Biomedical subjects
Publications and source records attributed to A C James.
All known isolates of Leptospira interrogans obtained in Trinidad, Grenada and St. Vincent up to the end of 1979 are listed. There were 80 from Trinidad, 20 from Grenada and 2 from St. Vincent, representing at least 20 serotypes from 11 or more serogroups. Six of the serotypes were first reported from Trinidad. The leptospires were isolated from man, domestic animals and wildlife species.
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The absorption of 212Pb ions from bronchial epithelium to blood has been investigated in anaesthetized rabbits. The 212Pb ions were introduced by intubation either into the trachea or into smaller, more distal bronchi. Removal from lung was followed by external gamma-counting. Mucociliary clearance to the GI tract was blocked by tracheostomy. Two distinct phases of clearance from bronchial epithelium to blood were observed. Approximately 20% of deposited 212Pb is rapidly absorbed with a half-time of about 4 min, the remainder with a biological half-time of about 9 h, irrespective of the site of instillation in the bronchial tree. Two hours after deposition, the 212Pb remaining in lung was found to be partitioned between mucus and the bronchial epithelium, with a substantial but minor fraction in the epithelium. Uptake of 212Pb in the skeleton was estimated to be about 20% of the 212Pb entering the blood circulation. Removal by the kidneys, at 25%, was comparable with skeletal uptake. These results are compared with previously published work using rodents, dogs and man which demonstrated either rapid or slow absorption but not both phases occuring together.
Direct measurements of bronchial deposition in ventilated pig lungs are reported for radon daughter ions and condensation nuclei. Comparisons are made with deposition calculated from the theory of particle diffusion in steady, laminar air-flow. In segmental bronchi, the observed deposition of condensation nuclei was within about 25% of that calculated. Deposition was greater by up to a factor 2 in main stem and lobar bronchi. Deposition in the trachea depended upon the entrance conditions set by vocal cords. For thorium-B ions, deposition in segmental bronchi was a factor 4 less than calculated, apparently due to rapid hygroscopic growth. Clearance rates by dissolution from bronchial epithelium in vivo for lead and bismuth ions are also reported. Approximately 10% of 212Pb ions diffused into blood with a half-time of about 70 min and 30% of 212Bi ions with a much shorter half-time of about 7 min. The implications of these data in the calculation of radiation dose from inhaled radon daughters are discussed.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
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The development of an automated system for activity-weighted size distribution measurements now permits more complete exposure and dose assessment for indoor radon decay products. Exposures characterized by the semi-continuous measurement of activity-weighted size distributions of radon decay products were obtained over four test periods in three normally occupied houses, two of which were occupied by cigarette smokers. These measured activity size distributions were used to calculate exposure-dose conversion coefficients and the annual effective doses. These doses were found to be approximately two-fold higher than the values derived conventionally from the measured radon concentration, on the assumption that indoor exposure to 20 Bq m-3 radon gas concentration corresponds to an annual effective dose 1 mSv y-1. The degree to which aerosol-measurement-based dose estimates were higher than radon-gas-based estimates was found to be influenced if the study house occupant was a cigarette smoker. Reassessment of the measured PAEC-weighted radon progeny particle size distribution in terms of the classical "unattached" and "attached" modes yielded lower estimates of the exposure-effective dose conversion coefficient that were similar to the reference values derived from a recent study by the National Research Council. Thus, by not resolving the measured radon progeny PAEC that is associated with particles intermediate in size between the two classical radon progeny modes, the estimated annual effective doses were also found to be similar to the values derived conventionally from the measured radon gas concentration. It is concluded that the observed presence of 4 to 13% of the radon progeny PAEC in the size-range 1.5 to 15 nm diameter is a dosimetrically significant factor that appears to be commonplace in various home environments.