Development of a realistic human respiratory tract cast representing physiological thermal conditions

Toxicological assessment of inhaled aerosols and their effects on respiratory tissue cells requires accurate measurements of particle delivery, properties, evolution, and deposition in the human respiratory tract. These measurements are affected by both anatomical features and physiological factors, such as thermal conditions in the respiratory system. We constructed a segmented cast model, based on a realistic geometry of the human respiratory tract, equipped with features to control the temperature of the air flow. We then evaluated the thermal equilibrium of the air flow through the cast using both experimental measurements and computational fluid dynamics modeling. Uniform temperature distribution in the cast shell was achieved using parallel connection of the cast segments to a thermal bath by flow splitter. Air temperature inside the cast was shown to require <1 min to equilibrate with the temperature of the cast during internal circulation of hot water. Air flow temperature was shown to equilibrate with the cast temperature in the mouth-throat region, and a uniform temperature distribution was achieved in the other segments, resembling the thermal conditions of respiratory flow in the human lung. We showed that the cast successfully represents the physiological thermal conditions of the human respiratory system.