Wavelet transform as a potential tool for ECG analysis and compression

The recently introduced wavelet transform is a member of the class of time-frequency representations which include the Gabor short-time Fourier transform and Wigner-Ville distribution. Such techniques are of significance because of their ability to display the spectral content of a signal as time elapses. The value of the wavelet transform as a signal analysis tool has been demonstrated by its successful application to the study of turbulence and processing of speech and music. Since, in common with these subjects, both the time and frequency content of physiological signals are often of interest (the ECG being an obvious example), the wavelet transform represents a particularly relevant means of analysis. Following a brief introduction to the wavelet transform and its implementation, this paper describes a preliminary investigation into its application to the study of both ECG and heart rate variability data. In addition, the wavelet transform can be used to perform multiresolution signal decomposition. Since this process can be considered as a sub-band coding technique, it offers the opportunity for data compression, which can be implemented using efficient pyramidal algorithms. Results of the compression and reconstruction of ECG data are given which suggest that the wavelet transform is well suited to this task.     

Electrophysiological Studies of the Antrum Muscle Fibers of the Guinea Pig Stomach

The membrane potentials of single smooth muscle fibers of various regions of the stomach were measured, and do not differ from those measured in intestinal muscle. Spontaneous slow waves with superimposed spikes could be recorded from the longitudinal and circular muscle of the antrum. The development of tension was preceded by spikes but often tension appeared only when the slow waves were generated. Contracture in high K solution developed at a critical membrane potential of -42 mv. MnCl₂ blocked the spike generation, then lowered the amplitude of the slow wave. On the other hand, withdrawal of Na⁺, or addition of atropine and tetrodotoxin inhibited the generation of most of the slow waves but a spike could still be elicited by electrical stimulation. Prostigmine enhanced and prolonged the slow wave; acetylcholine depolarized the membrane without change in the frequency of the slow waves. Chronaxie for the spike generation in the longitudinal muscle of the antrum was 30 msec and conduction velocity was 1.2 cm/sec. The time constant of the foot of the propagated spike was 28 msec. The space constants measured from the longitudinal and circular muscles of the antrum were 1.1 mm and 1.4 mm, respectively.     

Increase of slow periodic modulation of EEG in a patient with Alzheimer's disease.

The recently described slow oscillations of amplitude of theta and alpha waves of the EEG (with a frequency below 0.08 Hz) in healthy subjects are attributed to the autonomic nervous system with control at the brain stem level. In the present pilot study, the slow brain rhythms were analyzed in a patient with Alzheimer's disease and were compared to a healthy subject. Dynamic analysis of the EEG was performed using time-frequency mapping which gives simultaneous time and frequency representation of the brain signal. This method comprises a transform of the filtered EEG signal into its analytic form and application of the Wigner distribution modified by time and frequency smoothing. It has been shown that the envelope of both theta and alpha activities oscillates at 0.04 Hz and 0.07 Hz in the healthy subject and at 0.03 Hz and 0.06 Hz in a patient with Alzheimer's disease. The amplitude of the slow oscillations of theta activity was substantially higher in the patient with Alzheimer's disease as compared with the healthy subject. It is being proposed that the increase of slow brain rhythms in the patient with Alzheimer's disease reflects an abnormal activity of the autonomic nervous system. However, the underlying pathophysiological mechanisms need to be further studied.     

Excitability of canine colon circular muscle disconnected from the network of interstitial cells of Cajal.

The 6 cpm omnipresent slow waves recorded in the circular muscle (CM) layer of canine colon are generated at the submucosal surface of the CM layer. After removal of the submucosal network of interstitial cells of Cajal (ICC), 66% of the CM preparations (25 of 38) were quiescent in Krebs solution. In the presence of carbachol, seven of nine of these spontaneously quiescent CM preparations demonstrated slow wave-like activity with mean frequency, duration and amplitude of 5.9 +/- 0.4 cpm, 2.8 +/- 0.5 s, and 0.8 +/- 0.2 mV, respectively. Similar slow wave-like activities were induced by TEA (seven out of eight quiescent CM preparations) with frequency, duration and amplitude of 6.1 +/- 0.2 cpm, 2.7 +/- 0.5 s, and 1.0 +/- 0.2 mV, respectively, and by BaCl2 (eight of eight quiescent CM preparations) with frequency, duration, and amplitude of 6.3 +/- 0.3 cpm, 1.8 +/- 0.2 s, and 0.5 +/- 0.1 mV, respectively. All the induced activities were abolished in the presence of 1 microM D600. CM preparations with the submucosal ICC network intact (ICC-CM) showed slow wave activity in Krebs solution at a frequency of 6.2 +/- 0.2 cpm, a duration of 3.6 +/- 0.2 s, and an amplitude of 1.0 +/- 0.1 mV (n = 22). When ICC-CM preparations were stimulated by BaCl2, carbachol, or TEA, the slow wave frequency did not change significantly, but the duration increased as well as the amplitude. In the presence of D600, the upstroke of slow waves remained and the frequency was not affected.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dynamics of potentials evoked in the auditory pathway and reticular formation of the cat. Studies during waking and sleep stages

Averaged evoked potentials in the inferior colliculus (IC), medial geniculate nucleus (MG) and reticular formation (RF) of chronically implanted and freely moving cats were measured using auditory step functions in the form of tone bursts of 2000 Hz. The most prominent components of the AEP of the inferior colliculus were a positive wave of 13 msec and a negative wave of 40–55 msec latency. The AEP of the medial geniculate nucleus was characterized by a large negative wave peaking at 35–40 msec. During spindle sleep and slow wave sleep stages changes in the AEPs of both nuclei occured.Transient evoked responses of the inferior colliculus, medial geniculate nucleus and reticular formation were transformed to the frequency domain using the Laplace transform (one sided Fourier transform) in order to obtain frequency characteristics of the systems under study. The amplitude characteristics of IC, MG. and RF obtained in this way revealed maxima in alpha (8–13 Hz), beta (18–35 Hz) and higher frequency (50–80 Hz) ranges. During spindle sleep stage a maximum in the theta frequency range (3–8 Hz) and during slow wave sleep maximum in the delta (1–3 Hz) frequency range appeared in the amplitude characteristics of these nuclei.The amplitude characteristics of the inferior colliculus and medial geniculate nucleus were compared with the amplitude characteristics of other brain structures. The comparison of AEPs and amplitude frequency characteristics obtained using these AEPs reveals that the existence of a number of peaks (waves) with different latencies in the time course does not necessarily indicate the existence of different functional structures or neural groups giving rise to these waves. The entire time course of evoked potentials and not the number and latencies of the waves, carries, the whole information concerning different activities and frequency selectivities of brain structures.Supported by Turkish Scientific and Technical Research Council Grant TAG-266.Presented in Part at the VIIIth International Congress of Electroencephalography and Clinical Neurophysiology in Marseilles, September 1–7, 1973.     

Subtractive hybridization unravels a role for the ion cotransporter NKCC1 in the murine intestinal pacemaker

In the small intestine, interstitial cells of Cajal (ICC) surrounding the myenteric plexus generate the pacemaking slow waves that are essential for an efficient intestinal transit. The underlying molecular mechanisms of the slow wave are poorly known. Our aim was to identify ICC-specific genes and their function in the mouse jejunum. Suppression subtractive hybridization using two independent ICC-deficient mouse models identified 56 genes putatively downregulated in the muscularis propria compared with wild-type littermates. Differential expression was confirmed by real-time quantitative PCR for the tyrosine kinase receptor KIT, the established marker for ICC, and for the Na(+)-K(+)-2Cl(-) cotransporter (NKCC1). Immunoreactivity for NKCC1 was detected in myenteric ICC but not in the ICC population located at the deep muscular plexus. NKCC1 was also expressed in enteric neurons and mucosal crypts. Bumetanide, an NKCC1 inhibitor, reversibly affected the shape, amplitude, and frequency of the slow waves. Similar alterations were observed in NKCC1 knockout mice. These data support the hypothesis that NKCC1 expressed in myenteric ICC is involved in the mechanism of slow waves in the murine jejunum.     

Analysis of spatiotemporal pattern and quantification of gastrointestinal slow waves caused by anticholinergic drugs

Anticholinergic drugs are well-known to cause adverse effects, such as constipation, but their effects on baseline contractile activity in the gut driven by slow waves is not well established. In a video-based gastrointestinal motility monitoring (GIMM) system, a mouse's small intestine was placed in Krebs solution and recorded using a high definition camera. Untreated controls were recorded for each specimen, then treated with a therapeutic concentration of the drug, and finally, treated with a supratherapeutic dose of the drug. Next, the video clips showing gastrointestinal motility were processed, giving us the segmentation motions of the intestine, which were then converted via Fast Fourier Transform (FFT) into their respective frequency spectrums. These contraction quantifications were analyzed from the video recordings under standardised conditions to evaluate the effect of drugs. Six experimental trials were included with benztropine and promethazine treatments. Only the supratherapeutic dose of benztropine was shown to significantly decrease the amplitude of contractions; at therapeutic doses of both drugs, neither frequency nor amplitude was significantly affected. We have demonstrated that intestinal slow waves can be analyzed based on the colonic frequency or amplitude at a supratherapeutic dose of the anticholinergic medications. More research is required on the effects of anticholinergic drugs on these slow waves to ascertain the true role of ICC in neurologic control of gastrointestinal motility.     

The myogenic component in distention-induced peristalsis in the guinea pig small intestine

In an in vitro model for distention-induced peristalsis in the guinea pig small intestine, the electrical activity, intraluminal pressure, and outflow of contents were studied simultaneously to search for evidence of myogenic control activity. Intraluminal distention induced periods of nifedipine-sensitive slow wave activity with superimposed action potentials, alternating with periods of quiescence. Slow waves and associated high intraluminal pressure transients propagated aborally, causing outflow of content. In the proximal small intestine, a frequency gradient of distention-induced slow waves was observed, with a frequency of 19 cycles/min in the first 1 cm and 11 cycles/min 10 cm distally. Intracellular recording revealed that the guinea pig small intestinal musculature, in response to carbachol, generated slow waves with superimposed action potentials, both sensitive to nifedipine. These slow waves also exhibited a frequency gradient. In addition, distention and cholinergic stimulation induced high-frequency membrane potential oscillations (~55 cycles/min) that were not associated with distention-induced peristalsis. Continuous distention produced excitation of the musculature, in part neurally mediated, that resulted in periodic occurrence of bursts of distally propagating nifedipine-sensitive slow waves with superimposed action potentials associated with propagating intraluminal pressure waves that caused pulsatile outflow of content at the slow wave frequency.     

Slow wave and spike action potentials recorded in cell cultures from the muscularis externa of the guinea pig small intestine.

Intracellular recordings were obtained to investigate whether slow wave and spike type action potentials are present in cell cultures of the muscularis externa from the guinea pig small intestine. The muscularis externa of the small intestine was dissociated by using specific purified enzymes and gentle mechanical dissociation. Cells were plated on cover slips and maintained in culture for up to 4 weeks. Dissociated cells obtained in this way reorganized themselves in a few days to form small cell clumps showing spontaneous movements. Intracellular recordings of these clumps displayed both spike and slow wave type action potentials. Spikes were observed on top of some slow waves and were abolished by the addition of nifedipine or the removal of extracellular calcium. Slow waves, however, were nifedipine insensitive and temperature sensitive, and were abolished by octanol (a gap junction blocker) and forskolin (an adenyl cyclase activator). Slow waves were never observed in small clumps (<50 microm), suggesting that a critical mass of cells might be required for their generation. These observations demonstrated for the first time the presence of nifedipine-insensitive slow waves in cell cultures of the muscularis externa from the guinea pig small intestine. Cell cultures allow rigorous control of the immediate environment for the cells and this should facilitate future studies on the molecular and cellular mechanisms responsible for the slow waves in the gastrointestinal tract.     

High frequency components in the spectrum of the visual evoked potential

The occurrence of short term high frequency components in the spectra of the VEP is usually overshadowed by larger amplitude slow waves which occur simultaneously with the high frequency waves. The high frequency components become evident when the time varying power spectra of short duration (250 ms) segments of the VEP are examined. Two types of short duration time varying power spectra are considered: one is obtained directly from overlapping time segments of the average VEP; and, the other is obtained by computing the spectra from the average autocorrelation functions of overlapping time segments of the data following each stimulus. The first yields the time varying properties for the spectra of the stimulus-synchronized data while, the latter shows the time varying properties of both the synchronized and unsynchronized data present.     

The effect of gastric electrical stimulation on canine gastric slow waves

This study determined the most efficient parameters of low-frequency/long-pulse gastric electrical stimulation (GES) required to entrain gastric slow waves and also evaluated the effect of entrainment and high-frequency, short-pulse GES on gastric electrical activity (GEA). Nine dogs were fitted with stimulation wires along the greater curvature. Entrainment was observed in six or seven animals, with long-pulse GES at six cycles per minute (cpm), at various combinations of current and pulse width and was directly related to the energy delivered. Entrainment was observed in four to seven animals, with GES at 12 cpm, and the maximal driven frequency was 6 cpm. Entrainment did not significantly increase the dominant power of GEA. High-frequency, short-pulse GES, using pulse trains of 14 Hz, 5 mA, and 330 micros, with 0.1 s on and 5 s off, and pulse trains of 40 Hz, 10 mA, and 330 micros, with 2 s on 3 s off, did not affect variables of GEA. We conclude that acute low-frequency GES but not high-frequency, short-pulse GES can entrain slow waves; the power of slow waves is not affected by either type of stimulation.     

Morphohistochemical and electrophysiological characteristics of the transverse striated muscles of the rabbit esophagus

A specific histochemical profile of the muscular tunic of the stomach has been revealed; its myons demonstrate a high succinate dehydrogenase and myofibrillar ATPase activity. Electrical activity of the oesophageal musculature has common features with biopotentials of the skeletal muscles and the smooth musculature of the stomach. The similiarity with the skeletal muscle biopotentials is evident as a peculiar spike activity, especially at the time of feeding. In electrograms of the striated oesophageal muscles slow waves are seen; they change at deprivation and feeding. Therefore, it is possible to compare them with the smooth musculature capable to generate slow waves.     

Connection between internal representation of rigid transformation and cortical activity paths

A canonical unitary representation of the Euclidean group on the range space of the Gabor transform is constructed from mathematical properties of the Euclidean group and the quaternions. The visual cortical activity pattern corresponding to a given retinal image is represented by a point in the range space of the Gabor transform. Paths experienced in apparent motion and mental rotation are represented by paths in the Euclidean group. The key hypothesis of the paper is that an action of the Euclidean group on the Gabor transform space brings the perceived paths into relation with corresponding successive neural microstructure activity patterns. Possible experimental tests are suggested.     

Use of a microelectrode array to record extracellular pacemaker potentials from the gastrointestinal tracts of the ICR mouse and house musk shrew (Suncus murinus)

BackgroundThe rhythmic contraction and relaxation of smooth muscles in the gastrointestinal (GI) tract is governed by pacemaker electrical potentials, also termed slow waves, which are calcium currents generated by interstitial cells of Cajal (ICCs). Malfunction of pacemaker rhythms contributes to a number of clinically challenging gastrointestinal motility disorders.MethodA microelectrode array (MEA) was used to record slow waves in vitro from intact GI tissues freshly isolated from the ICR mouse and Suncus murinus. The effects of temperature, extracellular calcium and potassium concentrations on pacemaker potentials were quantified using spatiotemporal metrics.ResultsPacemaker frequency decreased from the duodenum to the ileum in the mouse, but this phenomenon was less significant in Suncus murinus. In both the mouse and Suncus murinus, the stomach had a much lower pacemaker frequency than the intestine. Propagation velocity and amplitude were highest in the proximal intestine. Temperature significantly increased pacemaker frequency in the intestinal tissues of both species. Removal of Ca²⁺ from the medium inhibited pacemaker potential and increasing the Ca²⁺ concentration increased pacemaker frequency in the mouse ileum. Increasing K⁺ concentration decreased pacemaker frequency in the absence of nifedipine.ConclusionsThe MEA allows efficient investigation of gut pacemaker frequency and propagation.     

视觉系统初级信息加工的一种数学模型——<Ⅰ>模型的空间性质

本文用广义Gabor(EQ)函数作为视觉系统进行初级信息加工的核函数.所谓广义Gabor函数,就是把原始Gabor函数中的一个独立变量扩展到三个(即空间变量从一维推广到二维,再加时间变量),并相应地引入一些参数.本文中EG取二大类形式:各向同性系统中表达式和各向异性系统表达式.当EG取某一特定形式,而且其中参数取某些特定值时,本模型可分别定性描述电生理实验中发现的几种主要感受野类型(Kuffler,Hubel和Wiesel型等).在空间频率域中引入对数变换假设后,EG经付里叶变换后可很好地合成人眼调制传递函数(MTF)     

The effects of H2O2 on electromechanical activity of the ileum longitudinal muscle

The effects of H2O2 on electrical and mechanical activity of the longitudinal layer from the guinea-pig ileum were studied using sucrose-gap technique and the influence of H2O2 on ionic current was investigated in single smooth muscle cells by the patch-clamp method. In most of the preparations tested, the spontaneous activity observed was composed of slow waves with superimposed action potentials (APs). Both were resistant to tetrodotoxin and atropine. H2O2 (1 mmol/l) evoked sustained 3-5 mV membrane depolarisation, doubled the amplitude of the slow waves and increased their frequency, augmented the APs and reduced their splitting. These changes were accompanied with significant contraction, which had an amplitude comparable to that of the tonic component of 50 mmol/l K+-induced contraction. Calcium-free solution caused membrane depolarisation, reduction of the slow wave amplitude and frequency, disappearance of APs and decreased the mechanical tension of the preparations. Application of H2O2 (1 mmol/l) into the zero-calcium bath solution recovered the APs, which was accompanied by a low amplitude contraction. H2O2 (up to 1 mmol/l) increased the L-type calcium current (I(Ca)) both under conventional whole-cell patch-clamp configuration and under amphotericin-perforated patches by 16 +/- 3%. These data demonstrated that contractile response of the ileum longitudinal smooth muscle preparation evoked by H2O2 was mainly due to the enhanced electrical activity.     

Wavelet-based analysis of human blood-flow dynamics

To analyze signals measured from human blood flow in the time-frequency domain, we used the wavelet transform which gives good time resolution for high-frequency components and good frequency resolution for low-frequency components. Five characteristic frequency peaks, corresponding to five almost periodic rhythmic activities, were found on the time scale of minutes. These oscillations were characterized by time and spatial invariant measures. The potential of this approach in studying the blood-flow dynamics was illustrated by revealing differences between the groups of control subjects and athletes.     

The role of histamine in regulation of spontaneous electrical activity of the rat ureter and bordering to bladder area

The nature of the influence of histamine on the slow wave and spike spontaneous activity of both perirenal and peribladder bordering areas of the bladder zone has been studied. It is shown that under these conditions of activated renal section of the organ, in the distal part, the decrease in frequency of the slow waves occurred. The histamine effect also contributes to improvement of the conduction of the excitation wave propagating to the bladder, which destroys the coordination of spike activity of the latter with slow waves of ureteral bordering zone.     

大鼠实验性十二指肠溃疡的电活动特征

本实验用半胱胺经口给药方法诱发大鼠十二指肠球部溃疡。在离体条件下,以肠电慢波的频率和振幅为指标,观察了溃疡时十二指肠各部位的电活动变化。结果表明:(1)溃疡病变均选择牲地形成在十二指肠球部,溃疡中心在离幽门括约肌0.5cm左右处;(2)在幽门括约肌尾侧0.5cm处(形成溃疡部位)和1.0cm及2.0cm处(未形成溃疡部位)的溃疡大鼠十二指肠电慢波频率,均明显地高于对照组(P<0.05)而其振幅的变化不甚明显(P>0.05);(3)在幽门括约肌尾侧1.0cm处,十二指肠球部穿孔性溃疡大鼠的电慢波振幅明显地大于单纯性溃疡大鼠(P<0.05),而在幽门括约肌尾侧2.0cm处,穿孔性溃疡大鼠的电慢波频率明显高于单纯性溃疡大鼠(P<0.05)。以上结果提示:由半胱胺诱发的十二指肠球部溃疡对十二指肠电慢波频率有加速作用,并随溃疡病变的加重,十二指肠电慢波活动似有增强倾向。