clearance and a later, slow clearance fraction, fs, effected by particular uptake by tracheobronchial cells, e.g., macrophages and epithelial cells. According to this model, the calculated mucus velocities for each airway generation of the tracheobronchial compartment are normalized to a respective tracheal mucus velocity that is estimated for each of the age groups studied from an allometric function.
Results:
In general, tracheobronchial clearance efficiency undergoes a significant increase from childhood to young adulthood, reaching a maximum at 25-30 years and decreasing again from about 30 years to 60 years. Conversely to the improvement of clearance, the continuous change of airway morphometry with increasing age causes a decrease of the filtering effect in the trachea and main bronchi, which is of marked importance in infants. The modelling results demonstrate differences in tracheobronchial clearance between males and females, generally in the range from 0 to 5%, which are exclusively determined by the individual lung geometry.
Conclusions:
Based on theoretical computations it can be concluded that tracheobronchial clearance is a phenomenon that depends on both age and sex. Biological studies are necessary to determine the cellular and molecular mechanisms underlying the age-dependent development of tracheobronchial clearance.
The detailed study of tracheobronchial clearance of inhaled particles represents one of the basic research questions in lung medicine. The clearance efficiency varies in different age groups and between males and females.The differences can be partly clarified by the application of a well validated theoretical approach. This study applied a relevant model to children (1 year, 5 years, 10 years), juveniles (15 years), and adults of different ages (18, 21, 25, 34, 50, and 60 years) and to both sexes.
Methods:
The mathematical model used for clearance simulation is based on the concept of a stochastic lung structure and considers both early fast mucociliary clearance and a later, slow clearance fraction, fs, effected by particular uptake by tracheobronchial cells, e.g., macrophages and epithelial cells. According to this model, the calculated mucus velocities for each airway generation of the tracheobronchial compartment are normalized to a respective tracheal mucus velocity that is estimated for each of the age groups studied from an allometric function.
Results:
In general, tracheobronchial clearance efficiency undergoes a significant increase from childhood to young adulthood, reaching a maximum at 25-30 years and decreasing again from about 30 years to 60 years. Conversely to the improvement of clearance, the continuous change of airway morphometry with increasing age causes a decrease of the filtering effect in the trachea and main bronchi, which is of marked importance in infants. The modelling results demonstrate differences in tracheobronchial clearance between males and females, generally in the range from 0 to 5%, which are exclusively determined by the individual lung geometry.
Conclusions:
Based on theoretical computations it can be concluded that tracheobronchial clearance is a phenomenon that depends on both age and sex. Biological studies are necessary to determine the cellular and molecular mechanisms underlying the age-dependent development of tracheobronchial clearance.
ABBREVIATIONS
Ai-1: cross section area of airway i-1,
Ai: cross section area of airway i,
dg: geometric diameter of a deposited particle,
FRC: functional residual capacity,
FRCreference: functional residual capacity of a reference subject,
FRCsubject: functional residual capacity of a subject
of interest,
fs: fraction of slowly cleared particles,
ICRP: International Commission on Radiological,
Protection
Li: length of airway i,
sf: scaling factor,
td: mucus delay time,
TLC: total lung capacity,
tr,i: total residence time of particle in airway i,
VC: vital capacity
vi-1: mucus velocity in airway i-1
vi: mucus velocity in airway i
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