Kinetics of serotonin uptake in the intact lung

The pulmonary endothelium is capable of removing and metabolizing serotonin (5HT) carried in the venous blood. Thus the lungs can influence the arterial concentrations of 5HT. In addition, there is evidence that changes in the lung uptake of 5HT might portend more serious endothelial damage wherein the barrier function of the endothelium is compromised. This has been a stimulus for finding methods for evaluating these endothelial functions. These methods must be able to distinguish changes in whole organ function which result from changes in perfusion (e.g., cardiac output, redistribution of flow, etc.) from those resulting from changes in the function of the endothelial cells. When a bolus containing radio-labeled 5HT and an unmetabolizable indicator which is confined to the vascular space is injected into the pulmonary artery, the pulmonary venous or systemic arterial concentration curves contain information about both the convective transport and endothelial cell process involved. Some of this information can be interpreted quantitatively using a simple mathematical model.     

Applications of meta-analytic structural equation modelling in health psychology: examples,issues, and recommendations

ABSTRACT

Statistical methods play an important role in behavioural, medical, and social sciences. Two recent statistical advances are structural equation modelling (SEM) and meta-analysis. SEM is used to test hypothesised models based on substantive theories, which can be path, confirmatory factor analytic, or full structural equation models. Meta-analysis is used to synthesise research findings in a particular topic. This article demonstrates another recent statistical advance – meta-analytic structural equation modelling (MASEM) – that combines meta-analysis and SEM to synthesise research findings for the purpose of testing hypothesised models. Using the theory of planned behaviour as an example, we show how MASEM can be used to address important research questions that cannot be answered by univariate meta-analyses on Pearson correlations. Specifically, MASEM allows researchers to: (1) test whether the proposed models are consistent with the data; (2) estimate partial effects after controlling for other variables; (3) estimate functions of parameter estimates such as indirect effects; and (4) include latent variables in the models. We illustrate the procedures with an example on the theory of planned behaviour. Practical issues in MASEM and suggested solutions are discussed.     

Tissue Ablation with Irreversible Electroporation

This study introduces a new method for minimally invasive treatment of cancer—the ablation of undesirable tissue through the use of irreversible electroporation. Electroporation is the permeabilization of the cell membrane due to an applied electric field. As a function of the field amplitude and duration, the permeabilization can be reversible or irreversible. Over the last decade, reversible electroporation has been intensively pursued as a very promising technique for the treatment of cancer. It is used in combination with cytotoxic drugs, such as bleomycin, in a technique known as electrochemotherapy. However, irreversible electroporation was completely ignored in cancer therapy. We show through mathematical analysis that irreversible electroporation can ablate substantial volumes of tissue, comparable to those achieved with other ablation techniques, without causing any detrimental thermal effects and without the need of adjuvant drugs. This study suggests that irreversible electroporation may become an important and innovative tool in the armamentarium of surgeons treating cancer.     

中国健康女性红细胞压积参考值（温氏法）与地理因素的关系

为制定中国健康女性红细胞压积参与值（温氏法）的统一标准提供科学依据，本文研究了中国４３６个单位测定的２２１３５例健康成年女性的红细胞参考值（温氏法）与五项地理因素的关系。发现海拔高度是影响女性红细胞压积参考值最主要的因素，随着海拔高度的逐渐增大，女性红细胞压积参考值也逐渐的增大。用数学回归的方法推导出了一个多元回归方程。如果知道敢某地的地理因素，就可以用这个回归方程。估算这个地区的红细胞压积参考值     

Spherical harmonic-based finite element meshing scheme for modelling current flow within the heart

The paper describes a spherical harmonic-based finite element scheme for solving Poisson-type equations throughout volumes characterised by irregularly shaped inner and outer surfaces. The inner and outer surfaces are defined by spherical harmonics, and the volume in between these surfaces is divided into nested shells that are weighted averages of the inner and outer surfaces. The resulting mesh comprises hexahedral elements, wherein each hexahedral element is defined by inner and outer shells in the radial direction and divisions in the polar and azimuthal directions. The spacing between shells can be set to any desired value. Similarly, the size of the polar and azimuthal divisions can be specified. A test of the scheme on an anisotropic sphere, meshed with 720 nodes, yielded a relative error of 0.78% on the sphere's surface. As a comparison, a previously published combined finite element/boundary element scheme with a 946-node mesh produced a corresponding error of 3.57%.     

Multivariate Genetic Analysis of Brain Structure in an Extended Twin Design

The hunt for genes influencing behavior may be aided by the study of intermediate phenotypes for several reasons. First, intermediate phenotypes may be influenced by only a few genes, which facilitates their detection. Second, many intermediate phenotypes can be measured on a continuous quantitative scale and thus can be assessed in affected and unaffected individuals. Continuous measures increase the statistical power to detect genetic effects (Neale et al., 1994), and allow studies to be designed to collect data from informative subjects such as extreme concordant or discordant pairs. Intermediate phenotypes for discrete traits, such as psychiatric disorders, can be neurotransmitter levels, brain function, or structure. In this paper we conduct a multivariate analysis of data from 111 twin pairs and 34 additional siblings on cerebellar volume, intracranial space, and body height. The analysis is carried out on the raw data and specifies a model for the mean and the covariance structure. Results suggest that cerebellar volume and intracranial space vary with age and sex. Brain volumes tend to decrease slightly with age, and males generally have a larger brain volume than females. The remaining phenotypic variance of cerebellar volume is largely genetic (88%). These genetic factors partly overlap with the genetic factors that explain variance in intracranial space and body height. The applied method is presented as a general approach for the analysis of intermediate phenotypes in which the effects of correlated variables on the observed scores are modeled through multivariate analysis.     

Including Measured Genotypes in Statistical Models to Study the Interplay of Multiple Factors Affecting Complex Traits

The etiology of complex traits may perhaps best be conceptualized by an interplay of multiple factors that mediate the influence of the genes on the eventual outcome. The possibilities of studying aspects of this interplay using existing methods are generally limited. We therefore propose a model with observed and latent variables that does not impose restrictions on the number of variables or the direction of their causal relations and provides a general approach for fitting structural equation models to empirical data. The model is very flexible and (1) allows for genetic effects on the means, variances, and relations between variables, (2) can control for stratification effects on all these components, (3) can be fitted in nuclear families of any size, (4) is estimated using an interpretable parameterization, and (5) can incorporate di- and multi-allelic loci, marker haplotypes, multiple loci simultaneously, and parental genotypes. We indicate how the model can be estimated with the Mx software (Neale et al., 1999) and have written a program to enable geneticists who are not acquainted with Mx to fit their own submodels in a simple and efficient way. A simulation study showed that the model yielded correct Type I errors, unbiased parameter estimates, and satisfactory power to discriminate between alternative models. An example is also given that illustrates how the model could be applied to real data.     

中国健康中青年女性红细胞压积参考值（温氏法）与海拔高度的关系

为制定中国健康中青年女性红细胞压积参考值（温氏法）的统一标准提供科学依据，作者研究了中国１２５个单位测定的７２５６例健康中青年女性的红细胞压积参考值（温氏法）与海拔高度的关系，发现随着海拔高度的逐渐增大，健康中青年女性红细胞压积参考值（温氏法）也逐渐的增大。用数学回归的方法推导出了一个一元回归方程。如果知道了中国某地的海拔高度，就可以用这个回归方程，估算这个地区的健康中青年女性红细胞压积参考值。     

Shear Modulus of Elasticity of the Esophagus

Experimental and diagnostic procedures like distension of a balloon catheter, bougie, and esophagogastroduodenoscopy can induce shear deformation in the esophageal wall. However, the shear modulus of the esophagus is yet unknown. The aim of this study was to determine the esophageal shear modulus and its dependence on the circumferential and longitudinal stresses and strains in the rat. The constitutive equation including the shear deformation based on a pseudo-strain-energy function was generated. Results were obtained using a new triaxial instrument to perform simultaneous torsion, inflation, and longitudinal stretching tests. The shear modulus varied with the inflation pressure and the longitudinal stretch ratio. The shear modulus at the longitudinal stretch ratio of 1.5 and between inflation pressures of 0 and 2.0 kPa ranged from 5.43 to 185.01 kPa. The mechanical constant of the esophagus showed that the esophageal wall was anisotropic with different stiffness in the circumferential, longitudinal, and the shear directions. The stiffness in the longitudinal direction was higher than in the circumferential direction (P < 0.001). This test can be extended for further mechanical remodeling experiments and for other tubular organs such as the small intestine or blood vessels.     

一种新的血液本构方程理论和实验探讨

在低剪切率下血液表现出明显的非牛顿流体性质，牛顿流体本构方程不再适用。本文理论上分析了简化Oldroyd方程对描述血液力学性质的适用性，讨论该本相关系对剪切稀化、触变应力过程及复粘度的概括说明。本文还数值求解了阶跃剪切下的触变应力过程，计算结果与测量曲线作了对比。     

指甲的测量与临床意义

目的：为临床指甲的再植再造、修复整形提供形态学基础。方法：测量255例大学生的指甲长、指甲宽和手长、手宽等15项指标,并对其结果进行统计分析。结果：计算出男女各项指标的测量值。各均值的性别差异有显著性意义,各指甲长之间,各指甲宽之间均呈正相关,而指甲长与手长之间无相关关系,由其余各指推算拇指甲长的回归方程可靠。结论：临床指甲再造和整形时可依据各指甲长之间的回归方程来推算应设计的指甲长度,而不应按手长估计,同时要考虑指甲宽长间的比例。     

Differential human growth restudied

Background: The study of differential growth in various animals suggests that a similar growth pattern occurs throughout the bilateral animals. This growth pattern is based on the assumption that a quadratic equation describes the relationship between two body measurements, yielding a quadratic parabola in a graphic presentation.

Aim: Can human growth be studied by comparing body measurements? If the growth of one body part has a definite relation to the growth of another body part and if this relation can be expressed in a quadratic formula, then important conclusions can be reached.

Subjects and methods: An official database of the mean measurements of the Belgian population has been used.

Results: (1) The growth in human length is, from the beginning, constantly and negatively influenced by the growth in girth, so it is evident that growth has to stop; (2) The influence of the growth in girth is stronger in females, resulting in shorter females; (3) The growth of the human head is, from the beginning, constantly and negatively influenced by the growth in body length (both sexes show a very similar pattern); (4) Not all comparisons resulted in a quadratic parabola: the nipple distance is constantly at ～24% of the thoracic girth in males and young females.

Conclusion: The study of differential growth by using a quadratic parabola gives the answers to the questions “Why do we stop growing?” and “Why are women shorter than men?”.     

基于H—H方程的神经元模型

神经系统是一个庞大的系统，系统的结构不但从横向可以分为若干功能子系统，而且从纵向也可分为许多功能层次，各层次间不但物理构成有很大的差异，而且功能上也有相当的联系，下一层次是上一层次的基础，本文即是由此观点出发，研究在离子通道（亚细胞层次）的原理上，用仿真方法推导出神经元（细胞层次）的主要特性，由此可以建立神经元的模型（包括空间总和，时间总和，阈值，不应期，输出静特性，适应性）。本文还讨论了不能由离     

Theoretical analysis of the transient thermal clearance method for regional blood flow measurement

In the noninvasive transient thermal clearance method a metal plate at room temperature is attached to the investigated skin. The plate is thermally insulated from the environment, and so the tissue temperature, after an initial decrease, is increased at a rate which depends both on heat convection by blood and on tissue thermal conductivity. The corresponding bioheat conductivity equation is solved and the dependence of plate temperature on time and on blood flow discussed. It is shown that, for an appropriate choice of metal and plate thickness, regional blood flow can be derived from temperature/time curves.     

Modeling with Measured Genotypes: Effects of the Vitamin D Receptor Gene, Age, and Latent Genetic and Environmental Factors on Bone Mineral Density

We use empirical data to demonstrate a recently proposed framework for including measured genotypes in structural equation models (Van den Oord and Snieder, 2002). The sample consisted of 227 MZ pairs, 197 DZ pairs, and 41 DZ twins without co-twin. The mean age of the female twins was 57 years. The analysis aimed at studying the effect of the vitamin D receptor (VDR) gene polymorphism (VDRGP) on bone mineral density (BMD). Whereas age affected the BMD measures via independent pathways, the effects of the VDRGP plus latent genetic and environmental factors were consistent with a common pathway model. VDRGP explained 0.3% to 0.5% of the variance. These analyses demonstrated that (i) regardless of how much is known about the gene and its products at a molecular level, meaningful questions can be addressed concerning how genes co-act with other variables at a "higher" phenotypic level; (ii) measured genotypes can be treated like any other variable so that the whole structural equation models framework can in principle directly be applied; and (iii) measured genotypes do not need to have large effects to study mechanisms underlying complex traits, and it may even be argued that particularly genes with small effects are better studied within the context of models with multiple variables.     

Exploratory structural equation modeling for event‐related potential data—An all‐in‐one approach?

ERP data are characterized by high dimensionality and a mixture of constituting signals and are thus challenging for researchers to analyze. To address these challenges, exploratory factor analysis (EFA) has been used to provide estimates of the unobserved factors and to use these estimates for further statistical analyses (e.g., analyses of group effects). However, the EFA approach is prone to biases due to assigning individual factor scores to each observation as an intermediate step and does not properly consider participants, electrodes, and groups/conditions as differentiable sources of factor variance, with the consequence that factor correlations are inaccurately estimated. Here, we suggest exploratory structural equation modeling (ESEM) as a potential approach to address these limitations. ESEM may handle the complexity of ERP data more appropriately because multiple sources of variance can be formally taken into consideration. We demonstrate the application of ESEM to ERP data (in comparison with EFA) with an illustrative example and report the results of a small simulation study in which ESEM clearly outperformed EFA with respect to accurate estimation of the population factor loadings, population factor correlations, and group differences. We discuss how robust statistical inference can be conducted within the ESEM approach. We conclude that ESEM naturally extends the current EFA approach for ERP data and that it can provide a coherent and flexible analysis framework for all kinds of ERP research questions.     

Cable equation for a myelinated axon derived from its microstructure

A simplified cable equation that describes the subthreshold behaviour of a myelinated axon is derived from its microstructure. Specifically, a microcontinuum cable model of a composite axon is homogenised, yielding a familiar macrocontinuum cable equation of electrotonus, for which the space and time constants depend on microstructural electrical parameters. Activating functions for magnetic and electrical stimulation can be incorporated into this homogenised cable equation as sources or sinks of transmembrane potential. An integral solution to the forced cable equation is also presented for the subthreshold regime. Errors are introduced when myelin membrane resistance is assumed to be infinite.     

从随机行走模型到磁共振扩散权重成像

目的:利用布朗运动的随机行走模型导出磁共振扩散权重成像(DWI)公式,以验证随机行走模型对磁共振扩散权重成像的适用性。方法:从布朗运动的随机行走模型出发,分析存在梯度磁场情况下质子的扩散行为,计算梯度磁场对扩散运动中质子进动相位相散的积累,从而用统计方法算出在梯度磁场和扩散两个因素作用下导致的信号衰减,最后结合扩散成像序列导出磁共振扩散权重成像的信号强度公式。结果:证明了扩散运动中质子进动相位相散的积累符合高斯分布,导出了扩散所致信号衰减与梯度磁场及施加时间的关系,并进一步导出了脉冲梯度自旋回波序列(PGSE)的扩散权重成像公式——Stejskal-Tanner方程。结论:在磁共振扩散成像中人体水分子的扩散运动可视为随机行走。通过施加运动探测梯度(MPG)磁场,可将组织中水分子的扩散能力反映到图像亮度上。虽然Stejskal和Tanner也曾利用存在扩散和梯度磁场情况下的布洛赫方程导出了Stejskal-Tanner方程,但本文直接从随机行走模型出发导出该方程,为磁共振扩散权重成像的微观基础提供一个新的视角。     

Compact and accurate linear and nonlinear autoregressive moving average model parameter estimation using Laguerre functions

A linear and nonlinear autoregressive moving average (ARMA) identification algorithm is developed for modeling time series data. The algorithm uses Laguerre expansion of kernals (LEK) to estimate Volterra-Wiener kernals. However, instead of estimating linear and nonlinear system dynamics via moving average models, as is the case for the Volterra-Wiener analysis, we propose an ARMA model-based approach. The proposed algorithm is essentially the same as LEK, but this algorithm is extended to include past values of the ouput as well. Thus, all of the advantages associated with using the Laguerre function remain with our algorithm; but, by extending the algorithm to the linear and nonlinear ARMA model, a significant reduction in the number of Laguerre functions can be made, compared with the Volterra-Wiener approach. This translates into a more compact system representation and makes the physiological interpretation of higher order kernels easier. Furthermore, simulation results show better performance of the proposed approach in estimating the system dynamics than LEK in certain cases, and it remains effective in the presence of significant additive measurement noise.