The association between natural outdoor environments and common somatic symptoms.

There is growing evidence that urban natural outdoor environments (NOE) may positively impact health by reducing stress and stress-related symptoms. However, there is limited research investigating this link across a range of NOE indicators. This cross-sectional study investigated the association between neighbourhood NOE (availability, use, and satisfaction with NOE) and common somatic symptoms and the role of potential mediators. Data were analysed from 3481 adults from Barcelona (Spain), Doetinchem (Netherlands), Kaunas (Lithuania) and Stoke-on-Trent (United Kingdom). NOE data were obtained through self-reported data and environmental measurements. Common somatic symptom data were self-reported. Mixed effects regression models were used for analysis, with models adjusted for potential sociodemographic confounders. Higher satisfaction with neighbourhood NOE was associated with lower prevalence of common somatic symptoms (exp(ß) 0.97; 95% CI 0.96, 0.98); an association partially mediated by mental health, social cohesion and air quality concern. A longer time spent in NOE was associated with lower prevalence of common somatic symptoms in low socioeconomic status neighbourhoods (exp(ß) 0.98; 95% CI 0.96, 1.00). A higher number of neighbourhood green spaces (300m buffer) was associated with higher prevalence of common somatic symptoms (exp(ß) 1.03; 95% CI 1.00, 1.05). No statistically significant associations were found for other NOE indicators. Study findings suggest that higher satisfaction with NOE may be associated with lower prevalence of common somatic symptoms, with mental health, social cohesion and concern about air quality playing partial mediating roles. Little evidence was found of an association between objective NOE measurements and common somatic symptoms, underlining the importance of perceptions of NOE for conferring health benefits.

Quantitative health impact assessment of transport policies: two simulations related to speed limit reduction and traffic re-allocation in the Netherlands.

BACKGROUND: Few quantitative health impact assessments (HIAs) of transport policies have been published so far and there is a lack of a common methodology for such assessments. OBJECTIVE: To evaluate the usability of existing HIA methodology to quantify health effects of transport policies at the local level. METHODS: Health impact of two simulated but realistic transport interventions - speed limit reduction and traffic re-allocation - was quantified by selecting traffic-related exposures and health endpoints, modelling of population exposure, selecting exposure-effect relations and estimating the number of local traffic-related cases and disease burden, expressed in disability-adjusted life-years (DALYs), before and after the intervention. RESULTS: Exposure information was difficult to retrieve because of the local scale of the interventions, and exposure-effect relations for subgroups and combined effects were missing. Given uncertainty in the outcomes originating from this kind of missing information, simulated changes in population health by two local traffic interventions were estimated to be small (<5%), except for the estimated reduction in DALYs by less traffic accidents (60%) due to speed limit reduction. CONCLUSIONS: Quantitative HIA of transport policies at a local scale is possible, provided that data on exposures, the exposed population and their baseline health status are available. The interpretation of the HIA information should be carried out in the context of the quality of input data and assumptions and uncertainties of the analysis.

Personal exposure assessment studies may suffer from exposure-relevant selection bias.

We evaluated exposure-relevant selection bias within the framework of a study on personal air pollution exposure, using traffic data as exposure proxy. Based on random samples of 3000 (Basel) and 2532 (Helsinki) persons, 50 and 250 subjects, respectively, were recruited for direct monitoring and 250 (Basel, Helsinki) for indirect monitoring. In Basel, participants of direct monitoring as compared to non-participants were more likely to live at streets with low traffic volume (49% below 1st quartile vs. 27%). Adjusted for sex, age and nationality, an increase of 100 cars per hour was associated with 14% less participation (odds ratio (OR): 0.861; 95% CI: 0.731, 1.007). Although in Helsinki, traffic volume was neither significantly related to participation in direct nor indirect monitoring, the point estimates indicate a tendency to decreased participation with increasing traffic intensity at home. We conclude that selection bias regarding exposure-relevant characteristics is likely to occur when recruiting participants for studies including demanding personal exposure assessment. Correction for factors routinely collected may not fully account for exposure-relevant bias. This is of particular importance when using exposure data for modelling population exposure distributions, whereas in epidemiological studies, a reduced range of exposure must not a priori distort the exposure-response relationship.

Exposure to dust and its particle size distribution in California agriculture.

The aim of this study was to measure personal dust exposure levels and the dust particle size distribution during various agricultural operations in California. Personal dust exposure levels were measured with four-stage cascade impactors and respirable dust cyclones during field crop, fruit and nut farming, and dairy operations at three farms. Altogether, 103 cascade impactor measurements and 108 cyclone measurements were taken. High personal dust exposure levels were measured during various operations in particular during ground preparation operations such as land planing (geometric mean [GM] = 57.3 mg/m3, geometric standard deviation [GSD] = 2.4) and discing (GM = 98.6 mg/m3, GSD = 2.9). Dust particles were relatively large and the great majority belonged to the extrathoracic fraction. Dust levels were considerably lower when an enclosed cabin was present on the tractor; for example, during discing, dust exposure levels were reduced more than sixtyfold for the larger dust particle fraction and more than fourfold for the respirable dust fraction.

On segmentation of lung parenchyma in quantitative computed tomography of the lung.

Our purpose in this study was to investigate the influence of segmentation threshold and number of erosions on parameters used in quantitative computed tomography (CT) of the lung (erosions are shrink operations on the segmented area). Parameters assessed were mean lung density, area of the segmented lung, two percentiles, and the pixel index, which is the relative area of the histogram below -905 Hounsfield Units (HU). We analyzed images of ten emphysematous and ten nonemphysematous patients, that had been scanned at carina level in inspiration and expiration, using sections of 1, 2, 3, 5, and 10 mm in combination with a standard, a smooth, and an ultrasmooth reconstruction kernel. The lungs were segmented using pixel tracing at thresholds of -200, -400, and -600 HU with 0-4 erosions, followed by histogram analysis. The area of the segmented lungs decreased with 0.9%-3.2% per 100 HU decrease in threshold and with 2.2%-3.1% per erosion, dependent on patient group and respiratory status. Estimated mean lung density changed up to 30% by changing the threshold and the number of erosions. The pixel index and the 10th percentile depended only slightly on threshold and number of erosions, but the 90th percentile showed a strong dependence of up to 40%. It is concluded that the segmentation protocol can have a large impact on densitometric parameters and that standardization is mandatory for obtaining comparable results. Ideally a threshold equal to the average of the densities of lung and soft tissue should be used, but -400 HU will do in a limited but common density range (-910 to -790 HU). For densitometry two erosions are recommended, for volumetry zero erosions should be used.

CT lung densitometry: dependence of CT number histograms on sample volume and consequences for scan protocol comparability.

PURPOSE: Our goals were to determine the dependence of CT number histograms of the lung on section thickness and reconstruction filter and to evaluate the consequences for scan protocol conformity required for universally comparable densitometry of the lungs. METHOD: The effects of section thickness and reconstruction filter were parameterized with the CT's sample volume [V approximately (section thickness x in-plane resolution2)]. In a study of 31 patients, we determined as a function of V the following CT number histogram parameters: percentiles P(10) and P(90), pixel indexes PI(-905) and PI(-950), and standard deviation. RESULTS: Patient histogram parameters depended strongly on sample volume. Large differences were found between protocols using 1 and 10 mm sections. For small variations in somewhat larger sample volumes (> 8 mm3), discrepancies were much smaller. CONCLUSION: To obtain comparable histogram parameters, nearly identical sample volumes (> or = 8 mm3) should be used. When this condition is satisfied, available data suggest that universally comparable densitometry is feasible.

The CT's sample volume as an approximate, instrumental measure for density resolution in densitometry of the lung.

Ultimately CT-densitometry of the lung should give comparable results on all scanners. One prerequisite for this is the use of the same density resolution. Unfortunately, density resolution is impractical as a performance specifying parameter because it depends on the cellular material scanned. Therefore, another parameter that can be used for scanner and protocol characterization, and that does not depend on a special phantom, would be highly preferable. We investigated how well the CT's nominal sample volume (V), calculated from section thickness and in-plane spatial resolution as specified by the CT manufacturer, can serve as a simple measure, for density resolution. Six CT scanners were studied using foam and lung phantoms. On all scanners we observed for foam an approximately linear relation between density resolution and V-1/2. Density resolution on different scanners varied to some extent. These differences can be interpreted as being caused by deviations of the true sample volume from the nominal value: the 95%-confidence interval runs for instance for V = 8 mm3 from 4.6 mm3 to 16.9 mm3. Acceptability of this spread depends on the consequences for parameters of clinical interest, like percentiles and pixel indexes. To evaluate this we used data from a previous patient study on the dependence of histogram parameters on sample volume. With these data it is found that large interscanner differences in histogram parameters are possible for small values of V, as used in thin-section densitometry. For larger values of V, as required for a more adequate density resolution, the differences are much smaller and probably acceptable when compared to other sources of variability in lung densitometry. In conclusion, for sections of at least 2 mm and smooth reconstruction filters, corresponding to V > or = 8 mm3, the CT's nominal sample volume might be used for interscanner and interprotocol comparison of density resolution.

Respiratory allergy in laboratory animal workers: a retrospective cohort study using pre-employment screening data.

OBJECTIVES: To study the role of exposure, atopy, and smoking in the development of laboratory animal allergy (LAA) in a retrospective cohort study. METHODS: Between 1977 and 1993, 225 people received a pre-employment screening when they started a job at a Dutch research institute where they were going to work with laboratory animals. After active follow up 136 of them (60.4%) could be traced and were sent a questionnaire with extensive questions on allergic symptoms, smoking habits, and job history. 122 people (89.7%) sent back a completed questionnaire. Those who were accepted for a job at the institute and did not have allergic symptoms at the start of the job were selected as cohort members. After selecting people with complete data on start and end date of jobs, exposure intensity, atopy, and smoking, the cohort consisted of 99 people with an average time of follow up of 9.7 years. LAA was defined as a positive response to a set of questions in the questionnaire. The mean number of hours a week a person was exposed to laboratory animals at entry of the cohort was used as a surrogate for exposure, and was divided into four categories. RESULTS: 19 cohort members (19.2%) reported LAA. More people with asthmatic symptoms were found in the high exposure categories. More atopic than non-atopic people reported asthmatic symptoms (13% v 6%). The mean time until development of symptoms of LAA was about 109 months in non-atopic people (n = 9), and 45 months in atopic people (n = 10) (t test; P < 0.05). Time until development of symptoms of LAA was shorter at a higher intensity of exposure, except for those exposed for less than two hours a week. A proportional hazard regression analysis showed that exposure and atopy were significant determinants of LAA. An increased relative risk (RR) was found for non-atopic people exposed to laboratory animal allergens for more than two hours a week. Atopic people had an even higher risk when exposed to laboratory animals for more than two hours a week (RR above 7.3). Sex, smoking, and age were not risk factors. More atopic than non-atopic people were absent from work or transferred because of allergies. CONCLUSIONS: This study showed that exposure and atopy are significant predictors of LAA and that the risk of developing LAA remained present for a much longer period (> 3 y) than considered before.

Density resolution in quantitative computed tomography of foam and lung.

This study was performed to assess density resolution in quantitative computed tomography (CT) of foam and lung. Density resolution, a measure for the ability to discriminate materials of different density in a CT number histogram, is normally determined by quantum noise. In a cellular solid, variations in mass in the volumes sampled by CT cause an additional degradation of density resolution by the linear partial volume effect. The sample volume, which is directly related to spatial resolution, can be varied by choosing different section thicknesses and reconstruction filters. Several polyethene (PE) foams, as simple models of lung tissue, and five patients were investigated using various sample volumes. For the uniform PE foams, density resolution could be directly determined as the full width at half maximum of CT number histograms. Density resolution for foams with cell sizes of 0.8-1.5 mm was dominated by effects caused by the limited sample size, not by quantum noise. The relative magnitudes of density resolution could roughly be explained with a model for a hypothetic random cellular solid. Since lungs are not of uniform density, analysis of patient data was more complicated. A combined convolution least-squares fit procedure, together with information obtained in the studies of foam, were used to determine density resolution in lung studies. Density resolution, both for foams and lung, was strongly dependent on sample volume, and was quite poor for thin sections and sharp filters. Consequently, histogram-shape related parameters are sensitive to the spatial resolution chosen on CT. Thin section densitometry, using a 1-mm section with a standard or high resolution filter, is not recommended except in determining average density. When using thicker sections, an in-plane spatial resolution similar to section thickness is advised.

Associations of PM10 and airborne iron with respiratory health of adults living near a steel factory.

The association between daily PM10 (particles with a median aerodynamic diameter of < or = 10 microns) and iron particle concentrations and respiratory health was studied in a population of adults selected for current or recent bronchodilator use. Acute changes in respiratory health were measured as changes in peak expiratory flow (PEF), and daily prevalence of respiratory symptoms and medication use as recorded in a diary. The study period was October 11 through December 22, 1993. The study population included 32 adults living near a large steel industry in Wijk aan Zee, the Netherlands. During the study period, 24-h average PM10 concentrations in Wijk aan Zee ranged from 36 to 137 micrograms/m3 while the 24-h average concentrations of iron, silicon, sodium, and manganese ranged from approximately zero to 6.95, 1.84, 12.02, and 0.37 micrograms/m3 respectively. The steel industry was found to contribute significantly to the PM10 concentrations, and especially to the iron and manganese concentrations in the air. The association of changes in respiratory health with changes in PM10, iron, sodium, and silicon was evaluated using a time series approach. A statistically significant decrease in PEF was found to be associated with increasing PM10 concentrations. Stronger associations were found for smokers than for nonsmokers, and for subjects reporting many chronic respiratory symptoms than for subjects reporting few such symptoms. Increased concentrations of iron tended to be associated with a decline in PEF, with a lag of 2 to 3 d, although the association did not reach statistical significance.(ABSTRACT TRUNCATED AT 250 WORDS)