Aerosols consist of two phases: a gas phase and particle phase, either liquid or solid. Mathematical modeling of the three principal processes (impaction, sedimentation and diffusion) which determine the amounts of deposition of particles at various levels of the respiratory system is in agreement with the majority of experimental data, the upper airways behaving as a very effective filter for particles with an aerodynamic diameter greater than 2 micron. Below such a diameter, particles are capable of being deposited at all levels along the tracheo-bronchial system or in the terminal respirator units. This scale of micronic aerodynamic diameters furthermore corresponds to atmospheric aerosols with a long duration (monodispersed aerosols). Such findings have obvious consequences both in terms of the physiopathology of respiratory disorders as well as the therapeutic or diagnostic use of aerosols. In order to better define the deposition of infra-micronic particles, we used the Liu and Whitby analyser for measurement of particle concentration for diameters of between 0.0042 micron and 0.75 micron. The aerosol inhaled was ordinary atmospheric air with a stable profile. The respiratory tract of the subject was free of any particles after 5 respiratory cycles through a filter. Overall, expired particle concentrations decreased exponentially with the increase in apnea at the end of inspiration. This decrease was all the more marked when pulmonary capacity was smaller. These findings were apparently related to the increased probability of deposition by diffusion as the dimension of the air spaces decreases.
Lung dusts were investigated, post-mortem, in twenty-five miners from mixed metal mines, tunnels, and quarries who had exposed to high concentrations of mixed dust containing about 20-25% free crystalline silica. The character of the relations found between the amount of quartz per 100 g dry tissue and the clinical, X-ray and pathological findings is similar to that established in coal miners. The difference lies in the fact that with equal amounts of quartz per 100 g dry tissue, there is less silicosis in coal miners than in our cases; the average residence time of retained dust is longer in coal miners, but its quartz per cent is lower.
Deposition of half-micron particles from steady inspiratory flows was measured in the daughter branches of the second bifurcations in a symmetric airway model consisting of two successive generations of bifurcation. Two different configurations were studied: (1) both bifurcations in the same plane and (2) the second bifurcation normal to the plane of the first. The results indicate that the deposition in the daughter branches in configuration (2) is relatively uniform, while that in configuration (1) has a distinct second deposition hot spot, in addition to the one at the carinal ridge. The deposition velocities in the branch which has secondary flows in the opposite sense to those in its parent branch are about 50% lower than those in other types of branches. The deposition patterns are consistent with the observed flow profiles in these tubes.
Rats have been dosed over a 6-week period with U.I.C.C. standard reference samples of amosite, crocidolite and chrysotile A, each at three concentrations: 1,5 and 10 mg/m3. Mass concentrations in the exposure chambers were monitored daily. Because the M.R.E. gravimetric sampler was found to undersample some of these dusts at high concentrations, a sampler with a vertical elutriator was developed. Data on other physical parameters of the dust clouds were also obtained and it was found that the fibre number (greater than 5 micron in length) vs. mass correlation varied markedly between asbestos varieties. After dusting, the rats were sacrificed in five batches over a period of 4 months. The lungs of some animals were retained for pathological examination. This did not reveal any fibrosis although large numbers of fibres were visible, mostly within alveolar macrophages. The remaining lungs were analysed for their asbestos contents by a method based upon infrared spectrophotometry. The clearance data confirm earlier published reports that for rats dosed at similar mass concentrations of chrysotile and amphibole, those dosed with chrysotile retain considerably less dust in their lungs. The data also suggest that the retention and clearance of amphibole abestos may be dose related. Some mathematical treatment of the clearance data has been undertaken.
A topographic study of asbestos fibre content of lung and pleura of diversely exposed cases has been carried out. For heavily exposed cases with lung fibrosis, this study has stressed the distinctive behaviour of the peripheral lower lobe in the retention of asbestos fibres in the lung. In these areas were found the smallest asbestos concentrations but the largest fibres. For cases without lung fibrosis, the results clearly demonstrated an accumulation of asbestos fibres, especially of chrysotile type, in peripheral areas. These findings are to be related to the incidence of pleural mesothelioma associated with moderate or low exposure. The small variation of fibre concentration in the pleural plaques of diversely exposed subjects is pointed out.
: A survey has been made of 2209 gold miners in the Republic of South Africa. The result showed that there is a significant dose-response relationship between dust inhaled and both chronic bronchitis and airways obstruction. This is found in smokers, ex-smokers and non-smokers. The effect of smoking is more potent than that of dust but there does not appear to be a dose-response relationship in regard to smoking. The effect of smoking differs from the effect of dust in that ex-smokers show less bronchitis and less airways obstruction than smokers, but ex-miners do not show a similar advantage over working miners.
An examination of bulk talc samples imported into Great Britain has shown that they are extremely variable in their talc mineral content. Major contaminating minerals present with the talc are chlorite, carbonates and quartz. The chemistry of samples examined varied with their mineralogical content which also accounted for observed differences in particle morphology. Tremolite fibres were found in three samples, one of which contained the mineral as a major phase. No other varieties of asbestos were detected.
Uniform spherical 10-micrometer diameter particles of ZrO2 ceramic, containing various concentrations of PuO2, have been injected into the jugular vein of Syrian hamsters with subsequent permanent lodgement in the lung capillaries. The number of particles injected has varied from 2000 to 2 000 000 and the specific activity has been from 0.16 to 59 pCi/sphere so that lung burdens range from 0.2 to 700 nCi. To date, approximately 3000 hamsters have been committed to the experiment and two-thirds have died--the expected rate for normal animals. Little biological damage has been observed, and only five primary lung tumours have been found that may be due to radiation delivered to the lung. To provide a comparison to more uniform radiation, soluble polonium has also been instilled intratracheally. Results from the microspheres suggest that localized lung irradiation alone is not sufficient cause for tumour induction and is much less hazardous than diffuse exposure.
When rats breathed air containing approximately 70 mg m-3 of respirable crystalline silica 7 h daily for 10 days (2000 mg m-3 h) the surface tension forces of the alveolar lining film were reduced. This was shown both by surface tension measurements on lung extracts and by pressure-volume studies with air and saline filling of excised lungs. Larger quantities of inhaled silica produced similar effects. Chrysotile inhalation caused an even more marked decrease in the surface tension forces. In the chrysotile studies these findings were supported by biochemical estimations of the quantity of surfactant in the lungs, which was increased 10-fold by an inhalation of 6500 mg m-3 h. Electron microscopy showed an increased number of the type II alveolar cells which produce surfactant and of free phospholipid lattices in the air spaces of the lungs of rats exposed to chrysotile and silica. Both the surface tension and biochemical estimations on a control group of rats suggest that there is an increase in the amount of surfactant in the lungs up to about 12 months of age.
