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Quantification of lung doses from inhaled tobacco smoke

Institution: University of California, Irvine
Investigator(s): Robert Phalen, Ph.D.
Award Cycle: 1997 (Cycle 6) Grant #: 6RT-0066 Award: $425,728
Subject Area: General Biomedical Science
Award Type: Research Project Awards
Abstracts

Initial Award Abstract
This project studies two things: predicted accumulation of inhaled cigarette smoke in the lungs, and how long cigarette smoke stays in the air of a room. Because smoke is more comp-licated than most air pollutants, understanding these two health-related issues is scientifically challenging. Clouds of fresh cigarette smoke contain very large numbers of microscopic liquid drops, which are called particles. Because of this high concentration of particles, smoke clouds can behave in an unusual way, which is not seen with ordinary particles in the air, such as dust from a vacuum cleaner or water droplets from a mist sprayer. Before being diluted by the surrounding air, cigarette smoke clouds move as bodies with distinct shapes rather than as separate particles that drift apart in random directions. Persistent smoke rings blown by smokers are evidence of this cloud-type motion.

The research in this project involves studies of the effects of cloud-type motion on where and how much cigarette smoke accumulates in the human lung after the smoke is inhaled, and on the rate at which secondhand smoke clears from the air of rooms in which people are smoking. It has been known for a long time that more cigarette smoke deposits in the human lung than is predicted by computers when the effects of cloud motion are ignored. In addition, since the liquid drop particles in the smoke are so tiny, scientific calculations indicate that they should deposit in the very deepest parts of the lung. However, lung cancers often occur in the upper parts of the lung. Also, computer calculations indicate that clouds of cigarette smoke will fall out of the air slower than we have observed. This project works on improving the computer calculations so that they will better describe what takes place in reality.

The methods are innovative. Smoke accumulation in the lung will be studied using rubber and plastic models of lung airways which have the same sizes and shapes as airways in real human lungs. Airways in both the upper and lower parts of the lungs will be included, as will human-like breathing patterns. We will also study where one of the most likely lung cancer-causing agents in smoke deposits. The results from these experiments will be used to improve the predictions obtained using computer programs that calculate risks.

The effects of air movement, air temperature, and moisture in the air on the speed that secondhand smoke clears from a room will also be studied. In addition, how the presence of the smoker (in our case, a heated mannequin) affects the speed of clearing of smoke from a room will be examined. This information can be used to design efficient smoke control techniques for homes, offices, and other environments.

In summary, our project will produce needed information on the unusual behavior of clouds of cigarette smoke, and will generate new information which can be used to measure and control the risks of smoking.

Final Report
The purpose of this project was to examine the unique behavior of cigarette smoke in the human respiratory tract, and in indoor environments. It has long been known that cigarette smoke tends to deposit in the respiratory tract to a much greater degree than it would if only the individual motions of its constituent particles are considered. It was suspected that concentrated smoke behaved as clouds, rather than individual particles. Clouds of cigarette smoke have also been postulated to settle out of the environmental air due to gravity at a much greater rate than they would if their constituent particles acted independently. The proposed research investigates these phenomena from the viewpoint of human risk assessment, with a focus on environmental tobacco smoke (ETS).

Progress has been made in several areas including: smoke deposition in hollow airway models; the behavior of a carcinogen, B(a)P, a constituent of cigarette smoke; persistence of smoke in the air; and improvements to computer models used for quantifying risks from inhaled tobacco smoke. Hollow models of the small, medium and large human airways were constructed and exposed to cigarette smoke under various conditions. The evidence that cloud effects enhanced deposition was strong. The bronchial deposition patterns looked similar to those expected for 6-7 m aerodynamic diameter particles despite the fact that ETS particles are smaller than 1 m. The larger effective aerosol size greatly increases local doses in the bronchial airways. B(a)P depositions in the models indicated that this carcinogen can have a deposition pattern that differs from that of the main smoke’s particle mass. Thus, carcinogen risks may need to be evaluated using specific, experimentally-determined particle sizes for each chemical substance. As a product of this grant, a new TRDRP award has been made to Dr. Michael Oldham to follow up on our findings. Persistence studies of ETS in enclosed spaces (a small room) indicated that the rate of decay of smoke particles from the air depended on several factors including stirring of the air, ambient temperature and the presence of a heated human mannequin. These results have applications for controlling ETS in indoor environments. Our inhaled particle deposition computer code has been modified to allow for inclusion of some cloud-related smoke properties. This model is a beginning toward solving a complex problem. Also, a small workshop was held on the fundamentals of tobacco smoke cloud behavior. The workshop identified several fruitful approaches for future research, and a larger, follow-on, conference that will involve a larger community of researchers is being planned.

In summary, the project has clarified the aerodynamic behavior of ETS, produced literature contributions and fostered new projects.
Publications

Effects of breathing parameters on sidestream cigarette smoke deposition in a hollow model
Periodical: American Industrial Hygiene Association Journal Index Medicus:
Authors: Dendo RI, Phalen RF, Mannix RC, Oldham MJ ART
Yr: 1998 Vol: 59 Nbr: Abs: Pg: 381-387

Computational fluid dynamic predictions vs experimental results for particle deposition in an idealized airway model
Periodical: Aerosol Science and Technology Index Medicus:
Authors: Oldham MJ, Phalen RF, Heistracher T ART
Yr: 2000 Vol: 32 Nbr: Abs: Pg: 61-71

Methods for modeling particle deposition as a function of age
Periodical: Respiration Physiology Index Medicus:
Authors: Phalen RF, Oldham MJ ART
Yr: 2001 Vol: 128 Nbr: Abs: Pg: 119-130