Age-dependence and intersubject variability of tracheobronchial particle clearance

SUMMARY.Background: The detailed study of tracheobronchial clearanceof inhaled particles represents one of the basic research questionsin lung medicine. The clearance efficiency varies in different agegroups and between males and females.The differences can bepartly clarified by the application of a well validated theoreticalapproach. 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: Themathematical model used for clearance simulation is based on theconcept of a stochastic lung structure and considers both early fastmucociliary clearance and a later, slow clearance fraction, fs, effectedby particular uptake by tracheobronchial cells, e.g., macrophagesand epithelial cells. According to this model, the calculated mucusvelocities for each airway generation of the tracheobronchial compartmentare normalized to a respective tracheal mucus velocitythat is estimated for each of the age groups studied from an allometricfunction. Results: In general, tracheobronchial clearanceefficiency undergoes a significant increase from childhood to youngadulthood, reaching a maximum at 25-30 years and decreasingagain from about 30 years to 60 years. Conversely to the improvementof clearance, the continuous change of airway morphometrywith increasing age causes a decrease of the filtering effect in thetrachea and main bronchi, which is of marked importance in infants.The modelling results demonstrate differences in tracheobronchialclearance between males and females, generally in the range from0 to 5%, which are exclusively determined by the individual lunggeometry. Conclusions: Based on theoretical computations itcan be concluded that tracheobronchial clearance is a phenomenonthat depends on both age and sex. Biological studies are necessaryto determine the cellular and molecular mechanisms underlyingthe age-dependent development of tracheobronchial clearance.Pneumon 2011, 24(1):396-403.