Local lung deposition of ultrafine particles in healthy adults: experimental results and theoretical predictions

Abstract

Background: Ultrafine particles (UFP) of biogenic and anthropogenic origin occur in high numbers in the ambient atmosphere. In addition, aerosols containing ultrafine powders are used for the inhalation therapy of various diseases. All these facts make it necessary to obtain comprehensive knowledge regarding the exact behavior of UFP in the respiratory tract.

Methods: Theoretical simulations of local UFP deposition are based on previously conducted inhalation experiments, where particles with various sizes (0.04, 0.06, 0.08, and 0.10 µm) were administered to the respiratory tract by application of the aerosol bolus technique. By the sequential change of the lung penetration depth of the inspired bolus, different volumetric lung regions could be generated and particle deposition in these regions could be evaluated. The model presented in this contribution adopted all parameters used in the experiments. Besides the obligatory comparison between practical and theoretical data, also advanced modeling predictions including the effect of varying functional residual capacity (FRC) and respiratory flow rate were conducted.

Results: Validation of the UFP deposition model shows that highest deposition fractions occur in those volumetric lung regions corresponding to the small and partly alveolated airways of the tracheobronchial tree. Particle deposition proximal to the trachea is increased in female probands with respect to male subjects. Decrease of both the FRC and the respiratory flow rate results in an enhancement of UFP deposition.

Conclusions: The study comes to the conclusion that deposition of UFP taken up via bolus inhalation is influenced by a multitude of factors, among which lung morphometry and breathing conditions play a superior role.

Keywords: Deposition model; aerosol bolus; inhalation experiments; therapeutic aerosol; ultrafine particles (UFP); volumetric lung region.

Figure 1

Experimental and theoretical data (mean ± standard deviation) of local deposition fractions of particles measuring 0.04 µm in size after aerosol bolus inhalation: (A) males; (B) females.

Figure 2

Experimental and theoretical data (mean ± standard deviation) of local deposition fractions of particles measuring 0.06 µm in size after aerosol bolus inhalation: (A) males; (B) females.

Figure 3

Experimental and theoretical data (mean ± standard deviation) of local deposition fractions of particles measuring 0.08 µm in size after aerosol bolus inhalation: (A) males; (B) females.

Figure 4

Experimental and theoretical data (mean ± standard deviation) of local deposition fractions of particles measuring 0.10 µm in size after aerosol bolus inhalation: (A) males; (B) females.

Figure 5

Experimental and theoretical results (mean ± standard deviation) of regional particle deposition fractions in male and female subjects: (A) 0.04-µm particles; (B) 0.06-µm particles. Asterisks indicate significant (*, P<0.05) or highly significant (**, P<0.001) differences between experiment and model.

Figure 6

Experimental and theoretical results (mean ± standard deviation) of regional particle deposition fractions in male and female subjects: (A) 0.08-µm particles; (B) 0.10-µm particles.

Figure 7

Advanced modeling predictions: (A) effect of functional residual capacity (FRC) on local deposition fractions of 0.06-µm particles; (B) influence of respiratory flow rate (Q) on local deposition fractions of 0.06-µm particles (FRC =3,000 mL).