Search

The purpose of this article is to review previous chronic inhalation studies in rats with refractory ceramic fiber (RCF), the mathematical modeling efforts to describe the deposition, clearance, and retention of RCF fiber in the rat and human, and the concept of ''overload,'' and to assess the possibility that the maximum tolerated dose (MTD) was exceeded. Lastly, based on recent biopersistence and pulmonary clearance studies of several investigators with a particulate-free RCF, we examine the potential impact on the chronic RCF rat bioassay of coexposure to both RCF particulate and RCF fibers. The review concludes, inter alia, that RCF particulate coexposure probably had a major impact on the observed chronic adverse effects, that the MTD was probably exceeded at the highest exposure concentration of 30 mg/m3 in the rat bioassay, and that inclusion of the highest dose in the risk assessment process may overstate human health risk if a linear rather than nonlinear model is used. [ABSTRACT FROM AUTHOR]

The focus of public health concern and research in regard to environmental lung diseases has changed across the century. Illustrative agents include radon, indoor asbestos, environmental tobacco smoke, acidic aerosols, and oxidant gases. Tremendous progress has been made in understanding and preventing environmental lung diseases. However, we remain concerned about adverse consequences of breathing polluted outdoor and indoor air. In the persistent concerns about adverse effects of polluted air on the lung, a new emphasis is pervasive; the focus has shifted from avoiding clinical disease among highly exposed individuals to protecting the population from an unacceptable burden of risk. The technique of quantitative risk assessment has become increasingly important for characterizing the safety of environmental agents. The resulting emphasis on the final risk projection and attendant uncertainties may overly emphasize gaps in our knowledge. [ABSTRACT FROM AUTHOR]

To determine if near ambient levels of sulphuric acid aerosols, H2SO4, induce reductions in lung function in subjects with obstructive lung disease, 17 volunteers with asthma (age range 20–57 years) and 17 subjects with chronic obstructive pulmonary disease (COPD) (age range 52–70 years) were exposed to H2SO4 in a 45 m3 environmental chamber. All asthmatics showed evidence of mild obstructive lung disease [baseline FEV1/FVC = 0.65±0.09 (SD)]. COPD selection criteria were dyspnea on exertion, obstructive airways disease (FEV1/FVC = 0.56±0.09) and a lack of response to inhaled bronchodilators. By double-blind randomization, each subject inhaled either 100±μg m−3 NaCl (control) aerosol or 90±10 μg m−3 unencumbered breathing for a 2-h period on occasions separated by at least 1 week. On a bicycle ergometer, all subjects exercised for 10 min at work loads sufficient to at least quadruple minute ventilation after 10, 35, 60 and 90 min of exposure. We measured before, during and immediately after exposure FVC, FEV7, specific airway conductance (SGaw) and arterial oxygen saturation. Neither NaCl (control) nor H2SO4 exposure during exercise caused a significant decrease in FVC, FEV1 or SGaw from baseline in subjects with COPD. Although no statistical significant differences in per cent change in FVC were seen on control vs H2SO4 exposure days in asthmatic subjects, small reductions in FEV1 and SGaw (P < 0.02) from baseline were found after exercise during the exposure when compared to the NaCl exposure by cross-over t-tests. These findings suggest that near ambient levels of H2SO4 do not affect lung function in subjects with COPD but that adult asthmatic subjects may develop a mild increase in exercise-induced bronchospasm. [ABSTRACT FROM PUBLISHER]

Controlled human exposure studies with inhaled air pollutants frequently utilise mouth breathing. To determine the extent that the route of inhalation influences airway responses to particulate pollutants, we examined pulmonary responses of asthmatics breathing sulphuric acid (H2SO4) aerosols by oral or nasal inhalation. Asthmatics were exposed to H2SO4 aerosols in a 45 m3 chamber for one hour including 10 minutes of exercise or via a mouthpiece for 16 minutes during resting ventilation. We produced aerosols in concentrations of 100 //g/m3 and 450 //g/m3. We measured before and immediately after all exposures FVC, FEV1, and specific airway conductance (SGaw). At the 450 /ig/m3 concentration, there were remarkable similarities in airway responses despite the different exposure routes. Although the exposures were not strictly comparable in duration, we calculated tracheobronchial (TB) deposition for the two modes of aerosol administration and utilized contemporary models for deposition in explaining the lack of qualitative and quantitative distinctions in the pattern of response. [ABSTRACT FROM PUBLISHER]

Short-term inhalation experiments have been recently performed in rats to evaluate the biopersistence of man-made vitreous fibers (MMVFs). The number and size distribution of inhaled fibers in the rat lung were measured at different postexposure time points. These data were used for developing a mathematical model to describe the clearance kinetics of MMVFs in the rat lung. The model proposed a breakage scheme for long fibers during clearance. The breakage rates for different MMVFs were determined from the fiber size distribution data at different time points. The calculated breakage rate appears to be related to the in vitro dissolution rate; the more soluble a fiber, the faster the fiber breaks. [ABSTRACT FROM AUTHOR]