基于小波变换的离子单通道信号的分析方法

在单通道信号处理中引入尺度能量分布的概念 ,利用小波变换 ,通过提取具有特征频率的高频信号 ,可以在不失真的条件下将单通道信号清晰地检测出来 ,消除噪声干扰。本文提供的方法在离子通道信号处理中具有较普遍的意义     

基于小波变换的离子单通道信号的分析方法

在单通道信号处理中引入尺度能量分布的概念，利用小波变换，通过提取具有特征频率的高频信号，可以在不失真的条件下将单通道信号清晰地检测出来，消除噪声干扰。本文提供的方法在离子通道信号处理中具有较普遍的意义。     

基于快速平稳小波变换的特征提取方法分析fMRI数据

多尺度特征提取方法( MFE)利用离散小波变换,通过只重构有用信号所在小波尺度的方式,有效去除了fMRI数据里的干扰成分.但部分尺度重构会导致混频发生,而离散小波变换的结果对小波选取比较敏感.为此,本研究把有用信号最低频率所对应的小波尺度选为舍弃尺度,利用平稳小波变换矩阵算法代替常规的逐体素算法,用sym2、syml0和sym20等3个小波分析了视觉组块型和事件相关型fMRI试验数据.结果显示,所选舍弃尺度的方法避免了混频现象,3个小波给出了相同的且比SPM8更好的分析结果.在时间消耗上,3个小波基于矩阵算法分析一个被试的组块型数据只耗时61 s,sym2基于逐体素算法耗时42 min,SPM8耗时63 s.因此,所提出的方法是一种实用性更强的MFE方法.     

小波变换用于豚鼠脑干听觉诱发电位信号的特征提取

本文基于正交小波变换、分析了三类共３０例豚鼠脑干听觉诱发电位信号，表明这种信号经正交小波变换后，不但能够利用近似信号更简单准确地得到传统判别参数，而且能够利用不同尺度细节信号提取出原始信号在不同频带的能量之比为有效的新判据     

基于小波多分辨分析的脑干听觉诱发电位特征提取

本文应用小波变换方法从背景噪声中提取出脑干听觉诱发电位(BAEP)信号并进行特征识别。首先我们讨论了母小波和小波变换算法的选择,发现双正交母小波bior5.5和稳定离散小波变换(SWT)最适合BAEP信号的小波多分辨分析。通过D6尺度小波系数的相关性分析,发现相关性大于0.4的单次刺激记录具有较高的信噪比,使得仅数次刺激的叠加平均就能清晰地识别出BAEP信号的各个波。最后我们用此方法来挑选各次刺激记录,对每10次记录进行叠加平均和小波滤波结合消噪,并正确识别和计算出BAEP信号各个波的潜伏期。实验证明本方法通过小波系数相关性分析能有效选取单次刺激的BAEP记录,在大大减少刺激次数的同时,达到了更好的消噪效果。     

主成分分析和线性判别分析应用于心电信号特征提取和诊断算法研究

针对心脏疾病发病率高且不易自主检测的问题,提出了一种心电信号特征提取和分类诊断算法。首先对心电信号进行提升小波变换和改进半软阈值相结合的预处理变换,在去除心电信号的噪声后,利用主成分分析(principal component analysis,PCA)对心电信号进行降维,并利用核独立成分提取心电信号的非线性特征;同时离散小波变换提取去噪后心电信号的频域特征,基于线性判别分析(linear discriminant analysis, LDA)对频域统计特征进行降维处理。将两种不同的特征向量组成多域特征空间,最后利用支持向量机对多域特征空间分类,遗传算法对其参数进行寻优,从而实现心电信号特征的分类。实验结果表明,所提出的算法能够对5类心电节拍进行准确分类,分类效率达99.11%。     

基于小波变换的脊柱振动特征分析

为了研究切削过程中脊柱的振动特征,利用激光位移传感器测量皮质骨、脊髓和棘间韧带的振动幅度。出现切削过程引起的受迫振动时,由于脊髓、韧带等生物软组织表现为粘弹性,其作用相当于被动隔振体。应用离散小波变换对传感器的输出信号进行分解,通过比较不同尺度上小波能量分布来区别脊柱中的硬组织和软组织。实验结果表明,提出的方法能够准确辨识出皮质骨、脊髓和棘间韧带。     

结合小波变换和能量熵在膈肌肌电中去除心电干扰的应用

膈肌肌电(EMGdi)信号是一种由膈肌产生并蕴含着人体呼吸系统重要生理信息的生物电信号,该信号易受自身心电(ECG)信号的严重干扰。本文在小波变换的基础上,结合信息熵理论,提出了一种新的小波能量熵阈值去心电算法。该方法在对信号各层小波系数的分析基础上,将每层的系数信息量看成一个单独的信号源,将其分成N等份的小区间,通过系数能量熵的分布特性将其分成高能量熵和低能量熵两类分别进行绝对均值阈值处理,对阈值后的小波系数进行小波重构便得到降噪后的EMGdi信号。通过实验对比结果表明,该方法有效地去除了EMG-di信号的ECG干扰信号,更大程度地保留了EMGdi的信号特征。     

基于小波包变换的特征提取方法分析fMRI数据

多尺度特征提取(MFE)利用时频特性各异的小波变换尺度分割fMRI数据的频谱,藉此准确提取激活信号和去除干扰。但在多尺度分析中,小波包变换较小波变换分割频带更精细,因此更适合MFE分析fMRI数据。为此,基于小波包变换构建新的MFE,并设计小波包的矩阵算法代替逐体素的迭代算法快速提取激活信号,后用相关分析进行检测。分析听觉fMRI试验数据的结果表明,新MFE检测的激活区位置与原有MFE和国际权威方法统计参数图(SPM8)检测的位置相同,但检测的激活体素个数较原有MFE多13.2%,较SPM8多30.8%。而且新MFE采用矩阵算法分析听觉数据仅消耗31 s,采用逐体素迭代算法耗时48.5 min,SPM8耗时77 s。因此,小波包变换和矩阵算法赋予MFE更好的性能分析fMRI数据。     

基于小波能量熵特征的阻抗胃动力信号识别

采用生物电阻抗技术从人体上腹部体表提取的电阻抗信号,不但包含了常规的胃蠕动频率特征,而且携带有反映胃动力状况的更深层次的信息.提取并分析这些信息,对胃动力的检测与评价具有重要意义.对20名糜烂性胃炎患者的胃阻抗和胃电信号进行研究,经过小波滤波去噪后,进行多层小波包变换,计算小波能量熵并作为特征向量,采用3层BP神经网络进行模式分类.经一周治疗后,14名患者胃阻抗和胃电信号的小波能量熵值下降,以小波能量熵为特征向量的BP神经网络对治疗前后的识别正确率为80%.结果表明,小波能量熵能够从整体上表征胃动力信号时域和频域能量分布的复杂程度,可为胃肠病患者的疗效评价提供有效的特征描述.     

A novel method for analysis of single ion channel signal based on wavelet transform

A single ion channel signal was analysed by the power distribution fraction constructed by a discrete wavelet transform. Average opening time and energy distribution of the signal can be obtained directly by this method. The method can also be used when the signal is corrupted by noise. By contrast, the conventional frequency domain analysis method--power spectral density--is less effective. Power distribution fraction will therefore give more useful information in analysis of experimental ion channel signals, principally by giving values of the mean channel opening time. The method may be applied to distinguish different ion channels more efficiently and to find their reactions to drugs.     

Prolonged time course of glutamate-operated single channel currents in neuromuscular preparations of small crayfish and a membrane current triggered by glutamate channel gating

Single channel currents activated by glutamate were recorded by means of the patch-clamp technique in the abdominal superficial extensor muscle and the claw opener muscle of small (1-3 months old) and large (greater than 16 months old) crayfish. It was found that in small crayfish the time course of glutamate-operated single channel currents was prolonged by a factor of about 4 in these two preparations. In the abdominal superficial extensor muscle, single channel currents activated by 5 mmol/l glutamate had a mean burst length of tau = 2-3 ms in large crayfish and a mean burst length of tau = 8-9 ms in small crayfish. In the claw opener, for large crayfish tau congruent to 0.5 ms and for small crayfish tau = 1.5-2.5 ms resulted (500 mumol/l glutamate). Moreover, single channel currents with long time courses often slowly increased their amplitudes during the open time of the channel and current amplitudes did not decline completely to the baseline after channel closing. In addition, single channel currents with relatively constant amplitude were often followed by a small increasing and decreasing membrane current. The latter results suggest that glutamate channel gating might trigger a membrane current.     

Patch clamp experiments on nicotinic acetylcholine receptor-ion channels in bullforg sympathetic ganglion cells

Nicotinic acetylcholine-receptor ion channels (AChR channels) were studied in bullfrog sympathetic ganglion cells cultured for 1 day to 3 weeks, using a patch clamp technique. Microsuperfusion of ACh (2–10 M) to the ganglion cell under the whole cell clamp produced an inward current at membrane potentials negative to –60 mV, which had a fast onset and decay. This rapid ACh-induced current was accompanied by a large current fluctuation, decreased and increased in amplitude by membrane depolarization and hyperpolarization, respectively, and blocked by d-tubocurarine. Thus, this current must be induced by the nicotinic action of ACh, but not by a muscarinic effect to activate a slow cation-selective current. At depolarized levels more than –50 mV, Ach induced an additional inward current which was slow in time course, accompanied by no or decreased current fluctuation and increased in amplitude by membrane depolarization. Accordingly, this slow ACh-induced current could result from the suppression of a voltage-dependent K⁺ current (M-current: Brown and Adams 1980) by the muscarinic action of ACh. Fluctuation analysis of the rapid ACh-induced current at potentials negative to –50 mV revealed the elementary conductance of 14 pS and a power spectral density distribution of the double Lorentzian function which yielded the time constants of 5.4 and 62.5 ms at –60 to –80 mV. The variance of either component was independent of the mean current.Under both the cell-attached and outside-out modes, ACh (1–10 M: applied by microsuperfusion or bath application for the latter mode) caused single channel currents which reversed at a membrane potential close to 0 mV and had a conductance of 18–28 pS. In some patches, single channel currents of a smaller conductance (12 pS) were also observed in the presence of ACh. The open time distribution of the main AChR channel population followed a single or double exponential function depending on patches. The time constant of the single exponential distribution and that of the fast component of the double exponential distribution were similar and approximately 0.9 ms, while that of the slow component of the latter was 6.4 ms. Furthermore, the magnitude of each component in double exponential distributions varied largely among patches. These results suggest that there are at least two or three types of AChR channels in cultured bullfrog sympathetic ganglion cells: fast and slow AChR channels of 18–28 pS and possibly a fast AChR channel of smaller conductance of 12 pS.     

Quisqualate-activated single channel currents in neuromuscular preparations of small and large crayfish

Single channel currents elicited by 1-5 mumol/l quisqualate in neuromuscular preparations in large (greater than 16 month old) and small (1-3 month old) crayfish were recorded by means of the patch-clamp technique. In preparations from large crayfish single channel currents of variable amplitude (-1 to -12 pA) were induced by quisqualate. The mean burst lengths of these currents were tau approximately equal to 1-2 ms. In the opener muscle of the first walking leg and the contractor epimeralis muscle of small crayfish the mean burst lengths of single channel currents evoked by quisqualate were prolonged by a factor of about 4 (tau approximately equal to 5 ms). Moreover, in the opener muscle of the first walking leg of small crayfish single channel currents of small amplitude (-0.5 to -2.5 pA) were preferentially evoked by quisqualate. By contrast, in the contractor epimeralis muscle of small crayfish mainly single channel currents of large amplitude (-10 to -12 pA) were elicited by quisqualate. The results suggest that at the stage of neuromuscular development characterizing the small crayfish, gating properties of excitatory postsynaptic channels are different from those in adult crayfish. Furthermore, the results obtained in the opener muscle of the first walking leg of small crayfish are consistent with those obtained previously by means of the noise analysis technique.     

The properties of ionic channels measured by noise analysis in thin lipid membranes

Summary Noise analysis was performed on the membrane currents produced by the ion channel former gramicidin A in black lipid bilayer membranes. The average channel lifetime and the unit channel conductance can be determined from the autocorrelation function. The values agree with the independently obtained data from measurements of single channels. The dependence of this function on the channel density reveals information on the process of channel formation. The kinetic information is the same as that obtained by voltage clamp measurements.     

Analysis of polarization dynamics by singularity decomposition method

The driving point immittance (impedance or admittance) function is commonly used in electrical characterization of polarized materials and interfaces. The immittance function typically attenuates following a power function dependence on frequency. This fact has been recognized as a macroscopic dynamical property manifested by strongly interacting dielectric, viscoelastic and magnetic materials and interfaces between different conducting substances. Linear interfacial polarization processes which occur at metal electrode-electrolyte interfaces have been represented by the Fractional Power Pole [FPP] function in single or multiple stages. The FPP function is referred to as the Davidson-Cole function in the dielectrics literature. A related function widely used in mathematical modeling of dielectric and viscoelastic polarization dynamics is the Cole-Cole function. The fractional power factor which parametrizes the FPP or the Davidson-Cole function has been shown earlier to equal the logarithmic ratio of the locations of the pole-zero singularities. In this paper we first review a modified form of the singularity decomposition of the FPP function accomplished within a prescribed error range. The distribution spectrum and the corresponding simulation by a cascadeR-C network, as opposed to the synthesis by a ladderR-C network, are readily obtained as the next step in the simulation. The method is then applied to decompose the Cole-Cole function; the pole-zero placement of the singularity function is determined and the equivalent cascadeR-C network is synthesized.     

Voltage-dependent gating and block by internal spermine of the murine inwardly rectifying K+ channel, Kir2.1

The mechanism of inward rectification was investigated by recording single-channel currents through an inwardly rectifying  K⁺  channel (Kir2.1). cDNA encoding a wild-type (WT) channel, a mutant replacing Asp 172 with Asn (D172N), and a tandem tetramer WT-(D172N)2-WT, was transfected into COS-1 cells using the liposome method, and after 48–72 h single-channel currents were recorded in the inside-out configuration at 150 m m internal and external  K⁺  . Steady-state open probability of outward currents decreased with larger depolarizations. The activation curve was fitted with a single Boltzmann equation. The voltages of half-activation in the absence of spermine were +35.9 mV (WT), +55.0 mV (WT-(D172N)2-WT) and +76.7 mV (D172N). Open-time and zero-current-time histograms were constructed. The open-time histogram was fitted with a single exponential function. Two exponential functions were necessary to fit the closed-time histogram. In each channel, internal spermine at a concentration of 1–100 n m reduced the open time of the outward currents in a concentration-dependent manner and produced one blocked state without affecting the inward currents, suggesting that spermine acts as an open channel blocker. The normalized steady-state open probability-spermine concentration curve was fitted by saturation kinetics with a Hill coefficient of 1. On the assumption of the linear sequential state model, the unblock and blocking rates were estimated in each channel. Unblock rates depended on the number of D172N mutant subunits, but blocking rates did not. The results suggest that closing gates work independently of the spermine block and D172 is involved in both intrinsic gating and the spermine block.     

ATP-activated single-channel currents recorded from cell-free patches of pheochromocytoma PC12 cells.

Single-channel recordings were made using cell-free membrane patches (outside-out configuration) isolated from pheochromocytoma PC12 cells. ATP (50 microM) activated single channel currents in the isolated patches and the currents inactivated with a half-decay time of about 5s. The single channel conductance was about 13 pS in external solution with 140 mM Na. The amplitudes of the single-channel currents were decreased when external Ca was increased from 1.8 to 16.2 mM, suggesting that Ca blocks ion permeation through the channel. These properties of single-channel currents may underlie those of the macroscopic current.     

Quisqualate-sensitive glutamate receptors of the locust Schistocerca gregaria are antagonised by intracellularly applied philanthotoxin and spermine.

The effects of intracellularly and extracellularly applied synthetic analogues of delta-philanthotoxin (PhTX-433) and the polyamine spermine on the excitatory postsynaptic current (EPSC) of glutamatergic synapses and single channel currents gated by quisqualate-sensitive glutamate receptors (QUIS-R) on locust leg muscle have been compared. When applied extracellularly all 3 compounds reversibly antagonised the EPSC and the single channel currents. Antagonism was voltage independent, but use (agonist) dependent. Antagonism also occurred when they were injected into muscle fibres, but in this case it was not use dependent. It is proposed that spermine and the two toxins bind to the closed and open channel conformations of QUIS-R at a site near the intracellular opening of the channel gated by this receptor.