Theoretical deposition of nanotubes in the respiratory tract of children and adults

Abstract

Introduction: Nanotubes are assumed to contribute to a significant exacerbation of asthma and to enhance the risk of profibrotic effects in lungs being affected by this injury. Therefore, deposition of nanotubes in the lungs of subjects with different ages was subject to a detailed theoretical investigation.

Methods: Nanoparticle deposition was computed by application of well validated stochastic deposition model, including four main deposition forces (Brownian diffusion, inertial impaction, interception, gravitational settling). Nonspherical particle geometry was considered with the help of the aerodynamic diameter concept. Deposition was calculated for particles with diameters adopting values of 1, 10, and 100 nm as well as aspect ratios of 10, 50, and 100. Lungs of subjects with different ages were generated with the help of scaling factors and allometric functions. Inhalation was uniformly supposed to take place under non-strain conditions (sitting breathing conditions).

Results: Total deposition of nanotubes is significantly increased with proceeding age, with deposition probability being negatively correlated with particle size (diameter and aspect ratio). Whilst extrathoracic deposition is subject to a slight decrease from infants to adults, bronchial/bronchiolar and alveolar depositions are exponentially increased.

Discussion and conclusions: Due to an increase of nanotube deposition with proceeding age infants and children enjoy a certain protection from excessive particle exposure. This circumstance mostly reprieves their lungs from injuries induced by this sort of particles.

Keywords: Brownian diffusion; Monte-Carlo model; Nanoparticles; asthma; deposition; lung; lung deposition; stochastic model.

Figure 1

Logarithmic relation between airway diameter (mm) and airway length (mm) for lung generations 1 (trachea) to 12: (A) 1-year old infant; (B) 5-year old child; (C) 15-year old adolescent; (D) adult. Logarithmic regression functions and goodnesses of fit (R²) are additionally provided.

Figure 2

Age dependence of the lung scaling factor as well as diverse breathing parameters: (A) scaling factor; (B) functional residual capacity (FRC); (C) tidal volume (TV); (D) breathing frequency (BF); (E) breath-cycle time. Second-grade polynomial regression functions and goodnesses of fit (R²) are additionally provided.

Figure 3

Age dependence of total nanotube deposition in the respiratory tract: (A) tubes with 1 nm diameter; (B) tubes with 10 nm diameter; (C) tubes with 100 nm diameter. Solid lines yield an aspect ratio β of the tubes of 10, dashed lines an aspect ratio of 50, and dotted lines an aspect ratio of 100.

Figure 4

Age dependence of extrathoracic nanotube deposition in the respiratory tract: (A) tubes with 1 nm diameter; (B) tubes with 10 nm diameter; (C) tubes with 100 nm diameter. Solid lines yield an aspect ratio β of the tubes of 10, dashed lines an aspect ratio of 50, and dotted lines an aspect ratio of 100.

Figure 5

Age dependence of bronchial nanotube deposition in the respiratory tract: (A) tubes with 1 nm diameter; (B) tubes with 10 nm diameter; (C) tubes with 100 nm diameter. Solid lines yield an aspect ratio β of the tubes of 10, dashed lines an aspect ratio of 50, and dotted lines an aspect ratio of 100.

Figure 6

Age dependence of alveolar nanotube deposition in the respiratory tract: (A) tubes with 1 nm diameter; (B) tubes with 10 nm diameter; (C) tubes with 100 nm diameter. Solid lines yield an aspect ratio β of the tubes of 10, dashed lines an aspect ratio of 50, and dotted lines an aspect ratio of 100.