Dental fluorosis: its use as a biomarker

Several epidemiological studies, beginning with those of Dean and co-workers in the 1940's, clearly demonstrate the relationship between dental fluorosis in humans and the level of fluoride in water supplies. These studies and others have shown that, in a population, there is a direct relationship among the degree of enamel fluorosis, plasma and bone fluoride levels, and the concentration of fluoride in drinking water. However, dental fluorosis is a reflection of fluoride exposure only during the time of enamel formation, somewhat limiting its use as a biomarker. In addition, the degree of fluorosis is dependent not only on the total fluoride dose, but also on the timing and duration of fluoride exposure. At the level of an individual response to fluoride exposure, factors such as body weight, activity level, nutritional factors, and the rate of skeletal growth and remodeling are also important. These variables, along with an individual variability in response to similar doses of fluoride, indicate that enamel fluorosis cannot be used as a biological marker of the level of fluoride exposure for an individual.     

Influence of water temperature on thermal, circulatory and respiratory responses to muscular work

Different muscular exercises have been executed on a bicycle ergometer during immersion in water, the temperature of which varied between 20 and 40 degrees C. During submaximal works, O2 consumption was not modified by the temperature of the water. On the other hand, body temperature (rectal and muscular) are clearly influenced by environment. The temperature of the quadriceps varies from 37.7-38.5 degrees C when the bath temperature rises from 20-40 degrees C during the same work intensity corresponding to 1/3 of the individual maximal work capacity. The rectal temperature was always lower about 0.5 degrees C. Ventilation and heart rate underwent modifications which were significantly accentuated in hot water. Maximal O2 consumption does not reach its highest level in cold water. The low muscular temperature observed in these conditions seems to limit the aerobic metabolism and the working of the muscles. Maximal O2 consumption then rises in parallel with the increase in bath temperature and in body temperatures. In very hot water however (40 degrees C), when rectal temperature rises unduly, the circulatory demand linked to thermolysis becomes excessive, and maximal O2 consumption decreases.     

Body fat estimation in late pregnancy and early postpartum: comparison of two-, three-, and four-component models

Accurate methods for determining body fat mass during reproduction are necessary to evaluate energy balance. However, determination of fat mass is complicated during pregnancy by the accretion of water, which invalidates assumptions underlying standard two-compartment models. The extent to which the variability in body water during pregnancy invalidates use of pregnancy-corrected two-compartment models for determination of fat mass in individual women is unknown. Moreover, it is unclear whether body water returns to nonpregnant values by 2 wk postpartum, which is frequently used as the baseline in studies of postpartum women. The present study uses a four-component model as a criterion for evaluating two- and three-component models. Fifty-six healthy, normotensive women between the ages of 19 and 35 y were studied at 36 +/- 1 wk gestation and 15 +/- 2 d postpartum. Total body water (TBW), total body potassium (TBK), body density, and bone mineral content were measured by deuterium dilution, whole-body potassium counting, hydrodensitometry, and dual-energy X-ray absorptiometry (postpartum only), respectively. At 2 wk postpartum, hydration and density of fat-free mass (FFM) had not returned to nonpregnant values, and differed between lactating and nonlactating women (P < 0.05). Accordingly, standard TBW and body density estimates of fat mass differed from four-component estimates at both time points (P < 0.005). Moreover, our data indicate that even when pregnancy-specific values for hydration or density of FFM are used in TBW and body density models, individual fat mass estimates may differ by > 3 kg from the four-component value. Fat mass by TBK may differ by > 10 kg from fat mass by the four-component model during pregnancy, and by 6 kg postpartum. Use of standard two-compartment models to estimate fat mass results in significant error both during pregnancy and at 2 wk postpartum. Pregnancy-corrected two-compartment models produce reliable mean fat mass estimates during pregnancy, but individual fat mass estimates may vary widely from four-component values.     

Variability of powder characteristics and their effect on dimensional variability of powder injection moulded components

Abstract

In this study, the effect of powder characteristics and their variability on the dimensional variability of green and sintered PIM components has been examined for 316L stainless steel. Three lots of gas atomised and three lots of water atomised powders were characterised and used to make six batches of PIM compound. These compound lots were injection moulded using a cavity pressure transducer and screw position regulation controls. The moulded geometry was measured in the green state and sintered state for dimensional variability. The general findings are that gas atomised powder produce less dimensional variability than the water atomised powder from lot to lot, however, the water atomised powders produce less in lot dimensional variability and are generally less susceptible to distortion of cantilevered members during sintering. Also, the lot to lot variation in the powder characteristics, such as particle size and pycnometer density, have an effect on dimensional stability whereas variations in powder characteristics such as surface area, tap and apparent density, and chemistry have little effect on dimensional stability.     

Comparative molecular phylogeography of two Xenopus species, X. gilli and X. laevis, in the south-western Cape Province, South Africa

Xenopus gilli is a vulnerable anuran with a patchy distribution along the south-western coast of the Cape Province, South Africa. This species is sympatric with Xenopus laevis laevis, a widespread relative found over much of southern Africa. We examined the molecular phylogeography and population structure of the contact zone between these species to obtain information about historical biogeography and conservation management of this region. Analyses of the distribution, frequency, and cladistic and phenetic relationships among mitochondrial DNA haplotypes indicate that population subdivision is present in both taxa but that long-term isolation of sets of populations has occurred in X. gilli only. Haplotype and nucleotide diversity are also considerably higher within and among X. gilli ponds than X. l. laevis ponds in this region. We attribute the genetic segregation of X. gilli populations to ancient habitat fragmentation by ocean transgression into X. gilli habitat and to continued habitat alteration by human activity. The lower level of genetic diversity in X. L. laevis in this region is likely a result of a recent arrival of this taxon to the south-western Cape region relative to X. gilli. Population structure in X. l. laevis may be a result of isolation by distance. Clear evidence exists for at least two management units within X. gilli and strongly supports the establishment of protective measures east of False Bay in order to conserve a substantial portion of this species' extant genetic diversity.     

Neutral temperature range in incubators: performance of equipment in current use and new developments

Low-birth-weight neonates should be nursed at thermoneutrality inside incubators. Thermoneutrality control is essential to enhance body growth and to reduce neonatal illnesses and mortality. Guidelines have been published to provide the thermoneutral range, but the recommendations did not always take into account all ambient and physiological parameters influencing thermoneutrality. In most marketed incubators, the heat supply is controlled through convective air flow (closed incubators) or through radiant power density (radiant warmer beds). The heating unit (on/off cycling or adjustable proportional control) is activated by an error signal calculated from the difference between a controlled temperature and a reference value preset by the clinician. The controlled variable can be either the incubator air or the skin temperature of the anterior abdominal region of the neonate. The neonate's size, thermal properties of the mattress and of incubator walls, air temperature and humidity, air velocity, incubator wall temperatures all influence the heat exchanges between the neonate and the surroundings, and, consequently, modify the obtention of thermoneutrality. Moreover, studies of the physiological mechanisms by which the neonate regulates body heat storage suggest that metabolic rate, behavior, vigilance level, nursing care, and heater control processes should also be taken into account. Little attention has been paid to these factors, and incubator performances are often disappointing. This article reviews the different factors that modify thermoneutral condition. An attempt is made to suggest new ways to design equipment incorporating these factors in algorithms controlling heater processes in order to reach the optimal thermal environment in which the neonate should be nursed.     

稀土6063变形铝合金阳极氧化与电解着色的研究

本文系在硫酸、硫酸亚锡溶液中对添加有稀土的6063变形铝合金进行了阳极氧化和电解着色。比较系统地研究了氧化电解液的浓度、温度、时间、电流密度对膜层厚度的影响;以及着色电流密度、电压、时间对膜层色度的影响。结果证实,稀土可以明显地提高6063变形铝合金氧化膜厚度和电解着色的色度,稀土含量以0.30％为好。     

Secondary coverage of the yolk by the body wall in the direct developing frog, Eleutherodactylus coqui: an unusual process for amphibian embryos

Eleutherodactylus coqui develops directly from a large 3.5-mm egg to a froglet, without an intervening tadpole stage. We have examined the development of the body wall, a structure whose behavior has been altered in this derived development. In an event that is unusual for amphibian embryos, the yolk mass is secondarily surrounded by the body wall, which originates near the embryo's trunk. The epidermis of the body wall is marked by melanophores, and the rectus abdominis, which will form the ventral musculature, is near its leading edge. As the body wall expands, the epidermis, melanophores, and rectus abdominis all move from the dorsal side to close over the yolk at the ventral midline. The original ectoderm over the yolk undergoes apoptosis, as it is replaced by body wall epidermis. Intact muscles are not required for ventral closure of the body wall, despite their normal presence near the advancing edge. Comparative examination of embryos of Xenopus laevis and Rana pipiens suggests that ventral closure does not occur in species with tadpoles. The expansion of dorsal tissues over the yolk, as illustrated by E. coqui, may have been important in the origin of amniote embryos.     

Impact of safe water for drinking and cooking on five arsenic-affected families for 2 years in West Bengal, India

The groundwater in seven districts of West Bengal, India, covering an area of 37,000 km2 with a population of 34 million, has been contaminated with arsenic. In 830 villages/wards more than 1.5 million people, out of the total population, drink the arsenic-contaminated water. Safe water from a source having < 0.002 mg 1(-1) arsenic has been supplied for 2 years to five affected families comprising 17 members (eight of them with arsenical skin-lesions) of different age groups for impact assessment study in terms of loss of arsenic through urine, hair and nail. The study indicates random observable fluctuations of arsenic concentration in urine among members on different scheduled sampling days with a declining trend, particularly during the first 6 months. Furthermore, the investigation showed that despite having safe water for drinking and cooking, the study group could not avoid an intake of arsenic, time and again, through edible herbs grown in contaminated water, food materials contaminated through washing, and the occasional drinking of contaminated water. After minimizing the level of contamination, a noteworthy declining trend after 8 months was observed in urine, hair and nails in all the cases, but not to that level observed in a normal population, due to prevailing elevated background level of arsenic in the area. The eight members, who had already developed skin lesions, are far from recovering completely, indicating a long-lasting damage. Statistical interpretation of the data are considered.     

Wind Mixing in Temperature Simulations for Lakes and Reservoirs

A one-dimensional mathematical formulation for simulating the wind mixing of the surface layers in reservoirs and lakes is developed. Emphasis is placed on the estimation of the net available wind-supplied energy for mixing by taking into consideration the variability of the wind in time. The formulation of the dynamics of the wind-mixed layer presented in this paper is implemented in a modified version of the one-dimensional Massachusetts Institute of Technology reservoir model. The model was used to predict the annual cycle of the thermal structure of Spada Lake in northwestern Washington State. A complete record of inflow and outflow water temperatures, temperature profiles in the reservoir, and meteorological data at the site over a 16-month period provided the basis for verifying the model. Special effort was made to screen and analyze these data to assure their quality. The application of the temperature model in Spada Lake produced good agreement between simulated and observed temperature profiles. Noticeable features of this application are the accurate simulation of the growth of the wind-mixed layer in the fall and the prediction of the exact time of formation and melting of the ice cover in the winter. These features could not have been predicted accurately without accounting for the variability of the wind pattern and its effect on the net available energy for mixing, as it was found in earlier simulations with simpler formulations of the wind-mixing effect.     

Extralenticular expression of Xenopus laevis alpha-, beta-, and gamma-crystallin genes

PURPOSE: Extralenticular expression of alpha- and beta-crystallin genes has been demonstrated in mammals and expression of gamma-crystallin genes has been shown in Xenopus laevis. To determine a possible correlation between lens determination and crystallin gene expression, the site of expression of (a member of) the alpha-, beta-, and gamma-crystallin gene families was observed before and during lens formation in X. laevis. METHODS: The partial complementary DNAs (cDNAs) of alpha A- and beta A4-crystallin and a gamma-crystallin were cloned from an X. laevis lens cDNA library. The corresponding antisense RNAs were used to analyze the expression of these genes during X. laevis development by wholemount in situ hybridization. RESULTS: Expression of the beta A4- and gamma-crystallin (but not alpha-crystallin) genes could first be detected in the animal cap of the X. laevis gastrula. The beta A4- and gamma-crystallin messengers were also found in the first stage of lens development, when the ectodermal tissue overlying the optic vesicle thickens to form the lens placode. alpha A-crystallin messenger RNAs were only detectable when the lens epithelial cells were formed. CONCLUSIONS: In contrast to observations in most vertebrates, expression of the beta A4- and gamma-crystallin genes was observed to precede that of the alpha A-crystallin gene during lens development of X. laevis, reflecting the determination that in amphibians, the (presumptive) fiber cells are formed before the epithelial cells, whereas in vertebrates, the order is reversed. Expression of beta A4- and gamma-crystallin genes in the ectodermal tissue of the X. laevis gastrula shows that these genes are expressed when this tissue gains competence for lens formation.     

Comparison of tamoxifen effects on the actions of triiodothyronine or growth hormone in the ovariectomized-hypothyroid rat

Recent studies have suggested that a subset of estrogen responses arise via modulation of triiodothyronine (T3) actions, and depend on T3 for expression: other estrogen responses are not T3-dependent. Moreover, tamoxifen acts as a full estrogen agonist in T3-dependent responses but behaves as an antiestrogen in T3-independent responses. T3 directly induces a variety of metabolic enzymes and proteins, and also induces rat growth hormone (GH). Thus, some T3-dependent tamoxifen effects might reflect modulation of GH rather than T3 actions. To address this issue, tamoxifen effects on somatotropic and metabolic actions of T3 and GH were compared in ovariectomized rats with methimazole-induced hypothyroidism. Rats were given T3 (10 micrograms/kg/day) or ovine GH (2 mg/kg/day) with or without tamoxifen (0.5 mg/kg/day) for 30 days. GH was poorly effective in producing a sustained increase in somatic growth in hypothyroid rats compared to T3; nonetheless, GH effects to increase body weight, tibia length and serum insulin-like growth factor I while decreasing fat mass and evoking small increases in body temperature were not inhibited by tamoxifen. Tamoxifen also did not inhibit GH trends to increase tibia bone mineral density. T3 increased body temperature, insulin-like growth factor I levels and all measures of somatic growth and, unlike GH, increased food intake and tended to decrease tibia bone mineral density. Tamoxifen inhibited the somatotropic actions of T3 (including increases in insulin-like growth factor I levels), and produced significant increases in tibia bone mineral density only in T3-treated rats. Tamoxifen had no effect on T3 actions to increase food intake or body temperature. T3 alone increased fat mass and exhibited a tendency to decrease serum triglycerides: tamoxifen had no effect on these parameters in the absence of T3. However, coadministration of tamoxifen with T3 produced a marked decrease in fat mass and increased serum triglycerides. GH had no effect on serum triglycerides in either the presence or absence of tamoxifen. Serum glucose levels appeared normal in all groups. The data indicate that multiple tamoxifen effects on growth and metabolism may reflect modulation of T3 rather than GH actions.     

Mastocytosis: magnetic resonance imaging patterns of marrow disease

To investigate the validity of the prediction of body water compartments by multi-frequency impedance in Indonesians, 42 adults (19 males and 23 females) were recruited in Jakarta, the capital of Indonesia. Extracellular water (ECW) and total body water (TBW) were measured with dilution techniques and predicted from body impedance at 1 and 100 kHz, respectively, using prediction formulas developed in a Dutch population. Furthermore, body weight, body height and body density were measured and as a measure of body build TBW/height and ECW/height were calculated. Percent ECW of body weight in both males (26 +/- 3%) and females (23 +/- 2%) was higher compared to the Dutch reference population, and also the body water distribution (ECW/TBW) was higher (0.46 +/- 0.04) compared to the reference population. TBW/height and ECW/height appeared to be considerably lower in the Indonesian group compared to the reference group, indicating a more slender body shape. TBW was overestimated by 1.8 +/- 2.4 and 2.5 +/- 1.3 kg in males and females, respectively. ECW was underestimated in males by 0.1 +/- 1.2 kg and slightly overestimated in females (0.1 +/- 1.0 kg). After corrections for differences in body build and body water distribution the bias of the predicted TBW was markedly reduced from 2.2 +/- 1.9 to 1.3 +/- 1.8 kg (males and females combined). For ECW the bias after correction for body water distribution and body build was 0.3 +/- 0.6 kg (males and females combined). It is concluded that multi-frequency impedance is suitable for the prediction of body water compartments at the population level but, due to differences in body build and body water distribution, validation in a larger group of Indonesian subjects is needed to avoid systematic prediction errors.     

Synthesis and activity of partial retro-inverso analogs of the antimetastatic laminin-derived peptide, YIGSR-NH2

Very low birth weight (VLBW) children at school age show variability in their outcome, compared with normal birth weight children, although many early physical and health differences are equalized by middle childhood. Studies of nonhandicapped VLBW children have found a higher rate of school retention and school problems in this population. Differences in intelligence have been reported, although these are often confounded by socioeconomic factors such as educational level of the parent. Few studies today of children born in the late 1970s and early 1980s have related school age outcome to central nervous system (CNS) status, yet for learning disabilities or other neuropsychological deficits, this may be highly relevant. Better understanding of medical risk factors, however, will not affect the decisive influence of social factors on their expression in the school age child.     

Neural activity affects distribution of glutamate receptors during neuromuscular junction formation in Drosophila embryos

The prevalence of diseases associated with obesity, such as cardiovascular disease and diabetes mellitus, is higher in the spinal cord injury (SCI) population. Specifically, the mortality rate for cardiovascular disease is 228% higher in the SCI population. In addition, 100% of SCI individuals have osteoporosis in the paralysed extremities. These diseases are related to physical activity level, the level of the spinal cord lesion, and time post injury. Physically active SCI men and women have above-average fat mass (16 to 24% and 24 to 32%, respectively, compared with 15% for able-bodied men and 23% for able-bodied women), while sedentary SCI individuals have 'at-risk' levels of body fat (above 25% and 32%, respectively). The proportions and densities of the 3 main constituents comprising the fat-free body (mineral, protein and water) are altered following SCI. Bone mineral content decreases by 25 to 50%, and the magnitude of reduction is dependent on the level, completeness and duration of SCI. Because of denervation resulting in skeletal muscle atrophy, total body protein reduces by 30%, and total body water relative to bodyweight decreases by 15% following SCI. Indirect methods based on 2-component body composition models assume constant proportions and densities of mineral, protein, and water in the fat-free body. As a result, prediction equations based on 2-component models yield invalid estimates of fat and fat-free mass in the SCI population. Therefore, future research needs to directly quantify the proportions and densities of the constituents of the fat-free body in the SCI population relative to age, sex, physical activity level, level of the spinal cord lesion and time post injury, and to develop equations based on multicomponent body composition models.     

Identification and quantification of intrinsic optical contrast for near-infrared mammography

Near-infrared spectroscopy has been used to quantify the composition of healthy female breast tissue in vivo. By collecting transillumination spectra in the wavelength range 680-1100 nm at 7-9 positions on the breasts of five female volunteers, an attempt was made to quantify the intra- and intersubject variability of breast composition. The dominant absorbers are water, lipids and hemoglobin. Hemoglobin concentration in the breast is substantially lower than that in the brain or muscle (less than 10 microM). The measured deoxyhemoglobin concentration can vary by up to 100% between different positions on the same breast. Water and lipid concentrations can show similar variability. Phantom and simulation studies demonstrate that this variability is not due to the effects of tissue boundaries on the measurements. The low hemoglobin concentration implies that optical breast imaging should be performed at wavelengths below about 850 nm to ensure that the image contrast comes predominantly from hemoglobin. Intrasubject variability could have implications for the ability of optical imaging to discern tumors from background contrast variations.     

Ionizing radiation and genetic risks. VI. Chronic multifactorial diseases: a review of epidemiological and genetical aspects of coronary heart disease, essential hypertension and diabetes mellitus

This paper provides a broad overview of the epidemiological and genetical aspects of common multifactorial diseases in man with focus on three well-studied ones, namely, coronary heart disease (CHD), essential hypertension (EHYT) and diabetes mellitus (DM). In contrast to mendelian diseases, for which a mutant gene either in the heterozygous or homozygous condition is generally sufficient to cause disease, for most multifactorial diseases, the concepts of genetic susceptibility' and risk factors' are more appropriate. For these diseases, genetic susceptibility is heterogeneous. The well-studied diseases such as CHD permit one to conceptualize the complex relationships between genotype and phenotype for chronic multifactorial diseases in general, namely that allelic variations in genes, through their products interacting with environmental factors, contribute to the quantitative variability of biological risk factor traits and thus ultimately to disease outcome. Two types of such allelic variations can be distinguished, namely those in genes whose mutant alleles have (i) small to moderate effects on the risk factor trait, are common in the population (polymorphic alleles) and therefore contribute substantially to the variability of biological risk factor traits and (ii) profound effects, are rare in the population and therefore contribute far less to the variability of biological risk factor traits. For all the three diseases considered in this review, a positive family history is a strong risk factor. CHD is one of the major contributors to mortality in most industrialized countries. Evidence from epidemiological studies, clinical correlations, genetic hyperlipidaemias etc., indicate that lipids play a key role in the pathogenesis of CHD. The known lipid-related risk factors include: high levels of low density lipoprotein cholesterol, low levels of high density lipoprotein cholesterol, high apoB levels (the major protein fraction of the low density lipoprotein particles) and elevated levels of Lp(a) lipoprotein. Among the risk factors which are not related to lipids are: high levels of homocysteine, low activity of paraoxonase and possibly also elevated plasma fibrinogen levels. In addition to the above, hypertension, diabetes and obesity (which themselves have genetic determinants) are important risk factors for CHD. Among the environmental risk factors are: high dietary fat intake, smoking, stress, lack of exercise etc. About 60% of the variability of the plasma cholesterol is genetic in origin. While a few genes have been identified whose mutant alleles have large effects on this trait (e.g., LDLR, familial defective apoB-100), variability in cholesterol levels among individuals in most families is influenced by allelic variation in many genes (polymorphisms) as well as environmental exposures. A proportion of this variation can be accounted for by two alleles of the apoE locus that increase (ε4) and decrease (ε2) cholesterol levels, respectively. A polymorphism at the apoB gene (XbaI) also has similar effects, but is probably not mediated through lipids. High density lipoprotein cholesterol levels are genetically influenced and are related to apoA1 and hepatic lipase (LIPC) gene functions. Mutations in the apoA1 gene are rare and there are data which suggest a role of allelic variation at or linked LIPC gene in high density lipoprotein cholesterol levels. Polymorphism at the apoA1--C3 loci is often associated with hypertriglyceridemia. The apo(a) gene which codes for Lp(a) is highly polymorphic, each allele determining a specific number of multiple tandem repeats of a unique coding sequence known as Kringle 4. The size of the gene correlates with the size of the Lp(a) protein. The smaller the size of the Lp(a) protein, the higher are the Lp(a) levels. (ABSTRACT TRUNCATED)     

Myxococcus xanthus sasN encodes a regulator that prevents developmental gene expression during growth

Myxococcus xanthus multicellular fruiting body development is initiated by nutrient limitation at high cell density. Five clustered point mutations (sasB5, -14, -15, -16, and -17) can bypass the starvation and high-cell-density requirements for expression of the 4521 developmental reporter gene. These mutants express 4521 at high levels during growth and development in an asgB background, which is defective in generation of the cell density signal, A signal. A 1.3-kb region of the sasB locus cloned from the wild-type chromosome restored the SasB+ phenotype to the five mutants. DNA sequence analysis of the 1.3-kb region predicted an open reading frame, designated SasN. The N terminus of SasN appears to contain a strongly hydrophobic region and a leucine zipper motif. SasN showed no significant sequence similarities to known proteins. A strain containing a newly constructed sasN-null mutation and Omega4521 Tn5lac in an otherwise wild-type background expressed 4521 at a high level during growth and development. A similar sasN-null mutant formed abnormal fruiting bodies and sporulated at about 10% the level of wild type. These data indicate that the wild-type sasN gene product is necessary for normal M. xanthus fruiting body development and functions as a critical regulator that prevents 4521 expression during growth.     

Timing of menopause, reproductive years, and bone mineral density: a cross-sectional study of postmenopausal Japanese women

Age at menopause has been found to be associated positively with bone mineral density, and age at menarche has been found to be associated negatively with bone mineral density. However, there have been few studies on the relations of timing of menopause and length of the reproductive period with bone mineral density. The purpose of this study was to examine the relations of timing of menopause and reproductive years (calculated as age at menopause minus age at menarche) with mineral density of the second metacarpal bone in postmenopausal Japanese women. The study population consisted of 1,035 naturally menopausal women aged 40-70 years who were screened in 1996-1997. Using computed x-ray densitometry, the authors measured bone mineral density by analyzing radiographic films of the right second metacarpal bone. Using the women with early menopause (age < 49 years) as the reference group and adjusting for age, subjects with late menopause were at decreased risk for low bone mineral density (odds ratio (OR) = 0.69, 95% confidence interval (CI) 0.49-0.97). After adjustment for additional covariates (grip strength, physical activity, body mass index, smoking, and calcium intake), the association was unchanged (OR = 0.70, 95% CI 0.50-0.99). Postmenopausal women with more reproductive years (> or = 40 years) were at decreased risk for low bone mineral density compared with those with fewer reproductive years, after adjustment for age (OR = 0.73, 95% CI 0.40-1.30) and potentially confounding factors (OR = 0.76, 95% CI 0.41-1.37); the p-value for trend was not statistically significant. In multiple linear regression analysis, early menopause and fewer reproductive years were independent predictors of low bone mineral density. In this study, postmenopausal Japanese women who had a late menopause and more reproductive years were at decreased risk for low bone mineral density, and may therefore be less prone to osteoporosis.     

Birthweight and neonatal outcome at the Muhimbili Medical Centre, Dar es Salaam, Tanzania

BACKGROUND: The level of residual noise in auditory brainstem responses (ABR) depends not only on the number of averages but also on the amplitude of background noise and on the frequency of artifacts. This paper describes the influence of digital filtering and of different methods of artifact suppression on the residual noise of ABRs. METHOD: Amplitude of background noise was estimated for 1033 ABRs recorded under suprathreshold stimulation (70 and 90 dB nHL) in 251 subjects. In 45 ABR recordings in 15 subjects, all 4000 individual sweeps were stored for off-line simulation. The power spectrum of background noise was investigated using an FFT analyzer. RESULTS: A great variability of mean noise amplitude was found both between subjects and in the recordings for each subject. Depending on the slope of the analogue 100-Hz high-pass filter, mean RMS values of background noise of 4.2 microV (6 dB/Oct.) and 2.5 microV (12 dB/Oct.), respectively, were found. Digital high pass filtering before averaging was found to increase the signal-to-noise ratio (SNR) considerably. CONCLUSIONS: Results indicate that (i) effective suppression of low-frequency noise components can only be achieved by zero phase digital filtering and (ii) if clipping of noise amplitude to 25 microV is used, optimized artifact rejection as weighted averaging or adopted artifact rejection levels have only small effect on the SNR.