Modeling the dose distribution of H2SO4 aerosols in the human tracheobronchial tree

Radiation dose to the human respiratory tract from inhalation of radon-222 and its progeny

In this article the regional dose equivalent for exposure to 1 working level month (WLM), the annual effective dose equivalent and the dose equivalent conversion factor due to the inhalation of short-lived radon progeny (218Po, 214Pb and 214Bi/214Po) are calculated with a dosimetric model. Experimental results of aerosol size characteristics, unattached activity fractions, equilibrium factors, and activity size distributions of the short-lived radon progeny in indoor and outdoor atmosphere are summarized. Dose calculations based on these results show that the changes in dose rate values are influenced by the different model assumptions concerning deposition probabilities of aerosol particles in the respiratory system during inhalation, the sensitivity of different cells (epithelial, basal) to radiation and assuming nose or mouth breathing. The inverse relationship between the unattached fraction of potential alpha-particle energy in room air and the radioactive equilibrium between radon gas and its progeny indicates that dose equivalent is closely related to the concentration of radon gas averaged over a period of exposure.

Behavior of hygroscopic pharmaceutical aerosols and the influence of hydrophobic additives

The high temperature and relative humidity in the lung can result in the hygroscopic growth of susceptible aerosol particles or droplets. The term hygroscopic growth describes the increase in particle diameter which occurs as the result of association with water vapor. The influence of hygroscopicity upon lung deposition of aerosols has been a productive area of research in industrial hygiene, environmental sciences, and inhalation toxicology. Many pharmaceutical inhalation aerosols display hygroscopic behavior in their passage through the airways; however, the effect has been neglected. Controlling the phenomenon of hygroscopic growth and, thus, the related lung deposition of aerosols might result in the therapeutic advantage of targeting the site of action. Such an approach might also allow identification of the location of pharmacologic receptor sites in the lung. This Review discusses an approach to achieving control of hygroscopic growth of aerosol particles. Theoretical and experimental studies have indicated that inhaled particle diameters increased significantly for drugs commonly administered to the lung. The presence of certain additives, notably glycerol, cetyl alcohol, and lauric and capric acids, has been demonstrated to reduce the growth of particles under conditions approaching those in the lung. Very few quantitative studies of the nature discussed herein have appeared in the literature. It is conceivable that an aerosol particle could be fabricated of known initial size and density, and by implication, deposition characteristic, and this might be induced to follow specific growth kinetics to enhance deposition in a particular region of the lung. Thus, physical targeting of regions within the lung might be achieved.

Epidemiologic and toxicologic evidence for chronic health effects and the underlying biologic mechanisms involved in sub-lethal exposures to acidic pollutants

Since the 1880s, a disparate and extensive literature has evolved examining the biologic effects of acidification on cells. More recently, effects on the health of human and other species of acidic agents contained, for example, in pollutants have been suggested, particularly relating to long-term exposures. This paper provides a review of the epidemiologic and toxicologic evidence concerning health effects--particularly carcinogenicity--attributable to sub-lethal acid exposure. Underlying biologic mechanisms that explain adverse health outcomes include pH modulation of toxicity for a number of xenobiotics (including carcinogens, genotoxins, and teratogens), and low-pH-induced changes of cells involving, for example, alterations in mitotic and enzyme regulation. More focused research is recommended to test the relationship between long-term exposures to acidic agents (with a consequent lowered cellular pH) and various health effects.

Deposition of sulfuric acid mist in the respiratory tracts of guinea pigs and rats

Radiolabeled sulfuric acid mists in the size range of 0.4-1.2 micron mass median aerodynamic diameter (MMAD) were generated at 20 and 80% relative humidity at concentrations from 1.3 to 20 micrograms/l. Guinea pigs and rats were exposed to these aerosols by the nose-only route for short periods (30 s) and were quickly sacrificed and dissected. The regional respiratory-tract deposition patterns were measured. The results indicate that regional deposition fraction is positively correlated with droplet size of the sulfuric acid but is not correlated with atmospheric concentration or relative humidity over the ranges of the parameters studied. A comparison of the data obtained in these studies with those from earlier studies indicates that the deposition of sulfuric acid in the respiratory tract of rats is greater than for nonhygroscopic aerosols having similar MMADs. This may be due to the growth of the droplets in the high humidity of the respiratory tract.

Deposition of sulfuric acid mists in the respiratory tract of beagle dogs

Beagle dogs were exposed to 35S-labeled sulfuric acid mists. The size range of the mist droplets was 0.4-1.1 micrometer mass median aerodynamic diameter (MMAD), and the external relative humidity was 20 or 80%. Immediate isolation of the respiratory tract and measurement of radioactivity in specified portions allowed determination of regional deposition. It was found that inhaled sulfuric acid mists in the size ranges studied had deposition patterns similar to those for dry aerosols. The effect of hygroscopicity for these aerosols was not dominant in determining the site of deposition.

Cellular lung dosimetry for inhaled radon decay products as a base for radiation-induced lung cancer risk assessment. I. Calculation of mean cellular doses

Lung cancer induction is commonly regarded as the most important somatic risk arising from the inhalation of radon and its decay products. Relating carcinogenesis to radiation exposure needs a detailed knowledge of the cellular dose distribution in the human respiratory tract. Different dosimetric models have been developed for the determination of cellular doses, particularly for the basal cells of the bronchial epithelium which are considered as the critical cells for lung cancer induction. Part 1 of the paper describes the influence of various environmental as well as anatomical and physiological factors on the resulting dose. Significant inter- as well as intra-subject variabilities of structural components of the human lung, respiration characteristics and clearance mechanisms demonstrate the necessity of applying stochastic models in lung dosimetry.