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PubMed2003

Indoor radon levels and lung cancer risk estimates in seven cities of the Bahawalpur Division, Pakistan.

Indoor radon concentration levels were measured in seven major cities of the Bahawalpur Division, Pakistan. These included Fort Abbas, Minchin Abad, Hasilpur, Bahawalpur, Liaqatpur, Rahimyar Khan and Sadiq Abad. In order to select houses for this survey, the inhabitants were approached through their school-registered children. Due to several constraints, only those 100 houses were chosen in each city that were relatively the best representatives of the built-up area. The selected houses were then divided into live categories according to the house locations and building characteristics. CR-39 detectors, placed in polyethylene bags. were installed at head height in bedrooms and sitting rooms of all the selected houses and were exposed to radon and its daughter products for 90 days. Four such measurements were performed over a year in order to average out the seasonal variation in radon levels. After exposure, all the detectors were etched and counted under an optical microscope. The track densities of four measurements were averaged out and related to radon concentration levels. The radon levels were found to be 20, 20, 26, 28, 34, 42, 47 Bq m(-3) in the bedrooms and 24, 26, 27, 26, 37, 40, 43 Bq m(-3) in sitting rooms of Hasilpur, Rahimyar Khan, Minchin Abad, Fort Abbas, Sadiq Abad, Bahawalpur and Liaqatpur respectively. The observed variation in the radon level may be attributed to the geological variation in the area. Based on the observed data, excess lung cancer risk was assessed using the risk factors recommended by the USEPA, UNSCEAR and the ICRP. According to the EPA model, the lifetime excess lung cancer risk due to the lifetime exposure is found to vary from 12-102 per million per year in the houses surveyed. This variation is from 16-114 and 26-62 per million per year if UNSCEAR and ICRP limits are applied respectively.

Air Pollutants, Radioactive↗
PubMed2003

The combined effects of hardness, pH, and dissolved organic carbon on the chronic toxicity of Zn to D. magna: development of a surface response model.

The effect of changes in pH, hardness, and dissolved organic carbon (DOC) and the possible interactions among these parameters on the chronic toxicity of zinc to D. magna were investigated. Based on a Central Composite Design, models were developed that can explain the observed variation in EC(10) and EC(50) as a function of these toxicity modifying factors. All three parameters significantly altered the observed effect concentrations based on net reproductive rate. The largest differences in 21-day EC(10)s and EC(50)s caused by these factors were 10.1 and 4.9, respectively. An increase in pH and/or DOC decreased zinc toxicity. The significant interaction between pH and DOC on observed chronic Zn toxicity is in accordance with earlier reported increased sorption efficiency of Zn to humic substances at higher pH levels. Lowest Zn toxicity was observed in tests performed with moderately hard test media (between 200 and 300 mg/L as CaCO(3)). Lower or higher hardness of the test medium resulted in lower effect concentrations. Based on physico-chemical characteristics of the test media, developed models can be used to explain the variation between reported NOECs for Zn and may improve current environmental risk assessment procedures of metals.

Animals↗
PubMed1997

Squamate Harderian gland: an overview.

BACKGROUND: The Harderian gland is an orbital feature found in most terrestrial vertebrates. Although there have been several reports on the structure of the squamate Harderian gland, there has been little recent discussion as to its potential function. This article reviews both the recent morphological observations and their implications on the potential functions of the squamate Harderian gland. METHODS: Literature on the gross structure, histochemistry, and ultrastructure of the squamate Harderian gland and associated structures was reviewed. These observations were then used to assess morphologically the likelihood of the proposed functions. RESULTS: A high level of morphological variation was found in the squamate Harderian gland. Three functional hypotheses, including roles in orbital lubrication, digestion, and vomerolfaction, were considered. Both morphology of the squamate Harderian gland and the presence of alternate secretory sources suggest that it is unlikely to function in orbital lubrication. There is little evidence to suggest a function in digestion. Both the presence of the connecting lacrimal apparatus and the reduced intrinsic secretory capacity of the vomeronasal organ suggest that the Harderian gland may function in vomerolfaction. CONCLUSIONS: The most likely role of the squamate Harderian gland seems to be in vomerolfaction. Morphological variations observed in the Harderian gland may mirror the different degrees and mechanisms of vomerolfaction. Further studies, including comparative morphological, experimental, and microchemical analyses, are required to test this hypothesis.

Animals↗
PubMed1981

Autopsy sampling and elemental analysis: errors arising from post-mortem changes.

The implication of post-mortem changes such as cell swelling, imbibition and autolysis on the elemental composition of body organs has been studied in rats. Liver has been chosen as an example. Retaining the liver inside the intact dead body for different periods of time at ambient temperature induced significant changes in its weight due to post-mortem tissue degeneration. Livers from animals that were frozen at -15 degrees C also showed significant decreases in weight when they were thawed on the third day. The effect of these changes on the concentrations of various elements depended on the association of the elements with extracellular fluid and intracellular components. For example, concentration of K+ was affected more by the lysis of the cell and sustained losses up to 30 per cent. in relation to the control values, while the total content was reduced by more than 40 per cent. as a result of both lysis and tissue liquefaction. For Na+, differences ranging from +10 to -20 per cent. in concentrations and +20 to -40 per cent. in total content were observed which could be explained by the movement of fluid in and out of the organ. Among trace elements, variation observed for iron ranged from -20 to +40 per cent., while both copper and zinc were found to fluctuate between -20 and +20 per cent. The loss observed in the total content in the liver for the five trace elements studied (Cu, Fe, Mn, Rb and Zn) was found to be about 20 to 40 per cent.

Animals↗
PubMed1990

Variation in heart disease mortality across census tracts as a function of overdispersion and social class mixture.

Variation in heart disease (HD) mortality rates across census tracts is greater than expected given binomial error and available explanatory variables. We extended an extra-binomial variation model for rates standardized by the direct method. The overdispersion parameter accounted for 36 per cent of the observed variation in standardized rates. Ignoring overdispersion resulted in a change in an estimate of the effect of social class on HD mortality and substantial underestimation of the error of the estimates of such effects. Ecologic regression on the proportional mixture of social classes within tracts provided an appealing approach to the problem of estimating fixed effects with aggregated data.

Adolescent↗
PubMed2004

Short-term variations in delta(13)C of ecosystem respiration reveals link between assimilation and respiration in a deciduous forest.

We present a comprehensive dataset of hourly, daily, and monthly measurements of carbon isotope measurements of CO(2) in canopy air from a temperate deciduous forest with the aim to identify the relevance of short-term variations in the isotopic signature of ecosystem respiration (delta(13)C(R)) and to understand its underlying physiological processes. We show that during daytime low vertical mixing inside the canopy can lead to decoupling of the air in the lower and upper canopy layer resulting in large spatial variation of delta(13)C in CO(2) of canopy air. Intercept of Keeling Plots also showed large temporal variation (3.8 per thousand) over the course of the day demonstrating that intercepts can differ between day and night and suggesting that choosing the right time for sampling is essential to capture the isotopic signature of ecosystem respiration (delta(13)C(R)). delta(13)C(R) as obtained from night-time measurements showed large variation of up to 2.65 per thousand on a day-to-day basis, which was similar to the observed variation of delta(13)C(R) over the seasonal cycle (3.08 per thousand). This highlights the importance of short-term physiological processes within ecosystems for the isotopic composition of CO(2) in the atmosphere, not reflected by bulk plant and soil organic samples. At daily and monthly time scales, delta(13)C(R) increased with increasing ratio of vapour pressure deficit to photosynthetically active radiation, measured 4-5 days before. This suggests that ecosystem respiration was isotopically linked to assimilation. Furthermore, assimilates recently fixed in the canopy seem to form a labile carbon pool with a short mean residence time that is respired back to the atmosphere after 4-5 days.

Air↗
PubMed2004

Circadian rhythms of locomotor activity in the subterranean Mashona mole rat, Cryptomys darlingi.

The Mashona mole rat, Cryptomys darlingi, is a social, subterranean African rodent that is rarely, if ever, exposed to light, and that exhibits a regressed visual system. This study investigated locomotor activity patterns of Mashona mole rats (n=12) under different light cycles. Activity was measured using either infrared captors (n=8) or running wheels (n=4). The mole rats entrained their activity to a standard (LD 12:12) photoperiod. They displayed either a nocturnal or diurnal activity preference with one bout of activity and one bout of rest. Therefore, as a species, the Mashona mole rat did not show a clear nocturnal or diurnal activity preference. When the LD (12:12) light cycle was inversed, the animals switched their activity, too. Under constant dark (DD), most mole rats (73%) showed a free-running circadian activity rhythm, but under constant light (LL), only some (36%) did. The free-run period of the rhythm (tau) ranged from 23.83 to 24.10 h. The remaining animals were arrhythmic. There was large interindividual and intraindividual variations in the rate and extent of entrainment, time of activity preference, and activity patterns. Possible reasons for the observed variations are discussed. It is concluded that the Mashona mole rat has an endogenous activity rhythm which approximates 24 h, that the mole rat can distinguish between light and dark, and that the endogenous clock utilises this photic information as a zeitgeber.

Animals↗
PubMed2000

A physiologically-based explanation of disparity attraction and repulsion.

Westheimer and Levi [(1987) Vision Research, 27, 1361-1368] found that when a few isolated features are viewed foveally, the perceived depth of a feature depends not only on its own disparity but also on those of its neighbors. The nature of this interaction is a function of the lateral separation between the features: When the distance is small the features appear to attract each other in depth but the interaction becomes repulsive at larger distances. Here we introduce a two-dimensional extension of our recent stereo model based on the physiological studies of Ohzawa, DeAngelis and Freeman [(1990) Science, 249, 1037-1041] and demonstrate through analyses and simulations that these observations can be naturally explained without introducing ad hoc assumptions about the connectivity between disparity-tuned units. In particular, our model can explain the distance-dependent attraction/repulsion phenomena in both the vertical-line configuration used by Westheimer [(1986) Journal for Neurophysiology, 370, 619-629], and the horizontal-line-and-point configuration used by Westheimer and Levi. Thus, the psychophysically observed disparity interaction may be viewed as a direct consequence of the known physiological organization of the binocular receptive fields. We also find that the transition distance at which the disparity interaction between features changes from attraction to repulsion is largely determined by the preferred spatial frequency and orientation distributions of the cells used in the disparity computation. This result may explain the observed variations of the transition distance among different subjects in the psychophysical experiments. Finally, our model can also reproduce the observed effect on the perceived disparity when the disparity magnitude of the neighboring features is changed.

Computer Simulation↗
PubMed2004

Analysis of variance components in gene expression data.

MOTIVATION: A microarray experiment is a multi-step process, and each step is a potential source of variation. There are two major sources of variation: biological variation and technical variation. This study presents a variance-components approach to investigating animal-to-animal, between-array, within-array and day-to-day variations for two data sets. The first data set involved estimation of technical variances for pooled control and pooled treated RNA samples. The variance components included between-array, and two nested within-array variances: between-section (the upper- and lower-sections of the array are replicates) and within-section (two adjacent spots of the same gene are printed within each section). The second experiment was conducted on four different weeks. Each week there were reference and test samples with a dye-flip replicate in two hybridization days. The variance components included week-to-week, animal-to-animal and between-array and within-array variances. RESULTS: We applied the linear mixed-effects model to quantify different sources of variation. In the first data set, we found that the between-array variance is greater than the between-section variance, which, in turn, is greater than the within-section variance. In the second data set, for the reference samples, the week-to-week variance is larger than the between-array variance, which, in turn, is slightly larger than the within-array variance. For the test samples, the week-to-week variance has the largest variation. The animal-to-animal variance is slightly larger than the between-array and within-array variances. However, in a gene-by-gene analysis, the animal-to-animal variance is smaller than the between-array variance in four out of five housekeeping genes. In summary, the largest variation observed is the week-to-week effect. Another important source of variability is the animal-to-animal variation. Finally, we describe the use of variance-component estimates to determine optimal numbers of animals, arrays per animal and sections per array in planning microarray experiments.

Algorithms↗
PubMed1989

Value of the gamma camera renogram in the differential diagnosis of acute tubular necrosis and rejection in the early post-transplant period. Comparison with biopsy findings.

A group of 128 consecutive patients was identified on whom renal isotope studies had been performed during the first 2 months after renal transplantation and within 7 days of transplant biopsy. The prospective renogram and biopsy reports were reviewed and graded into 4 categories: severe rejection, predominant rejection, predominant acute tubular necrosis (ATN) and pure ATN. Two extreme patterns of renogram were identified: a sharp rise with a fast decline in the first min, attributed to ATN, and a slowly rising curve with no early peak occurring in severe rejection although not specific to this condition. There was a continuous intermediate spectrum. There was no inter-observer variation in gradings at the 2 ends of the spectrum. In the middle part the difference between 2 independent observers never exceeded more than 1 grade. There was good correlation between the biopsy and renogram gradings, with a discrepancy of more than 1 grade in only 5 patients; 2 of these, with severe rejection on the renogram, showed predominant ATN on biopsy, but the final clinical diagnosis was severe rejection (false positive biopsies). Two patients with biopsies showing severe rejection had a sharp initial up-slope in the renograms but a slower down-slope (over 4 min compared with 1 min in true ATN). With better definition of the criteria these renograms would not have been graded as ATN. There was 1 patient in whom no satisfactory explanation for the discrepancy was found (presumed false positive renogram). When properly defined criteria are used to interpret renograms, this simple test is at least as reliable as renal biopsy in differentiating ATN from rejection in the early post-transplant period, especially in the presence of anuria or severe oligurea.

Acute Kidney Injury↗
PubMed1994

The use of RAPD for identifying and classifying Musa germplasm.

Using the technique of random amplified polymorphic DNA (RAPD), we have identified 116 amplification products in Musa germplasm using nine primers. This has enabled us to identify RAPD markers that are specific to each of nine genotypes of Musa representing AA, AAA, AAB, ABB, and BB genomes. The pattern of variation observed following the application of multivariate analyses to the RAPDs banding data is very similar to the pattern of variation defined using morphological characters and used to assign Musa material into the different genome classes.

Base Sequence↗
PubMed2006

Variations in arterial blood pressure and photoplethysmography during mechanical ventilation.

We analyzed ventilation-induced changes in arterial blood pressure and photoplethysmography from waveforms obtained by monitoring 57 patients in the operating room and intensive care unit. Analysis of systolic and pulse pressure variations during positive pressure ventilation, DeltaUp, DeltaDown, and changes in the preejection period on both arterial and photoplethysmographic waveforms were possible in 49 (86%) patients. The pulse pressure variation and preejection period were similar when calculated using both arterial blood pressure and photoplethysmography, whereas the other variables were different. Photoplethysmographic pulse variation >9% identified patients with arterial pulse pressure variation >13% (area under ROC curve = 0.85) or DeltaDown >5 mm Hg (area under ROC curve = 0.85). In hypotensive patients, photoplethysmographic pulse variation >9% remained the best threshold value (pulse pressure variation >13%: area under ROC curve = 0.90; DeltaDown >5 mm Hg: area under ROC curve = 0.93) for predicting fluid responsiveness. In conclusion, this study showed that pulse variations observed in the arterial pressure waveform and photoplethysmogram are similiar in response to positive pressure ventilation. Furthermore, photoplethysmographic pulse variation > 9% identifies patients with ventilation-induced arterial blood pressure variation that is likely to respond to fluid administration.

Adult↗
PubMed2002

Systematic identification of splice variants in human P/Q-type channel alpha1(2.1) subunits: implications for current density and Ca2+-dependent inactivation.

P/Q-type (Ca(v)2.1) calcium channels support a host of Ca2+-driven neuronal functions in the mammalian brain. Alternative splicing of the main alpha1A (alpha1(2.1)) subunit of these channels may thereby represent a rich strategy for tuning the functional profile of diverse neurobiological processes. Here, we applied a recently developed "transcript-scanning" method for systematic determination of splice variant transcripts of the human alpha1(2.1) gene. This screen identified seven loci of variation, which together have never been fully defined in humans. Genomic sequence analysis clarified the splicing mechanisms underlying the observed variation. Electrophysiological characterization and a novel analytical paradigm, termed strength-current analysis, revealed that one focus of variation, involving combinatorial inclusion and exclusion of exons 43 and 44, exerted a primary effect on current amplitude and a corollary effect on Ca2+-dependent channel inactivation. These findings significantly expand the anticipated scope of functional diversity produced by splice variation of P/Q-type channels.

Alternative Splicing↗
PubMed2003

Explaining variations in reported diabetes prevalence in general practice: how much variation is explained by differences between practice populations?

There are large variations in reported diabetes prevalence within United Kingdom (UK) populations. Linear regression was used to investigate whether population characteristics could explain the variation in prevalence between 19 practices with relatively complete diagnostic recording. Population obesity and South Asian ethnicity largely explained observed variation in prevalence (adjusted R2 = 0.80). When adjusted for obesity and ethnicity, the deprivation score was no longer a predictor of diabetes prevalence. If true variation in prevalence between practices is largely predicted by population ethnicity and obesity, these population characteristics could be used to predict expected prevalence and to assess the completeness of practice registers.

Aged↗
PubMedDate not supplied

Serum thyroid hormone concentrations and weight loss relationships in eight obese women during semistarvation.

Eight obese female patients were studied over a period of 15 days whilst on 300 kcal diet. Serum levels of thyroxine and free throxine index were not altered significantly by semistarvation. A TRH test performed before and after the diet showed no appreciable change. Weight loss was intially rapid but later slowed despite good patients compliance. Serum concentrations of T 3 and reverse T 3 (rT3) early decreased (p less than 0.01) and increased (p less than 0.05) respectively, but returned towards control levels even before discontinuation of semistarvation. There was a positive correlation between the percentage decrease in body weight and the percentage increase in serum rT 3 (p less than 0.001), and a negative correlation between decrease in body weight and decrease in serum T 3 (p less than 0.001). Our results do not suggest that the variations in serum triiodothyronines limit the weight loss; it is probable, on the contrary, that the weight loss promotes the observed variations in thyroid hormones by as yet unknown adaptive metabolic forces.

Adult↗
PubMed2004

Enhanced diastereoselectivity via confinement: photoisomerization of 2,3-diphenylcyclopropane-1-carboxylic acid derivatives within zeolites.

From the perspective of asymmetric induction, the photochemistry of 24 chiral esters and amides of cis-2,3-diphenylcyclopropane-1-carboxylic acid from excited singlet and triplet states has been investigated within zeolites. The chiral auxiliaries placed at a remote location from the isomerization site functioned far better within a zeolite than in solution. Generally, chiral auxiliaries with an aromatic or a carbonyl substituent performed better than the ones containing only alkyl substituents. A model based on cation-binding-dependent flexibility of the chiral auxiliary accounts for the observed variation in de between aryl (and carbonyl) and alkyl chiral auxiliaries within zeolites. Cation-dependent diastereomer switch was also observed in select examples.

Journal Article↗
PubMed1999

Primordial noble gases from Earth's mantle: identification of a primitive volatile component

Carbon dioxide well gases in Colorado, New Mexico, and South Australia show excesses of (124-128)Xe correlated with (129)I-derived (129)Xe and (20)Ne/(22)Ne ratios that are higher than the atmospheric (20)Ne/(22)Ne ratio. The xenon isotopic data indicate the presence of a solarlike component deep within Earth. The presence of this component in crustal and upper mantle reservoirs may be explained by a steady-state transport of noble gases from the lower mantle, which still retains much of its juvenile volatile inventory. These measurements also indicate that the mantle source of these noble gases in the carbon dioxide well gases cannot be the source of Earth's present atmosphere. The variations observed in (129)Xe/(130)Xe between solar wind xenon, Earth's atmosphere, and mantle samples may be generated by variations of iodine/xenon in terrestrial reservoirs, as opposed to rapid early degassing.

Journal Article↗