Simulation and minimisation of the airway deposition of airborne bacteria

Respiratory infections represent one of the most important bioaerosol-associated health effects. Bacteria are infectious micro-organisms that may, after inhalation, cause specific respiratory diseases. Although a large number of inhalable pathogenic bacteria have been identified and the related respiratory symptoms are well known, their airway transport and deposition are still not fully explored. The objective of this work was to characterise the deposition of inhaled bacteria in different regions of the lung and to find the optimum breathing modes, which ensure the minimum chance of a bacterial infection in a given environment. For this purpose a stochastic computer lung model has been applied. In order to find the breathing pattern that yields the lowest deposited fraction of the inhaled particles, multiple simulations were carried out with several combinations of tidal volumes ranging from 400 to 2000 ml, and breathing cycles ranging from 2 to 10 s. Particle aerodynamic diameters varied between 1 and 20 mum, and simulations were performed for both nose and mouth breathing conditions. Present computations demonstrated that regional (extrathoracic, tracheobronchial, acinar), lobar, and generation number-specific deposition distributions of the inhaled particles are highly sensitive to their aerodynamic diameter and to the breathing parameters. According to our results, mouth breathing with short breathing periods, no breath hold, and low tidal volumes minimises the total respiratory system deposition. On the other hand, lung (bronchial and acinar) deposition can be minimised by a breathing mode characterised by short breathing cycles through the nose with long breath holds after exhalations and high tidal volumes.