Showing papers in "Medical & Biological Engineering & Computing in 1981"
TL;DR: In this paper, the ascending aorta of eight anaesthetised dogs under control conditions, after volume expansion and after haemorrhage, was measured by means of two different methods.
Abstract: Pressure and flow were measured in the ascending aorta of eight anaesthetised dogs under control conditions, after volume expansion and after haemorrhage. For each case the characteristic impedance of the proximal aorta Zc was determined by means of two different methods. Zc was calculated in the time domain as the slope of the pressure-flow relationship in early ejection. For each case, six different values were also obtained in the frequency domain by averaging the impedance moduli in six different frequency ranges. Time- and frequency-domain values agreed well. Statistical analysis showed that both methods can be used to study changes in Zc. However, the time-domain method is easier to apply and does not require steady-state conditions.
93 citations
TL;DR: The special mechanism of the ionic conduction in the keratin layer is indicated as one of the causes for non-linearity in the current dependency of the skin impedance and in Lissajous figures.
Abstract: This paper describes the non-linear electrical properties of the skin during the passage of a sinusoidal current from the standpoint of the constant-current method. The non-linearity occurs in the current dependency of the skin impedance and in Lissajous figures. It exhibits both rapid and slow variations. The concept of a non-linear impedance and its equivalent circuit are introduced for a sinusoidal voltage. With regard to the current dependency of the impedance it can be said that both the starting point and the degree of the dependency vary with frequency and impedance. The nonlinearity is more apparent with a larger current, a lower frequency, and a higher impedance. with an increasing current, the ionic conductance increases and the polarisation admittance decreases. Lissajous figures are formed when the voltage is distorted notably from the sinusoidal wave form. Detailed investigations are undertaken for the elliptic figures, third harmonics, rectification, and breakdown of the skin appearing with a decrease of the frequency and increase of the current. Finally, the special mechanism of the ionic conduction in the keratin layer is indicated as one of the causes for non-linearity.
84 citations
TL;DR: A computer-based system has been developed that enables the continuous measurement of cardiac output at rest as well as during exercise and may facilitate the physiological investigation of cardiac function during exercise.
Abstract: A computer-based system has been developed that enables the continuous measurement of cardiac output at rest as well as during exercise. The respiratory and motion artefacts appearing in the first derivative of the transthoracic impedance change (dZ/dt) were eliminated by adopting an ensemble averaging technique. A sufficiently high correlation was observed between cardiac outputs determined by the impedance and CO2 rebreathing methods. The system may facilitate the physiological investigation of cardiac function during exercise.
76 citations
65 citations
TL;DR: Initial results have shown that an informative display which would be almost impossible to obtain with conventional electrodes can readily be produced, and that the long-term stability of the device is good.
Abstract: The detection of extracellular potentials in nervous tissue with conventional microelectrodes has many limitations. The number of sites at which activity can be detected in one experiment is small, and the noise performance of the system is frequently poor. A monolithic integrated circuit array of microelectrodes and buffer amplifiers has been built, enabling potentials to be detected simultaneously at nine sites, and substantially reducing the noise caused by electrostatic pick-up. The electrodes and buffer amplifiers were made on a silicon substrate using a fabrication process based on standard i.c. processing techniques. With an off-chip multiplexer, the potentials at each electrode have been displayed simultaneously on a normal oscilloscope in experiments on slices of rat brain tissue. Initial results have shown that an informative display which would be almost impossible to obtain with conventional electrodes can readily be produced, and that the long-term stability of the device is good.
61 citations
TL;DR: The utility and sufficiency of Karhunen-Loeve expansions for reducing the dimension of electromyographic patterns was demonstrated and Cluster analysis was used to separate the constituent patterns into major groups.
Abstract: The population distribution of the electromyographic patterns from several muscles in 25 normal subjects walking at free speed was investigated. The utility and sufficiency of Karhunen-Loeve expansions for reducing the dimension of electromyographic patterns was demonstrated. Cluster analysis was used to separate the constituent patterns into major groups.
48 citations
44 citations
TL;DR: A method of locating analytically the precise position in the object space of an image point such as a foreign body using simple stereo X-ray pictures and digitised co-ordinates of common image points identified in the stereo pictures is described.
Abstract: A method of locating analytically the precise position in the object space of an image point such as a foreign body using simple stereo X-ray pictures and digitised co-ordinates of common image points identified in the stereo pictures is described.
37 citations
TL;DR: An extension of this concept is introduced, which avoids the error caused by variations in bubble volume by means of a modulation of the ambient pressure, realised in practice by a low frequency ultrasound wave of known amplitude.
Abstract: Fairbank andScully (1977) have suggested using the interaction between ultrasound and air bubbles in noninvasive manometry. In this paper, an extension of this concept is introduced, which avoids the error caused by variations in bubble volume. This is accomplished by means of a modulation of the ambient pressure, realised in practice by a low frequency ultrasound wave of known amplitude. It is further suggested that use be made of the pulse-echo amplitude from a single bubble as the primary parameter from which the hydrostatic pressure can be derived. The new method has been analysed theoretically and by a model experiment. Problems expected in clinical applications are discussed. The most promising areas for its application are intracranial and intrauterine pressure measurements.
35 citations
TL;DR: A new heterodyne ultrasound doppler blood velocitymeter has been constructed that operates in two switchable frequencies and is switchable in pulsed or continuous mode.
Abstract: A new heterodyne ultrasound doppler blood velocitymeter has been constructed. The instrument operates in two switchable frequencies (1·5 MHz and 6 MHz) and switchable in pulsed or continuous mode.
34 citations
TL;DR: The study of the relation between gastric myo-electrical activities recorded from serosal and cutaneous electrodes is hindered by the poor quality of the cutaneous signal, which could be minimised by suitable filtering of the signal.
Abstract: The study of the relation between gastric myo-electrical activities recorded from serosal and cutaneous electrodes is hindered by the poor quality of the cutaneous signal. This hindrance could be minimised by suitable filtering of the signal. Since it is not yet clear which aspects of the cutaneous signal constitute valuable information, the filter process should not affect phase, amplitude, frequency and waveform of the gastric component, while noise components should be suppressed strongly. The system design of a modified adaptive filter that meets these requirements is described. The filter was implemented on a digital Nova 2 minicomputer. the filter performance is described and tested.
TL;DR: A simple design, which fulfils these needs, is proposed and is proposed for hermetic packages that are incorporated in neurological prostheses.
Abstract: The size, shape and materials of construction for hermetic packages that are incorporated in neurological prostheses are considered. A simple design, which fulfils these needs, is proposed.
TL;DR: After a survey of therapeutic electrical stimulation a model is proposed which could explain some of the phenomena observed when stimulating patients with deficits of the locomotor system and shows why stimulation could not increase the unbalanced state and thus impair the clinical picture of the patient.
Abstract: After a survey of therapeutic electrical stimulation a model is proposed which could explain some of the phenomena observed when stimulating patients with deficits of the locomotor system. Introducing non-linear characteristics of synaptic efficacies, the afferent diffuse barrage of signals due to electrical stimulation is selectively ‘channelled’ to synapses which are not at their saturation points. Electrical therapy thus either improves the balance between general excitation and inhibition or it does not exert any therapeutic effect. The model also shows why stimulation could not increase the unbalanced state and thus impair the clinical picture of the patient.
TL;DR: The time sequences for impedance and potential variations do not have the same form when the skin is stressed as when it is relaxed, giving the relationship between potential and deformation a nonlinear character.
Abstract: Potential and impedance variations were studied with varying mechanical stress upon the skin. The size of the potential variations in the skin and the mechanical stress possess a nonlinear relationship which varies between individuals. The impedance variations did not bring about the potential variations. The time sequences for impedance and potential variations do not have the same form when the skin is stressed as when it is relaxed. The rapid initial potential variation upon stressing had a calculated rise time of 30 ms. The rise time during relaxation was 40s. The difference in rise time gives the relationship between potential and deformation a nonlinear character.
TL;DR: It is concluded that the use of the modified adaptive filter forms a valuable tool in the study of the electrogastrographic signal.
Abstract: The modified adaptive filter method described in Part 1 was applied to 16 stretches of (cutaneous) electrogastrographic signal of 17·07 min duration. A signal-to-noise ratio improvement of about 8 dB was achieved. The most characteristic feature of the filter method appeared to be that wave-form and phase of the gastric component of the electrogastrographic signal are preserved. It is concluded that the use of the modified adaptive filter forms a valuable tool in the study of the electrogastrographic signal.
TL;DR: In vivo applications of laser Doppler velocimetry to the measurement of blood flow in narrow vessels are likely to be confined to certain accessible vascular systems.
Abstract: The application of laser Doppler velocimetry to the measurement of blood flow in narrow vessels is considered. Particular attention is paid to the effect of the finite laser probe volume (velocity gradient averaging). Successful in vitro results are reported but it is concluded that in vivo applications are likely to be confined to certain accessible vascular systems.
TL;DR: No significant difference exists between meanin vivo ϱ values determined for the three species at corresponding haematocrits despite different thoracic anatomy and circulatory dynamics, and the best estimate of mean ϱin vivo within the normal Hct range is 135Ω cm.
Abstract: The accuracy of impedance cardiography for measurement of stroke volume (SV2) has been controversial. This could be, in part, due to the use in the Kubicek formula of the bench-determined blood resistivity (ϱ)-haematocrit (Hct) relationship, which does not take into account factors such as complex blood-velocity movements. In the present studyin vivo, ϱ was calculated in dog, rabbit and man from the rearranged Kubicek formula, ϱ=(SV. Zo2)/(L2. dZ/dt max T); the stroke volumes used in the calculation being derived at different Hcts in the different species from the independent techniques of electromagnetic flowmeter, direct Fick, and direct Fick and thermodilution, respectively. Thein vivo ϱ-Hct relationship is linear, inverse and nearly constant over the range of Hcts tested (dog 26–62%, man 31–48%, rabbit 37%). No significant difference exists between meanin vivo ϱ values determined for the three species at corresponding haematocrits despite different thoracic anatomy and circulatory dynamics. Thus, the best estimate of mean ϱin vivo within the normal Hct range is 135Ω cm, the use of which will result in a SV2 accuracy of better than ±10%.
TL;DR: A real-time spectrum analyser interfaced to an Intel 8085 microprocessor system and programmed to calculate pulsatility index in real time, which has proved to be very reliable and most useful.
Abstract: One of the disadvantages of indices derived from ultrasonic Doppler signals is that they are not normally available instantaneously. In an attempt to overcome this problem, a real-time spectrum analyser has been interfaced to an Intel 8085 microprocessor system and programmed to calculate pulsatility index in real time. The only additional patient signal required is a simple three-lead e.c.g. which is used for timing purposes. Although the device has only been in clinical use for a short time it has proved to be very reliable and most useful.
TL;DR: A hermetically-sealed glass-packaged implantable multichannel auditory nerve-stimulator was developed that can be used both as a hearing aid for the deaf—in conjunction with an external wearable sound processor—and as a research tool for the development of speech processing strategies.
Abstract: A hermetically-sealed glass-packaged implantable multichannel auditory nerve-stimulator was developed that can be used both as a hearing aid for the deaf—in conjunction with an external wearable sound processor—and as a research tool for the development of speech processing strategies. It allows the use of stimulation frequencies up to 5kHz, contains eight completely independent channels, has a very low power consumption and is exceptionally transparent to digital as well as analogue stimulation waveforms. It was implemented in thin film hybrid technology using c.m.o.s. active circuits. The supply power as well as the stimulation signal are transmitted over a single 12MHz f.m.-carrier.
TL;DR: A method of gait analysis was used to estimate the loads in the knee joint and an analysis was made of the repeatability of the measurements for a group of 72 patients.
Abstract: A method of gait analysis was used to estimate the loads in the knee joint. An analysis was made of the repeatability of the measurements for a group of 72 patients. Data from 418 patients were reviewed to show the variation with coronal angle of the knee of the loading.
TL;DR: Four human adult mandibles were selected, a rosette strain guage was applied in the angle region bilaterally and a single element strain gauge was applied on the posterior surface of both condyles and condylar necks to simulate the action of the anterior temporal, masseter and internal pterygoid muscles.
Abstract: Four human adult mandibles were selected, a rosette strain guage was applied in the angle region bilaterally and a single element strain gauge on the posterior surface of both condyles and condylar necks. Each mandible, together with a brass replica of the upper arch and the glenoid fossa, were placed together on a supporting frame and loads were applied to simulate the action of the anterior temporal, masseter and internal pterygoid muscles. Strains were recorded in maximum intercuspation and after insertion of a rubber frame between the lateral teeth. Strains in the angle region were greater on the working side than on the balancing side. However, in the condylar region the balancing side strains were higher than on the working side. This can be attributed to the different orientation of strains on the two sides.
TL;DR: The ringdown counting method demonstrated a reasonably reproducible pattern when counting events against load; that is, each fracture remained essentially quiet until over 50% of load to failure had been applied as discussed by the authors.
Abstract: 11 New Zealand white rabbits with 45 degree midshaft oblique osteotomies were stressed in shear while monitoring acoustic emission events. The ringdown counting method demonstrated a reasonably reproducible pattern when counting events against load; that is, each fracture remained essentially quiet until over 50% of load to failure had been applied. The rate of events to load increased sharply just before and during failure. This technique has clinical possibilities.
TL;DR: This expression is derived based on a non-linear viscoelastic model, with elastic moduli depending exponentially on strain, in accordance with the results of previous measurements, and shows good agreement with the values predicted by the above mentioned expression.
Abstract: In order to relate the results of measurements on strips of urinary bladder wall to clinical measurements on the intact urinary bladder, an expression is derived for the dependence of the viscoelastic response of bladder-wall material on strain rate This expression is based on a non-linear viscoelastic model, with elastic moduli depending exponentially on strain, in accordance with the results of previous measurements The results of measurements performed on strips of bladder-wall material at different strain rates show good agreement with the values predicted by the above mentioned expression
TL;DR: The computer software and hardware of the first computer-controlled radiotherapy unit in the UK is discussed and has been used to give conformation therapy using a dynamic technique.
Abstract: The computer software and hardware of the first computer-controlled radiotherapy unit in the UK is discussed. The basic unit is a MS 90 Mobaltron (made by T.E.M. Ltd.) which has been modified by the manufacturers to operate under computer control. Since January 1980 it has been used to give conformation therapy using a dynamic technique. The unit and the principle of this technique are briefly discussed in the introduction.
TL;DR: An implantable hermetic package for the intersection unit of a row-and-column visual prosthesis is described and some figures for production yield and in vitro performance are included.
Abstract: An implantable hermetic package for the intersection unit of a row-and-column visual prosthesis is described. Some figures for production yield andin vitro performance are included.
TL;DR: The magnetic field arising from action currents associated with the propagation of an action potential along a cylindrical fibre is considered and the equivalent current sources of the magnetic field are precisely the difference in axial current density on each side of the membrane.
Abstract: This paper considers the magnetic field arising from action currents associated with the propagation of an action potential along a cylindrical fibre. The equivalent current sources of the magnetic field are precisely the difference in axial current density on each side of the membrane. Fibre bundles are considered by superposition. The total magnetic field varies as 0(1/R3) hence it is quadrupolar. The equivalent source is more strongly related to the discontinuity in conductivity between the membrane andsurrounding media than directly to the ionic (primary) currents.
TL;DR: Of the features considered, many were found to be workload related, but only five, namely a power density variance, a right to left power ratio, an anterior to posterior phase angle and two coherency ratios, showed task-dependent behaviour.
Abstract: The e.e.g. was recorded from the left and right parietal and temporal regions of the scalps of 23 normal subjects while they were mentally at rest and then while they were executing tasks intended to engage, firstly, their dominant cerebral hemispheres, and secondly then their nondominant hemispheres. In each of the alpha and gamma frequency bands, 43 features of the e.e.g. expressed in terms of average power densities, coefficients of power density variation, coherencies and phases were calculated for each of the subjects. A method of separating the features which were related to the nature of the mental task from those which were related only to the mental workload represented by each of the tasks is presented. Of the features considered, many were found to be workload related, but only five, namely a power density variance, a right to left power ratio, an anterior to posterior phase angle and two coherency ratios, showed task-dependent behaviour. In this latter group, only two features point to the lateralisation of verbal and spatial cognitive processes to the dominant and nondominant cerebral hemispheres. The problem of the confounding of cerebral and mygenic effects and possible bias in the results owing to this effect is discussed.