Duration Of Exposure Time Research Articles

High-resolution computed tomography (HRCT) in the detection of ?early asbestosis?

Two radiologists reviewed in masked fashion 144 standard chest radiographs, previously judged as normal by other readers, within a cohort of asymptomatic shipyard workers exposed to amosite. Among the 144 workers we selected subjects (n = 72) who fitted the following criteria: (1) documented occupational exposure to asbestos; (2) absence of any clinical symptomatology suggestive of asbestosis or of any other lung disease. Thirty-eight of them had standard chest radiogrphs that were confirmed as normal by both our radiologists, while 34 showed suspected pleural plaques or a very slight parenchymal involvement. These 72 subjects underwent high-resolution CT (HRCT): pleural plaques were shown in 33, parenchymal alterations in 7, and both pleural and parenchymal involvement in 13. HRCT findings were strictly correlated to the duration of amosite exposure and to the latency time since first exposure. Sensitivity, specificity and diagnostic accuracy values of standard chest radiographs were calculated with respect to HRCT and found to be, for pleural and parenchymal findings respectively: sensitivity 53% and 19%; specificity 72% and 94%; accuracy 60% and 72%. In conclusion, pleural and/or pulmonary involvement in asbestos-exposed workers can be shown by HRCT before the appearance of any symptomatology and abnormality on chest radiography. Furthermore the HRCT findings are correlated to the duration of exposure and latency time. time.

Heat generation in hydroxyapatite-coated implants as a result of CO 2 laser application

Previous studies have demonstrated that heat may induce bone resorption and minimize the regenerative capacity of bone. This finding is of potential clinical importance because the carbon dioxide laser may often be used to surgically expose dental implants. However, little is known about the actual amount of heat generated at the implant-bone interface. This experiment measured heat generation on the surface of dental implants exposed to the carbon dioxide laser. A total of 90 trials were performed. A complete factorial (3 x 3 x 2) experimental design was used to evaluate the interactions among laser wattage output (4, 8, and 15 watts), duration of exposure time (1, 5, or 15 seconds) and variations in emission conditions (pulsed or continuous laser mode). Linear increases in temperature to temperatures greater than 50 degrees C were observed with increases in wattage output or duration of exposure time. The pulse mode generated significantly less heat. The results of this study suggest that caution should be used when using the carbon dioxide laser for second stage dental implant surgery.

Drug Interaction Effects on Antitumour Drugs (X): Exacerbation of Cisplatin Lethality by Bacterial Lipopolysaccharide in Mice

To determine whether bacterial endotoxin (lipopolysaccharide, LPS from Escherichia coli) could modulate the lethality of cisplatin (CDDP) in mice, animals were treated with LPS (1 mg/kg, intraperitoneally) 24 hr and 1 hr before administration of cisplatin. A 1.6-fold increase in 8-day cumulative mortality was observed in LPS-treated mice compared to the mortality of those injected with saline before CDDP administration. The duration of previous exposure time to LPS appeared to be an important determinant of the potentiating effect, as many more mice died after 24 hr pretreatment than after 1 hr. Because renal toxicity remains a serious limitation to the effective use of CDDP, we determined whether LPS could also enhance CDDP-induced renal injury. CDDP markedly induces an increase in blood urea nitrogen (BUN) levels in LPS-treated mice. Treatment with LPS did not affect urinary excretion or renal tissue levels of total platinum, or the plasma pharmacokinetics of free and total platinum. Despite the potentiating effect of LPS on CDDP-induced lethality, it appeared that LPS can provide some enhancement of kidney function, because pretreatment of LPS enhanced an increase in BUN values.

A clinical study of acute carbon monoxide intoxication

To obtain the basic data of prognosis of acute carbon monoxide(CO) intoxication, one hundred and sixteen cases of CO intoxication defined by carboxyhemoglobin(COHb) and admitted via emergency room of Yeungnam University Hospital from Oct. '85 to April' 89 have been clinically analyzed and evaluated, including delayed postanoxic encephalopathy(DPE) and the following results were obtained. 1. The ratio of male to female was 1:1.5 and mental state was drowsy mostly(26.2% of 116 cases) 2. The more disturbed the mental state, the more decreased was the arterial pH and , which may be the result of metabolic acidosis. 3. The early laboratory findings in patients of CO intoxication were as follows : leukocytosis-65.5%, increase of hematocrit-23.3%, hyperglycemia-19.8%, increase of GPT-19.8% increase of creatinine-0.9%, and glucosuria-12.1%. 4. The early findings of EKG were abnormal in 35.3% : change of rhythm-25.0%, abnormal ST segment-15.5% (change of rhythm and abonormal ST segment-5.2%) but the conduction disorder was not present. 5. The abnormal EEG above mild degree was 93.1%, of which moderate was most frequent(80.2%). 6. The incidence of DPE was 7.8% among all admitted CO patients. DPE cases had long duration of exposure time(8 hours), severe leukocytosis(20,000) and an abnormal EEG(MA).

APPLICATION OF TOXICOKINETIC MODELS TO ESTABLISH BIOLOGICAL EXPOSURE INDICATORS<xref ref-type="fn" rid="fn1"><sup>*</sup></xref>

This article is a critical review of the application of toxicokinetic models to the biological monitoring of occupational exposure to industrial chemicals. The experimentally based toxicokinetic models are used to determine the elimination half-lives, the metabolic clearance, the elimination rate constants and the volume of distribution. The physiologically based multicompartmental simulation models, which describe the uptake, distribution and elimination of inhaled or percutaneously adsorbed organic solvents, contributed to the understanding of the transport of the xenobiotics in the body. They are used for describing and predicting the dependence of concentrations of indicators of exposure in biological specimens on the extent of exposure and time (duration of exposure and sampling time), and for depicting the contribution of various biological and exposure factors to differences in biological response to the exposure. In biological monitoring, toxicokinetic models are used for matching biological concentrations and body burden of indicators of exposure with extent of inhalation or dermal exposure, and for predicting half-lives. They lay the grounds for the strategy used in collecting biological specimens and controlling external and internal factors which alter the biological concentrations and possibly increase the health risk from the exposure. Elimination half-lives are used as guidelines in selecting the appropriate indicators of exposure, in designing the procedure for the collection of biological specimens, and in interpreting the measured data. Predictive models are needed for heavy metals, particulates and compounds undergoing binding to constituents of tissues.

Prevalence of vibration-induced white finger and assessment of vibration exposure among travertine workers in Italy.

Among 76 stonedrillers and stonecutters/chippers working in the Rapolano travertine quarries (Tuscany, Italy), 27 subjects (35.5%) were affected with vibration-induced white finger (VWF). The median latent period for VWF was ten years (range 0.1-26 years). A VWF prevalence of 8% was found among 60 comparable controls (P less than 0.0001). Vibration measurements showed that the frequency-weighted accelerations for two rock-drills and two small chipping hammers ranged from 19.7 to 36.4 m/s2. Weighted accelerations between 2.4 and 4.1 m/s2 were measured on the handles of a vertical grinder and a hand cutter. Vibration data, daily exposure time and total duration of exposure period were used to calculate two indicators of vibration dose such as the four-hour, energy-equivalent, frequency-weighted acceleration (m/s2) and the vibration exposure level (dB). A significant association between the vibration exposure level and the severity of VWF stages was observed among the travertine operators. The dose-effect relationship proposed by ISO 5349 was not suitable for the data of the present study because it overestimates the risk due to hand-transmitted vibration in the travertine workers. Finally, the results of a cold test indicated that the rewarming time of fingertips to room temperature was more prolonged in the operators with VWF than in those without VWF and in the controls.

Radiation exposure and protection in cardiac catheterization laboratories

Cardiac catheterization with angiography can deliver the greatest dose of x-radiation of any diagnostic medical examination. The physicians and technologists in the angiography room receive low-level scattered radiation over a period of months to decades. Although the radiobiology is complex, the physicians who perform cardiac catheterization should be familiar with the potential genetic and somatic effects of radiation and with the methods to reduce or eliminate x-ray exposure. The aim of radiation protection criteria is to reduce the risk of cancer death to less than the fatality risk for other occupations regarded as safe. This report is a review of the literature relating to radiation exposure and protection in cardiac catheterization laboratories. Catheterization personnel have control over the time duration of exposure, placement of technologists, shielding, location of equipment and monitoring of dose received.

Exposure to terpenes: effects on pulmonary function.

Forty-eight subjects exposed to terpenes (mean air concentration 258 mg m-3) and 47 unexposed subjects, all employed at sawmills, were studied with regard to symptoms and pulmonary function. Dyspnoea and chest oppression were significantly increased in the exposed subjects compared to the unexposed controls. A reduced FEV1, on spirometry and an increased CV% and slope of the alveolar plateau (phase III) on single breath nitrogen washout were seen on Monday morning before exposure to terpenes. There was no correlation between exposure time (duration of employment) and lung function impairment. A day of industrial exposure to terpenes caused no further change in any lung function variable. The unexposed controls showed normal spirometry and nitrogen washouts. The findings indicate a slight stable lung function impairment of an obstructive nature which does not necessarily undergo further deterioration with increased duration of exposure.

Correlation between DNA repair of embryonic fibroblasts and different life span of 3 inbred mouse strains

Primary mouse fibroblast cultures were established from 10 day old embryos of 3 inbred strains with a genetically determined different life expectancy. The capacity for unscheduled DNA synthesis following u.v. irradiation was studied in these cells at various passage levels of the in vitro ageing process. The mouse fibroblasts show considerable repair synthesis corresponding to the duration of exposure time. The capacity for induction of unscheduled DNA synthesis was different in the cells of each strain and correlated to the natural life span of the animal. In each case, however, the ability to perform repair synthesis was subjected to an age-associated decline, although semiconservative DNA synthesis and proliferative potential of the cells was not changed until the cultures entered phase III passages.

Overwinter Survival and Spring Emergence of the Bollworm1 in Arkansas2

Overwinter survival and spring emergence patterns of the bollworm, Heliothis zea (Boddie), were studied in relation to several environmental variables at Dell (northeast) and Newport (north central), AR, during 1972–73 and 1973–74. High fall mortality was attributable to the rainfall and temperature patterns which immediately succeeded larval placement in the field. Effective water drainage was critical for successful overwinter survival. Rainfall, freezing soil temperatures, and duration of exposure (time) accounted for 89.8% of the variation in the overwinter survivorship curves for both locations combined. Time, soil temperatures ≥55°F (12.8°C), incident solar radiation, and rainfall accounted for 96.4% of the variation in the spring emergence patterns at Newport. Overwinter survival ranged from 0.0–5.8% and was higher in the lighter soil types than in clay soils. Percent moth emergence at Newport was ca. 15 times greater than at Dell, which partially explains the differences between the 2 locations in the summer bollworm population densities.

The effect of exposure time on the foveal size of Panum's area

It has been found that the duration of exposure time affects the size of Panum's area. As the exposure time increases from 5 to 100 msec, the mean foveal size of Panum's area measured on three subjects increases rom 1.97ȃ to 3.87ȃ when the criterion of diplopia is used. The increase in size with longer exposure time may be explained in terms of the critical integration time needed in order to establish a constant size of Panum's area or it may be due to the effect of irradiation with longer exposure time.

Threshold ultrasonic dosages for structural changes in the mammalian brain.

The relationship between the acoustic intensity and the time duration of exposure, for a single pulse, necessary to produce a threshold lesion in the cat brain was studied. Focused ultrasound of 1, 3, and 4 MHz was employed with intensities ranging from 102 to 2×104 W/cm2 with the corresponding pulse durations from 7 to 2×10−4 sec, respectively. Three types of lesions were observed attending three regions. At the lower intensities and long time durations of exposure, the lesion is produced by a thermal mechanism. At the highest intensities and shortest time durations, cavitation is believed to be the mechanism responsible for the sometimes randomly appearing lesions. At intermediate dosages, the lesions are formed by a mechanical mechanism which is thus far not well understood. These results exhibit good agreement with that of other investigators on both the cat and the rat brain.

A Study of Humidification in the Thermal Life Determination of Motorette Insulation Systems

The moisture conditioning cycle is the most critical factor in the functional evaluation of rotating machinery insulation systems. An analysis is made of some of the humidity problems currently existing, particularly in respect to the use of the now proposed IEEE 117 Test Procedure and the NRL-designed condensation chamber. A time-dependence ratio of surface-to-bulk absorption has been discovered that varies with the degree of thermal aging. This is explored. Cautionary measures are given for use of the condensation chamber with recommendations as to temperature differentials and exposure-time durations needed to ensure stable test conditions.

A BINOCULAR VIEWING APPARATUS FOR SENSORY THRESHOLD STUDIES IN CHILDREN.

An apparatus is described for obtaining binocular hue detection threshold data from children and adults. Incorporated in the design are standard lighting conditions (illuminant C) and the control of exposure time duration of a variable stimulus. The device was designed to be portable to permit data collection in schools and elsewhere, and provision was made for the easy removal and replacement of stimulus producers.

Effects of Dietary NaF on Dairy Cows. II. Effects on Milk Production

Summary A study of the tolerance of lactating cows to added dietary increments of a soluble fluoride (NaF) over a 5 1/2-yr. period has been made. The results indicate that under adequate nutritional and husbandry conditions, levels of 50 p.p.m. of fluorine fed as NaF produced no direct deleterious effect upon milk secretion. Sustained fluorine ingestion, with average intake levels of 1.5, and peak intakes of 1.7 or more, mg. of F/kg body weight, led to a reduction of milk and butterfat production in certain cows, as the result of anorexia toward NaF-containing feed, which was accompanied by excessive weight loss and stiffness in the legs. These results indicate further that the effect of fluorine fed in the form of NaF on milk production was a secondary effect conditioned by a curtailed feed intake. The cows in this study tolerated 30 p.p.m. fluorine in their ration, whereas 40 p.p.m. was apparently near the marginal zone of tolerance and 50 p.p.m. in the ration resulted in the development of fluorine toxicosis. The addition of calcium reduced the toxicity of the added NaF. A latent period of from 2 to 5 yr. elapsed between the time the fluorine effects were first noticed on the incisor teeth and the development of other physiologic effects, including the inhibition of milk production. Thus, these studies contribute further evidence to show that the development of fluorine toxicosis is a function of the duration of exposure (time), as well as of level of ingestion. Prolonged dry periods allowed sufficient recovery from debilitating fluorosis for subsequent normal lactation and milk production.