Effects of breathing parameters on sidestream cigarette smoke deposition in a hollow tracheobronchial model

The effects of variations in cyclic breathing parameters (i.e., tidal volume and breath frequency) have been the subject of few studies devoted to the deposition of submicrometer aerosols in the human respiratory tract. Therefore, a series of experiments was performed to investigate whether the deposition efficiency (DE) of sidestream cigarette smoke is altered by varying tidal volume and breath frequency in a child-size hollow tracheobronchial (TB) model while maintaining a fixed minute ventilation rate of 5 L/min. Under cyclic flow conditions with tidal volumes of 100 mL (50 breaths/min), 250 mL (20 breaths/min), 500 mL (10 breaths/min) and 750 mL (6.7 breaths/min), sidestream cigarette smoke was passed through replicas of an idealized hollow TB model. The smoke deposits were extracted and then quantitated spectrophotometrically. The experiments revealed a significant difference in DE between the 100-mL tidal volume (DE = 6.0%) and the 750-mL tidal volume (DE = 11.1%). Under equivalent steady flow conditions, the mean DE was 21.5%. A trend was evident in the data--DE increased as tidal volume increased (and breathing frequency decreased)--suggesting that the influence of diffusion and secondary flows on DE becomes greater as the air residence time increases and the degree of air turbulence decreases. The results provide evidence of the importance of breathing parameters when attempting to model in vivo deposition of environmental tobacco smoke and other similar-size respirable aerosols.