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[An improved method for estimating daily intake of environmental contaminants using Monte-Carlo simulation].

We previously developed a new method for estimating intakes of environmental contaminants, called Estimated Ecological Daily Intake (EEDI), which is based on food consumption data. This method accurately estimates the intakes of food additives and contaminants and provides rough estimates of averages and distribution curves for the target population. By this method, we originally considered only food consumption, but did take into account the contamination level of each food article. Therefore, we attempted to improve EEDI by incorporating contamination levels of foodstuffs. Practically, we developed an improved Estimated Ecological Daily Intake estimation method for the daily intake of food contaminants and additives, and estimated daily intake of environmental contaminants based on food consumption data of 159 female volunteers, assuming that the contamination level follows Poisson distribution. The results obtained are as follows: 1) Estimated intakes were found to be accurate enough to obtain important values of distribution, such as mean, maximum value, mode, and median, which could be used to determine a standard. 2) Comparing the distribution of the estimated intakes, with that of intakes estimated by the fixed contamination level, the class-containing mode became lower and the class-containing the maximum value became higher. 3) This method was shown to provide information on the risk or probability of exceeding tolerable intake due to excessive food consumption or eating highly contaminated foods.

Eating↗

The structure of genealogies and the distribution of fixed differences between DNA sequence samples from natural populations.

When two samples of DNA sequences are compared, one way in which they may differ is in the presence of fixed differences, which are defined as sites at which all of the sequences in one sample are different from all of the sequences in a second sample. The probability distribution of the number of fixed differences is developed. The theory employs Wright-Fisher genealogies and the infinite sites mutation model. For the case when both samples are drawn randomly from the same population it is found that genealogies permitting fixed differences are very unlikely. Thus the mere presence of fixed differences between samples is statistically significant, even for small samples. The theory is extended to samples from populations that have been separated for some time. The relationship between a simple Poisson distribution of mutations and the distribution of fixed differences is described as a function of the time since populations have been isolated. It is shown how these results may contribute to improved tests of recent balancing or directional selection.

Base Sequence↗

Uneven perfusion within single cat muscles: nitric oxide and citrate synthase play no role.

There is an unexplained, marked regional heterogeneity in perfusion within single skeletal muscles both in dogs and rabbits. We asked if a similar distribution of perfusion was present within cat muscles. If present, we wanted to assess the possible roles of nitric oxide (NO) mediated vasodilation and citrate synthase (CS) activity for the regulation of this perfusion pattern. Perfusion was determined in 0.25 g regions within the gastrocnemius muscles by trapping of microspheres. We studied awake or anesthetized cats before and during inhibition of NO-formation using N-monomethyl-L-arginine. The CS activity was determined in homogenates of these regions. The coefficient of variation corrected for the Poisson distribution of microspheres (CVc) for the regional perfusion averaged 0.39. Despite a 25% reduction in perfusion to the whole muscles as compared to control, the uneven distribution of perfusion was not affected by blocking NO formation. Regional perfusion was not correlated to regional CS activity. Even if the regional distribution of CS activity also showed a scatter, mean coefficient of variation corrected for methodological error = 0.20, it was markedly less than that for perfusion. We conclude that neither NO vasodilation nor CS activity play an important role in the regulation of the regional perfusion pattern within single cat muscles.

Anesthesia↗

Autoradiographic evidence for many segregating DNA molecules in the chloroplast of Ochromonas danica.

Light-grown cells of Ochromonas danica, which contain a single chloroplast per cell, were labeled with [methyl-(3)H]thymidine for 3 h (0.36 generations) and the distribution of labeled DNA among the progeny chloroplasts was followed during exponential growth in unlabeled medium for a further 3.3 generations using light microscope autoradiography of serial sections of entire chloroplasts. Thymidine was specifically incorporated into DNA in both nuclei and chloroplasts. Essentially all the chloroplasts incorporated label in the 3-h labeling period, indicating that chloroplast DNA is synthesized throughout the cell cycle. Nuclear DNA has a more limited S period. Both chloroplast DNA and nuclear DNA are conserved during 3.3 generations. After 3.3 generations in unlabeled medium, grains per chloroplast followed a Poisson distribution indicating essentially equal labeling of all progeny chloroplasts. It is concluded that the average chloroplast in cells of Ochromonas growing exponentially in the light contains at least 10 segregating DNA molecules.

Autoradiography↗

A unit density method of grain analysis used to identify GABAergic neurons for electron microscopic autoradiographs.

The distribution of electron microscopic autoradiographic grains over neurons in cerebellar cultures incubated with [3H]gamma-aminobutyric acid ([3H]GABA) was examined. With the unit density method of grain analysis, the number of grains over each structure was tested against the total grain density for the entire section. If an individual structure has a grain density higher than the expected grain density, it is considered one of the group of heavily labeled structures. The expected grain density for each structure is calculated based on the area for that structure, the total grain density and the Poisson distribution. A different expected grain density can be calculated for any P value required. The method provides an adequate population of structures for morphological analysis but excludes weakly labeled structures and thus may underestimate the number of labeled structures. The unit density method of grain analysis showed, as expected, a group of cell bodies and synapses that was labeled heavily. Cultures incubated with other [3H]amino acids did not have any heavily labeled synaptic elements. In addition, serial section analysis of sections showed that synapses heavily labeled with [3H]GABA are seen in adjacent section. The advantage of the unit density method of grain analysis is that it can be used to separate two groups of metabolically different neurons even when no morphological differences are present.

Alanine↗

Nanometre localization of single ReAsH molecules.

ReAsH is a red-emitting dye that binds to the unique sequence Cys-Cys-Xaa-Xaa-Cys-Cys (where Xaa is a noncysteine amino acid) in the protein. We attached a single ReAsH to a calmodulin with an inserted tetracysteine motif and immobilized individual calmodulins to a glass surface at low density. Total internal reflection fluorescence microscopy was used to image individual ReAsH molecules. We determined the centre of the distribution of photons in the image of a single molecule in order to determine the position of the dye within 5 nm precision and with an image integration time of 0.5 s. The photostability of ReAsH was also characterized and observation times ranging from several seconds to over a minute were observed. We found that 2-mercaptoethanesulphonic acid increased the number of collected photons from ReAsH molecules by a factor of two. Individual ReAsH molecules were then moved via a nanometric stage in 25 or 40 nm steps, either at a constant rate or at a Poisson-distributed rate. Individual steps were clearly seen, indicating that the observation of translational motion on this scale, which is relevant for many biomolecular motors, is possible with ReAsH.

Amino Acid Sequence↗

Maximum likelihood estimation for cytogenetic dose-response curves.

In vitro dose-response curves are used to describe the relation between chromosome aberrations and radiation dose for human lymphocytes. The lymphocytes are exposed to low-LET radiation, and the resulting dicentric chromosome aberrations follow the Poisson distribution. The expected yield depends on both the magnitude and the temporal distribution of the dose. A general dose-response model that describes this relation has been presented by Kellerer and Rossi (1972, Current Topics on Radiation Research Quarterly 8, 85-158; 1978, Radiation Research 75, 471-488) using the theory of dual radiation action. Two special cases of practical interest are split-dose and continuous exposure experiments, and the resulting dose-time-response models are intrinsically nonlinear in the parameters. A general-purpose maximum likelihood estimation procedure is described, and estimation for the nonlinear models is illustrated with numerical examples from both experimental designs. Poisson regression analysis is used for estimation, hypothesis testing, and regression diagnostics. Results are discussed in the context of exposure assessment procedures for both acute and chronic human radiation exposure.

Chromosome Aberrations↗

Regional heterogeneity of myocardial blood flow within the rabbit left ventricle during haemorrhagic hypotension.

Several studies have reported an extensive regional heterogeneity in myocardial blood flow. The reported coefficients of variation for regional myocardial perfusion range from about 0.2 to 0.4 in normotensive animals. The spatial distribution of myocardial perfusion during haemorrhagic hypotension seems not to have been assessed. The goal of the present study was to determine the regional heterogeneity in myocardial blood flow within the rabbit left ventricle during normal conditions and after haemorrhagic hypotension. Radioactive microspheres were infused into the left ventricle in barbiturate anaesthetized rabbits over either 30 or 120 sec. The haemorrhagic hypotension was induced by bleeding, so that mean arterial blood pressure was reduced to about 50% of control. The left ventricles were divided into samples of about 0.025 g each. Regional heterogeneity in the blood flow was expressed as the coefficient of variation corrected for the Poisson distribution of microspheres (CVc). The CVc was 0.37 +/- 0.09 (mean +/- SD) during control and 0.41 +/- 0.11 after bleeding, the CVc obtained after bleeding being somewhat higher than during control (P < 0.05). We obtained a high correlation coefficient (tau about 0.68) between regional perfusion values at control and after bleeding which indicates a stable perfusion pattern within the myocardium. We conclude that the regional distribution of coronary blood flow within the left ventricle is markedly heterogenous during control condition and that this pattern is not changed during haemorrhagic hypotension.

Animals↗

Protein folding by distributed computing and the denatured state ensemble.

The distributed computing (DC) paradigm in conjunction with the folding@home (FH) client server has been used to study the folding kinetics of small peptides and proteins, giving excellent agreement with experimentally measured folding rates, although pathways sampled in these simulations are not always consistent with the folding mechanism. In this study, we use a coarse-grain model of protein L, whose two-state kinetics have been characterized in detail by using long-time equilibrium simulations, to rigorously test a FH protocol using approximately 10,000 short-time, uncoupled folding simulations starting from an extended state of the protein. We show that the FH results give non-Poisson distributions and early folding events that are unphysical, whereas longer folding events experience a correct barrier to folding but are not representative of the equilibrium folding ensemble. Using short-time, uncoupled folding simulations started from an equilibrated denatured state ensemble (DSE), we also do not get agreement with the equilibrium two-state kinetics because of overrepresented folding events arising from higher energy subpopulations in the DSE. The DC approach using uncoupled short trajectories can make contact with traditionally measured experimental rates and folding mechanism when starting from an equilibrated DSE, when the simulation time is long enough to sample the lowest energy states of the unfolded basin and the simulated free-energy surface is correct. However, the DC paradigm, together with faster time-resolved and single-molecule experiments, can also reveal the breakdown in the two-state approximation due to observation of folding events from higher energy subpopulations in the DSE.

Kinetics↗

Statistical dynamic image reconstruction in state-of-the-art high-resolution PET.

Modern high-resolution PET is now more than ever in need of scrutiny into the nature and limitations of the imaging modality itself as well as image reconstruction techniques. In this work, we have reviewed, analysed and addressed the following three considerations within the particular context of state-of-the-art dynamic PET imaging: (i) the typical average numbers of events per line-of-response (LOR) are now (much) less than unity, (ii) due to the physical and biological decay of the activity distribution, one requires robust and efficient reconstruction algorithms applicable to a wide range of statistics and (iii) the computational considerations in dynamic imaging are much enhanced (i.e., more frames to be stored and reconstructed). Within the framework of statistical image reconstruction, we have argued theoretically and shown experimentally that the sinogram non-negativity constraint (when using the delayed-coincidence and/or scatter-subtraction techniques) is especially expected to result in an overestimation bias. Subsequently, two schemes are considered: (a) subtraction techniques in which an image non-negativity constraint has been imposed and (b) implementation of random and scatter estimates inside the reconstruction algorithms, thus enabling direct processing of Poisson-distributed prompts. Both techniques are able to remove the aforementioned bias, while the latter, being better conditioned theoretically, is able to exhibit superior noise characteristics. We have also elaborated upon and verified the applicability of the accelerated list-mode image reconstruction method as a powerful solution for accurate, robust and efficient dynamic reconstructions of high-resolution data (as well as a number of additional benefits in the context of state-of-the-art PET).

Algorithms↗

The distribution of cardiac macrophages in myocardial ischaemia and cardiomyopathy.

AIMS: Recent evidence has implicated the macrophage as an effector cell in the inflammatory processes in transplant rejection, as well as cardiac disease, including coronary atherosclerosis. Although the latter is a vascular disease, the entire myocardium is affected. We have previously demonstrated the presence and distribution of macrophages in the 'normal' human heart. In this paper the distribution of myocardial macrophages, in the various chambers of the failing human heart, from cases of coronary atheroma and cardiomyopathy undergoing heart transplantation is documented. METHODS AND RESULTS: Tissue blocks were removed at specific sites taken from six cases with ischaemic heart disease (IHD) (four males, two females, age range 54-62 years), and four cases with idiopathic dilated cardiomyopathy (IDCM) (three males, one female, age range 18-49 years). These were compared with hearts from five cases of sudden death, unrelated to heart disease. Sections were stained with a CD68 pan macrophage marker. Positive cells were enumerated in 20 random fields. Results were analysed using a generalized linear modelling method using a Poisson distribution. Macrophages were identified within the interstitium and often close to blood vessels in all hearts. Macrophages from IHD hearts demonstrated the most intense staining and were often larger and more elongated than those found in 'normal' control hearts. Macrophages were also often degranulated and staining was diffuse in the interstitium. Overall, there were significantly more macrophages in most areas from IHD hearts than from IDCM hearts or control hearts (P < 0.001). CONCLUSIONS: Significantly more macrophages were found in all four chambers in diseased hearts compared with controls. Macrophage numbers were higher in the atria than in ventricles in the diseased myocardium. This study suggests selective recruitment of macrophages into the atria in the disease states studied.

Adolescent↗

Electron microscopy of DNA excision repair patches produced by human cell extracts.

To characterize the process by which the mammalian nucleotide excision repair complex interacts with DNA to recognize and repair lesions, we have investigated the size and distribution of repair patches induced by human cell extracts in ultraviolet light-irradiated plasmid DNA. Repair synthesis was carried out in a buffer substituting biotinylated dUTP for dTTP, to allow repair patches to be detected by electron microscopy after streptavidin/colloidal gold labelling. Individual repair events on circular plasmids that had undergone repair synthesis in cell extracts were scored as gold particles bound specifically to irradiated molecules. Samples of over 2000 irradiated and unirradiated plasmids were counted. Repair synthesis at ultraviolet light photoproducts typically replaced about 30 nucleotides, since 69% of patches contained only one particle of 10 nm gold and 24% of patches contained two gold particles (each covering approx. 29 nucleotides). In addition, the ordering of repair events among damaged plasmids closely fitted a Poisson distribution, indicating that repair of lesions is achieved via a non-processive, random diffusion mechanism. This suggests that the repair complex is not intrinsically processive.

Biotin↗

Nonrandom frequency distribution of mitoses in rat lobuloaveolar mammary gland epithelium.

A quantitative microscopic technique was employed to examine the distribution of mitotic activity in the rat mammary gland. The frequency distribution of mitoses per unit volume of lobuloalveolar mammary gland epithelium in virgin Lewis/Mai rats at each phase of the estrous cycle were determined and compared to the expected Poisson frequency distributions, assuming random mitotic activity. Both pooled data and data from individual rats were compared to expected Poisson distributions. At each phase of the estrous cycle, the pooled observed distributions deviated significantly from Poisson distributions. Sixty-seven percent (72/108) of the observed frequency distributions obtained from individual rats also deviated significantly from expected Poisson distributions. These data indicate a nonrandom distribution of mitoses in rat lobuloalveolar mammary gland epithelium. This observation suggests that local cell products and/or a variation in the extent of replicative synchrony of lobuloalveolar cell populations may determine in part the pattern of mitotic activity in this tissue. A nonrandom distribution of mitoses in mammary epithelium may have significance in relation to the genesis of hyperplastic and neoplastic lesions of the mammary gland.

Animals↗

Clonal distribution of osteoprogenitor cells in cultured chick periostea: functional relationship to bone formation.

Folded explants of periosteum from embryonic chick calvaria form bone-like tissue when grown in the presence of ascorbic acid, organic phosphate, and dexamethasone. All osteoblast-like cells in these cultures arise de novo by differentiation of osteoprogenitor cells present in the periosteum. To study the spatial and functional relationships between bone formation and osteoprogenitor cells, cultures were continuously labeled with [3H]thymidine for periods of 1-5 days. Radioautographs of serial 2-microns plastic sections stained for alkaline phosphatase (AP) showed maximal labeling of 30% of fibroblastic (AP-negative) cells by 3 days while osteogenic cells (AP-positive) exhibited over 95% labeling by 5 days. No differential shifts in labeling indices, grain count histograms of fibroblastic and osteogenic cells or numbers of AP-positive cells were observed, indicating no significant recruitment of cells from the fibroblastic to the osteogenic compartment. Despite the continuous presence of [3H]thymidine, less than 35% of both osteoblasts and osteocytes were labeled at 5 days, indicating that only one-third of the osteoprogenitor cells had cycled prior to differentiation. Spatial clustering of [3H]thymidine-labeled cells was measured by computer-assisted morphometry and application of the Poisson distribution to assess contagion. Cluster size and number of labeled cells per cluster did not vary between 1-3 days, but the number of clusters increased 20-fold between Day 1 and Day 3. Clusters were predominantly AP-positive and located close to bone. Three-dimensional reconstruction from serial sections showed that clusters formed long, tubular arrays of osteogenic cells up to eight cells in length and located within 2-3 cell layers from the bone surface. Selective killing of S-phase cells with two pulse labels of high specific activity [3H]thymidine at 1 and 2 days of culture completely blocked bone formation. These data indicate that a very small population of cycling osteoprogenitor cells is essential for bone formation in vitro and give rise to relatively small numbers of clonally distributed progenitors with limited proliferative capacity. The progeny of these clusters undergo restricted migration and differentiate into osteoblasts.

Alkaline Phosphatase↗

[Cytogenetic study of thyroid patients treated with external irradiation or radioiodine].

Where clinically permitted, either external irradiation or radioiodine therapy is usually recommended for the treatment of differentiated thyroid cancer patients. This paper describes an attempt to clarify the radiation burden and the distribution of radiation doses on the lymphocytes in consequence of these two therapeutic modalities, and the circumstances of the applicability of biological dosimetry. Thyrotoxic patients with intact thyroid glands underwent 131I therapy were also analysed for this purpose. An analysis was made of the extent to which exposure to local neck irradiation (50 Gy) or radioiodine therapy (1734-2600 MBq) causes chromosomal aberrations in the lymphocytes of thyroid disease patients after total or subtotal thyroidectomy, or thyrotoxic patients with intact thyroid glands (185-595 MBq). The irradiated volume of lymphatic tissues played the most important role in the formation of chromosomal aberrations. External irradiation caused 10-times more aberrant cells than 131I therapy did in cancer patients. In thyrotoxic patients the lower therapy doses of radioiodine caused a significantly higher frequency of aberrations than that observed in thyroid cancer patients. Selective radiosensitivity of lymphocytes was supported by the analysis of the Poisson distribution of aberrations, which suggested a homogeneous dose distribution only in 131I-treated and thyroidectomized cancer patients. In conclusion, we suggest that the results of studies of the genetic alterations in the lymphocytes exposed to radioiodine, under well-defined circumstances should not be ignored before the mode of radiation treatment is chosen. On the other hand, in the modelling of accidental environmental radioiodine exposure, only thyrotoxic patients with an intact thyroid gland and heterogeneous dose-distribution are a suitable group.

Adult↗

Measuring survival rates from sudden cardiac arrest: the elusive definition.

BACKGROUND: Measuring survival from sudden out-of-hospital cardiac arrest (OOH-CA) is often used as a benchmark of the quality of a community's emergency medical service (EMS) system. The definition of OOH-CA survival rates depends both upon the numerator (surviving cases) and the denominator (all cases). PURPOSE: The purpose of the public access defibrillation (PAD) trial was to measure the impact on survival of adding an automated external defibrillator (AED) to a volunteer response system trained in CPR. This paper reports the definition of OOH-CA developed by the PAD trial investigators, and it evaluates alternative statistical methods used to assess differences in reported "survival." METHODS: Case surveillance was limited to the prospectively determined geographic boundaries of the participating trial units. The numerator in calculating a survival rate should include only those patients who survived an event but who otherwise would have died except for the application of some facet of emergency medical care-in this trial a defibrillatory shock. Among denominators considered were: total population of the study unit, all deaths within the study unit, and documented ventricular fibrillation cardiac arrests. The PAD classification focused upon cases that might have benefited from the early use of an AED, in addition to the likely benefit from early recognition of OOH-CA, early access of EMS, and early cardiopulmonary resuscitation (CPR). Results of this classification system were used to evaluate the impact of the PAD definition on the distribution of cardiac arrest case types between CPR only and CPR + AED units. RESULTS: Potential OOH-CA episodes were classified into one of four groups: definite, probable, uncertain, or not an OOH-CA. About half of cardiac arrests in the PAD units were judged to be definite OOH-CA events and therefore potentially treatable with an AED. However, events that occurred in CPR-only units were less likely to be classified as definite or probable OOH-CA events than those in CPR + AED units (43% versus 55%, odds ratio 0.78, 95% confidence interval 0.57-1.07). The study retained sufficient power to permit a statistical analysis of the alternative hypothesis that the CPR + AED method results in twice as many survivors as a CPR-only approach. The result is critically dependent on the denominator used for calculating survival rates; but the analysis does not require a denominator as the numerators will have identical Poisson distributions (counts for rare events) under the null hypothesis since randomization distributes the risk of cardiac arrest evenly between the two arms. CONCLUSION: Reported OOH-CA rates and survival rates vary widely, depending upon the definitions applied to events. Rigorous assessment of treatments applied to improve survival can be obscured by inappropriate definitions. Large-scale randomized interventions designed to improve survival from OOH-CA can be evaluated based upon the absolute numbers of patients surviving, rather than a change in the proportion surviving.

Cardiopulmonary Resuscitation↗

Use of the scan statistic on disaggregated province-based data: foot-and-mouth disease in Iran.

The spatial scan statistic was applied to density-smoothed data that approximated the spatial distribution within the area and reduced the potential bias produced when location data have been aggregated for large areas. The method is illustrated, using data on the location of foot-and-mouth disease (FMD) outbreaks in Iran. Data examined were 4477 FMD outbreaks reported on a per province basis between June 1996 and September 2003. A kernel density of the outbreak locations was estimated, using a fixed radius and the centroid of each province as the designated location of all cases reported for the province. The radius that produced a density map with the highest correlation with expert opinion was 4 degrees (latitude/longitude). Livestock density was used as a proxy for the underlying population at risk of acquiring FMD. Livestock and outbreak density maps were overlain to obtain the number of outbreaks and livestock in each of 15,599 cells covering the mapped surface of the country. A spatial scan statistic was applied to the density-smoothed data assuming that the outbreaks had a Poisson distribution. Results were compared with those obtained using a spatial scan statistic on provincially aggregated data. Application of the spatial scan statistic on the density-smoothed data allowed identification of clusters (P<0.01) related more to the actual geographic distribution of cases (expert opinion) and of animals at risk, than to the distribution of the provinces. Significant clusters of FMD were identified that coincided with roads, neighboring countries, and high-density population areas, suggesting that the region may represent a route for cross-continent transmission of FMD.

Animals↗

A spatio-temporal analysis of BSE cases born before and after the reinforced feed ban in France.

A spatio-temporal analysis was carried out to see how the risk distribution of bovine spongiform encephalopathy (BSE) in France changed depending on the period of birth. The data concerned the 539 BSE cases born in France after the ban (BAB) of meat and bone meal (MBM) in 1990 and detected between July 1, 2001 and December 31, 2003, when the surveillance of BSE was comprehensive. Seventy-two of these cases were born after the reinforced (second) ban (BASB) in 1996, which involved the removal of BSE-risk materials and cadavers from the processing of MBM. The Ederer-Myers-Mantel (EMM) time and space cluster test was applied, after classifying the cases by trimester and region of birth, BAB or BASB status, and dairy or beef status. Then disease mapping was performed for four successive birth periods, three for the BAB cases (January 1991 through June 1994, July 1994 through June 1995, July 1995 through June 1996), and one for the BASB (July 1996 through October 1998). It was elaborated with the Bayesian graphical modelling methods and based on a Poisson distribution with spatial smoothing. The parameters were estimated by a Markov Chain Monte Carlo (MCMC) simulation method. The main finding was that the areas with the highest risk of BSE changed largely from one birth period to another; from the west, it reached the east of France for birth cohort 1994-1995 and the southwest for birth cohort 1995-1996. The EMM test identified a peak risk in this region both for dairy and beef cattle in the fall 1995. The spatial distribution of the risk for the BASB cases matched the spatial pattern of risk for the preceding BAB birth cohort quite well; this was in favour of a common origin of the infection of the BAB and BASB cases, despite the complementary control measures.

Animal Feed↗