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Many complex systems share similar statistical characteristics. In this Letter, a turbulence analogy is proposed for the long-term heart rate variability of healthy humans. Based on such an analogy, the equivalence of an inertial range is found and a cascade model, which captures the statistical properties of the heart rate data, is given.
PURPOSE: We examined effects on kidney function and morphology of a partial ureteropelvic junction obstruction induced late in the postnatal nephrogenesis period of the pig. We compared the results to a similar study on pigs with obstruction induced early in the nephrogenesis period. MATERIALS AND METHODS: A total of 20 14-day-old pigs were included in the study. Fifteen animals were randomized to partial unilateral obstruction and 5 were sham operated. Kidney function and morphology were analyzed regarding glomerular filtration rate, renographic functional share and total kidney volume at the age of 4, 12 and 24 weeks. RESULTS: At age 4 weeks hydronephrosis was found in all obstructed kidneys included in the study. Four obstructed kidneys had renographic functional share 40% or greater and 1 deteriorated to less than 40% at 24 weeks. A total of 11 obstructed kidneys had a functional share less than 40%, 5 increased to a share greater than 40% at age 24 weeks and 3 had decreasing share from age 4 to 24 weeks. Single kidney glomerular filtration rate of the contralateral kidneys was significantly increased at all ages. Volume of the contralateral kidney was significantly increased at age 4 and 12 weeks. CONCLUSIONS: The variability and course of renographic functional share in kidneys subjected to partial obstruction at age 2 weeks was similar to findings obtained in pigs obstructed at age 2 days. In contrast to these our study showed compensatory increase in function and size of the contralateral kidney, suggesting that contralateral compensation is an ability gained late in the nephrogenesis period.
The study of social networks has become an increasingly utilized method of examining the relationship between injection drug users' social environment and risk of HIV. This study examined relational aspects of two injection drug users (IDUs) within a single social network as they relate to sharing syringes. Data presented in this study were derived from baseline interviews of 508 IDUs from Baltimore, MD. Analyses were performed separately for male and female participants in an effort to understand gender differences in social aspects of syringe sharing. Among this sample, women shared syringes with a significantly higher percentage of injecting partners compared to men. In separate multilevel logistic regression models, significant variables associated with males' and females' syringe sharing were: sharing drugs daily with female injecting partners, injecting partners' provision of drugs when indexes' were withdrawing, being sexual partners, and injecting partners' injecting speedballs. Factors associated with male injecting dyads sharing of syringes were: being kin, injecting partners' injection of heroin and daily drug use, and drinking alcohol together. Results from this study demonstrate the usefulness of examining relationship characteristics of injecting dyads related to syringe sharing as they differ between men and women.
A study was made of the factors associated with high-risk behavior and intention to change among 126 intravenous drug users (IVDU) seen at drug treatment centers. Needle-sharing in the last month was associated with intravenous cocaine use, whereas sharing water or drug preparations was associated with variables related to the level of instruction or the reduction in the number of syringes shared in the last month. The intention to abandon high-risk behavior was not associated with the information, attitudes, or norms of the group, but was associated with the perception of personal capacity for reducing high-risk behavior. Finally, the importance and applications of these results in health counseling for IVDUs is discussed.
The phase G1-tumour cells of 76 lung clones obtained from rat transplantable rhabdomyosarcoma had near triploid mean DNA content (the diploid index (DI) = 1.46-2.05) and the phase G1/o-stromal cells was characterized by the diploid DNA content. The percent of tumour cells in lung clones determined by flow cytometry varied from 19.7 to 70.9. A correlation is found between the following items: DI; coefficients of variability of DNA content in tumour and stromal cells; the share of the tumour cells in clones and the coefficient of variability of the DNA content in stromal cells; percentage of the tumour cells in the So+ (G2 + M) phase and percentage of the stromal cells etc. Positive correlation is revealed between the coefficient of variability of the DNA content in tumour cells and coefficients of variability of the DNA content in stromal cells (r = 0.83), the negative one (r = 0.38)--between the coefficient of variability of the DNA content of stromal cells of clones and percentage of tumour cells which produce artificial lung metastasis.
Tuberculosis patients relapse if treatment is not continued for 6 months, because chemotherapy fails to convert the patients' response from the necrotizing pattern characteristic of disease (Koch phenomenon) to the nonnecrotizing bactericidal function required for optimal immunity. We need to understand the nature of these two immunological states and how to convert one to the other. Studies in mice and humans implicate differences in cytokine profiles and in metabolism of adrenal steroids. Either enhanced susceptibility or protection can be evoked in mice with appropriate doses of a killed environmental saprophyte. This emphasizes the importance of shared epitopes and may explain the geographically variable efficacy of Mycobacterium bovis Bacillus Calmette Guérin vaccination. Unlike soluble antigens of M. tuberculosis itself, which tend to evoke necrosis, the shared mycobacterial epitopes evoke little skin-test reactivity in patients. Preparations of these epitopes show potential as immunotherapeutic agents to convert the response from necrotic to bactericidal mode.
Claviceps purpurea specific to grasses in salt marsh habitats (Group G3) has previously been identified on Spartina spp. in two locations: New Jersey, USA and southern England. We have identified this subgroup of C. purpurea (G3) in 11 distinct populations including western Europe, South America, and along the Atlantic and Pacific Coasts of the USA. In addition, G3 C. purpurea was discovered on a new host grass genus, Distichlis. Unweighted pair group mean analyses of AFLP and RAPD data reveal distinct structure in G3 C. purpurea populations. Pacific coast populations show little diversity, suggesting they may have been introduced recently in that region. 43 isolates, representing 11 populations were identified as G3 based on the presence of an EcoRI restriction site in the 5.8S ribosomal DNA, and a clear genetic separation from isolates representing the other two C. purpurea subgroups (G1 and G2). In addition, all isolates originating from Spartina densiflora, S. foliosa, S. alterniflora, and S. anglica were identified as belonging to G3. RAPD and AFLP analyses supported the recognition of three discrete groups within C. purpurea and revealed high genetic variability between groups, with only 1.8% of polymorphic markers shared across all isolates. Similarly, analysis of molecular variation (AMOVA) revealed that genetic variability was mainly due to variations between groups (63.5%) rather than within groups (28.5%) or within populations (7.96%). G3 isolates were 35% similar, Pacific coast isolates 83% similar. Ninety percent similarity among isolates from the San Francisco Bay Area suggests this is a recently introduced population.
This paper discusses problems that are common to both the epidemiologic risk-factor approach and the demographic variable-based approach to studying population health. We argue that there is a shared reluctance to move away from a narrow variable-based thinking that pervades both disciplines, and a tendency to reify the multivariate linear procedures employed in both disciplines. In particular, we concentrate on the difficulties generated by classical variable-based approaches that are especially striking when one neglects selection processes and the use of strategies to minimize its effects. We illustrate these difficulties in terms of the so-called "Hispanic Paradox", which refers to comparative health advantages that some Hispanic groups appear to have. We find that much of what is conceived by demographers and epidemiologists as a paradox may not be paradoxical at all.
BACKGROUND: In order to identify, in a sample of heroin intravenous drug users (IVDU), those factors associated with the predominant risk behaviour related to the transmission of HIV-1 infection--sharing of injection equipment--a cross-sectional survey was carried out in Valencia, Spain from 1987 to 1992. METHODS: Informed consent and pertinent data were obtained from 3755 heroin IVDU recruited at two public AIDS Information Centres in two cities in the region of Valencia. Data were gathered on sociodemographic variables, and sexual and drug use behaviour by interview. The subjects were subsequently tested for HIV-1 antibody. A univariate analysis was carried out to identify variables that were significantly associated with sharing injection equipment. A logistic regression model was used to control for possible confounders. RESULTS: The IVDU who were teenagers, prostitutes (OR = 1.95), who had antibodies to HIV-1 (OR = 1.30) or who had an IVDU steady partner were at significantly higher risk for sharing of injection equipment. Higher levels of education, condom use (OR = 0.65) and living in the smaller city (OR = 0.75) were inversely related to sharing injection equipment. CONCLUSIONS: Our results suggest that different subgroups of IVDU have different characteristics that place them at different risk for HIV-1 infection. These characteristics should guide the design and intensity of specific preventive interventions. Teenagers and IVDU with low educational levels should be targetted for special attention by health authorities.
Sexual orientation, sexual identity, and sex-dimorphic behaviors were assessed concurrently and retrospectively, for childhood, in 95 pairs of male monozygotic (MZ) twins and 63 pairs of dizygotic (DZ) twins. There was a significantly higher rate of adult homosexuality among the MZ than among DZ twins. We employed a model-fitting approach using LISREL to test for genetic and environmental influences on variation for each trait singly and on the covariation among all six traits (three for childhood and three for adulthood). Univariate analyses confirmed the presence of familial factors for five of the six variables but were generally unable to distinguish shared environmental from genetic influences. Hierarchical tests of multivariate models supported the existence of an additive genetic factor contributing to the covariance among the variables. More restrictive multivariate models yielded a significant genetic influence on sexual orientation. Because of the different rates of orientation by zygosity and because of the restrictive nature of some of the multivariate models, our results are best considered tentative but do suggest that further biometrically oriented studies of sexual orientation and its correlates would be worthwhile.
Using microdata from the 1970 and 1980 censuses, we specify and test multilevel models of fertility determination for four Southeast Asian societies--Indonesia, Peninsular Malaysia, the Philippines, and Thailand. Social context is indexed by provincial characteristics representing women's status, the roles of children, and infant mortality. These contextual variables are hypothesized to have direct and indirect (through individual socioeconomic characteristics) effects on current fertility. The contextual variables account for a modest but significant share of individual variation in fertility and about one-half of the total between area variation in fertility. The women's status contextual variables, particularly modern sector employment, have the largest and most consistent effect on lowered fertility. The results based on the other contextual variables provide mixed support for the initial hypotheses.
Chi-square trend analysis is a useful technique for testing the statistical significance of dose-response associations between morbidity or mortality variables and degree of parental or maternofetal antigen sharing.
BACKGROUND CONTEXT: The goal of spinal instrumentation is to stabilize involved motion segments while fusion occurs. Although some degree of load sharing is necessary for fusion, the ability of the instrumentation system to transfer the load may vary. PURPOSE: The purpose of this study is to formulate a mathematical relationship between load sharing and load transfer of specific spinal instrumentation systems using a well-accepted mechanical model. STUDY DESIGN/SETTING: Forty-eight American Society for Testing Materials standard ultra high molecular weight polyethylene cylinders were used as per designation F 1717-96, standard test methods for static and fatigue for spinal implant constructs in a corpectomy model. METHODS: Twenty-four spinal assemblies consisting of anterior plates, anterior rod, and posterior rods were subjected to compression bending tests using a MTS Bionix servo-hydraulic material testing apparatus. Each implant was tested in compression bending with and without the addition of a titanium load-sharing cage. The force applied was the independent variable, and the displacement was the dependent variable. The stiffness was determined for each setup with and without the addition of an anterior load-sharing cage. RESULTS: The average axial compressive stiffness of a system increased by a factor of 8.5 with the addition of the load-sharing cage. An inverse relationship existed between the compressive stiffness of the construct and its relative increase achieved with the addition of the load-sharing cage. The compressive stiffness of the system with the addition of the load-sharing cage approached that of the anterior device itself as the system flexibility increased. The ability of instrumentation systems to load share or load transfer and their respective stiffness was determined. CONCLUSIONS: The 5-mm rod screw posterior system was compared with the 7-mm Ti posterior system with the addition of one and two devices for transverse traction (DTTs). The rods with the increased diameter had a stiffness of 1723 n/mm with one DTT and 1815 n/mm with two DTTs. The addition of an anterior cage had little effect on the stiffness of these systems. Anterior plate and screw/rod systems were analyzed and showed similar mechanical behavior to the 5-mm posterior rod/screw systems. A significant increase in stiffness was realized with the addition of an anterior cage. A means to determine the load sharing/transferring properties of a spinal instrumentation system is presented. This technique will allow the amount of load transferred from the fusion mass to the instrumentation to be predicted.
In longitudinal studies with dropout, pattern-mixture models form an attractive modeling framework to account for nonignorable missing data. However, pattern-mixture models assume that the components of the mixture distribution are entirely determined by the dropout times. That is, two subjects with the same dropout time have the same distribution for their response with probability one. As that is unlikely to be the case, this assumption made lead to classification error. In addition, if there are certain dropout patterns with very few subjects, which often occurs when the number of observation times is relatively large, pattern-specific parameters may be weakly identified or require identifying restrictions. We propose an alternative approach, which is a latent-class model. The dropout time is assumed to be related to the unobserved (latent) class membership, where the number of classes is less than the number of observed patterns; a regression model for the response is specified conditional on the latent variable. This is a type of shared-parameter model, where the shared "parameter" is discrete. Parameter estimates are obtained using the method of maximum likelihood. Averaging the estimates of the conditional parameters over the distribution of the latent variable yields estimates of the marginal regression parameters. The methodology is illustrated using longitudinal data on depression from a study of HIV in women.
The term "selection bias" encompasses various biases in epidemiology. We describe examples of selection bias in case-control studies (eg, inappropriate selection of controls) and cohort studies (eg, informative censoring). We argue that the causal structure underlying the bias in each example is essentially the same: conditioning on a common effect of 2 variables, one of which is either exposure or a cause of exposure and the other is either the outcome or a cause of the outcome. This structure is shared by other biases (eg, adjustment for variables affected by prior exposure). A structural classification of bias distinguishes between biases resulting from conditioning on common effects ("selection bias") and those resulting from the existence of common causes of exposure and outcome ("confounding"). This classification also leads to a unified approach to adjust for selection bias.
Several novel UDP glycosyltransferase (UGT) genes, mainly UDP glucuronosyltransferases, have been identified in the human, mouse and rat genomes and in other mammalian species. This review provides an update of the UGT nomenclature to include these new genes and prevent the confusion that arises when the same gene is given different names. The new genes are named following previously established recommendations, taking into consideration evolutionary relatedness and the names already in general usage in the literature. The mammalian UGT gene superfamily currently has 117 members that can be divided into four families, UGT1, UGT2, UGT3 and UGT8. The 5-exon genes of the UGT1 family each contain a unique first exon, plus four exons that are shared between the genes; the exons 1 appear to have evolved by a process of duplication, leading to the synthesis of proteins with identical carboxyl-terminal and variable amino-terminal domains. Exon-sharing is also seen with the 6-exon UGT2A1 and UGT2A2 genes. However, UGT2A3 and those of the UGT2B (six exons), UGT3 (seven exons) and UGT8 gene families (five or six exons) do not share exons and most likely were derived by a process of duplication of all exons in the gene. Most UGT1 and UGT8 enzymes have been characterized in detail; however, the catalytic functions of the UGT3A enzymes and several UGT2 enzymes remain to be characterized.
As of 1992, more than 4,200 pancreas transplants were reported to the International Pancreas Transplant Registry. Of these, more than 2,600 were performed in the United States, and of these, more than 2,100 have been transplanted since the inception of the UNOS Registry in October 1987. The analyses here are only of the UNOS data. Pancreas transplants performed in conjunction with a liver (either cluster or noncluster) or a heart were excluded from the analysis, and only those performed as a solitary procedure or in conjunction with a kidney were included. Emphasis was placed on those performed with the bladder drainage (BD) technique (96%). In the overall analysis of BD cadaveric pancreas transplants (n = 1,879), 1-year patient survival and pancreas graft function survival rates were 91% and 71%, respectively, 87% and 66% at 2 years, and 81% and 59% at 3 years. There were no differences according to gender, but 1-year graft survival rates were significantly higher in recipients 45 years or younger (72%) (n = 1,679) than in those older than 45 (64%) (n = 200). There were no significant differences according to graft preservation times of less than 12 (n = 749), 12-24 (n = 940), 24-30 (n = 79), and more than 30 (n = 9) hours, function rates at 1 year being 71%, 72%, 72%, and 44%, respectively. When analyzed according to the 3 major recipient categories (simultaneous pancreas/kidney transplants [SPK] [n = 1604]; pancreas after kidney transplants [PAK] [n = 166]; and pancreas transplants alone [PTA] [n = 109]), patient survival rates were no different (91%, 92%, and 92% at 1 year, respectively), but pancreas graft survival rates were significantly higher in the SPK than in the PAK and PTA categories (75%, 48%, and 49%, at 1 year, respectively). In the SPK group, kidney graft survival rates at 1 year were 84%. Outcomes were also compared according to whether induction immunotherapy included ALG, OKT3, or neither. In the SPK category, there was no difference among the protocols, with 1-year graft survival rates being 76% in the ALG (n = 838), 76% in the OKT3 (n = 416), and 72% in the Neither (n = 299) group.(ABSTRACT TRUNCATED AT 400 WORDS)
Computational sequence analysis of 10 available archaean histone-like proteins has shown that this family is not only divergently related to the eukaryotic core histones H2A/B, H3, and H4, but also to the central domain of subunits A and C of the CCAAT-binding factor (CBF), a transcription factor associated with eukaryotic promoters. Despite the low sequence identity, it is unambiguously shown that the core histone fold shares a common evolutionary history. Archaean histones and the two CBF families show a remarkable variability in contrast to eukaryotic core histones. Conserved residues shared between families are identified, possibly being responsible for the functional versatility of the core histone fold. The H4 subfamily is most similar to archaean proteins and may be the progenitor of the other core histones in eukaryotes. While it is not clear whether archaean histones are more actively involved in transcription regulation, the present observations link two processes, nucleosomal packing and transcription in a unique way. Both these processes, evidently hybrid in Archaea, have originated before the ermergence of the eukaryotic cell.