Predicting the dynamic effects of rubella vaccination programmes

In the Netherlands, prepubertal girls have been vaccinated against rubella since 1974 (the UK strategy). Recently the Dutch Health Council advocated the introduction of an elimination strategy: vaccination of 1- and 9-year-old children. Dynamic effects of both strategies are studied using deterministic and stochastic models. Estimates of several epidemiological parameters are given. All computations and simulations were performed using as much field data as possible. Under the old strategy a new equilibrium is expected around the years 1995 to 2000; the new strategy is estimated to eliminate rubella (CRS) in large parts of the population 3 to 5 years after its initiation. Possible consequences of the new strategy on a cluster of people who refuse vaccination are investigated.     

Bifurcation properties of the two process model

Abstract Daan's two process model is known to be one of the most powerful models, covering various situations from free-running to sleep deprivation. In this study, bifurcation properties of the model dynamics as function of a gap, D , between the threshold processes are clarified using a circle map. As a function of D , we will show that the model has the different types of the mutual entrainment regions that are intervened by the tangent bifurcation. The variable behavior of human circadian rhythm is suggested to be systematically understood based on the bifurcation properties of the two process model.     

三次抛物线配合方法在碘缺乏病区居民患病率分析中的应用

<正>在碘缺乏病区,居民甲状腺肿患病率在年鹅分布上的特征,可用二次抛物线加以描述[l].根握资料类型的不同,可选择更为适合的三次抛物线来描述.根据现场调查资料,本文采用三次抛物线方法进行配合,并将配合结果与二     

大白鼠游泳输出功测定仪的研制和疲劳方程Y＝A＋B／T的建立

研制了可以直接连续测量大鼠游泳输出功率的仪器，建立了一个理想的动物模型，通过分析对功率曲线进行函数拟合，得出了代表疲劳发生、作功能力下降的双曲线方程，通过分析衰竭时间和功、功率等参数的关系提出了衰竭阈概念。     

Modification of DiFrancesco-Noble equations to simulate the effects of vagal stimulation onin vivo mammalian sinoatrial node electrical activity

We present a new mathematical model for vagal control of rabbit sinoatrial (SA) node electrical activity based on the DiFrancesco-Noble equations. The original equations were found to be unstable, resulting in progressive cycle by cycle depletion or accumulation of ions in intra- and extracellular compartments. This problem was overcome by modifying the maximum Na−K pump current and the time constant for uptake of intracellular calcium. We also included a formulation for the acetylcholine (ACh)-activated potassium current which was consistent with experimental data. This formulation was based on kinetics first proposed by Osterrieder and later modified by Yanagihara. The resulting model exhibits cycle-cycle ionic stability, and includes an ACh-activated potassium current which accurately reproduces experimentally observed effects of vagal stimulation on both the membrane potential and its timederivative. Simulations were performed for both brief-burst and prolonged vagal stimulation using simplified square wave profiles for the concentration of ACh in the synaptic cleft space. This protocol permits the isolation of cardiac period dynamics caused by changes in membrane potential and intra- and extracellular ionic concentrations from those caused by other mechanisms including the dynamics of ACh release, diffusion, hydrolysis and washout. Simulation results for the effects of brief-burst single cycle stimulation on the cardiac period agree closely with experimental data reported in the literature, accurately reproducing changes in membrane potential and the phasic dependency of the response to the position of vagal stimulus bursts within the cycle. Simulation of the effects of prolonged vagal stimulation accurately reproduced the steady-state characteristics of heart period response, but did not yield the complex multimodal dynamics of the recovery phase, or the pronounced post vagal tachycardia observed experimentally at the termination of the stimulus. Our results show that the major chronotropic effects of vagal stimulation on the SA cell membrane can be explained in terms of the ACh-activated potassium current. The effects of this membrane current however are generally fast acting and cannot contribute to any long lasting dynamics of the cardiac period response. The modified DiFrancesco-Noble model presented in this article provides a valuable theoretical tool for further analysis of the dynamics of vagal control of the cardiac pacemaker.     

Infertility: Avoidance of triplet pregnancies by elective transfer of two good quality embryos

Attempts to increase the probability of a successful pregnancyin in-vitro fertilization (IVF) treatment by increasing thenumber of embryos transferred automatically also increase theprobability of multiple pregnancies and their attendant risks.Even where the number of transferred embryos is limited to amaximum of three as in this and other centres, there is a highincidence of twins and triplets. The question therefore ariseswhether the number of transferred embryos should be furtherlimited to a maximum of two in cases where the prognosis isotherwise good. The only objection to this idea is a possiblelowering of pregnancy rate. The present study set out to investigatethis question. No significant lowering of pregnancy rate wasfound, so that limiting the number of transferred embryos totwo where the prognosis is otherwise good has now become standardpractice in our centre. A good IVF prognosis was defined bythe following criteria: first attempt for IVF, less than 37years old, and good embryo development. From 183 patients fulfillingthese criteria, 80 agreed to the transfer of two embryos (group1) and 103 opted for a triple transfer (group 2). Patient characteristicsand embryology results were similar in the two groups. In group1, 34 patients (42.5%) became pregnant and in group 2, 50 (48.5%).This difference is not significant. Similarly, twin pregnancyrates in both groups were high; eight twin pregnancies (23.5%)in group 1 and 12 (24%) in group 2. For the triplet pregnancyrate of 18% (nine triplet pregnancies) in group 2, there wasobviously no parallel in group 1. After thawing about half ofthe cryopreserved embryos and subsequently replacing them, preliminarycumulative pregnancy rates of 52.5% in group 1 and 53.4% ingroup 2 were obtained. Future results from cryopreservationshould provide relatively better outcomes for group 1 sinceall the patients in this group had at least one embryo frozenand fewer embryos replaced in the fresh cycle.     

306名大学生错失恐惧与社交媒体倦怠的关系:睡眠质量和负性情绪的链式中介作用

目的 探讨大学生睡眠质量、负性情绪在错失恐惧与社交媒体倦怠间的中介作用。 方法 采用错失恐惧量表、社交媒体倦怠量表、匹兹堡睡眠质量指数量表、抑郁-焦虑-压力量表简体中文版对306名大学生进行调查。 结果 错失恐惧、社交媒体倦怠、睡眠质量和负性情绪之间呈两两正相关;错失恐惧能正向预测社交媒体倦怠;睡眠质量和负性情绪在错失恐惧和社交媒体倦怠之间起单独中介作用,且睡眠质量和负性情绪在错失恐惧与社交媒体倦怠之间起链式中介作用,负性情绪各维度效应皆成立。 结论 睡眠质量和负性情绪能够为错失恐惧对社交媒体倦怠的影响提供一个解释机制,大学生的错失恐惧既可以直接影响其社交媒体倦怠水平,也可以通过睡眠质量、负性情绪的独立中介效应以及睡眠质量-负性情绪的链式中介效应间接影响。     

Comparison of mathematically determined blood lactate and heart rate “threshold” points and relationship with performance

Summary The purpose of this study was to investigate the relationship between threshold points for heart rate ( ) and blood lactate (Th_1a) as determined by two objective mathematical models. The models used were the mono-segmental exponential (EXP) model of Hughson et al. and the log-log (LOG) model of Beaver et al. Inter-correlations of these threshold points and correlations with performance were also studied. Seventeen elite runners (mean, SD = 27.5, 6.5 years; 1.73, 0.05 m; 63.8, 7.3 kg; and maximum oxygen consumption of 67.8, 3.7 ml · kg^–1 · min^–1) performed two maximal multistage running field tests on a 183.9-m indoor track with inclined turns. The initial speed of 9 km · h^–1 (2.5 m · s^–1) was increased by 0.5 km · h^–1 (0.14 m · s^–1) every lap for thef _c test and by 1 km · h^–1 (0.28 m · s^–1) every 4 min for the la test. After fitting the la or thef _c data to the two mathematical models, the threshold speed was assessed in the LOG model from the intersection of the two linear segments (LOG-1a; LOG-f _c) and in the EXP model from a tangent point (TI-1a; TI-f _c). Th_1a and speeds computed with the two models were significantly different (P<0.001) and poorly correlated (LOG-1a vs LOG-f _c:r=0.36, TI-1a vs TI-f _c:r=0.13). In general, were less well correlated with performance than Th_1a. With two different objective mathematical models, this study has shown significant differences and poor correlations between Th_1a and . Thus thef _c inflection point with Conconi's protocol is a poor indicator of the la breakpoint with a conventional multistage protocol and a weaker indicator of running performance.     

Complement-derived polypeptide C3adesArg as a mediator of inflammation at the blood-brain barrier in a new experimental cat model

Summary The effect of the complement-derived polypeptide C3adesArg as a mediator of inflammation in the central nervous system was examined. Twenty-five anesthetized cats received 4 mg of this polypeptide by intraventricular injection, 20 cats who served as controls received saline. Cerebrospinal fluid (CSF) was sampled 3 h after intraventricular injection and the brains were removed. For assessment of the permeability of the blood-brain barrier the CSF penetration of four antibiotics, which were given intravenously, was measured. Five control animals were employed for each antibiotic (tobramycin, ampicillin, imipenem, fosfomycin), whereas six C3adesArg-treated animals were used for each antibiotic and seven for tobramycin. Besides CSF levels of glucose, the prostanoids 6-keto-prostaglandin F₁, thromboxane B₂ and prostaglandin E₂ were measured. The morphological examinations in the CSF sediments and histological brain sections in the C3adesArg-treated animals disclosed a distinct inflammation with leptomeningeal and perivascular infiltration of polymorphonuclear granulocytes compared to normal findings in the controls. The CSF/serum ratios of all of the antibiotics were markedly elevated compared to controls, indicating a blood-brain barrier disruption. The levels of all prostanoids were significantly higher in the treatment group than in the control group, whereas the glucose levels were lower. These findings are in accordance with a granulocytic meningitis as seen in some infections at the acute stage. It is concluded that C3adesArg acts as a mediator of inflammation in the central nervous system.     

The GABA hypothesis of kindling: Recent assay studies

The GABA (gamma-aminobutyric acid) hypothesis of kindling suggests that the permanent changes caused by the kindling procedure result from a loss of GABA-mediated inhibition. Pharmacological studies have generally supported this hypothesis: GABA-complex antagonists accelerate (or stimulate) kindling, whereas GABA-complex agonists retard (or reverse) it. Assay studies, however, have presented an inconsistent picture. Earlier studies found no GABAergic brain changes after kindling, whereas recent studies have reported postkindling changes in a number of GABA-related parameters. The crucial difference seems to be that earlier studies assayed GABA parameters in "whole tissue," whereas recent studies have concentrated on "synaptic" GABA. As indicated by recent studies, when the "metabolic pool" is excluded, kindled subjects show a variety of persistent abnormalities in the GABA system. These data are generally consistent with the GABA hypothesis of kindling.