Colin Dickens

British American Tobacco, Londinium, England, United Kingdom

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Publications (7)13.33 Total impact

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    ABSTRACT: The real-time effective particle density of cigarette smoke was determined using a Centrifugal Particle Mass Analyzer (CPMA) and Differential Mobility Spectrometer (DMS). A Puff Inhale Exhale (PIE) simulator was used to produce the smoke from various research and commercial cigarettes following the International Standard Organization (ISO) puffing parameters (35 ml puff of 2 s duration, every 60 s) or the Health Canada Intense (HCI) puffing parameters (55 ml puff of 2 s duration, every 30 s). The impact of modifying parameters, such as smoke mass, cigarette format, filter type, inhalation volume and mouth hold period, on the effective particle density was also investigated. All of the effective density functions were found to be independent of particle size within the bias uncertainty of the measurement system, indicating that the cigarette smoke particles likely had a spherical morphology. Trends in the average effective particle densities were observed for the different cigarettes and puffing parameters. While all of these shifts were within the bias uncertainty of the CPMA-DMS system, two-sample t-tests and the Tukey method were used to identify where the shifts were statistically probable. However due to the complexity of cigarette smoke, the aerosol mechanisms behind most of these shifts were unknown and require further investigation. For all of the tested cases the average effective particle density, considering puffs 3 to 6, varied from 1090 to 1518 kg/m3, with a majority (9 out of 16 cases) falling within 1300 to 1394 kg/m3. The Tukey method identified no statistical change in the effective particle density over the duration of an ISO puff, but it did identify significant differences between effective densities produced by different cigarettes.
    Full-text · Article · May 2015 · Journal of Aerosol Science
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    ABSTRACT: The steady-state effective particle density of mainstream smoke from a University of Kentucky 3R4F reference cigarette was determined using a Differential Mobility Analyzer (DMA) and Centrifugal Particle Mass Analyzer (CPMA). The cigarette smoke was generated using a smoking machine under ISO puffing parameters (35 ml puff of 2 s duration, every 60 s) and collected in a Tedlar® bag. This smoke generation process resulted in the first puff of the smoking cycle aging approximately 7 minutes longer than the last puff. The effective particle density (measured immediately upon completion of the last puff) was found to be independent of the particle mobility size, indicating the particles have a spherical morphology, with an average density of 1180±113 kg/m3. Particle coagulation was also found to occur within the Tedlar® bag by comparing particle mobility size distributions, measured with a Scanning Mobility Particle Sizer (SMPS), against an analytical model. This model showed that particle coagulation dominated the particle number concentration decay within the Tedlar® bag compared to particle diffusion or settling losses. Therefore cigarette smoke particles must have a liquid component to maintain a constant effective particle density function in the presence of coagulation. After the 7 minute filling process, the effects of particle aging time and initial particle number concentration in the Tedlar® bag on the effective particle density were found to be small and indistinguishable within the bias uncertainty of the measurement system.
    Full-text · Article · Sep 2014 · Journal of Aerosol Science
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    ABSTRACT: Background / Purpose: Significant deposition (> 20%) of mainstream cigarette smoke has been measured in the mouth. However, current mathematical models underestimate cigarette smoke deposition in oral airways. The goal of this study was to investigate various deposition mechanisms of inhaled cigarette smoke in an oral airway model. Main conclusion: Inclusion of the deposition mechanisms of coagulation, hygroscopicity, and thermophoresis did not account for the elevated deposition of cigarette smoke particles in the oral cavity. Future work will involve more realistic puffing and inhalation scenarios (e.g., transient airflow, expanding oral cavity).
    Full-text · Conference Paper · Aug 2014
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    ABSTRACT: 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.
    Full-text · Article · Dec 2013 · Inhalation Toxicology
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    ABSTRACT: ABSTRACT: There 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. The 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. These 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.
    Full-text · Article · Aug 2011 · Chemistry Central Journal
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    ABSTRACT: 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.
    No preview · Article · Mar 2009 · Journal of Physics Conference Series
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    ABSTRACT: Many studies suggest limited effectiveness of spray devices for nasal drug delivery due primarily to high deposition and clearance at the front of the nose. Here, nasal spray behavior was studied using experimental measurements and a computational fluid dynamics model of the human nasal passages constructed from magnetic resonance imaging scans of a healthy adult male. Eighteen commercially available nasal sprays were analyzed for spray characteristics using laser diffraction, high-speed video, and high-speed spark photography. Steadystate, inspiratory airflow (15 L/min) and particle transport were simulated under measured spray conditions. Simulated deposition efficiency and spray behavior were consistent with previous experimental studies, two of which used nasal replica molds based on this nasal geometry. Deposition fractions (numbers of deposited particles divided by the number released) of 20- and 50-microm particles exceeded 90% in the anterior part of the nose for most simulated conditions. Predicted particle penetration past the nasal valve improved when (1) the smaller of two particle sizes or the lower of two spray velocities was used, (2) the simulated nozzle was positioned 1.0 rather than 0.5 or 1.5 cm into the nostril, and (3) inspiratory airflow was present rather than absent. Simulations also predicted that delaying the appearance of normal inspiratory airflow more than 1 sec after the release of particles produced results equivalent to cases in which no inspiratory airflow was present. These predictions contribute to more effective design of drug delivery devices through a better understanding of the effects of nasal airflow and spray characteristics on particle transport in the nose.
    Full-text · Article · Feb 2007 · Journal of Aerosol Medicine