Time-frequency methods for detecting spike activity of stomach

It has been hypothesised by many researchers that the spike activity signals of the stomach are responsible for triggering peristaltic contractions. Since most gastric motility disorders include an abnormality in the contraction pattern, it is very important to access this information non-invasively. The aim in this study is to use abdominal electrogastrogram (EGG) signals to detect the spike activity signals generated by the serosa of the stomach, and hence provide clinicians with a better method to monitor the motility state of the stomach. Through second and third-order spectral estimations performed on the serosal data obtained from canine experiments, it was concluded that the spike activity in serosal signals occupies a frequency range of 50-80 cycles per minute. An increase in this frequency range during strong antral contractions was observed both in the serosal and cutaneous power spectra. By using the 'continuous wavelet transform' with respect to a modified Morlet wavelet, the spike activity signals generated from the serosa of the stomach can be detected and quantified in time from the cutaneous EGG records. During phase III contraction episodes, a detection accuracy of up to 96% from the cutaneous EGG recordings was calculated based on the scored serosal spike activities simultaneously recorded.     

Bileaflet mechanical valve sound analysis using a continuous wavelet transform

Bileaflet mechanical valve closing sounds have splits, the duration of which is not constant in normally functioning valves. However, no reports have discussed the influences of valve malfunction on the split interval, neither have any studies discussed the fact that mechanical valve closing sound signals must be analyzed using a time-frequency analysis because they are nonstationary signals. The continuous wavelet transform (CWT), a time-frequency analyzing method using mother wavelets modified by scale numbers, was selected in this study for analyzing bileaflet valve closing sounds because it is easy to understand and has no limitations such as the cross-terms in the Wigner–Ville distribution or the tradeoff between time and frequency resolutions of the short-time Fourier transform. This study compares the properties of the mother wavelets of various CWTs and selects one that is suitable for detection of the clear split in bileaflet mechanical valve closing sound signals. This article also establishes a standard frequency analyzing system for bileaflet mechanical valve sounds. A preliminary study with chirp Doppler signals for comparing the frequency properties of the mother wavelets of various CWTs suggested that Ishikawa's modified Morlet CWT has better time and frequency resolution at the highest frequency scale. Morlet/power CWT analysis of normal in vivo bileaflet valve closing sounds of the ST. Jude Medical (SJM), ATS, and Carbomedics (CM) valves demonstrated clear splits of very short interval at the highest level of frequency. Detection of the disappearance of the split by using this analytical method may be the key to identifying bileaflet mechanical valve malfunction in outpatient departments.     

Microprocessor-based system for spike and eye-movement data acquisition and storage

A simple system for simultaneous recording of eye position and spike activity during on-line experimentation is described. The system is based on a relatively inexpensive and widely distributed personal computer. While the hardware is configured from commercially available products, the software has been developed in our laboratory. Data acquisition is controlled by a few routines whose logic is outlined, together with the main limitations and the possible improvements of the system itself.     

Wavelet analysis of bileaflet mechanical valve sounds

It has been reported that asynchronous leaflet closure in a bileaflet mechanical valve causes a split in the valve closing sound. We have previously reported that the continuous wavelet transform (CWT) with the Morlet wavelet as modified by Ishikawa (the Morlet wavelet) is the most suitable method among the CWTs for detecting a split in the bileaflet mechanical valve sound because this method can detect the highest frequency signal among the CWT methods with higher time resolution. This is the first article which discusses the acoustic properties of five types of bileaflet valves using the Morlet CWT. Similar behavior of the valve sound split intervals with wide fluctuations over consecutive heartbeats was found to be the common finding for all the bileaflet valves. This result suggests that fluctuation of the split interval proves the normal movement of both leaflets without movement disturbance. The mean differences in the split interval between these bileaflet valves were statistically significant, and the wavelet coefficients of the CWT showed characteristic scalographic patterns, such as a teardrop shape or a triangle beneath the split. However, these two findings gave no valuable information for the diagnosis of bileaflet valve malfunction. A split in the valve closing sound with a fluctuating interval was the common finding in these five normally functioning bileaflet valves, and careful observation of the split's behavior may be a key to diagnosis of bileaflet valve malfunction.     

An improved graphical method for pattern recognition from spike trains of spontaneously active neurons

Summary Spontaneous activity and rhythmical oscillations are common features of large neuronal networks in mammals. Detection of repetitive spike patterns or pacemaker activity during electrophysiological recording of spontaneous action potentials from single neurons can be difficult if a noisy background is present. This paper describes an improved method for an online spike train analysis based on joint interval histograms (JIH, Rodiek et al. 1962). By means of higher ordered JIH the discrimination of spike patterns with repetitive bursting activity or oscillations is possible even when randomly distributed action potentials appear. Examples of simulated spike trains and those recorded from cultured hippocampal neurons are presented.     

Volume conductor effects on the spatial resolution of magnetic fields and electric potentials from gastrointestinal electrical activity

An analysis of the relative capabilities of methods for magnetic and electric detection of gastrointestinal electrical activity is presented. The model employed is the first volume conductor model for magnetic fields from GEA to appear in the literature. A mathematical model is introduced for the electric potential and magnetic field from intestinal electrical activity in terms of the spatial filters that relate the bioelectric sources with the external magnetic fields and potentials. The forward spatial filters are low-pass functions of spatial frequency, so more superficial external fields and potentials contain less spatial information than fields and potentials near the source. Inverse spatial filters, which are reciprocals of the forward filters, are high-pass functions and must be regularised by windowing. Because of the conductivity discontinuities introduced by low-conductivity fat layers in the abdomen, the electric potentials recorded outside these layers required more regularisation than the magnetic fields, and thus, the spatial resolution of the magnetic fields from intestinal electrical activity is higher than the spatial resolution of the external potentials. In this study, two smooth muscle sources separated by 5 cm were adequately resolved magnetically, but not resolved electrically. Thus, sources are more accurately localized and imaged using magnetic measurements than using measurements of electric potential.     

Response of the electric activity in the human stomach to water and a solid meal

The gastric electric activity paces the contractions of the stomach and can be measured noninvasively using surface electrodes placed on the abdomen. In this paper, response of the gastric electric activity to water and a solid meal was investigated using surface electrodes. Applying an improved recording technique, power spectral analysis and statistical analysis methods, the gastric electric activity in preprandial, postwater and postprandial states was measured and analysed from ten healthy volunteers. To more convincingly show the effect of water and the solid meal on the gastric slow wave and gastric motility, simultaneous recordings of the cutaneous EGG and manometric activities in the stomach were performed in three gastroparetic patients. It was found that water does not induce contractions of the stomach, but the gastric slow wave amplitude increases (p<0·05) and frequency decreases (p<0·05). The solid meal results in an increase in both the amplitude (p<0·01) and the frequency (p<0·02) of the gastric slow wave. It appears that the postprandial EGG amplitude increases because of a combination of stomach contractions and gastric distension bringing the stomach closer to the recording electrodes. The slow wave frequency, however, correlates well with stomach contractions.     

用于QT间期检测的复合算法研究

目的为了提高QT间期检测精度，探讨一种多算法融合的QT间期自动检测算法。方法采用小波变换的方法检测Q点。采用不依赖阈值的波形面积算法检测T波终点。利用Physionet QT数据库中的数据评价算法的检测结果。结果检测误差均值为-0．36ms，标准差15．49ms；66．52％的检出误差被控制在20ms以内，92．12％的检出误差被控制在40ms,以内。结论该算法具有良好的稳定性，提高了QT间期的检测精度。     

Analysis of cardiac health using fractal dimension and wavelet transformation

Analysis of heart rate variation (HRV) has become a popular non-invasive tool for assessing the activities of the autonomic nervous system (ANS). HRV analysis is based on the concept that fast fluctuations may specifically reflect changes of sympathetic and vagal activity. It shows that the structure generating the signal is not simply linear, but also involves nonlinear contributions. These signals are essentially non-stationary; may contain indicators of current disease, or even warnings about impending diseases. The indicators may be present at all times or may occur at random in the time scale. However, to study and pinpoint abnormalities in voluminous data collected over several hours is strenuous and time consuming. This paper presents the continuous time wavelet analysis of heart rate variability signal for disease identification. Fractal dimension (FD) of heart rate signals are calculated and compared with the wavelet analysis patterns. The FD obtained indicates more than 90% confidence interval for all the classes studied.     

Amino acids 1 to 422 of the spike protein of SARS associated coronavirus are required for induction of cyclooxygenase-2

The causative agent of severe acute respiratory syndrome (SARS) has been identified as SARS-associated coronavirus (SARS-CoV). To evaluate the molecular mechanisms involved in the viral infection, in this study, we investigated the role of SARS-CoV Spike (S) protein in the regulation of cyclooxygenase-2 (COX-2). Expression of COX-2 stimulated by the S protein was verified by RT-PCR and western blot assay. To explore the relationship between S and COX-2, we constructed a series of plasmids containing truncated N-terminal fragments of the SARS-CoV S gene (designated from Sa to Si), which encoded truncated S proteins, and investigated whether these truncated proteins could induce effective expression of COX-2 in 293T cells. Our results showed that S_d that encoded a truncated S protein with 422 amino acid residues (from 1 to 422 aa), a part of 672 amino-acid S1 subunit is crucial for the induction of COX-2 expression. Immunofluorescence examinations also give the evidence that these N terminal 422 amino acids of the S protein were also required for the correct localization of the protein. We also compared S protein sequences of SARS-CoV isolated during the SARS break with that from palm civets, a possible source of SARS-CoV found in humans. S protein residues (344, 360), which mutated in the epitome from palm civet to human being were characterized in 3D modeling of 252–375 amino acid fragment. Collectively, these results indicate that S protein of SARS-CoV induces the expression of COX-2 and an N-terminal fragment of the Spike protein is crucial for the induction. Our finding may provide clue for the induction of inflammation by SARS-CoV and cast insight into the severity of the SARS epidemic.     

Study of transcutaneous and intraluminal measurement of gastric electrical activity in humans

Several authors have reported measurements of the human electrogastrogram (EGG), both with intraluminal electrodes and with improved noninvasive techniques. These methods provide information about the existence and frequency of gastric electrical activity (GEA) which may aid in diagnosing tachygastria. However, none of these methods have provided information regarding the direction and velocity of propagation of GEA. Such information could help isolates such abnormalities as gastro-oesophageal and antral reflux and gastric stasis. To ascertain the reliability of the extracorporal measurements, a new intraluminal electrode assembly was developed. This probe measures GEA through the mucosa at several locations simultaneously; yielding frequency, direction of propagation and velocity of the electrical activity.     

体表胃电图慢波提取方法的比较研究

体表胃电图(electrogastrogram,EGG)具有幅值小、频率低和窄带宽的特点,并且极易受到心电、呼吸以及运动等干扰.文中对三种常用的EGG慢波的提取方法进行了比较,包括自适应滤波、小波多尺度分解和经验模态分解,并将三种方法分别应用于模拟的含噪EGG信号以及临床EGG慢波的提取.研究结果表明,三种方法各有优缺点,均能有效地提取出EGG信号中的慢波成分.与自适应滤波相比,小波多分辨率分解和经验模态分解获得了更高的信噪比和更低的重构方差.     

Cortico-visceral interrelationships during periodic activity of the stomach

In chronic experiments on five dogs with stomach fistulas and bipolar electrodes (6–8 pairs) symmetrically implanted in the cranial bones we recorded simultaneously the activity of the stomach balloonographically and the electroencephalogram using the Nikhon Koden encephalograph with automatic analysis of the frequency spectrum within five ranges: 2–4, 4–8, 8–12, 12–20, and 20–30 oscill/sec. The correlation between the frequency spectrum of the EEG and the phases of periodic activity (PA) cycles of the stomach in the form of a regular shift in the predominance of fast (during contraction periods) or slow (during resting periods) components and its changes under the influence of atropine and food stimulants have been described. The EEG complexes typical of periods of contraction or resting are regarded as cortical correlates of the PA under conditions of good adaptation of the animals to the experimental situation. The changes in the correlation under conditions of actions used indicate a firmer association between the PA EEG correlates with other components of the PA rather than with the motor function of the stomach.Translated from Fiziologicheskii Zhurnal SSSR imeni I. M. Sechenova, Vol. 68, No. 4, pp. 478–489, April, 1982.     

Continuous time wavelet entropy of auditory evoked potentials

In this paper, the continuous time wavelet entropy (CTWE) of auditory evoked potentials (AEP) has been characterized by evaluating the relative wavelet energies (RWE) in specified EEG frequency bands. Thus, the rapid variations of CTWE due to the auditory stimulation could be detected in post-stimulus time interval. This approach removes the probability of missing the information hidden in short time intervals. The discrete time and continuous time wavelet based wavelet entropy variations were compared on non-target and target AEP data. It was observed that CTWE can also be an alternative method to analyze entropy as a function of time.     

Continuous Wavelet Analysis as an Aid in the Representation and Interpretation of Electrogastrographic Signals

This paper presents an application of the continuous wavelet transform (CWT) in the analysis of electrogastrographic (EGG) signals. Due to the nonstationary nature of EGG signals, the CWT method, which uses multiresolution scaled windows, gives a better time-frequency resolution than the short-time Fourier transform, which uses a fixed window. Spike activity due to gastric contraction was investigated through experiments on dogs. During spike activity we observed an increase in magnitude of the slow wave and the appearance of a low frequency component with half the frequency of the slow wave. Studies of the EGG signals from the small intestine are also presented to investigate the hypothesis that its slow wave might be confounded with spike activity in the stomach due to the similarity of their frequency ranges. © 1998 Biomedical Engineering Society. PAC98: 0230-f, 8759Wc     

Expert system approach to detection of epileptiform activity in the EEG

An expert system for the automated detection of spikes and sharp waves in the EEG has been developed. The system consists of two distinct stages. The first is a feature extractor, written in the conventional procedural language Fortran, which uses parts of previously published spike-detection, algorithms to produce a list of all spike-like occurrences in the EEG. The second stage, written in the production system language OPS5, reads the list and uses rules incorporating knowledge elicited from an electroencephalographer (EEGer) to confirm or exclude each of the possible spikes. Information such as the time of occurrence, polarity and channel relationship are used in this process. A summary of thedetected epileptiform events is produced which is available to the EEGer in interpreting the EEG. The performance of the expert system is compared with an EEGer using a 320s segment from an EEG containing epileptiform activity. The system detected 19 events and missed seven (false negative) which the EEGer considered epileptiform. There were no false positive detections.     

Dexamethasone induced changes of neural activity in the auditory cortex of rats

Previous studies have suggested that elevation of glucocorticoid level can alter auditory processing and may have relevance for auditory hallucinations. However, the neural mechanism underlying the glucocorticoid induced sensory change remains unclear. To examine the effects of glucocorticoid on the neuronal spike activities of sensory cortex, we topically applied dexamethasone (DEX), a glucocorticoid receptor agonist, to the auditory cortical surface of rats while recording single-unit extracellular spike activities in response to sound stimuli. Our major findings are: (1) a topical administration of DEX increased the cortical neural responses to pure-tone stimuli from 10 to 60 min after administration, while the peak response enhancement occurred at 20–30 min; (2) DEX not only markedly increased the magnitude of tone-evoked responses, but also extended the response duration and the frequency range of the neural responses; (3) the enhancement of neural responses was more salient at the higher frequency band; (4) the ratio of spontaneous firing rate between post- and pre-administration was negatively correlated with the unit's spontaneous firing rate before treatment. Our data confirm that DEX can modulate the neural activity at the cortical level and provide more information for understanding the mechanism of glucocorticoid-induced alterations in auditory processing.     

Relationship of presaccadic activity in frontal eye field and supplementary eye field to saccade initiation in macaque: Poisson spike train analysis

The purpose of this study was to investigate the temporal relationship between presaccadic neuronal discharges in the frontal eye fields (FEF) and supplementary eye fields (SEF) and the initiation of saccadic eye movements in macaque. We utilized an analytical technique that could reliably identify periods of neuronal modulation in individual spike trains. By comparing the observed activity of neurons with the random Poisson distribution generated from the mean discharge rate during the trial period, the period during which neural activity was significantly elevated with a predetermined confidence level was identified in each spike train. In certain neurons, bursts of action potentials were identified by determining the period in each spike train in which the activation deviated most from the expected Poisson distribution. Using this method, we related these defined periods of modulation to saccade initiation in specific cell types recorded in FEF and SEF. Cells were recorded in SEF while monkeys made saccades to targets presented alone. Cells were recorded in FEF while monkeys made saccades to targets presented alone or with surrounding distractors. There were no significant differences in the time-course of activity of the population of FEF presaccadic movement cells prior to saccades generated to singly presented or distractor-embedded targets. The discharge of presaccadic movement cells in FEF and SEF could be subdivided quantitatively into an early prelude followed by a high-rate burst of activity that occurred at a consistent interval before saccade initiation. The time of burst onset relative to saccade onset in SEF presaccadic movement cells was earlier and more variable than in FEF presaccadic movement cells. The termination of activity of another population of SEF neurons, known as preparatory set cells, was time-locked to saccade initiation. In addition, the cessation of SEF preparatory set cell activity coincided precisely with the beginning of the burst of SEF presaccadic movement cells. This finding raises the possibility that SEF preparatory set cells may be involved in saccade initiation by regulating the activation of SEF presaccadic movement cells. These results demonstrate the utility of the Poisson spike train analysis to relate periods of neuronal modulation to behavior.     

SARS-coronavirus spike S2 domain flanked by cysteine residues C822 and C833 is important for activation of membrane fusion

The S2 domain of the coronavirus spike (S) protein is known to be responsible for mediating membrane fusion. In addition to a well-recognized cleavage site at the S1-S2 boundary, a second proteolytic cleavage site has been identified in the severe acute respiratory syndrome coronavirus (SARS-CoV) S2 domain (R797). C-terminal to this S2 cleavage site is a conserved region flanked by cysteine residues C822 and C833. Here, we investigated the importance of this well conserved region for SARS-CoV S-mediated fusion activation. We show that the residues between C822-C833 are well conserved across all coronaviruses. Mutagenic analysis of SARS-CoV S, combined with cell-cell fusion and pseudotyped virion infectivity assays, showed a critical role for the core-conserved residues C822, D830, L831, and C833. Based on available predictive models, we propose that the conserved domain flanked by cysteines 822 and 833 forms a loop structure that interacts with components of the SARS-CoV S trimer to control the activation of membrane fusion.