Exposure of Danish workers to trichloroethylene, 1947-1989

The aim of this study was to investigate the exposure of Danish workers to trichloroethylene (TCE) and the factors that affected such exposure. Data from Danish health authorities were evaluated for use in an epidemiological study of possible adverse health effects of TCE. The paper files relating to 1,075 air measurements taken between 1947 and 1989 at 150 companies were examined to extract information about calendar year, company, industry, type of measurement, and worker. Multiple regression models were used to analyze the effects of various factors on the concentration of TCE. TCE concentrations decreased over the four decades studied. The geometric mean was 329 mg/m3 for measurements taken 1947-1959, and 260 mg/m3, 53 mg/m3, and 23 mg/m3, respectively, for the three subsequent decades. Regression analyses showed that 1) TCE concentrations decreased on average 4 percent per year before 1964 and 15 percent per year afterward; 2) area and personal measurements gave similar concentrations (for the same calendar period, industry, and duration of measurement); 3) longer-duration measurements were associated with lower TCE concentrations; 4) high TCE concentrations occurred in the iron and metal industry; and, 5) in this industry men were exposed to concentrations two times those of women. Moreover, this study indicated that both the exposure level and the proportion of exposed workers in Danish companies increased with decreasing number of employees. Epidemiological studies of health effects of TCE may benefit from evaluating potential risk within different strata of calendar time, number of company employees, sex, and type of industry.     

Second-line controller therapy for persistent asthma uncontrolled on inhaled corticosteroids: the step 3 dilemma

The asthma syndrome is characterised by airway inflammation with associated bronchial hyperresponsiveness (BHR) and reversible airflow obstruction. Therapy has benefited from an enhanced understanding of the pathophysiology of asthma and the resulting guidelines that emphasise the pivotal role of anti-inflammatory inhaled corticosteroids (ICS) as first-line therapy. Most patients with mild-to-moderate asthma can be adequately controlled on low-to-medium dosages of ICS alone. For patients with moderate-to-severe asthma who are not adequately controlled by ICS, it is unclear which medication should be added on. The two principal drugs under consideration are long-acting beta(2)-agonists (LABAs) and leukotriene antagonists (LTAs). Although both LABAs and LTAs are both effective at improving lung function, reducing symptoms and decreasing exacerbations, important differences exist that may determine the selection of one over the other in particular circumstances. LABAs and LTAs are equally effective at reducing exacerbations and improving symptoms and quality of life when used as add-on therapy. LABAs tend to be more effective bronchodilators than LTAs. Although LABAs stabilise the airway smooth muscle, they do not affect the underlying inflammatory process. Their long-term use also leads to subsensitivity of response to both LABAs and short-acting beta(2)-agonists (SABAs). The subsensitivity of response to SABAs is more pronounced in the presence of acute bronchoconstriction, which could be relevant during an acute attack. When combined with an ICS, LTAs provide additive non-steroidal anti-inflammatory properties and alleviate associated BHR, but do not induce subsensitivity of response. Not only is the efficacy of LTAs maintained over time, but also they do not affect the response to SABAs as reliever therapy. LTAs also have beneficial effects in patients who have concomitant allergic rhinitis, thus treating the unified airway. The choice between LABA and LTA as add-on therapy will therefore be determined by the needs of the individual patient in terms of providing anti-inflammatory versus bronchodilatory control. For patients with poor lung function where bronchodilatation is required, then an LABA would seem to be a logical choice. For the patient whose lung function is less impaired, with evidence of ongoing BHR where bronchoprotection is needed (e.g. exercise, allergen, cold air), or when there is concomitant allergic rhinitis, then an LTA would be more suitable.     

Reaxotomy of chronically injured rubrospinal neurons results in only modest cell loss

Among the most promising therapeutic strategies to facilitate axonal regeneration after spinal cord injury is the transplantation of various cellular substrates into the injury site. With the establishment of a glial scar and cyst at the injury site over time, the implantation of such cells in the chronic injury setting may require some resection of these nonpermissive elements, which could concomitantly reinjure already severed axons. This study evaluates the response of chronically injured rubrospinal neurons to such a second axotomy. Our findings indicate that the second axotomy does not lead to an accelerated loss of rubrospinal neurons, which represents an important finding for those who evaluate axonal regeneration of this motor system in chronic transplantation studies.     

Directional selection is the primary cause of phenotypic diversification

Selection is widely accepted as the principal force shaping phenotypic variation within populations. Its importance in speciation and macroevolution has been questioned, however, because phenotypic differences between species or higher taxa sometimes appear to be nonadaptive. Here, we use the quantitative trait locus (QTL) sign test to evaluate the importance of directional selection in phenotypic divergence. If a trait has a history of directional selection, QTL effects should be mostly in the same direction; otherwise QTLs with antagonistic effects should be common. Analysis of QTL effects for 572 traits from 86 studies revealed significantly fewer antagonistic QTLs than expected under neutrality, a result that validates Darwin's claim that phenotypic diversification is caused mainly by selection. Moreover, interspecific trait differences were more strongly or consistently selected than intraspecific differences, strengthening a growing consensus among students of speciation that directional selection is the primary cause of speciation. Contrary to studies of selection in contemporary populations, life history traits appear to be selected more strongly than morphological traits, but traits related to the timing of development are weakly selected relative to most other traits.     

Dual-energy digital subtraction chest radiography: technical considerations

In the evaluation of asbestos-related pulmonary and pleural abnormalities, conventional chest radiography has been shown to have a low sensitivity for the detection of lung nodules and subtle interstitial disease. Pleural plaques may simulate pulmonary nodules, and interstitial processes can be masked by adjacent pleural abnormalities. Dual-energy digital subtraction chest radiography may enable investigators to characterize asbestos-related pulmonary and pleural abnormalities with greater accuracy. "Soft-tissue" images, designed to remove pleural calcifications, may allow for better evaluation of the lung parenchyma. "Bone" images, designed to remove soft-tissue structures, may enhance the detection of pleural calcifications. In this pictorial essay we illustrate the methods, technical considerations, and limitations of dual-energy digital subtraction chest radiography performed with global subtraction weighting factors.