Colin Dickens

Assessment of an in vitro whole cigarette smoke exposure system: The Borgwaldt RM20S 8-syringe smoking machine

BackgroundThere have been many recent developments of in vitro cigarette smoke systems closely replicating in vivo exposures. The Borgwaldt RM20S smoking machine (RM20S) enables the serial dilution and delivery of cigarette smoke to exposure chambers for in vitro analyses. In this study we have demonstrated reliability and robustness testing of the RM20S in delivering smoke to in vitro cultures using an in-house designed whole smoke exposure chamber.ResultsThe syringe precision and accuracy of smoke dose generated by the RM20S was assessed using a methane gas standard and resulted in a repeatability error of ≤9%. Differential electrical mobility particle spectrometry (DMS) measured smoke particles generated from reference 3R4F cigarettes at points along the RM20S. 53% ± 5.9% of particles by mass reached the chamber, the remainder deposited in the syringe or connecting tubing and ~16% deposited in the chamber. Spectrofluorometric quantification of particle deposition within chambers indicated a positive correlation between smoke concentration and particle deposition. In vitro air-liquid interface (ALI) cultures (H292 lung epithelial cells), exposed to whole smoke (1:60 dilution (smoke:air, equivalent to ~5 μg/cm2)) demonstrated uniform smoke delivery within the chamber.ConclusionsThese results suggest this smoke exposure system is a reliable and repeatable method of generating and exposing ALI in vitro cultures to cigarette smoke. This system will enable the evaluation of future tobacco products and individual components of cigarette smoke and may be used as an alternative in vitro tool for evaluating other aerosols and gaseous mixtures such as air pollutants, inhaled pharmaceuticals and cosmetics.

Component-specific, cigarette particle deposition modeling in the human respiratory tract

Abstract Inhalation of cigarette smoke particles (CSP) leads to adverse health effects in smokers. Determination of the localized dose to the lung of the inhaled smoke aids in determining vulnerable sites, and identifying components of the smoke that may be responsible for the adverse effects; thus providing a roadmap for harm reduction of cigarette smoking. A particle deposition model specific to CSP was developed for the oral cavity and the lung by accounting for cigarette particle size growth by hygroscopicity, phase change and coagulation. In addition, since the cigarette puff enters the respiratory tract as a dense cloud, the cloud effect on particle drag and deposition was accounted for in the deposition model. Models of particle losses in the oral cavities were developed during puff drawing and subsequent mouth-hold. Cigarette particles were found to grow by hygroscopicity and coagulation, but to shrink as a result of nicotine evaporation. The particle size reached a plateau beyond which any disturbances in the environmental conditions caused the various mechanisms to balance each other out and the particle size remain stable. Predicted particle deposition considering the cloud effects was greater than when treated as a collection of non-interacting particles (i.e. no cloud effects). Accounting for cloud movement provided the necessary physical mechanism to explain the greater than expected, experimentally observed and particle deposition. The deposition model for CSP can provide the necessary input to determine the fate of inhaled CSP in the lung. The knowledge of deposition will be helpful for health assessment and identification and reduction of harmful components of CSP.

Puffing and inhalation behaviour in cigarette smoking: Implications for particle diameter and dose

Inhalation of tobacco smoke aerosol is a two-step process involving puffing followed by inhalation. Measured smoke deposition efficiencies in the lung (20-70%) are greater than expected for smoke particles of diameter 150 -- 250 nm CMD. Various mechanisms have been put forward to explain this enhanced deposition pattern, including coagulation, hygroscopic growth, condensation and evaporation, changes in composition, or changes in inhalation behaviour. This paper represents one of a series of studies seeking to better quantify smoke chemistry, inhalation behaviour and cumulative particle growth. The studies have been conducted to better understand smoke dosimetry and links to disease as part of a wider programme defining risk and potential harm reduction. In this study, it was noted that particle deposition increased with increasing inhalation depth, and that smoke inhalation volumes were generally greater than normal tidal breathing volumes. A weak association was observed between particle diameter and puff flow, but no strong association between particle diameter and retention efficiency.

Steady-state mass-mobility measurements of cigarette smoke using a CPMA

Tobacco smoke is a dynamic formation of gaseous and particulate material. The density of particulate phase can change due to evaporation condensation and alter its mass and mobility. Therefore these aerosol characteristics are important for modelling lung deposition or smoke particle transport in air. The mass and mobility of cigarette smoke particles was measured using a Centrifugal Particle Mass Analyzer (CPMA) and Differential Mobility Analyzer (DMA). The experimental setup, shown in Figure 1, placed a DMA and Condensation Particle Counter (CPC) upstream of a CPMA. The DMA selected the particles based on electrical mobility, while the upstream CPC accounted for the particle concentration decreasing in the bag over time. The CPMA then further classified the particles by mass-to-charge ratio. By stepping the CPMA through the particle mass range and counting the number of classified particles with the downstream CPC the mass-classified concentration peak was determined for the set DMA mobility size.

CFD simulations of mainstream cigarette smoke particle growth and deposition in the oral airways

CFD Model • A 3D computational fluid dynamics (CFD) model of the mouth-throat region was developed from CT scans (Fig. 1) • Steady-state airflow was simulated for low-flow puffing scenarios (1.05 and 2.5 L/min) (Fig. 2) [2] • Transport and deposition of inhaled 0.1 – 0.5 μm particles was simulated • Lagrangian particle tracking was used to simulate deposition by inertial impaction, sedimentation, and diffusion • All CFD analyses were conducted using Fluent v14.0 (ANSYS, Inc.)