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Regional deposition of glass fibers was investigated in a physically realistic, human respiratory tract replica. The replica begins with the oral cavity and includes the airways up to the 7th generation of the tracheobronchial tree. Uniform diameter glass fibers were classified by length using a dielectrophoretic classifier and introduced into the replica at three steady-state flow rates (15, 30, and 50 LPM). A novel automatic image processing method was utilized to speed up the sample analysis and make it more reproducible. Fractional deposition was high in the oral cavity and the upper respiratory airways. Deposition density was higher in the first few generations of the tracheobronchial tree. Deposition efficiencies were compared with published data and good agreement was obtained. Our data confirmed that the deposition efficiency increased with increasing Stokes number indicating that impaction was the main deposition mechanism. The experimental data were used to propose new empirical models predicting fiber deposition in the tracheobronchial tree. [ABSTRACT FROM AUTHOR]

The inhalation route has a substantial influence on the fate of inhaled particles. An outbreak of infectious diseases such as COVID-19, influenza or tuberculosis depends on the site of deposition of the inhaled pathogens. But the knowledge of respiratory deposition is important also for occupational safety or targeted delivery of inhaled pharmaceuticals. Simulations utilizing computational fluid dynamics are becoming available to a wide spectrum of users and they can undoubtedly bring detailed predictions of regional deposition of particles. However, if those simulations are to be trusted, they must be validated by experimental data. This article presents simulations and experiments performed on a geometry of airways which is available to other users and thus those results can be used for intercomparison between different research groups. In particular, three hypotheses were tested. First: Oral breathing and combined breathing are equivalent in terms of particle deposition in TB airways, as the pressure resistance of the nasal cavity is so high that the inhaled aerosol flows mostly through the oral cavity in both cases. Second: The influence of the inhalation route (nasal, oral or combined) on the regional distribution of the deposited particles downstream of the trachea is negligible. Third: Simulations can accurately and credibly predict deposition hotspots. The maximum spatial resolution of predicted deposition achievable by current methods was searched for. The simulations were performed using large-eddy simulation, the flow measurements were done by laser Doppler anemometry and the deposition has been measured by positron emission tomography in a realistic replica of human airways. Limitations and sources of uncertainties of the experimental methods were identified. The results confirmed that the high-pressure resistance of the nasal cavity leads to practically identical velocity profiles, even above the glottis for the mouth, and combined mouth and nose breathing. The distribution of deposited particles downstream of the trachea was not influenced by the inhalation route. The carina of the first bifurcation was not among the main deposition hotspots regardless of the inhalation route or flow rate. On the other hand, the deposition hotspots were identified by both CFD and experiments in the second bifurcation in both lungs, and to a lesser extent also in both the third bifurcations in the left lung. • Limits of current methods in prediction of flow and high-resolution deposition in an airway geometry were investigated. • Experiments and simulations performed on a replica of airways - nasal and oral cavity and seven generations of TB branching. • The influence of the inhalation route on the flow field was negligible downstream of the glottis. • The carina of the first bifurcation was not among the main deposition hotspots regardless of the inhalation route. • Deposition hotspots identified in the second bifurcation in both lungs, and in both third bifurcations in the left lung. [ABSTRACT FROM AUTHOR]

Quantification of airway deposition of aerosol particles is essential for the assessment of health risks of detrimental particles. Knowledge of deposition distribution is important also in the case of treatment with aerosolised drugs. It is also worth considering that deposition of inhaled particles in severe asthmatics can be different from the deposition in healthy subjects due to the modified breathing parameters, airway geometry and lobar flow distribution. The aim of this study was to apply combined experimental and numerical techniques to quantify the upper airway and bronchial deposition of the inhaled microparticles in healthy individuals in comparison with asthma patients. Idealised and realistic physical and digital replicas of the human airways were constructed. Deposition fractions and efficiencies of inhaled polydisperse mannitol and chitosan particles in different airway sections were measured and calculated. Deposition fraction of polydisperse mannitol particles in the idealised airway geometry assuming breathing conditions of healthy subjects was 21.9% and 18.3% when determined experimentally and by numerical simulations, respectively. Experimental measurements of deposition fraction of chitosan particles in the same geometry, but assuming breathing parameters characteristic of severe asthmatics yielded 32%, while simulations provided 30.1% for the same conditions. Extrathoracic deposition fraction of mannitol particles in healthy subjects measured in the realistic geometry was 71.1%, while bronchial deposition fraction was 5.3%. The corresponding simulations yielded 76.2% and 8.9% deposition fractions in the upper and bronchial airways, respectively. There was a good agreement between the experimental and simulation deposition results also in the different predefined sections of the airways. Present pilot study proved that lobar flow redistribution due to severe asthma significantly modified the deposition distribution of micro-particles. Although the present results refer only to small groups of healthy and asthmatic individuals, it clearly demonstrates the capability of carefully validated models to simulate the deposition of micron-size particles in larger populations of both groups. • Deposition distribution of micro-particles in idealised and realistic upper and central airways was measured and simulated. • Deposition distribution of micro-particles in idealised and realistic upper and central airways was measured and simulated. • Good agreement of numerical and experimental data was found. • The modified breathing of asthmatics significantly changed the deposition distribution of micro-particles. • Combination of numerical and experimental techniques can be a powerful tool of the quantification of particle deposition. [ABSTRACT FROM AUTHOR]