Showing papers in "Medical & Biological Engineering & Computing in 1982"
TL;DR: Preliminary results are presented which suggest that the method of stimulating nerves using a time-varying magnetic field has the advantages over conventional electrical stimulation of being painless, and free of charge-storage artefact.
Abstract: THIS note describes a method of stimulating nerves using a time-varying magnetic field. Preliminary results are presented which suggest that the method has the advantages over conventional electrical stimulation of being painless, and free of charge-storage artefact. It is well known that nerve trunks are stimulated by externally applied voltage or current impulses, and this is regularly used as both a diagnostic and therapeutic aid (BUCHTAL and ROSENFALCK, 1966). Unfortunately this method of electrical stimulation has some drawbacks which cannot readily be overcome non-invasively. When a stimulus is applied via surface electrodes, most of the current will flow between the electrodes through the top living layers of the skin. If the nerve is relatively superficial, a significant proportion of the applied current will flow in the vicinity of the nerve, thereby stimulating it. However, the current cannot simply be increased to reach deep lying nerves, because it would be painful. The nerve fibres which convey pain impulses to the brain have endings in the skin and because the current density here is high, they will be stimulated despite their lower absolute sensitivity to stimulation than other fibres. In addition, high current densities near the surface of the skin can cause tissue damage. The use of a time-varying magnetic field to induce a current in the vicinity of a nerve, and thereby stimulate it, has been tried as a way of overcoming these difficulties by a number of authors, e.g. OBERG (1973), MAASS and ASA (1970), who used invasive methods. HALLGREN (1973) has described a circuit for a non-invasive magnetic stimulator, but did not give examples of the results obtained, or details of the position and current of the stimulation coil. The prototype 'magnetic stimulator ' used is a flat circular coil carrying a time-varying current to produce an
186 citations
TL;DR: It was concluded that the maximum volume pulsation occurs when the transmural pressure was equal to zero, i.e. the arterial wall isunloaded.
Abstract: To analyse the mechanism of the occurrence of the maximum volume pulsation in an artery during the application of counterpressure, the static, and dynamic pressure-volume (P-V) relationship was measured in excised arterial segments placed in a compression chamber. Teh volume change caused by perfusing the segment with a sinusoidal pump was detected by an infrared photoelectric plethysmograph during the application of counterpressure. It was revealed that the characteristic change in the amplitude of volume pulsation in response to the gradual change in the counterpressure was due to the nonlinearity of the P-V relation of the artery, and that the value of the counterpressure showing the maximum pulsation amplitude was coincided with the mean arterial pressure. From this evidence it was concluded that the maximum volume pulsation occurs when the transmural pressure was equal to zero, i.e. the arterial wall isunloaded. Based on the results a new oscillometric method for the indirect measurement of systolic and mean arterial pressure in an arterial segment was designed. Through the comparison of data with the actual pressure produced by perfusing the segment, it was demonstrated that systolic and mean arterial pressure can be indirectly measured by this technique within ±3 mm Hg error.
135 citations
TL;DR: The polarisation impedance of the platinum electrode was measured in physiological saline over six decades of frequencies down to 1 mHz and demonstrated the validity of Schwan’s limit law of linearity at very low frequencies.
Abstract: The polarisation impedance of the platinum electrode was measured in physiological saline (0·9% NaCl) over six decades of frequencies down to 1 mHz. The applicability, of Fricke’s phase angle rule was verified down to 10 mHz. The resistive shunt which emerges at lower frequencies was shown to be equivalent to the direct current (d.c.) impedance of the interface. A Cole-Cole (1941) type of relaxation model is proposed to describe the interface behaviour over all frequency ranges. Nonlinear polarisation measurments have demonstrated the validity of Schwan’s limit law of linearity at very low frequencies.
121 citations
TL;DR: With a new oscillometric method equipped with a transmittance infrared photoelectric plethysmograph, indirect systolic, and mean arterial pressures were measured in 12 normotensive and hypertensive subjects and a fairly good correlation between the pairs of simultaneous data was obtained.
Abstract: With a new oscillometric method equipped with a transmittance infrared photoelectric plethysmograph, indirect systolic, and mean arterial pressures were measured in 12 normotensive and hypertensive subjects with systolic and mean arterial pressures ranging from 55 to 163 mmHg and from 95 to 200 mmHg, respectively. The pressure values obtained by this method were compared with direct measurements of the brachial intra-arterial pressure recorded simultaneously. A fairly good correlation between the pairs of simultaneous data from these two methods were obtained.
106 citations
TL;DR: Two new simple models for the arterial tree input impedance are presented, obtained by paralleling the characteristic resistance of the 3-element windkessel model (Westerhof, 1968) with an inductance.
Abstract: Two new simple models for the arterial tree input impedance are presented. The first is a 4-element windkessel model, obtained by paralleling the characteristic resistance of the 3-element windkessel model (Westerhof, 1968) with an inductance. The second is a tube model with a complex load, which is characterised by four parameters also. The parameters of these models are estimated from aortic root pressure and flow, which are either simulated by a complex numerical model of the peripheral arterial tree or measured in dogs.
103 citations
TL;DR: In this paper, the potential and impedance variations were measured for electrode movements in electrolytes, and the streaming potentials were electrolyte-concentration dependent and in the order of 10μV.
Abstract: Movement-induced potentials of streaming potential type were studied in various electrode configurations. The geometric design of the electrode was important for the reduction of noise generated by the movements of gel. Potential and impedance variations were measured for electrode movements in electrolytes. The impedance variations were small and the streaming potentials were electrolyte-concentration dependent and in the order of 10μV. The same type of study was carried out for electrodes applied to the skin. The conclusion from this experiment is that skin deformation potentials dominate the disturbance pattern in this type of recordings.
51 citations
TL;DR: A system is described using up to 16 transducers to measure the pressure under the foot, the analogue signals from which are digitised online and stored on magnetic tape for subsequent computer analysis.
Abstract: The design of a suitable transducer to measure the pressure under the foot it presented. The transducer is attached to the sole of the foot and can, if required, be worn inside shoes. A system is described using up to 16 transducers, the analogue signals from which are digitised online and stored on magnetic tape for subsequent computer analysis. Examples of the data obtained form patients with arthritic involvement of the feet and from normal subjects, both walking with and without shoes, are given. The importance of the clinical application of this type of measurement is discussed.
51 citations
TL;DR: A generalisation of the equation used by Salazar (1964) to fit the pressure-volume relationship of normal human lungs between FRC and TLC is found to fit a variety of circulatory elements.
Abstract: A generalisation of the equation used bySalazar (1964) to fit the pressure-volume relationship of normal human lungs between FRC and TLC is found to fit the pressure-volume relationship of a variety of circulatory elements. The equation contains only two fundamental physiologic parameters: one a compliance constant k and the other a maximum element volume Vm. Fits of this equation to published atrial, ventricular, veneous, and arterial data are presented. Combined with the Poiseulle relationship, this equation is shown to fit data of flow resistance against transmural pressure for the pulmonary vascular system of a dog.
50 citations
TL;DR: In this paper, a simple comparison of gait assessments done at 50 frames per second with that done at 25 frames per seconds was made, and it was concluded that, when considering frame rate requirements inexpensive standard 16 mm cine cameras (24 fps) or television cameras (930 fps) can be used rather than the far more expensive higher speed systems.
Abstract: Conclusive analytical evidence is provided to show that higher speed cameras and optoelectric systems are not normally necessary for higher-level biomechanical assessments of pathological gait. The evidence comes from a simple comparison of gait assessments done at 50 frames per second with that done at 25 frames per second. Kinetic assessments that were sensitive to sampling rates showed insignificant differences. Example analyses of angular velocities, total body energy and joint muscle moments of both normal and pathological gait demonstrate the redundancy of the 50 Hz frame rate. Thus it was concluded that, when considering frame rate requirements inexpensive standard 16 mm cine cameras (24 frames per second) or television cameras 930 frames per second) can be used rather than the far more expensive higher-speed systems.
48 citations
47 citations
TL;DR: To explain the rapid, positive waves often seen in the skin-potential response a new theory based upon electrokinetic phenomena is proposed.
Abstract: The change in electrical characteristics of the skin owing to the psychogalvanic reflex has been investigated. The importance of using parallel values of admittance data is underlined because sweat-duct conductivity is anatomically in parallel with the rest of the skin. The response has been found to be mainly conductive, but small capacitive changes can appear. The effect of conductivefilm formation on the inside of the duct walls is discussed and emphasised. It is postulated that the dorsal side of the hand is as reflex-sensitive as palmar sites, but the lack of continuous sweat-gland activity and the conductive duct-wall films of dry skin often make the response disappear on nonpalmar skin sites. GSR on non-palmar skin sites can be a source of error if not adequately considered because just a deep breath may double skin conductance in seconds. To explain the rapid, positive waves often seen in the skin-potential response a new theory based upon electrokinetic phenomena is proposed.
TL;DR: The incorporation of artefact detection procedures into a simple peak searching algorithms, resulted in 99% of breaths being correctly detected.
Abstract: A series of algorithms are described which detect breaths, from the respiratory waveform obtained from indirect respiratory monitors. The major problem is that the waveform contains artefacts which must be identified as such and not identified as breaths. The algorithms are based around the detection of the peaks and troughs in the respiratory waveform. The incorporation of artefact detection procedures into a simple peak searching algorithms, resulted in 99% of breaths being correctly detected.
TL;DR: Time-distance parameters of the stride of 20 hemiplegic patients in their early stage of rehabilitation were studied in a follow-up program to characterise the gait of these patients and objective criteria were estabilished to express progress in the locomotor rehabilitation process ofThese patients.
Abstract: Time-distance parameters of the stride of 20 hemiplegic patients in their early stage of rehabilitation were studied in a follow-up program to characterise the gait of these patients. Based on the characteristics obtained, objective criteria were estabilished to express progress in the locomotor rehabilitation process of these patients. By grading the improvement of the parameters investigated during the follow-up period, the velocity was found first and thereafter, in a descending order, stride length, distance symmetry, double support time and stance time.
TL;DR: It is shown that singular value decomposition (s.v.d.) is an excellent tool for studying the limit properties of a feasible solution for the inverse problem in electrocardiography and leads to a noise filtering algorithm, which at the same time results in useful data reduction.
Abstract: In the paper it is shown that singular value decomposition (s.v.d.) is an excellent tool for studying the limit properties of a feasible solution for the inverse problem in electrocardiography. When s.v.d. is applied to the transfer matrix, relating equivalent heart sources to the skin potentials, it provides a measure of the observability. In an example presented, a series of orthonormal potential patterns on a pericardial surface are found in an order of decreasing observability. When s.v.d. is applied to a data matrix, consisting of skin potentials as a function of time and position, one finds the normalised principal components both in time and space. An appropriate use of the singular values leads to a noise filtering algorithm, which at the same time results in useful data reduction. Comparison of spatial potential patterns derived from both the transfer matrix and the data matrix may, finally, be used to evaluate the assumptions on the transfer.
TL;DR: The monocrystalline antimony pH electrode has several advantages over the conventional pH glass electrode; better accuracy, shorter rise time, smaller dimensions, and its use in combination with pressure sensors has added a new dimension to the diagnosis of functional disorders in the gastro-oesophageal region.
Abstract: Monocrystalline antimony electrodes have been shown to be suitable for thein vivo determination of pH in blood, tissue and in the upper gastro-intestinal canal. Thanks to their small dimensions it has been possible to mount them into conventional manometry catheters for oesophageal investigation. The monocrystalline antimony pH electrode has several advantages over the conventional pH glass electrode; better accuracy, shorter rise time, smaller dimensions. The monocrystalline antimony electrode has been used for long-term registration of gastro-oesophageal reflux, for the oesophageal acid clearing test and for identification of the pH gradient zone between the gastric and oesophageal mucosa. Its use in combination with pressure sensors has added a new dimension to the diagnosis of functional disorders in the gastro-oesophageal region.
TL;DR: The results suggest that the transfixation pin arrangement is the most important determinant of pelvic fixation stability, and that further investigation of posterior screw-plate fixation is warranted.
Abstract: The effectiveness of external fixation in the stabilisation of pelvic ring fractures was studied in a laboratory cadaveric series. Shearing displacements occurring at sacroiliac joint and symphysis pubis dislocation sites, due to simplified longitudinal loading of the sacrum in an Instron unit, were monitored using variable-impedence transducers. The rigidity of fixation was compared for the Slatis and the Bonnel single anterior frames, for coupled and uncoupled double anterior frames, and for combined anterior-plus-posterior fixation achieved with separate transfixation pin clusters, with through-and-through pin clusters, or with a posterior screw plate. The data showed that the use of posterior fixation provided greatly enhanced stabilisation compared to that achieved with anterior fixation alone. The complex double anterior frames performed only slightly better than did the simpler single anterior frames. In no case, however, was it possible to recover rigidity levels approaching those of the intact pelvis. The results suggest that the transfixation pin arrangement is the most important determinant of pelvic fixation stability, and that further investigation of posterior screw-plate fixation is warranted.
TL;DR: A new instrument for the monitoring of eye fixation and pupil size during the visual field examination is described, adapted to clinical measurements, requiring minimum subject training and minimising costs.
Abstract: A new instrument for the monitoring of eye fixation and pupil size during the visual field examination is described. Particular attention has been given to design an instrument adapted to clinical measurements, requiring minimum subject training. co-operation, discomfort and set up time. Relatively free head movements are permitted by the evaluation of eye orientation from the displacement of the corneal reflection with respect to the centre of the pupil. Considerable thought has also been given to the minimising of costs to permit the introduction of the instrument in the ophthalmic clinic.
TL;DR: A digital, many-compartment model of the human circulatory system, which simulates pulsatile blood flow and gas transport and exchange, has been developed and has been shown to properly simulate human data for passive breathing in a supine subject.
Abstract: A digital, many-compartment model of the human circulatory system, which simulates pulsatile blood flow and gas transport and exchange, has been developed. The model is specifically designed to study short-term whole-body acceleration gz encountered in modern aerial combat manoeuvres, and incorporates a realistic representation of the nonlinear elastic characteristics of circulatory elements and the related pressure-dependent flow resistance characteristic of these elements. The model has been shown to properly simulate human data for passive breathing in a supine subject. The computed carbon dioxide and oxygen partial pressures vary realistically around measured average partial pressures for human subjects. The computed time variation of pressures, circulatory chamber volumes and flow rates match corresponding human data. Under sinusoidal gz variations, the model predicts realistic variations of volumes, flows and pressures.
TL;DR: The reflection of pressure pulses from rubber tube junctions, covering a range of hydrodynamic mismatching, was determined by an impulse technique and agreed well with those calculated from area and elasticity measurements.
Abstract: The reflection of pressure pulses from rubber tube junctions, covering a range of hydrodynamic mismatching, was determined by an impulse technique. A 5 ms pressure impulse generated in the parent vessel was detected, together with any reflected pulse, by means of a catheter-tip pressure manometer. Similar measurements were carried out on the aortic trifurcation of an anaesthetised dog. In both cases the measured reflections agreed well with those calculated from area and elasticity measurements.
TL;DR: The dark adaptation functions derived with this device are comparable to those obtained with other instruments.
Abstract: A microprocessor-controlled light-emitting diode (l.e.d.) display is used to measure dark adaptation. The apparent intensity of the l.e.d. display is controlled by varying the pulse width while holding the pulse repetition rate constant. During the period of dark adaptation, the absolute threshold is measured by the method of limits. Separate series of threshold values are obtained for red and green l.e.d. stimuli. The design uses inexpensive programmable and conventional integrated circuits. Stimulus parameters, test administration, and data acquisition are under software control. The dark adaptation functions derived with this device are comparable to those obtained with other instruments.
TL;DR: The contribution of scalp blood flow to pulses obtained by cerebral electrical impedance plethysmography (rheoencephalography) has been investigated using a four-electrode (quadripolar) montage with brass disc electrodes 1 cm, 2 cm and 4 cm in diameter.
Abstract: The contribution of scalp blood flow to pulses obtained by cerebral electrical impedance plethysmography (rheoencephalography) has been investigated using a four-electrode (quadripolar) montage with brass disc electrodes 1 cm, 2 cm and 4 cm in diameter Three states of scalp perfusion were produced by the application of a tourniquet around the occipto-frontal circumference of the head, and blood flow in the scalp was monitored by means of reflection photoplethysmography and an electrical impedance technique When scalp perfusion was occluded, cerebral impedance pulse amplitude was reduced to 80% of that obtained during normal scalp flow; in the presence of maximal scalp flow as a result of the reactive hyperaemia induced by release of the tourniquet, cerebral impedance pulse amplitude was 30% greater than during normal scalp flow Altering electrode diameter did not affect the contribution of scalp flow to cerebral impedance pulse size The effect of changes in scalp flow did, however, increase when a bipolar electrode montage was used instead of a quadripolar montage
TL;DR: It was concluded that differential impedance plethysmography can be a useful tool in evaluating intra-thoracic processes, both in clinical care and physiological studies, and might provide new insight into the determination of cardiac output by impedance cardiography.
Abstract: A critical evaluation of the measurement of the transthoracic basic impedance Zo according to Kubicek's method revealed inhomogeneous electrical field-distributions in the region of the neck and the shoulders and in the region of the mammae in female subjects. These inhornogeneties were found to introduce uncontrollable errors, like position dependency into the measurements. Also the sensitivity is deteriorated and the comparability between subjects is lost. A method for measuring thoracic impedances that avoids those disturbances is proposed, and some examples of registrations are presented. The measurements seemed to depend on thoracic fluid content, blood pressure, physiological variations and age. It was concluded that differential impedance plethysmography can be a useful tool in evaluating intra-thoracic processes, both in clinical care and physiological studies. The increased reliability might provide new insight into the determination of cardiac output by impedance cardiography.
TL;DR: The method of constant-pressure c.s.f infusion is shown to be faster than the method of Constant-flow-rate c.
Abstract: Instrumentation developed for the direct study of the human cerebrospinal fluid (c.s.f.) system is described. The configuration consists of a servo pressure regulator, two pressure transducers, a special function generator, an electronic pressure limiter, a strain-gauge balance, a volume and flow-rate meter, a c.s.f. conductance calculator, a 4-channel pen recorder, an x/y pen recorder and an ink-jet recorder. It is possible to regulate the c.s.f. pressure to any value between — 2·0 and 10.0 kPa or to regulate the flow rat of fluid into or out of the patient or to perform simple bolus injections/withdrawals. The c.s.f. model used allows indirect calculation of the pressure in the sagittal sinus and the pressure difference between the subarachnoid space and the sagittal sinus. The instrumentation is currently used for the study of c.s.f. pressure, c.s.f. formation rate, c.s.f. absorption rate, conductance of c.s.f outflow pathways, c.s.f. pressure/volume relationship and neurosurgical shunt systems. We have shown that the method of constant-pressure c.s.f infusion is faster than the method of constant-flow-rate c.s.f. infusion in obtaining reliable measuremnts of c.s.f. outflow conductance.
TL;DR: An ultrahigh-energy hydrogen thyratron/SCR bidirectional waveform research defibrillator having a sinusoidal voltage source for inducing fibrillation and three pulse generators for generating defibrillsatory waveforms is described.
Abstract: Presented here is a description of an ultrahigh-energy hydrogen thyratron/SCR bidirectional waveform research defibrillator having a sinusoidal voltage source for inducing fibrillation and three pulse generators for generating defibrillatory waveforms. The first pulse generator uses an 18 kJ capacitor bank at 0·8, 1·6 or 2·4 kV discharged through the chest by two series-connected silicon-controlled rectifiers (SCRs). Two other series-connected SCRs in parallel with the bank terminate the discharge. The second pulse generator uses an 18 kJ bank at 5, 10 or 15 kV. Ceramic-enveloped hydrogen thyratrons in series with the chest initiate the discharge, and in parallel with the bank terminate the discharge. The third pulse generator supplies a reverse-current pulse when used with either the first or second pulse generators to produce bidirectional waveforms. An 18 kJ bank at 2·5, 5 or 10 kV is discharged by an SCR chain in series with the chest. The discharge is terminated by an SCR chain in parallel with the bank. Symmetrical bidirectional rectangular, truncated exponential, and untruncated exponential waveforms are generated by the first and third pulse generators with their respective banks at 2·4 and 2·5 kV, the second and third pulse generators with their banks at 5 kV, or the second and third pulse generators with their banks at 10 kV. The full energy-storage capabilities of the capacitor banks can be used in the first two arrangements; usable energy storage in the third arrangement is limited to about 10 kJ per bank.
TL;DR: Estimates of muscle velocity of shortening and mechanical power are obtained from the myoelectric signal during anisometric contractions and the results agree well with the actual velocity and power.
Abstract: The estimation of muscle tension and velocity of shortening from the myoelectric signal have been considered in numerous papers. These papers consider the estimates of each variable separately, with the other appearing in the estimation as a constant parameter. The work described in this paper develops a model for the relationship between a muscle’s mechanical outputs and the myoelectric signal. The model suggests that the myoelectric signal is related directly to the muscle mechanical power via a nonlinear differential equation in velocity of shortening. The model is general in that it includes as special cases the isometric and anisometric constant-velocity work of other authors and agrees with their experimental results. In this work anisometric experiments are performed on the biceps brachii muscle to verify the model. Estimates of muscle velocity of shortening and mechanical power are obtained from the myoelectric signal during anisometric contractions and the results agree well with the actual velocity and power. The model points out that the myoelectric signal is a direct measure of muscle tension only under isometric conditions.
TL;DR: This test is evaluated on monkeys before unilateral labyrinthectomy and for an extended period of time after, and is a powerful diagnostic tool applicable to disease of the labyrinth and central vestibular pathways.
Abstract: Pseudorandom vestibular rotatory stimuli covering the normal head movement range (0–6 Hz) and power spectrum analysis techniques are used to clinically evaluate the vestibulo-ocular reflex (v.o.r.). Measurements of compensatory eye movements are recorded during fixation of a stationary target, during fixation of a target moving with the subject and in darkness. The gain above 3 Hz quantifies vestibular function under all these conditions. A frequency-dependent v.o.r. asymmetry indicates the side of a peripheral lesion. The fixation suppression curve at medium frequencies quantifies visual-vestibular interaction. Thus the new test is a powerful diagnostic tool applicable to disease of the labyrinth and central vestibular pathways. This test is evaluated on monkeys before unilateral labyrinthectomy and for an extended period of time after.
TL;DR: Experimental results, obtained from eight patients subjected to a one-day controlled diet and feedback connected to the a.e.p., show an appreciable reduction in insulin consumption and an improved glycaemia response.
Abstract: A method is described to set up the parameters of a feedback-controlled artificial endocrinous pancreas (a.e.p.) at the optimal values for the individual patient. The method has been developed to reduce the insulin consumption that, in diabetics feedback-controlled by automatic a.e.p., is often higher than requested in the usual discontinuous therapy. The parameter values are obtained by a digital computer procedure based on feedback optimal control concepts. The procedure includes two steps: (a) parameter estimation of a mathematical model of the patient, subjected to a prolonged glucose load and (b) evaluation of some settable a.e.p. parameters that minimise a square integral performance index in the glycaemia excess and insulin infusion rate. This evaluation is performed on the set of patient model and a.e.p. equations, simulated on a digital computer. Experimental results, obtained from eight patients subjected to a one-day controlled diet and feedback connected to the a.e.p., with coefficients both set up following the manufacturer’s suggestions and computed as described above, show an appreciable reduction in insulin consumption and an improved glycaemia response.
TL;DR: The digital filter gave a 7dB reduction in the amplitude of the artefact, but the small improvement in the number of breaths correctly detected did not justify the inclusion of the filter in the automatic data analysis system.
Abstract: A major problem with impedance pneumography is the artefact on the respiratory waveform caused by the beating of the heart. Three filters are described for reducing the amplitude of this artefact; (i) signal averaging, (ii) analogue filtering, and (iii) digital filtering. A comparison of the three filters suggested that the digital filter was most appropriate for use with a computerised data analysis system. The digital filter gave a 7dB reduction in the amplitude of the artefact. The number of breaths correctly detected by the computerised data analysis system from the respiratory waveform was slightly greater than the number of breaths correctly detected from the unfiltered respiratory waveform. The small improvement in the number of breaths correctly detected did not justify the inclusion of the filter in the automatic data analysis system.