This research was supported by National Heart, Lung, and Blood Institute Grant HL-093113.

1.振荡下体负压（OLBNP） <ol><li>设备安装<ol><li>心电图导联II（ECG）：粘贴三个（或更多）的电极对被检者的躯干对心脏速率的整个研究过程中监测。 </li><li>氯丁橡胶裙：使用定制的氯丁橡胶裙密封的主题为下体负压室至髂嵴。把它围绕受验者的胸部它们被放置在仰卧罐之前，确保ECG信号仍然是足够的。确保它是温暖的，但不是那么严格，限制呼吸。 </li><li>下体负压室：有在床上的主题仰卧和操纵下体负压室它们的下面。如果下体负压室具有可调节车座（以尽量减少运动伪影没有抵消吸力的作用），确保在它的主题是坐在舒适。使用定制的有机玻璃隔板下调至主体的WAIST尺寸，以帮助密封所述腔室。密封围绕下体负压室用胶带氯丁橡胶裙子。 </li><li>下体负压腔压力：在下体负压腔连接到标准的压力传感器。校准压力传感器，以毫米汞柱。 </li><li>重复循环定时器附机械阀：将内置机械阀和重复循环定时器的下体负压室的习俗。 注：连接到两台电机控制的机械阀A延时继电器用负压和环境压力之间交替。延时继电器交替电压施加到电动机以固定的时间间隔来打开和关闭的腔室和真空之间的阀。这将创建一个下体负压腔的压力波形大致是方波的形状。调节循环时间为所需OLBNP频率。 </li><li>变变压器及真空：将一个标准的家用真空吸尘器的机械阀。堵塞真空成可变变压器，其允许电压施加到真空被控制。打开真空吸尘器，并调整可变变压器，直到目标下体负压压力（ 例如，30毫米汞柱）的实现。 </li><li>动脉血压：附加的非侵入性的光体积描记动脉压箍（ 例如 ，Portapres，Finapres）至一只手的手指（多个）。通过从相对的臂肱动脉比较压力示波压力保证测量精度。 </li><li> 2 MHz的经颅多普勒超声探头及固定装置<ol><li>使用2 MHz的脉冲多普勒探头受超声波大脑中动脉M1段在寺庙（ 即颞部窗口）。 </li><li>改变探测角，声波作用深度（〜55 MM），增益和发射功率，以最大化信号的光谱强度。 </li><li>使用固定装置有没有回来（ 即不是一个头带），使运动伪影不引入信号作为志愿者招解决多普勒探头到位s的负压力振荡。 注意：脑血流量可单侧或双侧来衡量，但在脑自动调节无差别预计半球之间，除非像中风或脑外伤局部损伤是目前20 </li></ol></li><li>过期的CO 2：使用附连到红外的CO 2分析仪鼻插管以监测过期的CO 2，并指示受试者对呼吸仅通过他们的鼻子。鉴于深远的影响动脉血二氧化碳对脑血流，21显示器CO 2遍布每一个研究。 </li></ol></li><li>数据采集<ol><li>设置模拟到动脉压，脑血流量，下体负压腔压力的数字转换，并且过期的CO 2，以获得至少为每信道50赫兹。收购心电图在1 kHz。 注意：虽然随后的分析处理低得多的频率信息（≤0.07赫兹）时，它是Critical监视的信号的质量的研究过程中被获得的。为50赫兹的采样速率将允许血压和脑血流量为伪像的检测的准确的可视化。 </li></ol></li><li>振荡下体负压协议<ol><li>打开真空并确保油箱压力稳定在-30毫米汞柱。 </li><li>设置重复周期定时器33秒，0.03赫兹OLBNP。 </li><li>调整多普勒探头（S），以确保最佳的信号。 </li><li>采集数据至少15个周期（500秒0.03赫兹），以确保有足够的信心PPR估计。如果时间允许，收集比这更多的数据，因为它会进一步提高信噪比。 </li><li>通过改变重复周期计时器的持续时间重复0.03赫兹，0.08赫兹之间的任何频率的上述步骤。 注：适用于以频率，但随机地改变主体之间的起始频率。 </li></ol></li></ol> 2.投影寻踪回归（PPR） <ol><li>数据预处理<ol><li>抽取和低通滤波<ol><li>打开Matlab的。键入命令“数据=重采样（数据，1，SR / 5）”（其中SR是原始采样率）的动脉压和脑血流量抽取5赫兹。 注意：任选地，低通滤波器（19 阶切比雪夫型II）与0.4 Hz的截止。过滤是多余的，因为后续的处理，而造成平均波形不依赖于峰值检测有时嘈杂的动脉压及脑血流信号。 </li></ol></li><li>神器去除<ol><li>使用原非抽取波形为指导，消除信号中的任何部分与文物和线性插值。如果这些部分占所述记录期间的10％以上，完全弃去记录。 注意：在这一点上，该波形被适当地处理为传统线性方法，例如传递函数的分析。</li></ol></li><li>带通滤波<ol><li>在Matlab中，键入：[B，A] = cheby1（1,1，[F - 0.005 F + 0.005] /（SRD / 2））的数据= filtfilt（B，A，detrend（数据，“线性”），以波段-pass过滤压力和流量在±0.005赫兹频带（第1次阶切比雪夫I型与通带波纹的1分贝）围绕OLBNP的频率（ 图2），其中F是主导OLBNP频率，SRD是抽取采样率（5赫兹后步骤2.1.1）和“数据”是抽取信号（动脉压或流）。 注意：这最小化潜在的干扰，并增加了信号 - 噪声比在后续的PPR分析。虽然占主导地位的动脉压力波动发生在下体负压的振荡频率，随机噪声中的信号会干扰压力 - 流量关系的推导。结果，而不带通滤波将是定性相似，但百分之方差Ëxplained（ 即，R 2）会较低。19 </li></ol></li></ol></li><li>投影寻踪回归估计 注意：使用内置函数“PPR”R中语言和环境统计计算，和/或经由其它的平台定制编写的函数，产生一个单一的脊功能（M = 1）的动脉压脑流关系。 <ol><li>在Matlab，输入命令“CVLabPPR（压力，流量）”。进入研究ID为XXXYYY，其中XXX为3个字母的代码，研究和YYY是主题ID三个数字字符。请在下面的格式研究日期：YYYY-MM-DD。输入数字测量＃（ 例如，“1”为第1天）。 </li><li>进入APM（进入FP供finapress或AL艺术行）。进入船（MCA，ACA或PCA）。输入“Y”或“N”来​​查询“你有正确的MCA测量？”输入“Y＆＃8221;或“n”来查询“你已离开马华测量？” 注意： <img alt="式（1）" fo:content-width="3in" src="/files/ftp_upload/51082/51082eq1.jpg" width="300" /> 对于每个输入（X 吨 -动脉血压）和输出（Y 吨 -脑血流）线性自回归传递函数（等式1 -括号内的术语）通过非参数的核函数（K m的传递;被称为“脊功能&#39;），其通过最小化均确定方误差。投影寻踪回归可以包括多个脊功能（ 即M&gt; 1）。然而，虽然它会降低平均平方误差，可能掩盖的脊功能的解释，由于它们之间的潜在相互作用。因为其主要目的是要获得动脉压和脑血流量该CA的关系的n为生理学上解释，PPR应当限于仅一个脊功能（M = 1）。 </li><li>分段线性参数。参数脊函数作为用于随后的统计分析（ 图3）的分段线性函数。对于MATLAB，使用布鲁诺陈德良的自由结点样条逼近。输入命令“BSFK（X，Y，K，nknots）”，其中k = 2的线性拟合和nknots = 3为三个区域。 注意：此标识的那些点处的动脉压脑流动关系的变化，以及范围，其中所述关系是近似线性的图3示出了结果的示意图。每个区域内的压力-流量关系的增益（ 即 ，线性斜率）提供脑自动调节的该地区内的效力的量度。较低的增益表明更有效的反调控的压力波动而高收益表示更被动FL流响应压力变化。 </li></ol></li></ol>

<ol>
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The authors declare that they have no competing financial interests.

精确定义的输入输出关系可以要求输入（在这种情况下，压力）积极跨越足够宽的范围内改变，观察输出响应。然而，自发产生的压力波动幅度非常不一致和小脑自动调节的频率范围内。27，这是在压力和自发流向变化显示具有高相关性周期和极低的相关性周期有关系的原因，并在振荡脑血流量似乎出现，没有明显的动脉压驱动器28 OLBNP 22提供的关键技术，以产生不同的频率和幅度的一致性动脉压力振荡，以评估脑血流响应。虽然可能有其它的方法可能提供类似的探针，这种方法允许在频率和/或幅度依赖关系赌注的严格测试威恩动脉压和脑血流速度。 以前的研究探索电位测量工具为脑自动调节已经使用动脉压和脑血流量（ 例如，传递函数分析）之间的关系的线性模型。压力和流量与无衰减的变化之间的密切的线性关系，观察时的压力振荡是比较快的， 即 &gt;〜10秒。然而，慢振荡（&gt;〜20秒），产生压力之间的关系和流量的逐渐变小线性相关。8,24如果关系不是高度线性相关（低R 2，低交叉谱相干性）可以没有任何信心的线性措施，如传递函数的增益和相位的精度。线性关系的缺乏指示重要的非线性是脑自动调节的特征的存在。事实上，就其本质而言，autoregulati对不适合通过线性方法表征;线性方法可以指示存在自动调节的或不存在，但不能描述其特性和它的有效性。 有迹象表明，比得上在它们的简单的线性方法，但是，可以评估输入（压力）和输出（流动）变量之间的非线性关系的方法。投影寻踪回归是一个简单的非参数，非理论，多元回归方法29,30并不断定一个先验的模型或承担线性输入输出关系。这些都是明显的优势特征是不完全了解一个系统。但是，应该指出的是，使用一个以上的脊功能将增加百分之方差解释，但在模糊特性的关系的生理解释为代价的。因此，建议投影寻踪回归仅限于一脊福nction。尽管如此，与单个脊功能概述在PPR方法可以解释在动脉压和脑血流量之间的关系的方差的显著部和显示特性的非线性关系是不同个体一致。 限制和可能的修改 振荡下体负压需要具体和突兀的设备和程序等不适合临床基础的评估。这可能是静止的足够的长度的记录可以用于脑自动调节的PPR分析提供足够的数据。然而，以往的工作表明，静止数据投影寻踪回归的性能比为0.03赫兹OLBNP数据分析显著恶化。虽然量化在休息期间0.03赫兹OLBNP压力流量的关系是相关的，19的适度通信只是表明，压力流量relationsh估计在休息IPS可能无法可靠地反映这些从0.03赫兹OLBNP而得。一种解决方案可以是生成通过缓慢，深eucapnic呼吸或反复蹲机架机动自动调节的频率范围内保持一致，以及较大的振幅的压力变动。这些方法已被证明产生可靠的大的压力波动，其可以提供跨越一个足够宽的范围内变化时，观察脑血流反应。31,32 虽然平均来说，投影寻踪回归可以解释显著量动脉压和脑流量波动之间的关系，解释差异可能是低在少数情况下（6〜19％）。低性能可以得出，例如，从呼吸型态如果频率和潮气量没有控制。然而，每一个生理测试有一些异常的观察，并且该方法也不例外。在1〜20观察测量差不应该吨削弱该方法的潜在效用。 未来的应用/结论 特性压力-流量关系可以改变在某些病理生理条件，如中风33和外伤性脑损伤。34如果准确关系可以在临床上获得，脑自动调节的投影寻踪回归可以具有更广泛的应用，并作为一种有用评估工具，其中OLBNP不可用。这可能是简单的动作（ 如深呼吸，大腿袖口，坐姿到站姿）和/或持续时间较长的休息录音，可能会导致可起诉派生脑自动调节媲美OLBNP数据压力-流的关系。尽管如此，基于实验室的测定不同的监管制度和他们的自身调节的非线性贡献可以提供独特的见解脑血管的控制，并允许直径灵知病理生理改变的脑自动调节（ 例如 ，脑外伤后）的。

通过该过程脑灌注保持恒定在宽范围内被称为“脑自动调节。”脑潮流响应1的原始观测系统的压力的支承反调节针对变化的动脉压力是非常重要的日常规脑灌注。虽然自动调节的表征是根据持续，控制低渗和高血压的研究，2,3-人们认识到，在耐压力引起的变化是“的振荡过程&#39;3包围的变化从10到90秒。4此外，内过去二十年间，对一个节拍逐拍基础5表明脑流量被调节在周期短短短心脏跳动。-6,7-脑血流速度的测量，这些节拍逐拍的数据表明，有效流缓冲对压力变化发生在因此时段短至〜15秒，它逐渐变得更大在更长的时间段。 如图8所示 ，作为高通滤波器的压力和流量的功能之间的关系，其中7,9-12血压较慢变化被有效地减弱和更快的振荡传递通过相对不受影响。 在表征频率脑自动调节的依存性的主要困难是在围绕感兴趣的频率动脉压缺乏突出自发波动（低于〜0.07赫兹或约15秒）。没有足够大的压力振荡，不能准确地量化脑血流量的响应。我们的实验室已通过使用被称为振荡下体负压（OLBNP）的技术处理该约束。这产生尾静脉血液量的变化成比例的在罐内的负压水平，由于降低了静脉压差。当负PRESSU重新被应用在设定的时间间隔，在中央静脉回流导致血压波动在OLBNP的频率振荡。这种方法已用于在不同的实验室数项研究。8,14-17这产生尾静脉血液量的变化成比例的在罐内的负压水平，由于减少静脉压差。当负压施加在设定的时间间隔，在中央静脉回流振荡导致动脉压力波动在OLBNP的频率。这种方法已用于在不同的实验室数项研究。8,15-18 即使能够产生围绕感兴趣的频率，血压波动显着的方法，还有一个复杂的因素：有非线性的脑自动调节显著的证据，特别是在最低频率8况且，没有强有力的理论指导。以存在于脑自动调节非线性的性质。因此，我们使用一个理论无关，在我们的分析中被称为投影寻踪回归（PPR）驱动数据的方法。19 PPR是一个非参数的方法中固有的系统没有任何先验假设为这些非线性性质的非线性关系进行表征。这是捕捉系统，其生理机能尚未被明确的非线性模型定义了一个决定性的优势。 PPR揭示的特征的非线性脑自动调节的类似于“经典自动调节曲线”首先通过拉森在1959年描述（ 图1）。2,19即，脑血流量保持在一定范围内的压力的动脉内相对恒定的，但被动跟踪以线性方式在该范围之外。这种形状变得更加明显，血压波动变得更慢。因此，线性分析不足以充分interrogaTE脑自动调节和依赖线性技术可能错过重要的信息。 在这篇文章中，我们详细介绍的方法来两个数据采集（实验室用OLBNP）和分析（PPR），我们使用在健康和疾病表征脑自动调节。

<table><tbody><tr><td>Transcranial Doppler Ultrasound</td><td>Compumedics DWL</td><td>Multi-Dop X digital</td><td>&amp;nbsp;2 MHz probe</td></tr><tr><td>ECG and Brachial BP</td><td>GE</td><td>Dash 2000</td><td></td></tr><tr><td>LBNP Tank</td><td>U. of Iowa Bioengineering</td><td></td><td>Custom Built</td></tr><tr><td>Mechanical Valve</td><td>U. of Iowa Bioengineering</td><td></td><td>Custom Built</td></tr><tr><td>Repeat Cycle Timer</td><td>Macromatics</td><td>TR-50826-07</td><td></td></tr><tr><td>Pressure Transducer</td><td>Gould</td><td></td><td></td></tr><tr><td>Photoplethysmographic finger pressure monitor</td><td>Finapres Medical Systems</td><td>Finometer PRO</td><td></td></tr><tr><td>CO&lt;sub&gt;2&lt;/sub&gt; gas analyzer</td><td>VacuMed</td><td>#17515 CO&lt;sub&gt;2&lt;/sub&gt; Analyzer, Gold Edition</td><td></td></tr><tr><td>Data acquisition system</td><td>AD Instruments</td><td>Data Acquisition Systems - PowerLab</td><td></td></tr></tbody></table>

assessing cerebral autoregulation via oscillatory lower body negative pressure and projection pursuit regression

由脑灌注保持恒定在宽范围的系统性压力的过程被称为“脑自动调节”。流对压力变化的有效阻尼发生在周期短至〜15秒，并逐渐变得更大在更长的时间段。因此，在血压较慢变化被有效地减弱和更快的变化或波动通过向脑血流相对不受影响。在表征频率脑自动调节的依存性的主要困难是在围绕感兴趣的频率动脉压缺乏突出自发波动（低于〜0.07赫兹或约15秒）。振荡下体负压（OLBNP）可被用于产生在中央静脉回流振荡导致在动脉压力波动在OLBNP的频率。此外，投影寻踪回归（PPR）提供了一个非参数方法characterizË系统固有的非线性关系，没有一个先验的假设，并显示性能非线性脑自动调节。 OLBNP产生动脉压力较大波动的负面压力振荡的频率变慢;然而，在脑血流的波动逐渐变得更低。因此，在PPR示出以0.05赫兹OLBNP频率和低于（20秒周期）的日益突出自身调节区域。这种方法也允许基于实验室的测定压力与脑流量之间的特性的非线性关系，并且可以提供独特的见解，以综合性脑控制以及生理改变的目标底层证券受损脑自动调节（ 例如 ，创伤性脑损伤，中风后等 ）。

从10毫米汞柱22 OLBNP振幅高达120毫米汞柱17已被用于增加动脉压的波动，但在30毫米汞柱OLBNP足以23,24和不超出cerebrovasculature的调控能力。17 OLBNP结果这种水平在血液中的压力振荡是是约15-20毫米汞柱的大小在0.03赫兹，这是不大于从就座要站立时发生的血压变化更大。25有一些限制，以在其内OLBNP可以产生动脉压力的变动范围内。自动调节器仅在〜0.07赫兹和较慢，因此上限是不是一个问题。然而，在产生的低频振荡低于0.03赫兹的困难是，对心血管系统的反调节对下体负压引起动脉压的变化的周期结束之前。 如图4所示，在0.025赫兹OLBNP我们实际看到的最大峰值血压波动在0.05赫兹。而脑自动调节器的频率响应的特点可以从0.03 Hz至0.08赫兹以限定的时间尺度内其自身调节是活动的，23,24 0.03赫兹和0.08赫兹OLBNP足够，因为它们代表了一系列自动调节功能的（ 即 ，一个宣判自动调节区域无法比拟的还是温和的）。 OLBNP产生于动脉压较大的波动作为负压力振动的频率变得更慢。 图5示出了动脉压力和随之而来的脑血流量的波动与OLBNP 0.08赫兹（12.5秒的周期）至0.03赫兹（33秒周期）。在较高的频率，脑血流量波动在音乐会与动脉压。该PPR说明了这一点;有在0.08赫兹，0.07赫兹（14秒周期），和0.0的较高频率动脉压和脑血流量之间的比例关系的线性6赫兹（16.6秒周期）。在OLBNP慢的频率，虽然动脉压力变动变大，在脑血流的波动逐渐更有效地衰减。因此，在PPR示出了在从0.05赫兹（20秒周期）OLBNP频率日益更加突出自动调节区域，以0.04赫兹（25秒周期），到0.03赫兹。在示出的例子中，在0.03赫兹，在PPR曲线清楚地类似于由拉森（ 图1）中描述的“经典自动调节曲线”。我们以前曾表明这一观察，不能简单地通过增加动脉压力变动幅度解释为振荡频率变得更慢。我们在OLBNP（因此，不同的压力波动的幅度）。19的不同大小已预先施加的PPR将数据从48个人尽管我们没有明确地探索之间自动调节范围和压力波动的大小的电势关系，我们再停泊在自动调节范围的变化仅为〜6％。因此，我们的现有结果清楚地表明，在PPR曲线与频率的变化不能完全由在压力波动的大小的变化进行说明。在同一研究中，我们评估自身调节的PPR特征是否可以通过单独的会话可重复性。这一分析表明，自动调节范围的期间0.03赫兹OLBNP斜率没有改变（Lin的一致性= 0.96，P &lt;0.001），从而使非线性压力-流量关系是在整个研究日相一致。 虽然脑血管床是由交感神经纤维以及支配，他们的自身调节作用还没有被广泛接受。26因此，我们的一些前期工作的探讨脑血管自动调节交感神经系统的潜在作用。24，我们找到了一个明确的角色交感神经系统在调节脑流，但我们瓦特ERE无法描述的关系具有去除交感神经的影响如何改变由于线性方法表征自动调节的局限性。 图6显示了之前（基线）从PPR应用程序数据的结果，并在0.05 Hz的交感神经阻滞后。整体曲线明显变得更加线性。此外，为0.03赫兹数据，其中自动调节是最明显的PPR分析表明，该自动调节区域的范围保持不变，但在该区域的增加斜率，反映不太有效的自动调节（ 图7）。 <img alt="图1" src="/files/ftp_upload/51082/51082fig1highres.jpg" /> 图1.“经典”自动调节曲线来源于静态的增加之间的关系，减少压力和稳态脑血流量。不变的流动沙漠的区域皮特改变压力（ 即 ，斜率= 0）是由区域界定，其中增加和减少压力导致比例脑血流量的变化。 <img alt="图2" src="/files/ftp_upload/51082/51082fig2highres.jpg" /> 图2.执行PPR分析必要的预处理。信号首先被抽取为5赫兹，然后带通在OLBNP的频率滤波（±0.005赫兹）。 <img alt="图3" src="/files/ftp_upload/51082/51082fig3highres.jpg" /> 图中0.03赫兹OLBNP来源于动脉压及脑血流的PPR分析脑自动调节曲线的参数3。 <img alt="图4" src="/files/ftp_upload/51082/51082fig4highres.jpg" /> <str翁&gt;图4 的功率谱示出了在动脉压力波动的幅度时OLBNP频率低于0.03赫兹（33秒周期）。请注意，有在0.025 2大峰中的动脉压谱功率和0.05赫兹（40和20秒周期），但是只有在0.025赫兹在下体负压频谱功率的单峰。此外，在压力的最大波动是在0.05赫兹，并会混淆的脑血流量的反应的解释。 <img alt="图5" src="/files/ftp_upload/51082/51082fig5highres.jpg" /> 图的OLBNP的效果从0.08到0.03赫兹的动脉压和脑血流量5.实施例。动脉压力变动变得较慢OLBNP较大而脑血流的波动变得更小。此自动调节功能由在底部面板中所示的PPR分析的结果进行说明。牛逼脑血流量，他自动调节区域逐渐变得更加明显较慢OLBNP。 <img alt="图6" src="/files/ftp_upload/51082/51082fig6highres.jpg" /> 图6.个人，平均从0.05科目赫兹OLBNP数据PPR自动调节曲线之前（基线）和交感神经阻滞后，需要注意的是狭窄的自动调节区域的交感神经阻滞后的损失。 <img alt="图7" src="/files/ftp_upload/51082/51082fig7highres.jpg" /> 图7.平均0.03赫兹OLBNP数据PPR参数之前和交感神经阻滞后，交感神经阻断了大脑自身调节曲线上的一个显着的效果自动调节的范围内，显着增加了坡（ 即更多的比例脑流量与压力变化的变化）。

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Assessing Cerebral Autoregulation via Oscillatory Lower Body Negative Pressure and Projection Pursuit Regression

Cerebral perfusion is maintained across a range of pressures via cerebral autoregulation. However, characterizing autoregulation requires prominent pressure fluctuations at regulated frequencies. The described protocol will show how oscillatory lower body negative pressure can generate pressure fluctuations to provide data for projection pursuit regression for quantification of the autoregulatory curve.

通过振荡下体负压和投影寻踪回归评估脑自动调节

The process by which cerebral perfusion is maintained constant over a wide range of systemic pressures is known as &#8220;cerebral autoregulation.&#8221; ...

assessing-cerebral-autoregulation-via-oscillatory-lower-body-negative

Universidad San Sebastian

Research

JoVE Journal

Biology

12.3K 次观看.  Harvard Medical School. Cerebral perfusion is maintained across a range of pressures via cerebral autoregulation. However, characterizing autoregulation requires prominent pressure fluctuations at regulated frequencies. The described protocol will show how oscillatory lower body negative pressure can generate pressure fluctuations to provide data for projection pursuit regression for quantification of the autoregulatory curve.

视频: Assessing Cerebral Autoregulation via Oscillatory Lower Body Negative Pressure and Projection Pursuit Regression

Tilt Testing with Combined Lower Body Negative Pressure: a "Gold Standard" for Measuring Orthostatic Tolerance

Orthostatic tolerance (OT) refers to the ability to maintain cardiovascular stability when upright, against the hydrostatic effects of gravity, and hence to maintain cerebral perfusion and prevent syncope (fainting). Various techniques are available to assess OT and the effects of gravitational stress upon the circulation, typically by reproducing a presyncopal event (near-fainting episode) in a controlled laboratory environment. The time and/or degree of stress required to provoke this response provides the measure of OT. Any technique used to determine OT should: enable distinction between patients with orthostatic intolerance (of various causes) and asymptomatic control subjects; be highly reproducible, enabling evaluation of therapeutic interventions; avoid invasive procedures, which are known to impair OT1.
In the late 1980s head-upright tilt testing was first utilized for diagnosing syncope2. Since then it has been used to assess OT in patients with syncope of unknown cause, as well as in healthy subjects to study postural cardiovascular reflexes2-6. Tilting protocols comprise three categories: passive tilt; passive tilt accompanied by pharmacological provocation; and passive tilt with combined lower body negative pressure (LBNP). However, the effects of tilt testing (and other orthostatic stress testing modalities) are often poorly reproducible, with low sensitivity and specificity to diagnose orthostatic intolerance7.
Typically, a passive tilt includes 20-60 min of orthostatic stress continued until the onset of presyncope in patients2-6. However, the main drawback of this procedure is its inability to invoke presyncope in all individuals undergoing the test, and corresponding low sensitivity8,9. Thus, different methods were explored to increase the orthostatic stress and improve sensitivity.
Pharmacological provocation has been used to increase the orthostatic challenge, for example using isoprenaline4,7,10,11 or sublingual nitrate12,13. However, the main drawback of these approaches are increases in sensitivity at the cost of unacceptable decreases in specificity10,14, with a high positive response rate immediately after administration15. Furthermore, invasive procedures associated with some pharmacological provocations greatly increase the false positive rate1.
Another approach is to combine passive tilt testing with LBNP, providing a stronger orthostatic stress without invasive procedures or drug side-effects, using the technique pioneered by Professor Roger Hainsworth in the 1990s16-18. This approach provokes presyncope in almost all subjects (allowing for symptom recognition in patients with syncope), while discriminating between patients with syncope and healthy controls, with a specificity of 92%, sensitivity of 85%, and repeatability of 1.1&plusmn;0.6 min16,17. This allows not only diagnosis and pathophysiological assessment19-22, but also the evaluation of treatments for orthostatic intolerance due to its high repeatability23-30. For these reasons, we argue this should be the "gold standard" for orthostatic stress testing, and accordingly this will be the method described in this paper.

We describe a "gold standard" for evaluating orthostatic tolerance (OT) using tilt testing with combined lower body negative pressure (LBNP). This can be combined with non-invasive evaluations of cardiovascular reflex control. Normal and abnormal responses are defined.

倾斜试验结合下体负压测量立位耐力的“金标准”

Orthostatic tolerance (OT)  refers to the ability to maintain cardiovascular stability when upright,  against the hydrostatic effects of gravity, and ...

科研

医学

Optimized System for Cerebral Perfusion Monitoring in the Rat Stroke Model of Intraluminal Middle Cerebral Artery Occlusion

The translational potential of pre-clinical stroke research depends on the accuracy of experimental modeling. Cerebral perfusion monitoring in animal models of acute ischemic stroke allows to confirm successful arterial occlusion and exclude subarachnoid hemorrhage. Cerebral perfusion monitoring can also be used to study intracranial collateral circulation, which is emerging as a powerful determinant of stroke outcome and a possible therapeutic target. Despite a recognized role of Laser Doppler perfusion monitoring as part of the current guidelines for experimental cerebral ischemia, a number of technical difficulties exist that limit its widespread use. One of the major issues is obtaining a secure and prolonged attachment of a deep-penetration Laser Doppler probe to the animal skull. In this video, we show our optimized system for cerebral perfusion monitoring during transient middle cerebral artery occlusion by intraluminal filament in the rat. We developed in-house a simple method to obtain a custom made holder for twin-fibre (deep-penetration) Laser Doppler probes, which allow multi-site monitoring if needed. A continuous and prolonged monitoring of cerebral perfusion could easily be obtained over the intact skull.

Cerebral perfusion monitoring has been demonstrated to improve accuracy in ischemic stroke models. Technical difficulties often limit the use of this essential tool for cerebrovascular research. In this video, an optimized system is shown to obtain a single or multi-site hemodynamic monitoring during intraluminal middle cerebral artery occlusion in rats.

优化系统的脑灌注监测在中风模型大鼠的大脑中动脉闭塞腔内

The translational potential of pre-clinical stroke research depends on the accuracy of experimental modeling. Cerebral perfusion monitoring in animal ...

Computerized Dynamic Posturography for Postural Control Assessment in Patients with Intermittent Claudication

Computerized dynamic posturography with the EquiTest is an objective technique for measuring postural strategies under challenging static and dynamic conditions. As part of a diagnostic assessment, the early detection of postural deficits is important so that appropriate and targeted interventions can be prescribed. The Sensory Organization Test (SOT) on the EquiTest determines an individual&#39;s use of the sensory systems (somatosensory, visual, and vestibular) that are responsible for postural control. Somatosensory and visual input are altered by the calibrated sway-referenced support surface and visual surround, which move in the anterior-posterior direction in response to the individual&#39;s postural sway. This creates a conflicting sensory experience. The Motor Control Test (MCT) challenges postural control by creating unexpected postural disturbances in the form of backwards and forwards translations. The translations are graded in magnitude and the time to recover from the perturbation is computed.
Intermittent claudication, the most common symptom of peripheral arterial disease, is characterized by a cramping pain in the lower limbs and caused by muscle ischemia secondary to reduced blood flow to working muscles during physical exertion. Claudicants often display poor balance, making them susceptible to falls and activity avoidance. The Ankle Brachial Pressure Index (ABPI) is a noninvasive method for indicating the presence of peripheral arterial disease and intermittent claudication, a common symptom in the lower extremities. ABPI is measured as the highest systolic pressure from either the dorsalis pedis or posterior tibial artery divided by the highest brachial artery systolic pressure from either arm. This paper will focus on the use of computerized dynamic posturography in the assessment of balance in claudicants.

Individuals with intermittent claudication exhibit poor balance compared to healthy controls. Computerized dynamic posturography is an objective method for measuring an individual's postural responses to balance disturbances. This provides an objective reflection of the person&#x2019;s ability to respond to situations under which sensory stimuli are altered and unexpected perturbations occur.

Computerized dynamic posturography with the EquiTest is an objective technique for measuring postural strategies under challenging static and dynamic ...

A Human-machine-interface Integrating Low-cost Sensors with a Neuromuscular Electrical Stimulation System for Post-stroke Balance Rehabilitation

A stroke is caused when an artery carrying blood from heart to an area in the brain bursts or a clot obstructs the blood flow to brain thereby preventing delivery of oxygen and nutrients. About half of the stroke survivors are left with some degree of disability. Innovative methodologies for restorative neurorehabilitation are urgently required to reduce long-term disability. The ability of the nervous system to reorganize its structure, function and connections as a response to intrinsic or extrinsic stimuli is called neuroplasticity. Neuroplasticity is involved in post-stroke functional disturbances, but also in rehabilitation. Beneficial neuroplastic changes may be facilitated with non-invasive electrotherapy, such as neuromuscular electrical stimulation (NMES) and sensory electrical stimulation (SES). NMES involves coordinated electrical stimulation of motor nerves and muscles to activate them with continuous short pulses of electrical current while SES involves stimulation of sensory nerves with electrical current resulting in sensations that vary from barely perceivable to highly unpleasant. Here, active cortical participation in rehabilitation procedures may be facilitated by driving the non-invasive electrotherapy with biosignals (electromyogram (EMG), electroencephalogram (EEG), electrooculogram (EOG)) that represent simultaneous active perception and volitional effort. To achieve this in a resource-poor setting, e.g., in low- and middle-income countries, we present a low-cost human-machine-interface (HMI) by leveraging recent advances in off-the-shelf video game sensor technology. In this paper, we discuss the open-source software interface that integrates low-cost off-the-shelf sensors for visual-auditory biofeedback with non-invasive electrotherapy to assist postural control during balance rehabilitation. We demonstrate the proof-of-concept on healthy volunteers.

A novel low-cost human-machine interface for interactive post-stroke balance rehabilitation system is presented in this article. The system integrates off-the-shelf low-cost sensors towards volitionally driven electrotherapy paradigm. The proof-of-concept software interface is demonstrated on healthy volunteers.

人机界面集成的低成本传感器，具有神经肌肉电刺激系统中风后康复平衡

A stroke is caused when an artery carrying blood from heart to an area in the brain bursts or a clot obstructs the blood flow to brain thereby preventing ...

神经科学

Development of an Algorithm to Perform a Comprehensive Study of Autonomic Dysreflexia in Animals with High Spinal Cord Injury Using a Telemetry Device

Spinal cord injury (SCI) is a debilitating neurological condition characterized by somatic and autonomic dysfunctions. In particular, SCI above the mid-thoracic level can lead to a potentially life-threatening hypertensive condition called autonomic dysreflexia (AD) that is often triggered by noxious or non-noxious somatic or visceral stimuli below the level of injury. One of the most common triggers of AD is the distension of pelvic viscera, such as during bladder and bowel distension or evacuation. This protocol presents a novel pattern recognition algorithm developed for a JAVA platform software to study the fluctuations of cardiovascular parameters as well as the number, severity and duration of spontaneously occurring AD events. The software is able to apply a pattern recognition algorithm on hemodynamic data such as systolic blood pressure (SBP) and heart rate (HR) extracted from telemetry recordings of conscious and unrestrained animals before and after thoracic (T3) complete transection. With this software, hemodynamic parameters and episodes of AD are able to be detected and analyzed with minimal experimenter bias.

The catheter of a telemetry device is implanted into the abdominal aorta in order to continuously collect beat-by-beat hemodynamic data from animals pre and post-high thoracic spinal cord transection. A novel JAVA software was employed to analyze hemodynamic parameters as well as frequency and intensity of spontaneous episodes of autonomic dysreflexia.

一个算法的开发与高位脊髓损伤使用遥测装置进行自主神经异常反射的动物的综合研究

Spinal cord injury (SCI) is a debilitating neurological condition characterized by somatic and autonomic dysfunctions. In particular, SCI above the ...

A Detailed Protocol for Physiological Parameters Acquisition and Analysis in Neurosurgical Critical Patients

Intracranial pressure (ICP) monitoring is now widely used in neurosurgical critical patients. Besides mean ICP value, the ICP derived parameters such as ICP waveform, amplitude of pulse (AMP), the correlation of ICP amplitude and ICP mean (RAP), pressure reactivity index (PRx), ICP and arterial blood pressure (ABP) wave amplitude correlation (IAAC), and so on, can reflect intracranial status, predict prognosis, and can also be used as guidance of proper treatment. However, most of the clinicians focus only on the mean ICP value while ignoring these parameters because of the limitations of the current devices. We have recently developed a multimodality monitoring system to address these drawbacks. This portable, user-friendly system will use a data collecting and storing device to continuously acquire patients&#39; physiological parameters first, i.e., ABP, ICP, and oxygen saturation, and then analyze these physiological parameters. We hope that the multimodality monitoring system will be accepted as a key measure to monitor physiological parameters, to analyze the current clinical status, and to predict the prognosis of the neurosurgical critical patients.

Recently, we have developed a portable multimodality monitoring system for the monitoring of various physiological parameters in neurosurgical critical patients. Detailed protocols on how to use this multimodality monitoring system are presented here.

神经外科危重患者生理参数采集与分析的详细方案

Intracranial pressure (ICP) monitoring is now widely used in neurosurgical critical patients. Besides mean ICP value, the ICP derived parameters such as ...

A Bedside, Single Burr Hole Approach to Multimodality Monitoring in Severe Brain Injury

Intracranial pressure (ICP) monitoring is a cornerstone of the intensive care management of patients with severe acute brain injuries, including traumatic brain injury. While elevations in ICP are common, data regarding the measurement and treatment of these ICP elevations are conflicting. There is increasing recognition that changes in the balance between supply and demand of brain tissue are critically important and therefore the measurement of multiple modalities is required. Approaches are not standard, and therefore this article provides a description of a bedside, single burr hole approach to multimodality monitoring that allows the passage of probes designed to measure not only ICP but brain tissue oxygen, blood flow, and intracranial electroencephalography. Patient selection criteria, operative procedures, and practical considerations for securing probes during critical care are described. This method is readily performed, safe, secure, and flexible for the adoption of a variety of multimodality monitoring approaches aimed at detecting or preventing secondary brain injuries.

A method of recording multimodality monitoring signals in patients with severe brain injuries using a bedside, single burr hole technique is described.

一种用于重型颅脑损伤多模态监测的床边单毛刺孔方法

Intracranial pressure (ICP) monitoring is a cornerstone of the intensive care management of patients with severe acute brain injuries, including traumatic ...

Standardized Hemorrhagic Shock Induction Guided by Cerebral Oximetry and Extended Hemodynamic Monitoring in Pigs

Hemorrhagic shock ranks among the main reasons for severe injury-related death. The loss of circulatory volume and oxygen carriers can lead to an insufficient oxygen supply and irreversible organ failure. The brain exerts only limited compensation capacities and is particularly at high risk of severe hypoxic damage.This article demonstrates the reproducible induction of life-threatening hemorrhagic shock in a porcine model by means of calculated blood withdrawal. We titrate shock induction guided by near-infrared spectroscopy&#160;and extended hemodynamic monitoring to display systemic circulatory failure, as well as cerebral microcirculatory oxygen depletion. In comparison to similar models that primarily focus on predefined removal volumes for shock induction, this approach highlights a titration by means of the resulting failure of macro- and microcirculation.

Hemorrhagic shock is a severe complication in seriously injured patients, which leads to life-threatening oxygen undersupply. We present a standardized method to induce hemorrhagic shock via blood withdrawal in pigs that is guided by hemodynamics and microcirculatory cerebral oxygenation.

由脑氧测量和猪期扩展血液动力学监测指导的标准化出血性休克诱导

Hemorrhagic shock ranks among the main reasons for severe injury-related death. The loss of circulatory volume and oxygen carriers can lead to an ...

Evaluating Postural Control and Lower-extremity Muscle Activation in Individuals with Chronic Ankle Instability

Computerized dynamic posturography (CDP) is an objective technique for the evaluation of postural stability under static and dynamic conditions and perturbation. CDP is based on the inverted pendulum model that traces the interrelationship between the center of pressure and the center of gravity. CDP can be used to analyze the proportions of vision, proprioception, and vestibular sensation to maintain postural stability. The following characters define chronic ankle instability (CAI): persistent ankle pain, swelling, the feeling of &#8220;giving way,&#8221; and self-reported disability. Postural stability and fibular muscle activation level in individuals with CAI decreased due to lateral ankle ligament complex injuries. Few studies have used CDP to explore the postural stability of individuals with CAI. Studies that investigate postural stability and related muscle activation by using synchronized CDP with surface electromyography are lacking. This CDP protocol includes a sensory organization test (SOT), a motor control test (MCT), and an adaption test (ADT), as well as tests that measure unilateral stance (US) and limit of stability (LOS). The surface electromyography system is synchronized with CDP to collect data on lower limb muscle activation during measurement. This protocol presents a novel approach for evaluating the coordination of the visual, somatosensory, and vestibular systems and related muscle activation to maintain postural stability. Moreover, it provides new insights into the neuromuscular control of individuals with CAI when coping with real complex environments.

Individuals with chronic ankle instability (CAI) exhibit postural control deficiency and delayed muscle activation of lower extremities. Computerized dynamic posturography combined with surface electromyography provides insights into the coordination of the visual, somatosensory, and vestibular systems with muscle activation regulation to maintain postural stability in individuals with CAI.

评估慢性脚踝不稳个体的姿势控制与下肢肌肉活化

Computerized dynamic posturography (CDP) is an objective technique for the evaluation of postural stability under static and dynamic conditions and ...

Evaluation of Cerebral Blood Flow Autoregulation in the Rat Using Laser Doppler Flowmetry

When investigating the body&#39;s mechanisms for regulating cerebral blood flow, a relative measurement of microcirculatory blood flow can be obtained using laser Doppler flowmetry (LDF). This paper demonstrates a closed skull preparation that allows cerebral blood flow to be assessed without penetrating the skull or installing a chamber or cerebral window. To evaluate autoregulatory mechanisms, a model of controlled blood pressure reduction via graded hemorrhage can be utilized while simultaneously employing LDF. This enables the real time tracking of the relative changes in the blood flow in response to reductions in arterial blood pressure produced by the withdrawal of circulating blood volume. This paradigm is a valuable approach to study cerebral blood flow autoregulation during reductions in arterial blood pressure and, with minor modifications in the protocol, is also valuable as an experimental model of hemorrhagic shock. In addition to evaluating autoregulatory responses, LDF can be used to monitor the cortical blood flow when investigating metabolic, myogenic, endothelial, humoral, or neural mechanisms that regulate cerebral blood flow and the impact of various experimental interventions and pathological conditions on cerebral blood flow.

This article demonstrates the use of laser Doppler flowmetry to evaluate the ability of the cerebral circulation to autoregulate its blood flow during reductions in arterial blood pressure.

使用激光多普勒流测量测量大鼠脑血流自动调节的评估

When investigating the body&#39;s mechanisms for regulating cerebral blood flow, a relative measurement of microcirculatory blood flow can be obtained ...