Showing papers in "Medical & Biological Engineering & Computing in 1995"

Advances in processing of surface myoelectric signals: Part 1.

Abstract: During sustained voluntary or electrically elicited muscle contractions the surface myoelectric signal is nonstationary and it undergoes progressive changes reflecting the modifications of the motor unit action potentials and their propagation velocity. In particular, during sustained electrical stimulation, the evoked signals show progressive amplitude, time scaling and shape modification. The quantitative evaluation of these changes is important for non-invasive muscle characterisation and may be performed in either the time or frequency domain using parametric and nonparametric spectral analysis as well as alternative methodologies. The paper introduces the detection techniques, reviews and compares the methods of spectral estimation based on FFT and autoregressive models, and discusses their applications and limitations in extracting information from the surface myoelectric signal with particular regard to myoelectric manifestations of localised muscle fatigue during sustained contractions.

Computer-aided detection of clustered microcalcifications on digital mammograms.

Abstract: A computer-aided diagnosis scheme to assist radiologists in detecting clustered microcalcifications from mammograms is being developed. Starting with a digital mammogram, the scheme consists of three steps. First, the image is filtered so that the signal-to-noise ratio of microcalcifications is increased by suppression of the normal background structure of the breast. Secondly, potential microcalcifications are extracted from the filtered image with a series of three different techniques: a global thresholding based on the grey-level histogram of the full filtered image, an erosion operator for eliminating very small signals, and a local adaptive grey-level thresholding. Thirdly, some false-positive signals are eliminated by means of a texture analysis technique, and a non-linear clustering algorithm is then used for grouping the remaining signals. With this method, the scheme can detect approximately 85% of true clusters, with an average of two false clusters detected per image.

Effects of electrode geometry and combination on nerve fibre selectivity in spinal cord stimulation.

Abstract: The differential effects of the geometry of a rostrocaudal array of electrode contacts on dorsal column fibre and dorsal root fibre activation in spinal cord stimulation are analysed theoretically. 3-D models of the mid-cervical and mid-thoracic vertebral areas are used for the computation of stimulation induced field potentials, whereas a cable model of myelinated nerve fibre is used for the calculation of the excitation thresholds of large dorsal column and dorsal root fibres. The size and spacing of 2-D rectangular electrode contacts are varied while mono-, bi- and tripolar stimulation are applied. The model predicts that the highest preferential stimulation of dorsal root fibres is obtained in monopolar stimulation with a large cathode, whereas dorsal column fibre preference is highest in tripolar stimulation with small contacts and small contact spacings. Fibre type preference is most sensitive to variations of rostrocaudal contact size and least sensitive to variations of lateral contact size. Dorsal root fibre preference is increased and sensitivity to lead geometry is reduced as the distance from contacts to spinal cord is increased.

Dielectrophoretic separation and enrichment of CD34+cell subpopulation from bone marrow and peripheral blood stem cells

Abstract: Dielectrophoresis has been used to enrich selected cell subpopulations in a mixed cell population by exploiting differential dielectric properties. Six-fold enrichment of stem cells expressing the CD34+ antigen has been achieved for bone marrow samples and peripheral blood, without the requirement for initial chemical treatment associated with immunoadsorption techniques.

Implantable data logging system for heart rate and body temperature: its application to the estimation of field metabolic rates in Antarctic predators.

Abstract: The metabolic rate of free-ranging animals is difficult to measure, but of great importance in understanding the interactions of a species with its environment. Heart rate can, if correctly validated and calibrated, give an estimate of metabolic rate, with both a fine time resolution and over long periods. The telemetry of heart rate is well documented, but is not appropriate over long ranges (possibly several thousands of kilometres) or for diving species. An implantable data logger has therefore been developed for the long term recording of heart rate and body temperature. The logger is built using hybrid and ASIC construction techniques, weighs 20 g and measures 55×24×6 mm. The device is programmable, and its solid-state memory holds over 70 days of data if, for example, heart rate is counted and stored every minute. Current consumption is 155 μA while logging, 50 μA during a programmable initial delay period, and less than 1 μA when the logger closes down after filling its memory. These loggers have been deployed for two field seasons in gentoo penguins, black-browed albatross and fur seals.

Relationship between stimulus amplitude, stimulus frequency and neural damage during electrical stimulation of sciatic nerve of cat.

Abstract: The relation is investigated between stimulus frequency, stimulus pulse amplitude and the neural damage induced by continuous stimulation of the cat's sciatic nerve. The chronically implanted electrodes were pulsed continuously and the effects of the electrical stimulation were quantified as the amount of early axonal degeneration (EAD) present in the nerves seven days after the continuous stimulation. The primary effect of stimulating at 100 Hz rather than 50 Hz was to cause an increase in the slope of the plot of the amount of EAD versus stimulus lower. There was a small amount of EAD in three of the nerves stimulated at 20 Hz, but there was no detectable correlation between the amount of EAD and the stimulus amplitude. This suggests that continuous electrical stimulation of peripheral nerves at a low frequency induce little or no neural damage, even if the stimulus amplitude is very high. A preliminary presentation of the results has been made elsewhere (Agnew et al., 1993)

Electrocatalytic glucose sensor

Abstract: An electrocatalytic sensor in catheter type of construction for determining glucose in body fluids, especially in the blood, having the following features: a tubular body made of bio-compatible material that is subdivided into three sections, a sleeve-shaped reference electrode arranged between the first and the second, or between the second and the third section of the tubular body, a sleeve-shaped working electrode arranged--correspondingly--between the second and the third, or between the first and the second section of the tubular body, said working electrode having a slit extending in longitudinal direction over the full length, a hydrophilic membrane stretched over the working electrode whose ends are guided through the slit into the interior of the electrode and which is held in the slit by a wedge made of bio-compatible material, a counter-electrode which seals the one end of the tubular body, and lead wires to the electrodes arranged within the tubular body which are brought to the outside through the other end of the tubular body.

Cerebral and muscle oxygen saturation measurement by frequency-domain near-infra-red spectrometer.

Abstract: Tissue oxygen saturation quantification was obtained using a frequency-domain multi-source method based on two wavelength light-emitting diodes. Brain saturation was 60.3 +/- 1.1% (n = 12). Brachioradial muscle saturation declined during forearm ischaemia and maximal voluntary contraction from 73.7 +/- 1.8 and 74.7 +/- 1.8% at rest to 44.2 +/- 3.3 and 61.4 +/- 2.9%, respectively.

Design optimisation of planar electrolytic conductivity sensors.

Abstract: Planar conductivity sensors are the subject of increasing interest as basic transducers for biosensors. The high degree of control of the performance characteristics undoubtedly forms an important argument in favour of conductivity-based sensing. The paper provides an outline of the design rules to be followed if an optimal design of a planar conductivity cell is required. Based on a simplified model, it is shown that the required accuracy establishes a lower limit to the overall sensor dimensions. This lower limit is expressed as a minimum longitudinal path length necessary to obtain the desired accuracy. Given an available area, the optimum ratio of electrode-width over inter-electrode spacing for a basic two-electrode structure is shown to be close to unity. Furthermore, it is shown that the decomposition of the two electrodes into an interdigitated structure decreases the accuracy of the device if all other parameters are considered constant. If the sensing region has to be limited to within a thin sensitive layer, the splitting is proposed of one of the electrodes into a compound electrode. The optimum lay-out of this compound structure is calculated as a function of the layer thickness.

Transducers for foot pressure measurement: survey of recent developments.

Abstract: Recent advances in the development of transducers for the measurement of vertical and shear forces acting on the plantar surface of the foot are reviewed. Barefoot and in-shoe discrete and matrix transducers are reviewed in terms of structure, operation, performance and limitations. Examples of capacitive, piezoelectric, optical, conductive and resistive types of transducer are presented. Where available, the current clinical status is specified.

Individually shaped volume conductor models of the head in EEG source localisation.

Abstract: Inverse solution techniques based on electroencephalograph (EEG) measurements have become a powerful means of gaining knowledge about the functioning of the brain. A model of the head and a potential computation method are necessary to describe the EEG problem mathematically. The generation of realistically shaped three-compartment models of the head is discussed. The isolated problem approach for the boundary element method is applied to develop a fast and accurate numerical solution of the EEG forward problem. Accuracy studies with this approach show that dipole positions can be reconstructed within a distance of 3 mm from the original positions. Inverse simulations indicate that the incorporation of the individual head shape may significantly influence the reconstructed dipole position but not its magnitude and orientation, in comparison with the commonly used three-sphere model. However, the presence of noise in the simulated potential data affects the solutions based on realistically shaped models more than those of the simple three-sphere model. The increased sensitivity of the former models to noise in the data remains a serious drawback for their practical application to EEG source localisations.

Development of a portable tissue oximeter using near infra-red spectroscopy

Abstract: NON-INVASIVE AND continuous monitoring of physiological conditions during cxcrcise is very important for clinical diagnosis, sports medicine, healthcare monitoring etc. For the continuous monitoring of cardiovascular conditions, several types of instruments have been developed, such as the Holter ECG (HOLTER, 1961; ISHn3A et al., 1990) and ambulatory blood pressure monitors (YAMAKOSHI, 1991); these instruments are now widely accepted for clinical and research use. On the other hand, for monitoring metabolic conditions which also provide important physiological information, only a few methods have been developed, such as MRS (WANG et al., 1990; ZATINA et al., 1986); they are expensive and complicated systems, and are not appropriate for use during exercise. The optical method is more convenient to use and is capable of detecting tissue metabolism, as has been shown in previous work (CHANCE et al., 1992). Therefore, this method may be useful as a portable monitor of metabolic conditions during exercise. Many attempts have been made to use this method for research. Study by the optical method began with the work of Kramer and Millikan, followed by the work of Chance and Weber on isolated tissue metabolism monitoring (KR~IER, 1935; MmLm~aq, 1937; CHANGE and WEBER, 1963). Jobsis first showed that near infra-red (NIR) region light has the characteristic of excellent penetration through biological tissues (JOBStS; 1977) after this the NIR method then attracted attention. Cope and Delpy and Rolfe et aL applied the multiwavelength NIR method to neonates, and Chance et al. applied simple ~jal wavelength spectroscopy for muscle studies (COPE and DELPY, 1988; ROLFE et aL, 1991; CHANCE et al., 1992). In recent years, Chance et. al. have developed quantitative noninvasive methods by using timeand frequency-resolved spectroscopy to determine the optical path length (CHANCE et aL, 1988; 1990). By using time-resolved spectroscopy, Delpy et al. esftmated the optical path length through tissue, and 9 Ferrari et a/. examined the spectral properties of muscle tissue (DELPY et al., 1988; FEBRARI et aL, 1992). However, many of these instruments, which have complex

Advances in processing of surface myoelectric signals: Part 2.

Abstract: The paper focuses on the analysis of myoelectric evoked potentials and their progressive scaling, as well as morphological changes using orthogonal basis functions with essentially finite time support; and the compression of the information content using principal component analysis. The application of the Hermite-Rodriguez and the associated Hermite functions is discussed as a means to provide compact information about the shape of the M-wave or of the power spectral density function of either voluntary or electrically elicited myoelectric signals; a means to estimate scaling factors; and a means to describe and classify nonstationarities. The principal component analysis shows the possibility of a compression ratio of at least 10: 1 in the storage of M-wave sequences. The paper also describes three methods for the estimation of delay between similar signals, and therefore for estimation of conduction velocity. They are based on normalised integrals, Fourier transform matching and matching in the time domain. In particular conditions they provide different results for the same pair of signals. The concept of delay and the performance of these methods are reviewed and discussed. The paper is not exhaustive. It has the main objective of making the reader aware of the wealth of methods available for nonstationary myoelectric signal analysis and conduction velocity estimation, and of the need to use them with knowledge of their respective advantages, disadvantages, peculiarties and limitations.

Beam optics design of compact gantry for proton therapy

Abstract: A new proton therapy facility for the treatment of deep-seated tumours is being assembled. The proton beam will be applied to the patient under computer control, using dynamic scanning of a focused proton pencil beam to produce a complete three-dimensional conformation of the dose to the target volume. The beam will be applied to the supine patient using a compact isocentric gantry for protons. By combining the scanning of the beam with the beam optics and by mounting the patient couch eccentrically on the gantry, the diameter of the rotating structure can be reduced to 4 m, which is the smallest diameter designed so far for a proton gantry. The paper describes the project especially from the point of view of the optics of the beam transport system of the gantry, including the beam line used to inject the beam into the gantry.

Cycle-to-cycle control of swing phase of paraplegic gait induced by surface electrical stimulation.

Abstract: Parameterised swing phase of gait in paraplegics was obtained using surface electrical stimulation of the hip flexors, hamstrings and quadriceps; the hip flexors were stimulated to obtain a desired hip angle range, the hamstrings to provide foot clearance in the forward swing, and the quadriceps to acquire knee extension at the end of the swing phase. We report on two main aspects; optimisation of the initial stimulation parameters, and parameter adaption (control). The initial stimulation patterns were experimentally optimised in two paraplegic subjects using a controlled stand device, resulting in an initial satisfactory swinging motion in both subjects. Intersubject differences appeared in the mechanical output (torque joint) per muscle group. During a prolonged open-loop controlled trial with the optimised but unregulated stimulation onsets and burst duration for the three muscle groups, the hip angle range per cycle initially increased above the desired value and subsequently decreased below it. The mechanical performance of the hamstrings and quadriceps remained relatively unaffected. A cycle-to-cycle controller was then designed, operating on the basis of the hip angle ranges obtained in previous swings. This controller successfully adapted the burst duration of the hip flexors to maintain the desired hip angle range.

Neuromuscular stimulation selectivity of multiple-contact nerve cuff electrode arrays.

Abstract: The feasibility of an electrical stimulation method selectively for activating skeletal muscles innervated by a common peripheral nerve trunk has been investigated. The method utilises ‘snugly’ fitting nerve cuffs that incorporate an array of 12 electrodes. These electrodes have been tested as four longitudinally aligned tripoles (located 90° apart on the cuff inner surface). In acute experiments on rabbit sciatic nerves, we have found that tripolar stimulation with this implant system is in general highly selective. ‘Field steering’, wherein a subthreshold transverse current is used in combination with a longitudinal tripolar current, tends to increase the selectivity of stimulation. On a rabbit sciatic nerve, a combination of adjacent longitudinal tripoles of the 12 electrode array generally yields a stimulation performance similar to that which would be expected if a 24 electrode array is used. This system may find a use in functional neuromuscular stimulation applications which require highly selective control over multiple muscles.

Multi-frequency static imaging in electrical impedance tomography: Part 1 instrumentation requirements

Abstract: Static images of the human body using electrical impedance tomography techniques can be obtained by measuring at two or more different frequencies. The frequencies used depend on the application, and their selection depends on the frequency behaviour of the impedance for the target tissue. An analysis using available data and theoretical models for tissue impedance yields the expected impedance and boundary voltage changes, therefore setting the measurement instrument specifications. The instrument errors produced by different sources are analysed, and, from this analysis it is possible to determine the feasibility of building the instrument, the limit values for some parameters (or components) and indications on the most suitable design of critical parts. This analysis also shows what kinds of error can be expected in the reconstructed images. It is concluded that it is possible to build an instrument with limited errors, allowing static images to be obtained. An instrument has been built that meets some of the design requirements and fails in others because of technological problems. In vivo images obtained with this instrument will be presented in Part 2 of this work.

Computational simulation of blood flow in human systemic circulation incorporating an external force field

Abstract: A quasi-one-dimensional non-linear mathematical model for the computation of the blood flow in the human systemic circulation is constructed. The morphology and physical modelling of the whole system (arteries, capillaries and veins) are completed by different methods for the different vessel generations. A hybrid method is used to solve the problem numerically, based on the governing equation (continuity, momentum and state equations), the input boundary conditions and the predetermined initial conditions. The two-step Lax-Wendroff finite-difference method is used to compute variables for each individual vessel, and the characteristic method is employed for the computation of internal boundary conditions of the vessel connection and the input and output system boundary conditions. Using this approach, blood flow, transmural pressure and blood velocity are computed at all vessel sites and for each time step. The pressure and flow waveforms obtained show reasonable agreement with clinical data and results reported in the literature. When an external conservative force field is applied to the system, the results computed from the model are intuitively correct. The term representing the external pressure added to the system by the muscle, which represents active control on the cardiovascular system, is also embodied in this model.

Analysis and development of AC biosusceptometer for orocaecal transit time measurements.

Abstract: axisymmetric vibrations of a spheroidal model of the head,' J. Biomech., 9, pp. 803-812 LIU, Y. K., CHANDRAN, K. B., and VoN ROSENBURG, D. U. (1975): 'Angular Acceleration of viscoelastic(kelvin) material in a rigid spherical shell--a rotational head injury model,' J. Biomech., 8, pp. 285-292 MERCHANT, H. C., and C~uSPtNO, A. J. (1974): \"A dynamic analysis of an elastic model of the human head,' .I. Biomech., 7, pp. 295-301 MISRA, J. C., and CI~,KRAVARrHY, S. (1984): 'A study on rotational brain injury,' J. Biomech., 7, pp. 459-466 NmA, (1990): Numerically Integrated Element for System Analysis, Engineering Mechanics Research Centre, Michigan Ntnu Ag.g.AS (1975): 'Dynamic analysis of a fluid filled spherical sandwich shell--a model of the human head,' J Biomech., 8, pp. 275-284 RUAN, J. S., KHALIL, T. B., and KING, A. I. (1991): 'Human head dynamic response to side impact by finite element modelling,' ASME J Biomech. Eng., 113, pp. 276-283 SHUGAR, T. A., and KATONA, M. G. (1975): 'Development of finite element model of the human head.' ASCE EM3, 109, E173, pp. 223-239 WARD, C. C., N[KRAVESH, P. E., and THOMPSON, IL B. (1978): 'Biodynamie finite element models used in brain injury research,' J Aviation Space, Env. Med., pp. 136-142 WARD, C. C., L--'KAN, M., and NAHUM, A. (1981): 'InWacranial pressure----a brain injury criterion.' Proc. 24th STAPP Car Crash Conf., pp. 163-185

Interface mechanics in external prosthetics : review of interface stress measurement techniques

Abstract: Instrumentation to measure accurately the stresses at the interface of a residual limb and prosthetic socket has a strong potential for use in prosthetic treatment. As a tool in the clinical setting, the device would allow a clinician to identify sites of excessive loading, information which could then be combined with clinical assessment of skin quality to determine regions of potential skin breakdown. Stress distributions for different prosthetic designs could be compared, facilitating a clinician's judgement to determine the optimal design for a patient. The instrumentation would have additional use in research as an evaluation tool for computer-based finite-element (FE) models. Stump-socket FE models predict stress distributions for proposed socket designs, thus offering advantages over interface stress measurement because evaluation can be conducted before a prosthesis is fabricated or put on an amputee patient. However, FE models must first be proven valid against experimental measurements before they can be considered accurate predictors of interface stresses. Current interface stress measurement techniques are described, with a concentration on a physical explanation of the advantages and limitations with each technique. New emerging technologies are discussed which are instruments that have been described but for which no data collected on amputees have been reported in the literature. The important new features of those technologies are also discussed.

Detection of brainstem auditory evoked potential by adaptive filtering.

Abstract: A method of detecting brainstem auditory evoked potential (BAEP) using adaptive signal enhancement (ASE) is proposed and tested in humans and cats. The ASE in this system estimates the signal component of the primary input, which is correlated with the reference input to the adaptive filter. The reference input is carefully designed to make an optimal and rapid estimation of the signal corrupted with noise, such as ongoing EEG. With a good choice of reference input, it is possible to track the variability of BAEP efficiently and rapidly. Moreover, the number of repetitions required could be markedly reduced and the result of the system is superior to that of ensemble averaging (EA). To detect BAEP in cats, only 30 ensemble averages are needed to obtain a reasonable reference input to the adaptive filter, and, for humans, 350–750 ensemble averages are sufficient for a satisfactory result. Using the LMS adaptive algorithm, individual BAEP can be obtained in real-time.

Numerical approximation of mathematical model for absorption of subcutaneously injected insulin

Abstract: A pharmacokinetic model is modified to enable quantitation of subcutaneous insulin absorption following insulin injections of soluble insulin and monomeric insulin analogues. The model for soluble insulin includes diffusion, equilibration between hexameric and dimeric insulin and absorption of dimeric insulin molecules. Numerical approximation is carried out by modelling the whole system as a capacitor-resistor network with lumped elements and discrete sources and sinks. By means of the analytical solution for monomeric-insulin absorption, it can be shown that the approximation scheme yields sufficiently accurate results. The modified model for soluble insulin demonstrates dose- and concentration-dependent insulin absorption within the range of therapeutic concentrations and volumes. Additionally, parameters are estimated from published glucose-clamp data. The results of the data fitting indicate that the model presented is adequate for pharmacological studies. The model is suitable for individual parameter estimation from the time course of plasma insulin or from the disappearance curves of radiolabelled injected insulin.

Impression technique for the assessment of oedema: comparison with a new tactile sensor that measures physical properties of tissue

Abstract: To measure tissue oedema, the impression technique and a new tactile sensor technique are compared and evaluated in a silicone rubber model and in an in vivo rat testis model. The principles of the two techniques differ in that the impression technique evaluates interstitial fluid flow FT and peak force F(0) when tissue is compressed, whereas the tactile sensor evaluates the hardness/softness or change in resonance frequency Δf when a vibrating rod is attached to tissue. Both techniques can detect changes in silicone hardness/softness or in hormone-induced changes of testes, interstitial fluid. Although both F(0) and FT are significantly correlated to Δf in the experiments, it is concluded that F(0) is the most promising impression parameter to give valuable information about the hardness of living tissue as compared with Δf. The comparison indicates that the impression technique in the most easy, to interpret, non-invasive tool to assess tissue oedema so far developed.

Non-polarisable dry electrode based on NASICON ceramic.

Abstract: A NASICON-type ceramic (high sodium ion conductor) is proposed to record bioelectric signals. The electrode does not need gel before its application. The principle of the measurements is based on a sodium ion exchange between the skin and the material. Electrical measurements performed in saline solutions show that the electrode is slightly polarisable. The skin-electrode impedance was investigated. The impedance decreases as a function of the time of application. The resistive component is the major source of the impedance change. This can be explained by the perspiration process which occurs immediately with time after the application of the NASICON-based electrode on the skin. The skin condition is also an important parameter. NaCl saline solution or abrasion causes the resistance to decrease markedly.

OKAS-3D: optoelectronic jaw movement recording system with six degrees of freedom.

Abstract: OKAS-3D is a further development of the single floating circle target tracker. This tracker consists of a cathode ray tube display, a lens in front of the display and a circular light-sensitive photocell placed in the image field of the lens. A small circular trace generated on the screen is focused around the photocell. The sinusoidal electrical output of the photocell contains all the relevant information regarding the position of the photocell relative to the image of the circular light trace. This gives the tracker the properties of a servo-controller with position feedback. In OKAS-3D three pairs of photocells are located on two lightweight frames attached to the upper and lower frontal teeth by individually adapted clutches. By using the formulas of rigid body mathematics, the motion of any point of the mandible can be reconstructed. The system permits a high sampling frequency of at least 300 Hz per photocell co-ordinate. The noise, linearity and accuracy are better than 0.08 mm, 0.07 mm and 0.13 mm for points in the lower incisal region, and better than 0.25 mm, 0.17 mm and 0.27 mm for points in the condylar region. Thus jaw movements can be recorded with a high spatial and temporal resolution.

Dynamic cross-spectral analysis of biological signals by means of bivariate ARMA processes with time-dependent coefficients.

Abstract: RAPID PROGRESS in the development of computer equipment and soRware techniques underlies the progress in investigating increasingly complex biological signals. The possibility of the simultaneous analysis of several measurements calls for the use of multivariate methods in analysing such multidimensional signals. In this sense, investigations into the relationship between the different components of multidimensional signals are of great importance. Therefore, more spectral analysis methods for biosignals now include bivariate spectral parameters. In particular, coherence spectra are also applied along with povcer spectra. In the ease of stationary signals, the calculation of cross spectra and coherence spectra based on Fourier transforms (FT) is the algorithm of choice in current strategies of analysis. However, most biological signals can be modelled only as a composition of stationary inter~Js, with very short durations. These signals also contain artefacts and noise. Methods based on the FT are limited by poor frequency resolution for short data intervals. The aim of this work is to introduce an adaptive fitting procedure for bivariate b & , M A models with time-varying parameters. Owing to the reoarsive structure of all algorithms involved, a continuous calculation of cross-spectral density is possible and allows a detailed time-coherence analysis. The ability of the estimations of adaptation to structural changes in the signals is demonstrated. The algorithm was tested in two main applications; EEG analysis and microcirculation in the retina.

Wavelets as alternative to short-time Fourier transform in signal-averaged electrocardiography.

Abstract: The paper reports experience of using the wavelet transform to build time-frequency distributions of the terminal portion of the QRS-complex. We used wavelets of Morlet at 12 scales, grouped in three sets, to analyse the frequency range 33–404 Hz. On the same patient data we applied the short-time Fourier transform and compared the results. Both representations reflected the time-frequency contents and detected irregular structures in the terminal portion of the QRS complex. The wavelet transform revealed more adequately QRS prolongations characteristic of patients prone to ventricular tachycardia. We may conclude that the wavelet transform can be a flexible alternative to short-time Fourier transform.

Conoidal dipole model of electrical field produced by the human stomach

Abstract: Spontaneous depolarisation and repolarisation due to ionic exchange are the main properties of smooth muscle cells in the human stomach. This change in the distribution of electrical charge results in the creation of an electric field. The field manifests itself as a potential difference (biovoltage), recorded both in vitro and in vivo and known as gastric electrical activity (GEA). The aim of the paper is to describe a computer model of this electric phenomenon, considering all anatomical and electrophysiological particularities of the stomach, and to simulate real in vivo experiments with a computer. In the proposed model, the depolarised smooth muscle cells are represented as organised electrical dipoles distributed with known density in an annular band that moves distally with increasing velocity. Computer simulations of in vivo experiments using this model not only give the waveform, duration, amplitude and frequency of GEA, but they also represent the phase lag between different channels, the difference in propagation velocity along greater and lesser curvatures, and the electric coupling between different parts of the stomach. The effects of changed electrode configuration, surface area and distance from the stomach are described. Mathematical modelling is done in spherical co-ordinates, and the simulations are performed in a specially designed user-friendly IBM PC environment. Some of the unsolved problems in cutaneous electrogastrography are also discussed.

Real-time compression of myoelectric data utilising adaptive differential pulse code modulation.

Abstract: The myoelectric signal, obtained by either surface or needle electrodes, is used in many areas of clinical research and diagnosis. The conventional method of storing such information is in digitised form on a computer. However, the bandwidth of the signal and the required resolution result in large memory requirements. Adaptive differential pulse code modulation is investigated as a method of reducing the memory requirements for myoelectric data storage. In this scheme, a 12-bit sample is reduced to four bits, thus reducing the memory requirements by a factor of three. In reality, this compression ratio is closer to 4∶1 owing to the fact that the widths of most memories are organised as multiples of eight bits.

Bio-acoustic signals from stenotic tube flow: state of the art and perspectives for future methodological development

Abstract: To study the degree of stenosis from the acoustic signal generated by the turbulent flow in a stenotic vessel, so-called phonoangiography was first suggested over 20 years ago. A reason for the limited use of the technique today may be that, in the early work, the theory of how to relate the spectrum of the acoustic signal to the degree of the stenosis was not clear. However, during the last decade, the theoretical basis for this and other biological tube flow applications has been clarified. Now there is also easy access to computers for frequency analysis. A further explanation for the limited diagnostic use of bio-acoustic techniques for tube flow is the strong competition from ultrasound Doppler techniques. In the future, however, applications may be expected in biological tube flow where the non-invasive, simple and inexpensive bio-acoustic techniques will have a definite role as a diagnostic method.