Showing papers in "Medical & Biological Engineering & Computing in 1989"
TL;DR: The review evaluates thresholds of peripheral nerve stimulation by complex current waveforms using a neuroelectric model employing Frankenhaeuser-Huxley membrane nonlinearities to derive excitation thresholds for monophasic and biphasic pulse sequences, as well as sinusoidal stimuli.
Abstract: The review evaluates thresholds of peripheral nerve stimulation by complex current waveforms. A neuroelectric model employing Frankenhaeuser-Huxley membrane nonlinearities is used to derive excitation thresholds for monophasic and biphasic pulse sequences, as well as sinusoidal stimuli. The model, along with principles of magnetic field induction, is used to derive criteria of acceptability for exposure to time-varying magnetic fields. Applications to pulsed gradient fields from magnetic resonance imaging devices are discussed.
278 citations
TL;DR: Although these forces were shown to act synchronously on both legs, they appeared to be asymmetrical in nature, with a typical vectorial pattern for every individual, which generally differed from that of normal subjects.
Abstract: Bilateral force measurements on the supporting limbs in postural sway while standing still were made to evaluate post-cerebral-vascular accident (CVA) patients during rehabilitation. Normal subjects of the same age group were tested as controls. From the force tracings obtained, three oscillation frequencies were identified, with orders of magnitudes of 7, 1 and 0.1 Hz, respectively, of which the middle frequency, i.e. that corresponding to 1 Hz, was selected for subsequent processing and analysis. These included the determination of relative sequence of the force vectors on both feet and evaluation of timings and amplitudes of the waveforms. Weight-bearing imbalance was defined in the vertical direction to express the difference between the average forces supported by each of the legs. In the horizontal plane, two parameters were defined: sway total activity (SA), to represent the vector summation of the absolute values of the horizontal force components acting on both legs; and asymmetry (ASYM) to express the difference in activities between the two legs. The results presented disclose the reactive force patterns acting on each of the legs of post-CVA hemiplegic individuals, in comparison with normal individuals. Although these forces were shown to act synchronously on both legs, they appeared to be asymmetrical in nature, with a typical vectorial pattern for every individual, which generally differed from that of normal subjects. Sway activity was found to be significantly higher in hemiplegics compared with the normal controls.
124 citations
TL;DR: Alternative, operator-independent methods for establishing HRV from continuous long-term ECG recordings of postmyocardial infarction patients seem to be as effective as previously reported methods which rely on operator-dependent data post-processing techniques.
Abstract: Reduced heart rate variability (HRV) has been reported as a predictor of mortality in recent myocardial infarction patients. However, its automated assessment in long-term ECG recordings is complicated by recording noise and beat-recognition errors which necessitate filtering of the computer-established sequence of beat-to-beat intervals, and visual checking and manual editing of the long-term recordings, making the whole method operator-dependent. To develop a fully automated method for analysis of HRV from 24 h ECG recordings, five filtering algorithms were combined with three methods of expressing HRV numerically and used to compare two groups of patients undergoing 24 h tape recordings of the ECG within the first two weeks after myocardial infarction. One group comprised 15 patients who later suffered death or ventricular tachycardia, the other group comprised 15 randomly selected uncomplicated cases. Using the same two groups of patients, three different methods of expressing HRV on a beat-to-beat basis were also compared empirically. The results show that alternative, operator-independent methods for establishing HRV from continuous long-term ECG recordings of postmyocardial infarction patients seem to be as effective as previously reported methods which rely on operator-dependent data post-processing techniques.
90 citations
TL;DR: In this paper, a noninvasive and noncontact technique based on the principle of laser speckle interferometry has been developed to record the cardiac displacements observed on the chest wall.
Abstract: A noninvasive and noncontact technique based on the principle of laser speckle interferometry has been developed to record the cardiac displacements observed on the chest wall. These displacements are then reconstructed in the form of three-dimensional plots, during the P, QRS and T-waves of the ECG. A comparison of these patterns shows that the mechanical activity of each region varies significantly during these phases of cardiac cycle. As these displacements depend on the clinical status of the heart, its use with a cardiac patient shows the functional changes of the affected regions in the form of alteration of these patterns.
83 citations
TL;DR: Theoretical relationships between the velocity waveform indices and the lumped resistances and capacitance of the system were obtained for different input pressure functions and the Fourier pulsatility index was evaluated for an arbitrary pressure function, and shown to behave like (PI)2 for the umbilical artery waveform.
Abstract: Various empirical indices such as the pulsatility index (PI) are widely used for quantitative analysis of Doppler ultrasound velocity waveforms. The physical interpretation of these indices was studied using a mathematical model. Although the method has more general applicability, this particular study was concerned with the umbilical-placental circulation. A lumped element electrical circuit equivalent was used, with each arterial branch represented by a resistor and a capacitor. The placental villous bed was modelled by a two-step parallel branching structure. Placental vascular disease was modelled either as obliteration of a fraction of the terminal branches, or as a fractional decrease in the radius of the vessels. The main features of both normal and abnormal umbilical artery waveforms can be reproduced by this simple model. Theoretical relationships between the velocity waveform indices and the lumped resistances and capacitance of the system were obtained for different input pressure functions. Over a wide range of physically reasonable conditions, the umbilical artery PI is approximately proportional to the ratio of the placental resistance to the umbilial artery resistance. The PI also depends on the pulsatility of the input pressure waveform. The Fourier pulsatility index was evaluated for an arbitrary pressure function, and shown to behave like (PI)2 for the umbilical artery waveform.
71 citations
TL;DR: An expert system for the automated detection of spikes and sharp waves in the EEG has been developed and the performance of the expert system is compared with an EEGer using a 320s segment from an EEG containing epileptiform activity.
Abstract: 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.
67 citations
TL;DR: In vitro experiments show that in vitro variation of the intracellular volume of blood by dilution and by shrinking and swelling of blood cells is detectable by this method, and in vivo too the method seems to detect intra- and extracellular fluid volumes separately.
Abstract: A method to measure intra- and extracellular conductivity is evaluated. In vitro experiments show that these two variables can be measured separately. The conductivity appears to depend on the concentration and fluid volume of the compartment concerned. In vitro variation of the intracellular volume of blood by dilution and by shrinking and swelling of blood cells is detectable by this method. In vivo too the method seems to detect intra- and extracellular fluid volumes separately. The course of these two variables during different strategies of haemodialysis is determined.
64 citations
TL;DR: The relationship between nerve stimulation, pulse amplitude and isometric muscle force was measured to investigate recruitment of motor units and indicated that small overlap of recruited motor unit groups occurred more often for intrafascicular than for extraneural electrodes.
Abstract: The relationship between nerve stimulation, pulse amplitude and isometric muscle force was measured to investigate recruitment of motor units. Force addition experiments were performed to obtain insight in the intersection of motor unit groups recruited by different electrodes. Intrafascicular and extraneural multielectrode configurations were used for nerve stimulation. Experiments were performed on rats. The common peroneal nerve was stimulated and the forces of the tibial anterior and extensor digitorum longus muscles were measured isometrically. Recruitment was more stable for intrafascicular electrodes than for extraneural electrodes. Especially for intrafascicular electrodes no strict inverse recruitment was observed. Force addition experiments indicated that small overlap of recruited motor unit groups occurred more often for intrafascicular than for extraneural electrodes.
63 citations
TL;DR: An adaptive cancellation technique is developed, which is simple and easy to implement for online processing and proved by experiments to be very efficient, i.e. the respiratory artefact can be completely cancelled, while the gastric signal component is not affected.
Abstract: Electrogastric measurements are useful for medical research and in clinical diagnosis. The measurements, however, contain very heavy respiratory artefact. Existing conventional frequency-domain filters cannot be used because of the possible overlap of the frequencies of the gastric signals and respiratory artefact. In the paper, the methods of measuring cutaneous and intraluminal gastric signals and reference respiratory signals are described. An adaptive cancellation technique is developed, which is simple and easy to implement for online processing. It is proved by experiments to be very efficient, i.e. the respiratory artefact can be completely cancelled, while the gastric signal component is not affected. Other possible applications in biomedical signal analysis are also discussed.
61 citations
TL;DR: Good stability of the leg was achieved during the cycling motion and this would appear to be a major advantage of functional neuromuscular stimulation cycling over functional neuroscular stimulation gait.
Abstract: The paper describes a device (Paracycle), that uses functional neuromuscular stimulation to exercise subjects, explore FNS technology and provide paraplegics with locomotion. The Paracycle is a four-wheeled cycling vehicle that may be used as a stationary exercise device or for locomotion. It incorporates a fully adjustable seat and an electric motor to assist or retard the cycling motion, as well as speed and direction controls. Furthermore, it has braces to fasten the feet to the pedals and to stabilise the ankle, as well as gearing to enable subjects with very small forces to move the vehicle forward. Results are presented for two cases studies. Good stability of the leg was achieved during the cycling motion and this would appear to be a major advantage of functional neuromuscular stimulation cycling over functional neuromuscular stimulation gait. Important areas for future research include a better understanding of the biomechanics of functional neuromuscular stimulation cycling and the development of Paracycle-like devices that can be used independently by paraplegics.
60 citations
TL;DR: A method is presented to measure transcellular fluid shifts during haemodialysis based on a simplified model of the electrical admittance of biological tissues that allows for the measurement of intracellular and extracellular conductivities and their ratios.
Abstract: A method is presented to measure transcellular fluid shifts during haemodialysis based on a simplified model of the electrical admittance of biological tissues. It allows for the measurement of intracellular and extracellular conductivities and their ratios. The method is noninvasive, clean and harmless, and can be easily computerised in order to be performed continuously. A typical example is given of a recording during haemodialysis.
TL;DR: The single unit power spectrum is investigated and the effects of firing rate mean and variance changes evaluated and results show that spectrum peaks will shift with firing rate and the median frequency is weakly dependent on firing rate.
Abstract: Changes in the power density spectrum of myoelectric signal with contraction level have been reported in the literature. These changes can be induced by a number of possible factors including recruitment of differing types of units, conduction velocity changes and firing rate changes. In the paper the single unit power spectrum is investigated and the effects of firing rate mean and variance changes evaluated. Motor unit signal simulation and experiments are carried out to verify predictions. The results show that spectrum peaks will shift with firing rate and the median frequency is weakly dependent on firing rate.
TL;DR: A bottom-up approach to the recognition problem in ECG waveforms is presented in the paper and the peak patterns and the segment patterns are considered primitive (nondecomposable) patterns.
Abstract: A bottom-up approach to the recognition problem in ECG waveforms is presented in the paper. This approach is based on the assumption that ECG waveforms are composite entities that can be decomposed into other simpler entities, these into other simpler ones etc., until peak patterns and segment paterrns are obtained. The peak patterns and the segment patterns are considered primitive (nondecomposable) patterns. The recognition is achieved by first recognising the primitive patterns and then recognising the (higher) ECG patterns using a bottom-up procedure.
TL;DR: Eating, drinking and writing have been achieved by two C4 quadriplegics using a system for generation of upper limb function in the totally paralysed arms of high level spinal cord lesion subjects.
Abstract: A system is presented for generation of upper limb function in the totally paralysed arms of high level spinal cord lesion subjects. The stimulation part of the system is voice operated, computer controlled, and uses high-resolution surface stimulation to generate arm and hand movements. Splinting, suspension, and voluntary upper trunk and shoulder girdle movements complement the stimulationgenerated movements. Eating, drinking and writing have been achieved by two C4 quadriplegics using the system.
TL;DR: It is pointed out that the stomach should be localised before the measurement and the electrodes should be attached along the longitudinal axis of the stomach, to show that the propagation direction of the electrogastric activities cannot be observed from cutaneous recordings.
Abstract: Electrogastric signals have been successfully measured both intraluminally and cutaneously. although it has been claimed by several researchers that the propagation direction of the electrogastric activities cannot be observed from cutaneous recordings, it is the aim of the paper to show that it is feasible. The reason why the propagation direction has never been observed from cutaneous recordings is that the reported methods for the abdominal measurements are not adequate. In the paper it is pointed out that the stomach should be localised before the measurement and the electrodes should be attached along the longitudinal axis of the stomach.
TL;DR: Quantifying skin blood flow from skin temperature reheat rates is shown to be limited by a lack of sensitivity and a dependence on subcutaneous fat thickness, although dynamic thermography is able to provide useful information on regional variations in skin perfusion which could not be reliably obtained from static temperature measurements alone.
Abstract: A new method of quantifying dermal perfusion on a regional basis using a dynamic thermographic technique is investigated. The technique is based on the relationship between dermal perfusion and the rate of skin surface reheating following the application of a transient cold challenge predicted by a theoretical model. Measurements were made using images from a Philips thermographic camera under rigorously controlled conditions. Experimentation on undisturbed volar forerm skin of normal subjects showed that measurements could be repeated with good accuracy but that differences in normalised reheat temperatures between subjects were highly dependent on subcutaneous fat thickness. Comparisons between normal and occluded foreams indicated that reheat temperatures were not sensitive to changes in low levels of dermal perfusion. Conversely, stimulation of dermal blood flow with prostaglandin E2 did produce significant differences from control conditions, but quantifying the axtent of this hyperaemia was limited by the effects of intersubject variations in fat thickness. Quantifying skin blood flow from skin temperature reheat rates is shown to be limited by a lack of sensitivity and a dependence on subcutaneous fat thickness, although dynamic thermography is able to provide useful information on regional variations in skin perfusion which could not be reliably obtained from static temperature measurements alone.
TL;DR: The result of the experiment shows that the BCGs of chickens and quail embryos are detected fully after about two-thirds of the incubation period has passed, which will enable the monitoring system to perform long-term HR measurement for developing avian embryos up to hatching.
Abstract: A noninvasive heart rate (HR) monitoring system for avian embryos has been developed based on the ballistocardiogram (BCG). The BCG was detected using a phonograph cartridge as a record of the velocity of the minute ballistic movements of the eggshell, which are generated by recoil and impact of heart contraction and blood ejection. The autocorrelation coefficients (ACCs) of the detected signal were computed to confirm whether the detected signal contained ballistic movement. An envelope of ACC was calculated by the monitoring system to measure the intervals between peaks and/or highly correlated parts in the ACC, and then the system obtained HR by measuring these intervals. To demonstrate the valid range of the detecting method, the BCGs of chickens and Japanese quail embryos of different ages were measured. The result of the experiment shows that the BCGs of chickens and quail embryos are detected fully after about two-thirds of the incubation period has passed. The monitoring system will enable us to perform long-term HR measurement for developing avian embryos up to hatching.
TL;DR: From Newton's equation and the continuity equation, an equivalent analogue circuit model can be derived for each small segment of the coronary arteries for good agreement with the reported effects of stenoses and heart rate on coronary blood flow.
Abstract: From Newton's equation and the continuity equation, an equivalent analogue circuit model can be derived for each small segment of the coronary arteries. Sapoznikov divided the coronary artery tree into 116 segments. By replacing each segment with its analogue circuit model, a final incremental network model was derived. The model was tested using typical physical parameters under normal conditions, as well as in the presence of coronary artery stenosis. In the case of stenosis, the arteriolar flow with and without autoregulation were compared. The model shows good agreement with the reported effects of stenoses and heart rate on coronary blood flow.
TL;DR: Although this is a kind of impedance plethysmograph, the volume change in a limb segment can be detected by this method without passing electric current through the limb.
Abstract: A new plethysmograph, the electric impedance cuff, was designed for the indirect measurement of blood pressure, volume elastic modulus Ev and compliance Ca in human limb arteries. This comprises a compression chamber filled with electrolyte solution and a tetrapolar electric impedance plethysmograph whose electrodes are placed inside the chamber; the former for controlling transmural arterial pressure Pt, and the latter for detecting total limb volume Vo, mean arterial volume
$$\bar V_a $$
and its variation ΔVa. Systolic and mean arterial pressure in the upper arms, forearms and fingers were measured by detecting pulsatile impedance variation during the gradual (3–5 mm Hg per heart beat) increase (or decrease) in chamber pressure by the volume oscillometric technique. Diastolic and pulse pressure ΔP were calculated from these pressure values. Compliance Ca=ΔV/ΔP and volume elastic modulus
$$E_v = \Delta P/(\Delta V_a /\bar V_a )$$
were recorded at various Pt levels, controlled by the compression pressure. Although this is a kind of impedance plethysmograph, the volume change in a limb segment can be detected by this method without passing electric current through the limb.
TL;DR: A new, noncontact system for measuring the heart rate of avian embryos in the egg has been developed using a laser speckle phenomenon based upon detection of egg movements attributable to cardiac contractions of the embryo by measuring the intensity fluctuation of Speckle produced in the proximity of the egg under laser light illumination.
Abstract: A new, noncontact system for measuring the heart rate of avian embryos in the egg has been developed using a laser speckle phenomenon. The system was based upon detection of egg movements attributable to cardiac contractions of the embryo by measuring the intensity fluctuation of speckle produced in the proximity of the egg under laser light illumination (i.e. noncontact measurement). The applicability of the noncontact system to determine the heart rate of developing chick embryos was examined simultaneously with a contact system employing an audio cartridge. Both systems were found to be feasible in determining the heart rate of embryos during the late prenatal and paranatal stages. With the aid of adeques signal processing, the measurement of cardiogenic movements of the egg can be used to count the heart rate during the middle stages of incubation.
TL;DR: Evidence is given that it is advisable to remove DC levels from the recorded data and the least-squares approach to estimation of the model parameters and hence of the EEG waveform, including the response, are described.
Abstract: Work undertaken to investigate the effect on EEG responses of ocular artefact removal by proportional electro-oculogram subtraction using the least-squares method is reported. The ocular artefact model and the least-squares approach to estimation of the model parameters and hence of the EEG waveform, including the response, are described. Results are presented to show that the response shapes become modified if ocular artefact removal is implemented recursively. This happens because the response is incorrectly treated as part of the random background EEG. The solution is to incorporate a model of the response within the ocular artefact removal algorithm. The results of tests on simulated data confirm these conclusions. The results of the incorporation of response models in removing ocular artefacts from CNV recordings are presented. Even with modelling recursive ocular artefact removal is found to modify the shape of the CNV, and so reliable results can only be obtained if the removal is implemented nonrecursively. Evidence is given that it is advisable to remove DC levels from the recorded data.
TL;DR: It is concluded that the basic frequency response model of a muscle under conditions similar to voluntary contraction consists of a linear, second-order system which is robust and independent of control strategy and force perturbation level.
Abstract: The frequency response model of the soleus muscle of the cat was determined as a function of various firing rate and recruitment control strategies and at various force oscillation levels We found that the basic frequency response models of the muscle during individual force oscillations at various control strategies in which the motor unit population of the muscle was fully recruited to obtain 50 per cent and up to 100 per cent of the maximum force, either concurrently with firing rate increase or at constant firing rate, were nearly identical The model consisted of a second-order, linear low-pass filter with double poles at 1·85 Hz and a pure time delay of 16 ms The model resulting from only firing rate increase from the frequency of fusion of the smallest motor unit to the maximum tetanic rate of the muscle while all the motor units were continuously active was nonlinear, and depended on the force's oscillation level This nonlinear response of the rate coding process is also identified as the source of the increased harmonic distortion in the model where the initial 50 per cent of the force was generated by fully recruiting all the motor units, and the final 50 per cent of the force was generated by firing rate increase We concluded that the basic frequency response model of a muscle under conditions similar to voluntary contraction consists of a linear, second-order system which is robust and independent of control strategy and force perturbation level
TL;DR: The method was found to discriminate between preselected elderly patients at risk on the one hand, and non-risk patients and healthy young adults on the other hand and no differences in blood flow responses were found, suggesting that age per se is not a factor in the formation of pressure sores.
Abstract: A method for measuring the susceptibility of a patient to develop decubitus ulcers is described and initially evaluated. It is based on an indirect, noninvasive measurement of the transient regional blood flow response after a test pressure load which simulates the external stimulus for pressure-sore formation. This method was developed to determine the individual risk of a patient and to study the subfactors which contribute to the susceptibility. This would also offer the possibility of evaluating the effect of preventive treatment aimed at reducing the susceptibility. The method was found to discriminate between preselected elderly patients at risk on the one hand, and non-risk patients and healthy young adults on the other hand. No differences in blood flow responses were found between the non-risk elderly patients and the healthy young adults. This suggests that age per se is not a factor in the formation of pressure sores. In the risk group the recovery time after pressure relief was found to be three times as long as the duration of the pressure exercise. This indicates that the recovery time after pressure exercise may be as important as the period of pressure exercise in deducing the risk of developing decubitus ulcers.
TL;DR: A comparison is made between the features of auditory evoked responses and of the contingent negative variation, and the usefulness of predictive statistical diagnosis in differentiating between subject groups is illustrated by application to normal subjects and Huntington's chorea patients.
Abstract: The techniques used and the results obtained in a spectral analysis of two specific responses in the human electroencephalogram are presented in this paper. The purposes are to show how the techniques may be applied to the necessarily short lengths of EEG data and to illustrate these techniques and the useful results obtained by relevant examples. The necessary data-processing procedures and precautions for transforming from the time to frequency domain are presented in a tutorial fashion. The importance of augmenting zeros, choice of the most appropriate data window and pretransformation of the data to avoid the combined effects of energy loss and low frequency content biasing caused by windowing is explained. The pros and cons of the tapered-cosine (Tukey) and Kaiser-Bessel windows are illustrated. The usefulness of applying certain statistical tests, which are based on a physical model of the responses, to the harmonic components of the responses is demonstrated. Thus a comparison is made between the features of auditory evoked responses and of the contingent negative variation, and the usefulness of predictive statistical diagnosis in differentiating between subject groups is illustrated by application to normal subjects and Huntington's chorea patients.
TL;DR: A finite-difference computer model has been used to determine the potential distributions arising from a dipole current source aligned parallel to the axis of bounding cylinders, finding the radial position of this source had large and nonlinear influence on the potentials along the dipole axis.
Abstract: A finite-difference computer model has been used to determine the potential distributions arising from a dipole current source aligned parallel to the axis of bounding cylinders. The radial position of this source had large and nonlinear influence on the potentials along the dipole axis. The accuracy of the computer simulation was established from comparison with an analytic solution of a simple geometry. Measurements using a conductance catheter in saline-filled cylinders also demonstrated the dependence of the conductance on the radial position. The dependence of the potential distribution on the radial position of the dipole places limits on the ultimate accuracy of the conductance catheter technique when used for the measurement of ventricular volume. Radial movement of the catheter within the ventricular cavity, resulting in changes in the potential distribution, could explain some artefacts that appear on volume recordings from the conductance catheter.