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Pathological changes of the ECG were examined in 10 adult dogs exposed to +Gz once a day or 3 times a day for three days a week during 2 to 12 weeks. In response to acceleration all of the dogs developed ECG changes. The frequency and level of these disorders were dependent on the acceleration magnitude and the health state that varied during repeated exposure. These findings were used to develop a 5-score scale for measuring ECG disorders and to identify phase changes in acceleration tolerance during repeated exposure to +Gz. It was also demonstrated that animals can be specifically trained to tolerate sustained and high acceleration +Gz.
In case-control studies, exposure to a risk factor often occurs at several levels, so the attributable risk at each level is of interest. In this paper, estimation for the 2 X 2 table (case-control status versus dichotomous exposure) and the 2 X k table (case-control status versus exposure at several levels) are reviewed along with an example. A method for finding confidence intervals for attributable risk in the 2 X k table is proposed, and its application to estimates adjusted across strata (the 2 X k X s case) is indicated. The results of a Monte Carlo study of the procedure demonstrate that the nominal and actual coverage probabilities agree satisfactorily for practical applications.
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This exploratory study examined the relationship between coping strategies of 136 African-American mothers, their exposure to community violence, and their interpersonal victimization. It is suggested that the disproportionate victimization of African-American women produces a cumulative triple threat for those who live amidst conditions of community violence in the following manner: a) exposure through daily living in the midst of unpredictable community violence; b) exposure to violence from witnessing violence in the neighborhood; and c) exposure to violence from disproportionately high rates of personal victimization. The findings suggest that coping strategies are used differentially as a function of the amount of violence within the social context, and the education and financial resources of the mothers. Mothers who live in lower-violence areas with college education preferred activism as a coping strategy, whereas those in high-violence areas with comparable incomes and education preferred reliance on prayer and instituting safety practices. Coping strategies differed based on whether mothers had been physical victims and witnesses to violence or had no personal experience with violence. This study lays the groundwork for a model of exploring the impact of the cumulative effects of violence on African-American mothers parenting in urban America.
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In clinical practice much more often one meets a necessity of repeated administration of fluorocarbon blood substitutes. The 19F(-)-NMR-spectroscopy has been used to study the kinetics of the blood and tissue fluorocarbon concentration after repeated administration of PFC emulsion. Analysis of the data suggests that redistribution of PFCs between organs and blood after their repeated administration is under control of Ostwald ripening depending on PFC physicochemical properties (water and lipid solubility), emulsion particle diameter etc and does not connect with activity of reticuloendothelial system.
A study with multiple exposure groups and large group sizes was performed to establish whether exposure to 60-Hz electric fields would result in reproductive and developmental toxicity. A response model was developed from previous results and tested in groups of rats exposed to electric fields at various field strengths. Female rats were mated, and sperm-positive animals randomly distributed among four groups: sham-exposed or exposed to 10, 65, or 130 kV/m, 60-Hz vertical electric fields. Animals were exposed for 19 hr/day throughout the experiment. During gestation, exposure to the higher field strengths resulted in slightly depressed weight gains of dams. Offspring were born in the field and remained with their dams through the suckling period. Numbers of pups per litter and pup mortality did not differ among the exposure groups. Dams exposed at 65 kV/m lost slightly more weight through the lactation period than the control group. Male pups exposed to higher field strengths gained slightly less weight from 4 to 21 days of age than did sham-exposed animals. At weaning, two F1 females per litter (randomly selected) continued on the same exposure regimen were mated at 11 weeks of age to unexposed males, and euthanized at 20 days of gestation. Uterine contents were evaluated, and all live fetuses were weighed and examined for external, visceral, and skeletal malformations. Fertility and gestational weight gain of F1 females were not affected by exposure, nor was prenatal viability or fetal body weight. No significant increase in the incidence of litters with malformations was observed. Although no developmental toxicity was detected, exposures produced physical changes in the dams, evidenced as a rust-colored deposit on the muzzle and ears (chromodacryorrhea) that increased in incidence and severity at 65 and 130 kV/m. Incidence of chromodacryorrhea was not significantly different between sham-exposed rats and those exposed at 10 kV/m.
The effect of single and multiple exposures to ozone (O3) on airway responsiveness and inflammation was examined in guinea pigs. Airway responsiveness, measured as acetylcholine concentration needed to increase baseline airway resistance (RL) by 250% (PC250), increased 1 h after exposure to ozone at 3 ppm for 3 h (-log PC250 from 3.88 +/- 0.17 to 4.78 +/- 0.18; P < 0.05), but returned to baseline at 8 h. An increase in neutrophil numbers was found at 8 h in bronchoalveolar lavage fluid (BALF). After O3 exposure on 4 successive days, baseline RL increased and airway responsiveness decreased at 1, 8 and 72 h (-log PC250 = 2.88 +/- 0.17, 2.83 +/- 0.10 and 3.12 +/- 0.08, respectively, compared to control value of 3.48 +/- 0.05). Repeated exposures to O3 also increased neutrophil numbers in bronchoalveolar lavage fluid and in bronchial submucosa. Thus, single exposure to O3 caused a rapid and transient increase in airway responsiveness, while multiple exposures induced a rapid but prolonged decrease in airway responsiveness associated with persistent bronchoconstriction. Both single and multiple exposures induced airway inflammation as evidenced by an increase in neutrophil influx. These studies demonstrated a dissociation between ozone-induced changes in airway responsiveness and neutrophil influx, and indicate that multiple exposures to O3 induce persistent bronchoconstriction with airway hyporesponsiveness.
A method has been developed for calculating the maximum permissible exposure for multiple wavelength lasers used in scanning laser ophthalmoscope systems. The method is based on the assumption that when the human eye is simultaneously exposed to multiple wavelength laser light, the thermal and photochemical effects on the retina are additive and independent of each other. A linear addition method is used to calculate multiple laser maximum permissible exposures for scanning laser ophthalmoscope systems. This paper also includes a discussion of possible synergistic effects of retinal biological effects caused by multiple laser exposure. An example is given to illustrate a conservative, theoretical approach to estimating the maximum permissible exposure for simultaneous multiple wavelength laser exposure.
The effect of single and multiple 2-h aminoglycoside exposures on the duration of the postantibiotic effect (PAE) and bacterial killing were investigated using a reference strain (ATCC 27853) and four clinical isolates of Pseudomonas aeruginosa. Concentration-dependent PAE and bacterial killing were demonstrated following single exposures to amikacin, gentamicin or tobramycin. Cultures were also repeatedly exposed to peak aminoglycoside concentration simulating traditional (three times a day) and once daily dosing regimens. Aminoglycoside re-exposures every 8 h at the original culture MIC produced significant, successive reductions in PAE (P < 0.05) and bacterial killing (P < 0.01) coincident with increases in culture MICs. Identical experiments re-exposing cultures to their predetermined, induced MICs demonstrated similar to significantly longer PAEs (P < 0.05) than those observed following first exposure. Multiple gentamicin or tobramycin exposures at 8 mg/L (traditional peak) every 8 h or 24 mg/L (once daily peak) once every 24 h both showed significant reductions in PAE (P < 0.05) and bacterial killing (P < 0.05) on repeated dosing. However, the once-daily high peak concentration exposure demonstrated significantly longer PAEs and greater bacterial killing both initially and upon re-exposure compared with the 8-hourly exposure. In addition, the once daily dosing regimen maintained substantially larger aminoglycoside concentration/MIC ratios. We conclude that multiple exposure of P. aeruginosa in-vitro, to aminoglycosides at the intervals tested, reduces the PAE and bacterial killing and increases the MICs.
Multiple exposures to halothane have been shown to have delayed effects on bromsulphthalein (B.S.P.) clearance. Rats were exposed to repeated halothane anaesthetics, and their livers were subsequently isolated and perfused. B.S.P. retention in the perfusate of these isolated livers was greatly increased one to three weeks after the last halothane exposure. In similarly pretreated animals at the same time period the B.S.P.-glutathione conjugating enzyme activity in homogenates of the livers was found to be depressed. These findings did not occur after multiple diethyl ether exposures or following a single exposure to halothane.
Multiple chemical sensitivity (MCS) is a syndrome in which multiple symptoms occur with low-level chemical exposure; whether it is an organic disease initiated by environmental exposure or a psychological disorder is still controversial. We report a 38-year-old male worker with chronic toluene exposure who developed symptoms such as palpitation, insomnia, dizziness with headache, memory impairment, euphoria while working, and depression during the weekend. Upon cessation of exposure, follow-up neurobehavioural tests, including the cognitive ability screening instrument and the mini-mental state examination, gradually improved and eventually became normal. Although no further toluene exposure was noted, non-specific symptoms reappeared whenever the subject smelled automotive exhaust fumes or paint, or visited a petrol station, followed by anxiety with sleep disturbance. During hospitalization for a toluene provocation test, there was no difference between pre-challenge and post-challenge PaCO(2), PaO(2), SaO(2) or pulmonary function tests, except some elevation of pulse rate. The clinical manifestations suggested that MCS was more relevant to psychophysiological than pathophysiological factors.
Multiple primary cancer (MPC) relating to occupational exposure was studied. The study consisted of a literature survey, survey of on-going research and our project on the frequency and nature of MPC in an occupational cohort of Japanese dyestuff workers followed from 1962 through 1983. From the review of the literature and on-going research there is little information on MPC and existing findings are mostly incomplete. However, a few occupational agents known to be carcinogenic to more than two organs, i.e. arsenic or radium, have been reported to cause MPC. In our follow-up of occupational bladder cancer cases, increased MPCs compared with a matched control group of nonoccupational cases were observed, but further investigation is necessary for a final conclusion. Finally, epidemiologic problems inherent to the study of MPC, including occupational studies, are discussed.