Application of a bioelectric field model of the ERG to the effect of vitreous haemorrhage

A model of the spatial distribution of ERG potentials was used to determine whether blood in the vitreous could sufficiently attenuate potentials initiated in the retina. This topic is of importance to clinicans in helping to determine the functional status of the retina prior to a possible vitrectomy. The results of the model demonstrated that vitreous haemorrhage could not significantly reduce the ERG. Nor could the vitreous blood account for a reduced ratio of b to a waves when ERG frequencies were considered. A reduced or altered ERG Would be due to another cause(s) and might preclude vitrectomy if the function of the retina were impaired.     

On the magnetic field and the electrical potential generated by bioelectric sources in an anisotropic volume conductor

The electrical conductivity in biological tissue is often dependent on the direction of the fibres. In the paper the influence of this anisotropic nature on the electrical potential and magnetic field generated by a current dipole is studied analytically. Three different methods are discussed. The volume conductor is described by piecewise homogeneous compartments and the interfaces between compartments are either parallel or perpendicular to one of the principal axes. To illustrate the methods, the influence of the anisotropic nature is computed for a two-layered medium. It turns out that the influence on both the potential and the magnetic field cannot be ignored. However, for some commonly used models of the head and torso, a certain component of the magnetic field is not influenced by the anisotropy.     

Changes of the e.e.g. during a c.n.v. paradigm

An experimental set-up and a method of analysis are described which permit the performance of e.e.g. analysis under contingent negative variation (c.n.v.) conditions with repeated stimulation. Investigations of six subjects showed a significant reduction in the average power in the alpha band immediately after the imperative stimulus, which lasted only about 1 second. In the interstimulus interval during the c.n.v. a less marked power reduction could be observed. Since the reduction of the average power in the alpha band was approximately the same for both hemispheres and since it was also dependent on the modality of the stimulus, an interrelation-ship is assumed between the directed attention and the reduction observed. This appears to allow the possibility of objectively analysing cortical functions by means of an analysis of scalp recordings under c.n.v. conditions.     

有锥度角的主动脉弓血液脉动流数值分析

目的 探求在正常生理脉动流条件下主动脉弓内血液流动速度和压力脉动分布，为动脉粥样硬化的成因和排除方法的研究提供理论依据。方法 运用计算流体力学方法和血流动力学的基本原理，对具有锥度角的主动脉弓内血液脉动流动进行数值模拟和可视化分析。结果 计算获得了具有锥度角的主动脉弓内血液流动在心动周期不同时刻的压力分布、速度分布、流线分布。结论 主脉弓内的血液脉动流流态表现复杂的原因是多方面的，而其中最为重要的原因就是主动脉弓的锥度角和曲率。     

Recognition of shape from the frequency spectrum of the e.m.g.

Visual processing is one of the important aspects of research into an intelligent robot and upper extremity prostheses. The study has shown the relationship between the recognition of shape and the electromyogram generated in the human on the surface of the extensor carpi radialis muscle. To observe the corresponding electric signals, the subject was placed inside a shielded room with Ag?AgCl electrodes located at two points on his skin. The two electrodes were spaced 50 mm apart, but variation of the separation in the range 5–10 mm had no effect on the e.m.g. Three spectral peaks (100, 160 and 250 Hz) for the response are obtained for each shape. The frequencies corresponding with the peak values in the spectra are the same, and are independent of the shapes. Shape recognition can therefore be quantified as an e.m.g. spectral variation.     

Filter bank analyser for automatic analysis of the e.m.g.

An electronic e.m.g. analyser is described which can continuously analyse the r.m.s. amplitude and the frequency components of the e.m.g. over the frequency range of 35 to 350 Hz. The analyser uses 10 active bandpass filters to measure some of the frquency components of the e.m.g. The amplitude of the frequency components of the e.m.g. are then processed by an analogue computer to calculate their median frequency. An r.m.s. converter is used to calculate the r.m.s. amplitude of the e.m.g. The degree of fatigue induced in the muscle is then quantified from the downward shift of the centre frequency of the e.m.g. Four subjects were asked to exert brief contractions at tensions up to 100% of their maximum strength and fatiguing isometric contraction at tensions of 25, 40 and 70% of their maximum strength to test the operation of the analyser. As a basis for comparison, the e.m.g. recorded during these contractions was also processed through Fourier analysis on a digital computer. The results of these experiments shows a striking similarity of the results between the two techniques.     

Model of the heart and its applications to the e.c.g.

The human body with the heart as an active electrical source has been modelled by three sets of harmonic polyphase generator voltages or spinning vectors; each set being confined to one of the three standard planes, i.e. the frontal plane, the horizontal plane and the sagittal plane. The equivalent circuit for one of the standard planes, the frontal plane, has been developed and analysed. The identical method of approach for the analysis of e.c.g. voltages in the two other planes has been pointed out and a typical multidimensional case analysis of this model is given. This model has been shown to satisfy a general version of the Burger law and also a general version of the Goldberger augmented lead voltages. The modified Wilson central terminal (w.c.t.) has also been found not to be at the electrical zero of the system. it has further been observed, and confirmed by experiment, that the vector sum of harmonic currents towards the modified w.c.t. is zero, irrespective of the different values of externally connected resistors and without assuming the modified w.c.t. at the electrical zero of the system, i.e. Kirchhoff’s harmonic-current law is satisfied at the modified w.c.t. For equal values of external resistors, the vector sum of the phase voltages and augmented lead voltages also become zero. The model has further been used to study the effect of a number of standard leads placed in the frontal plane while recording the e.c.g., on the maximisation of: (a) the e.c.g. voltages between the standard leads placed over the human body; (b) the e.g.c. voltage between the modified w.c.t. and a reference point on the body; (c) the ratio of the e.c.g. Goldberger voltage to the corresponding phase voltage; and (d) the values of the e.c.g. phase voltages. The effects of the number of electrodes placed in the horizontal and sagittal planes on the respective groups of e.c.g. voltages are discussed. By controlling the number of electrodes in any one of the three standard planes, when the e.c.g. voltages are maximised, it has been shown that the signal-to-noise ratio for those e.c.g. voltages will be increased.     

Delineation of the QRS complex using the envelope of the e.c.g.

A new algorithm for QRS delineation has been developed. Based on the envelope of the e.c.g. signal a delineation function is defined, which yields a single positive pulse for each complex. From this function the onset and end of the QRS or, alternatively, a fiducial point is determined. To remove low-frequency component such as S-T abnormalities without distortion of the QRS complex, a filter with time-varying characteristics is used. The accuracy of the method has been evaluated in a test set of different QRS complexes obtained from coronary care patients. For QRS onset, the standard deviation of the difference between automated and manual determination was 7 ms in normal beats and 14 ms in ectopic beats. With simulated noise added to each waveform an average dispersion of 7 ms was observed in the recognition of the QRS onset at a signal-to-noise ratio of 15 dB. The corresponding dispersion in the location of a fiducial point was 2 ms. Using simulated e.c.g. data, the stability of the method is demonstrated for transitions between different waveform morphologies. Presented in part at ‘Computers in cardiology’, Florence, 23rd–25th September 1981     

Feature characterisation of shape from the frequency spectrum of the e.m.g.

Many studies related to human sensation have been made from the viewpoints of engineering, medical science and psychology. The problem of the quantification of sensation is of great importance and cannot be ignored, although only a few papers on this subject have appeared. This paper discusses the relationship between the recognition of shapes and the electromyogram (e.m.g.) generated in the human on the surface of the muscle involved. To observe the e.m.g., the subject was placed inside a shielded room with Ag−AgCl electrodes located at two points on the skin. The two electrodes were spaced 50 mm apart, but variations of the separation in the range 5–7 mm had no effects on the e.m.g. Three spectral peaks (100, 160, 250 Hz) for the response were obtained for each shape (sphere, tetrahedron, cube). The frequencies corresponding with the peak spectral values in the response are the same, and are independent of the forms. Shapes can therefore be characterised by the spectral forms of the forms.     

A field model of left-right asymmetries in the pattern regulation of a cell

Dynamical models can offer insights into important aspects ofpatterns that recur throughout the biological world, such asglobal symmetries, mirror images, and pattern reversals, etc.Building on phenomenological rules of pattern formation (e.g.E. M. Nelsen and J. Frankel, 1986, Dev. Biol. 114, 53), theauthor developed a mathematical model of a morphogenetic field,expressed as a vector field, which contains the informationto specify a pattern. The dynamics of the field arises fromthe minimization of a nonlinear energy density functional, aquartic polynomial of the field together with field gradienteffects. This model was successfully applied in detail to surfacepatterns observed in right-handed Tetrahymena, where reproducibleregions of left- and right-handed domains appear during regulation.Counterpart experiments on left-handed patterned cells suggestan intrinsic asymmetry between right- and left-handed patterningin this biological system, causing left-handed cells to followdifferent regulation pathways from the right-handed cells. Weshow that the energy minimization approach can account for thisglobally different behaviour in a version of the model withsmall local asymmetry.     

Effect of electrode parameters on the bandwidth of the surface e.m.g. power-density spectrum

The effect of the electrode configuration (unipolar against bipolar), the electrode separation, the electrode position and the electrode contact area on the bandwidth of the power density spectrum of the surface e.m.g. has been studied. The dependence of the half-power point bandwidthB on the interelectrode distanced can be described by the regression function B_Hz=810/d_mm+58. The unipolar electrode configuration yields an e.m.g. signal with the smallest bandwidth. Neither a variation of the electrode position nor a variation of the electrode contact area has a significant effect on the bandwidth of the e.m.g.     

Primary midline developmental field. II. Clinical/epidemiological analysis of alteration of laterality (normal body symmetry and asymmetry)

Lubinsky [Am J Med Genet 3: 23–28, 1987] has suggested that the properties of the midline involve early determinative informational processes and are related to the midline's position and definition of the body's plane of symmetry. Opitz [Am J Med Genet 21: 175-176, 1985, BD: OAS XXIX(1): 3–37 1993] has pointed out that the laterality sequences represent a midline developmental field complex. Thus, bilateral left-sidedness (with asplenia) and bilateral right-sidedness (with polysplenia) have been considered laterality sequences or syndromes if cause is known. Using the malformed infants registered by the Spanish Collaborative Study of Congenital Malformations (ECEMC), we performed a clinical/epidemiological analysis of the relationship between midline defects and alteration of normal body asymmetry and symmetry. The results support the assumption that both conditions could be consequence of disturbances in the midline primary developmental field. © 1995 Wiley-Liss, Inc.     

Summation of fibre potentials and the e.m.g.-force relationship during the voluntary movement of a forearm

A linear mathematical model of the electromyogram (e.m.g.) has been developed for the biceps muscle. The number of motor units (and therefore muscle fibres) contributing to the resultant e.m.g. at any stage of movement has been found from the force analysis of elbow flexion. The depths of various motor units and the phase difference between the recruitment of any two motor units have been formulated using a spiral spread of recruitment sequence. The attenuation of individual motor-unit action potentials due to varying depths has been taken into consideration, and due regard has been taken of the length-tension diagram of a muscle while performing the force analysis. Attention has been focused on the flexion of the elbow joint, in which a method of finding the individual contribution of the biceps and brachialis muscles has been developed and applied. The results predicted by the model have been verified by experiments. The model can also be extended to the e.m.g. of other fast skeletal muscles. The conditions and limitations for such generalisations have been stated and discussed.     

Digital filtering of the e.c.g.—a comparison of low-pass digital filters on a small computer

Algorithms for moving average, recursive and “Fourier transform” low-pass linear digital filters are described, with reference being made to the methods of design. The characteristics, including frequency, phase and impulse responses, of four specific filters are discussed in detail. In addition, some of the practical problems of programming these filters are considered. Factors such as execution times are evaluated in concluding which designs are most appropriate for filtering electrocardiograms.     

不对称入口速度剖面对颈动脉分叉模型不定常流场和壁面切应力的影响

目的研究不对称入口速度剖面对动脉粥样硬化易发部位壁面切应力的影响。方法建立颈动脉TF-AHCB数值模型,设置不对称速度剖面入口条件,用CFD作数值模拟。计算不同时相、不同入口条件下的颈动脉窦流场和壁面切应力分布,分析与动脉粥样硬化有关的流场特征和切应力特征。结果入口速度剖面偏斜可以增加颈动脉窦壁面低切应力区面积,提高切应力梯度。结论不对称入口速度剖面可能是诱发动脉粥样硬化发生的一个危险因子。     

Improvement of the detectability of simulated pathological tremour e.m.g.s by means of demodulation and spectral analysis

In e.m.g.s recorded from patients with pathological tremours, the tremour cannot often be recognised by visual inspection. Demodulation of tremour e.m.g.s improves the detectability of the tremour, but the signal-to-noise ratio remains poor. In this study, demodulated artificially generated tremour e.m.g.s and e.m.g.s from a patient with a pathological tremour were subjected to digital spectral analysis. Power spectra, phase and coherence functions of the modulating and demodulated signals were calculated. The result is that the detectability is improved from a modulation depth of 60% in modulated noise to 2–4% after demodulation and spectral analysis. The results suggest a useful application of the demodulator and analysing software to tremour e.m.g.s in clinical practice.