Effects of preload, afterload and inotropy on dynamics of ischemic segmental wall motion

OBJECTIVES: This study sought to explore the separate and combined effects of changes in preload, afterload and contractility on the dynamics of systolic bulging. BACKGROUND: The extent of ischemic systolic bulging has been shown to be mechanically disadvantageous to left ventricular pump performance. The factors that determine ischemic segmental wall motion have not been systematically studied. METHODS: Fourteen beagles were instrumented with sonomicrometers, micromanometer pressure gauges and a balloon in the inferior vena cava. Regional function was evaluated before and after 90 s of proximal left circumflex coronary artery occlusion. Occlusions were repeated after increasing systolic pressure by 5 to 10 (afterload I) and 15 to 20 mm Hg (afterload II) with graded aortic occlusion during inotropic stimulation with dobutamine (2.5 and 5 micrograms/kg body weight per min intravenously), with simultaneous 5 micrograms/kg per min dobutamine infusion and afterload II and during 2.5% halothane (negative inotrope) concentration. A 20-min recovery period was allowed between each stage of the experiment so that regional function returned to its preocclusion level. Ischemic wall motion was characterized by percent systolic bulging and its peak positive systolic lengthening rate (+dL/dt). RESULTS: Because bulging is markedly influenced by regional preload, systolic bulging was characterized over a wide range of end-diastolic lengths of the ischemic segment during caval balloon occlusion. During each intervention, a decrease in regional preload increased the extent of percent systolic bulging. This preload dependency was more pronounced with dobutamine infusions. An increase in afterload was not associated with increased percent systolic bulging at any given preload. At a predetermined preload, bulging was not appreciably altered when an increase in left ventricular systolic pressure was not associated with a change in peak positive first derivative of left ventricular pressure (+dP/dt) but was significantly worse when peak +dP/dt increased. Dobutamine caused a dose-dependent increase in percent systolic bulging and peak +dL/dt that was positively correlated with peak +dP/dt. CONCLUSIONS: By using different loading and inotropic interventions and analyzing the regional wall motion behavior over a range of regional preloads, we can conclude that preload and rate of pressure (tension) development are the principal determinants of systolic bulging. Increases in left ventricular pressure alone had a minimal effect on systolic bulging.     

用小直径空心纤维薄膜分流过滤葡萄酒

介绍了当今世界上葡萄酒生产过程中，对过滤工序的要求。采用小直径空心纤维薄膜的分流过滤法具有很多优点，在德国占据了很大的市场份额，将在欧洲市场上快速发展起来，具有光明的前景。     

洗尽铅华看“WAP”

在过去的3年中，WAP（无线应用协议）曾经红极一时，又很快被冷落一旁。喧嚣过后，一切归于沉寂。很多业内人士认为，WAP失败的命运似乎已经无法避免，然而，这是否是关于WAP结局的定论？本文通过回顾WAP在我国的发展及对WAP协议集进行详尽的分析，力图以客观求实的观点论述WAP发展的未来。     

Does the choice of antihypertensive therapy influence haemodynamic responses to induction, laryngoscopy and intubation?

We have measured haemodynamic responses to induction of anaesthesia, laryngoscopy and intubation in 103 mild-moderate hypertensive patients (83 patients (diastolic pressures < or = 110 mm Hg) currently receiving one of four monotherapies (ACE inhibitors, group A; beta adrenoceptor blocking drugs, group B; calcium channel antagonists, group C; diuretics, group D) and 24 were untreated hypertensive patients). Anaesthesia was induced with fentanyl 1.5-2.0 micrograms kg-1 and thiopentone 3-5 mg kg-1. Tracheal intubation was facilitated by vecuronium 0.1 mg kg-1 and anaesthesia maintained with enflurane and nitrous oxide in oxygen. Systolic and diastolic pressures (SAP, DAP) were measured at 1-min intervals by a non-invasive oscillometric method and cardiac output (CO) and stroke volume (SV) by thoracic bioimpedance. Induction of anaesthesia was associated with a decrease in SAP, DAP and CO in groups A-D (P < 0.05). Heart rate (HR) decreased in groups A and D (P < 0.01) and systemic vascular resistance (SVR) decreased in groups A and B (P < 0.05). SAP and HR increased in all groups after laryngoscopy and intubation (P < 0.01) as did SVR in groups A, B and D (P < 0.02). CO was unaltered. Similar changes occurred in the untreated hypertensive patients, although nine of 24 patients exhibited HR > or = 100 beat min-1 after laryngoscopy and intubation. Comparison of the changes in SAP, DAP, CO and SVR with time showed no differences in the five treatment groups; changes in HR were significantly less in group B compared with the other groups (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

灌注桩常见质量问题的处理

丹东地区采用灌注桩的工程比较普遍,但常见质量问题的处理,往往还是被忽视了,这将引起严重的后果,所以必须认真对待。     

An Orthogonal Least Squares based approach to FIR designs

This paper is concerned with the application of forward Orthogonal Least Squares (OLS) algorithm to the design of Finite Impulse Response (FIR) filters. The focus of this study is a new FIR filter design procedure and to compare this with traditional methods known as the fir2() routine provided by MATLAB.     

医用Ti-15Mo合金的再结晶动力学及时效响应研究

本文研究了新型医用Ti-15Mo合金的固溶态和时效态的显微组织及力学性能响应,分析了合金的相组成及其转变关系。通过对固溶处理的温度、时间与β相晶粒尺寸的关系的系统研究,分析Ti-15Mo合金晶粒长大过程中的动力学影响因素。采用显微组织观察和硬度测试的方法对于不同时效条件下相变化进行分析,阐述了不同相变及组织状态对于性能的影响作用,揭示了Ti-15Mo合金组织的相变过程及其对于性能的影响机制。从而为该合金在材料应用方面的研究提供良好的基础。     

单相流体在多孔介质中的流动和换热研究

本介绍了单相流体在多孔介质内部的传热和流动过程及其研究方法,给出单相流体大多孔介质内部传热的数理模型,对模型的有效性进行了验证。同时分析了流速、孔晾率、固体颗粒的直径大小及固体骨架和流体的导热系数之比等因素对多孔介质内部传热和流动的影响,提出了增加传热而不使流动阻力过多增加的方法．     

γ全能谱测井技术代表核测井的发展方向

本文简单地回顾核测井的发展历史。从γ源、中子源及γ、中子与地层相互作用的理论出发,以获得测井信息量的多少为基础,根据勘探开发中解决地层评价问题的能力和地质效果的好坏以及技术水平的可能,论述了γ全能谱测井技术是核测井技术发展的方向。同时,叙述了近年来γ能谱技术的现状和今后几个方面的可能发展。     

不同有机化合物在TiO2负载活性炭纤维上的

以环氧树脂为炭质前驱体将TiO₂粉体粘附于ACF表面，然后在N2气氛460 ℃焙烧，树脂热解、逸失使剩余残炭成为二者之间的连接体，获得TiO₂/ACF复合产品。ACF负载TiO₂后，其比表面积降低，但仍很好地维持了ACF的孔隙结构。由SEM可知，纳米级单体TiO₂颗粒以微小团簇结构分布于ACF表面。以对氨基苯酚、亚甲基兰和β-环状糊精三种不同分子尺寸的有机化合物为探针，通过TiO₂/ACF对它们的光催化降解研究发现，化合物自身分子尺寸对其降解程度有重要影响。具有适宜分子尺寸亚甲基兰的去除程度最高，TiO₂/ACF的降解速率高于悬浮态P25，在重复利用过程中未见降低。通过对比三种有机分子在有、无紫外光照下的去除程度，可确认有机分子是被降解而非吸附于TiO₂/ACF上。