Showing papers in "Medical & Biological Engineering & Computing in 1987"

Description and application of a system for locomotor rehabilitation.

Abstract: OYE OF the most important goals in rehabilitation is to allow the patient to walk safely and to restore a near normal gait pattern. Even after conventional treatment, some patients are still unable to walk well. Neurological gait studies point out the inability of the patient to support his body weight while moving forward (CHrN et al., 1982). In fact, a disturbance of weight transference over the affected limb during stance, and a slow walking speed were present in most neurological patients (CARLSOO et al., 1974; MIZRAH1 et al., 1982a). We are proposing a new gait training strategy based on the adult spinal animal model; a strategy of progressively increasing the amount of weight supported by the patient combined with locomotor training (RosSIGNOL et al., 1986; BARBEAU and ROSSIGNOL, 1987). The purpose of this paper is to describe the progressive partial weight bearing training system (Fig. 1) developed for locomotor rehabilitation of patients with neurologically impaired gait. mechanism is incorporated. Other safety features include the ability of both the operator and the patient to stop the treadmill smoothly in 2 s (Fig. ld).

Use of cardan angles to locate rigid bodies in three-dimensional space.

Abstract: A method of locating rigid human body segments in three-dimensional space is presented. This method has the advantages of being applicable to any body segment and in following anatomical movement patterns. The location of each segment is defined by the location of its proximal endpoint and by a set of three cardan angles of the third kind. Cardan angles sequentially rotate a rigid body about each of its three body fixed axes. Examples on how cardan angles can be used to represent segment orientation are given. Exact and best-fit solutions used in solving segment location are described.

Ventricular fibrillation detection by a regression test on the autocorrelation function

Abstract: The paper investigates quantitative differences in the signal characteristics of ventricular fibrillation (VF) and other cardiac arrhythmias. The analysis procedure comprises two steps: calculation of a short-term autocorrelation function (ACF) followed by a regression test on a plot of peak magnitudes of the ACF against lag values (the ACF/lag plot). We detect VF by testing the hypothesis that the ACF/lag plot of VF does not pass a linear regression test. Analysis of 31 separate episodes (of VF and other ventricular arrhythmias), each comprising three successive segments of 1·5s each produced the following results: (1) 100 per cent sensitivity (Se), 62 per cent specificity (Sp) and 74 per cent test efficiency (TE) after analysis of the first segment; (2) 100 per cent Se, 86 per cent Sp and 90 per cent TE after the second segment; and (3) 100 per cent Se, 100 per cent Sp and 100 per cent TE after the third segment. This method quantifies the notion that VF signals are nonperiodic with a random amplitude distribution, whereas ventricular tachycardia (VT) signals are usually periodic with more uniform amplitude distributions. Accurate discrimination and identification of VF can be very important in intensive-care settings, as well as in the design of automatic cardioverters and defibrillators.

Effect of valve closure time on the determination of respiratory resistance by flow interruption.

Abstract: The resistance of the respiratory system to flow may be conveniently assessed by the flow-interruption technique, in which the flow of gas at the mouth of a subject is suddenly interrupted, while the pressure just distal to the point of interruption, is recorded There is a rapid change in pressure immediately upon interruption, presumably giving the resistive pressure drop across the pulmonary airways This is followed by a further slow change in pressure reflecting stress relaxation in the respiratory system and possibly gas redistribution between different regions of the lung The diagnostic potential of the post-occlusion pressure signal is dependent on the airway opening being occluded effectively instantaneously We present a description of an occlusion valve we have designed and built for performing rapid airway occlusions We are able to measure the closing characteristics of our valve precisely, and show that its finite closure time of 12 ms causes the initial rapid drop in pressure to be underestimated by about 7 per cent A simple numerical correction scheme allows us to estimate this pressure drop correctly to within one or two per cent

In vivo evaluation of signal processors for laser Doppler tissue flowmeters.

Abstract: The performance of different signal processors for laser Doppler tissue flowmeters was evaluated by the use of a well defined flow model comprising a segment of the feline intestinal wall. The processor that, apart from being based on the calculation of the first moment of the power spectral density, also takes into account the effect of multiple scattering in a number of blood cells gave an output signal that was linearly related to the intestinal wall perfusion as recorded independently by a drop-counting technique. At a recording bandwidth of 12 kHz, this linear relationship was valid for the entire flow range 0–300 ml min−1 100 g−1 (r=0·98). The processor based on the first moment of the power spectral density alone under-estimated the highest flow rates by about 35 per cent, while within the flow range 0–100 ml min−1 100 g−1 this processor also gave an output signal linearly related to flow at a recording bandwidth of 12 kHz (r=0·96). When the bandwidth was limited to 4 kHz, the output signals from both processors were linearly related to flow only within the range 0–100 ml min−1 100 g−1 (r=0·90). The output signals recorded with the 4 kHz systems were, however, generally only about 65 per cent of those recorded with the 12 kHz systems.

Running spectrum analysis as an aid in the representation and interpretation of electrogastrographic signals.

Abstract: The recording of gastric myoelectrical activity by means of cutaneous electrodes attached to the external abdominal wall is termed electrogastrography. Respiration and motion artefacts hamper the interpretation of electrogastrographic signals. Running spectrum analysis, using the fast Fourier transform, seems to provide a concise spectral representation of electrogastrographic data. In this paper the concept of running spectrum analysis is presented in detail using test signals consisting of frequency modulated sine waves and actual recordings from dog and man. Especially the visual interpretable representation in appropriate plots is emphasised and discussed. It is demonstrated that tachygastrias with a duration of the order of 30s can easily be recognised in the spectra. In most cases the gastric frequency can be recognised in the spectra. It is concluded, therefore, that running spectrum analysis has to be considered an attractive noninvasive method to study gastric myoelectrical activity in dog and man.

Orthogonal electrocardiogram derived from the limb and chest electrodes of the conventional 12-lead system.

Abstract: Methods of computing orthogonal X, Y and Z voltages representing the equivalent heart dipole activity are described. These components were obtained as linear functions of voltages from the limb and chest electrodes of the conventional 12-lead system. The coefficients of these linear functions are given and a close relationship with the Frank lead system is demonstrated. Two methods were used to obtain transformation coefficients—lead vector approach and statistical least-squares fit. ECG data from 92 individuals (healthy and with cardiac disorders) were used to obtain adequate coefficient values.

Estimation of the conduction velocity of muscle action potentials using phase and impulse response function techniques.

Abstract: Two new techniques are described for calculating the conduction velocity of action potentials in muscle fibres from surface EMG recordings in human subjects. In the first method the conduction velocity is determined from the impulse response function calculated from the two EMG signals. The peak of this function onsists of a single peak located at the delay between the signals. The velocity probability density distribution is then estimated from this impulse response function. The mode of this distribution occurred at 5 m s−1. The second technique uses the phase part of the frequency response function relating the two EMG signals to determine the conduction velocity. These two new approaches overcome some of the limitations associated with estimating conduction velocity from the maximum absolute value of the cross-correlation function, and provide additional information about the conduction velocity.

Single-fiber laser Doppler flowmetry. A method for deep tissue perfusion measurements.

Abstract: A laser Doppler flowmeter with one optical fibre guiding light to and from the tissue under study has been developed. The outer diameter of the probe equals the optical fibre diameter (0·5 mm). The small size makes it useful for studying the deep tissue perfusion in organs. Differential-channel operation was compared with the single-channel operation and the benefit of this technique was evaluated theoretically as well as in a fluid model resembling tissue perfusion. The signal-to-noise improvement ratio was calculated and found to be related to the number of coherence areas detected and to the broadband noise of the laser. In vivo experiments in the gastrocnemius muscle of the pig were performed to compare the results from the single-fibre technique with those of the electromagnetic flowmeter. Linear regression analysis of femoral blood flow data obtained with the electromagnetic flowmeter and local muscle blood flow measured with the single-fibre technique showed a correlation coefficient of 0·88 (n=36, p<0·001).

Electromechanical impactor for producing experimental spinal cord injury in animals.

Abstract: Previous experiments indicated that the mechanical properties (compliance and mobility) of spinal cord tissue vary by ±50 per cent from the mean in different individuals of the same species. In order to apply a consistent force or compression to tissues of varying mechanical properties, feedback control of the contusion device would be desirable. A new device has been designed and used by the author which will produce experimental spinal cord injuries in animals by direct contusion of the exposed cord. The motion of the impact head is feedback controlled through all phases of advance, compression and withdrawal. Force and displacement are recorded in computer random access memory for later processing and graphical printout. A wide range of impact intensities and resultant injuries are achievable. The correlation coefficients between linear compression of the cord and gait scores and lesion volume range from 0·70 to 0·89. Thus, the neural deficit is highly predictable from the impact parameters. This should result in a significant reduction in the number of animals needed in any one experimental group.

Effect of resistive discontinuities on waveshape and velocity in a single cardiac fibre.

Abstract: A computer model of a one-dimensional cardiac fibre of resistively coupled cells is used to investigate the influence of the junction resistance on the nature of conduction. The results of the simulations are presented and indicate that the effect of the junction on both intracellular and extracellular waveshape and on the velocity of propagation depends on the size and frequency of the coupling resistance and the kinetics of the active membrane. Significant changes in these factors are not observed without the generation of prepotentials in the action potential upstroke. The absence of this ‘signature’ in microelectrode recordings of activity in ventricular muscle suggests that under normal conditions cardiac tissue behaves as a functional syncytium.

Analysis of application possibilities of autoregressive modelling to Doppler blood flow signal spectral analysis.

Abstract: The spectral analysis of Doppler blood flow velocity signals enjoys wide-spread interest owing to the exhaustive information on the signal which it yields. The discrete Fourier transform is the most extensively used method of analysis. However, the statistical stability of such analysis is poor; spectral smoothing, which improves the statistical stability, also results in greater width and poorer resolution of the spectrum. Autoregressive modelling has been found to give better results when analysing small sample volumes obtained from a pulsed velocimeter (narrow spectrum), even for short data lengths.

Surface EMG spectral changes with muscle length.

Abstract: References BABBS, C. F. and WHISTLER, S. J. (1978) Evaluation of the operating internal resistance, inductance, and capacitance of intact damped sine wave defibrillators. Med. Instrum., 12, 34-37. BENNETT, P. I. and JONES, V. C. (1982) Portable defibrillator monitor for cardiac resuscitation. Hewlett-Paekard J., 22-28. CONNELL, P. N., EwY, G. A., DAHL, C. F. and EwY, M. D. (1973) Transthoracic impedance to defibrillator discharge. Effect of electrode size and electrode-chest wall interface. J. Electrocardiol., 6, 313-317. CRAMPTON, R. (1980) Accepted, controversial and speculative aspects of ventricular defibrillation. Proor. Cardiovasc. Dis., 23, (3), 167-186. DAHL, C. F., EWY, M. D. and THOMAS, E. D. (1976) Transthoracic impedance to direct current discharge: effect of repeated countershocks. Med. Instrum., 10, 151-154. EwY, G. A., EwY, M. D., NUTTALL, A. J. and NUTTALL, A. W. (1972) Canine transthoracic resistance. J. Appl. Physiol., 32, 91-94. EwY, G. A., HORAN, W. J. and EwY, M. D. (1977) Disposable defibrillator electrodes. Heart & Lung, 6, 127-130. EwY, G. A., HELLMAN, n. A., MCCLUNG, S. and TAREN, D. (1980) Influence of ventilation phase on transthoracic impedance and defibrillation effectiveness. Crit. Care Med. 8, 164-166. GEDDES, L. A., TACKER, W. A., ROSBOROUGH, J. P., MOORE, A. G. and CABLER, P. S. (1974) Electrical dose for ventricular defibrillation of large and small animals using precordial electrodes. J. Clin. Invest., 53, 310-319. GEDDES, L. A., TACKER, W. A., CABLER, P., CHAPMAN, R. and KIDDER, H. (1975) The decrease in transthoracic impedance during successive ventricular defibrillation trials. Med. Instrum., 9, 179-180. GEDDES, L. A. (1976) Electrical ventricular defibrillation, in HILL, D. W. and WATSON, B. W. (Eds.) IEE medical and electronics monographs 18-22. Peter Peregrinus, 42-72. KERBER, R. E., GRAYZEL, J., HOYT, R., MARCUS, M. and KENNEDY, J. (1981) Transthoracic resistance in human defibrillation. Influence of body weight, chest size, serial shocks, paddle size and paddle contact pressure. Circulation, 63, 676682. MACHIN, J. W. (1978) Thoracic impedance of human subjects. Med. & Biol. Eng. & Comput., 16, 169-178. PATTON, J. N. and PANTRIDGE, J. F. (1979) Current required for ventricular defibrillation. Br. Med. J., l, 513-514. TACKER, W. A. and PARIS, R. (1983) Transchest defibrillation effectiveness and electrical impedance using disposable conductive pads. Heart & Lun9, 12, 510-513.

Feasibility of developing a method of imaging neuronal activity in the human brain: a theoretical review.

Abstract: A theoretical analysis has been performed to suggest directions for research into the development of a device which could image neuronal electrical activity in the human brain in three dimensions. Proposed criteria for the device are a spatial resolution of 1 mm3 and temporal resolution, after averaging to a repeated stimulus, of 1 ms for events related to the action potential, or 1 s for metabolic changes. It is proposed that, for the rapid changes related to the action potential, electron spin resonance using a potential-sensitive spin, label, impedance imaging and NMR are suitable in principle but that only ESR and impedance methods may have sufficient sensitivity and these merit further assessment. For metabolic changes, NMR and PET may be used as at present, and ESR may be developed in time, but images based on these changes would have limited value in that they could only give an indirect, index of neuronal discharge. Unique reconstructions based on the EEG or MEG are theoretically, impossible, and imaging using X-rays, microwaves, or ultrasound may be possible in principle but these techniques would not be sufficiently sensitive.

Investigation and improved performance of optical fibre probes in laser Doppler blood flow measurement.

Abstract: Laser Doppler flowmetry with optical-fibre beam transmission is a sensitive fast and convenient method of measuring tissue blood flow. However, its sensitivity can also be a problem because of movement artefacts. This study applies some basic considerations of fibre optics and Rayleigh light scattering to the field of laser Doppler blood flow meters. Practical suggestions are given by which movement arterfacts can be reduced by choice of optical fibres, attention to probe geometry, cladding the fibres to reduce their movements and in the method of application. Experiments which test the normalisation circuitry of laser Doppler instruments are described and the effects of movement artefacts on the interpretation of the pulsatile component of laser Doppler records are also discussed. Probe and fibre line movements cause high-frequency intensity fluctuations due to speckle movement. The intensity fluctuations produce an apparent Doppler shift much greater than the Doppler shift produced by the relative movements of probe and tissue. It has been found that it is important to ensure that the fields of view of the illuminating and detecting fibres do not overlap at the skin surface and that probe contact with the skin surface should be maintained.

Study of transcutaneous and intraluminal measurement of gastric electrical activity in humans.

Abstract: Several authors have reported measurements of the human electrogastrogram (EGG), both with intraluminal electrodes and with improved noninvasive techniques. These methods provide information about the existence and frequency of gastric electrical activity (GEA) which may aid in diagnosing tachygastria. However, none of these methods have provided information regarding the direction and velocity of propagation of GEA. Such information could help isolates such abnormalities as gastro-oesophageal and antral reflux and gastric stasis. To ascertain the reliability of the extracorporal measurements, a new intraluminal electrode assembly was developed. This probe measures GEA through the mucosa at several locations simultaneously; yielding frequency, direction of propagation and velocity of the electrical activity.

Reliable and efficient deconvolution technique based on total linear least squares for calculating the renal retention function.

Abstract: By deconvolving the activity/time curves obtained from the blood and kidney, the renal retention function can be calculated, yielding useful clinical data. However, the current deconvolution techniques are not very reliable; they are sensitive to the inaccuracies present in the data. A more reliable, stable and efficient deconvolution technique based on the singular value decomposition, total linear least squares (TLLS), is proposed and its properties are described. The applicability of TLLS as a deconvolution technique in renography is discussed and demonstrated. Results from simulation, as well as from clinical data, are presented to show the advantages of the use of TLLS with respect to noise rejection in the data. They confirm the superiority of TLLS over the current deconvolution techniques. It is concluded that TLLS needs no smoothing and is a powerful, efficient, reliable and stable deconvolution technique.

Combined 2.25 MHz ultrasound velocity and bone mineral density measurements in the equine metacarpus and their in vivo applications.

Abstract: A simple noninvasive ultrasound method is described for estimating the transverse cortical bone ultrasound velocity and the cross-sectional area of the equine third metacarpal bone (MC3). The method relies on measuring the time of flight of the ultrasound for each of two pathways, via the cortical shaft and through the central medulla. Ten metacarpal bones of approximately the same dimensions were selected to evaluate the method and to determine the practiocal correction factors Factors were established for the ovality of the external cortical boundary and the medullary cavity as well as corrections for the presence of the splint bones (second and fourth metacarpal bones, MC2 and MC4) which influence, the total cortical cross-sectional area. Conventional single-photon absorptiometry was used to measure the bone mineral content which, together with the cross-sectional area determined ultrasonically, was then used to estimate the bone mineral density. The bone mineral density was also determined for some bone sections from ash weight and volume. The compact bone density (i.e. relative density) together with the ultrasound velocity were then used to estimate a modulus of elasticity in the transverse direction.

Microprocessor-based cardiopulmonary rate monitor.

Abstract: A portable microprocessor-based noninvasive cardiopulmonary heart rate monitor is described for use in situations in which direct contact with the subject is either impossible or undesirable. Low-power Doppler microwaves are employed to measure the chest movements associated with the expansion and contraction of the heart and the lung. After proper analogue signal conditioning, the signal is digitised and processed by an Intel-85 microprocessor system. Pattern-recognition techniques are applied to extract the heart and respiration rates. The algorithm is tested on anaesthetised rats. The system has also been tested on a limited number of human subjects. Results indicate that the meter can detect the desired physiological signals, with good accuracy, of a standing or supine human subject wearing ordinary clothing.

Fibre-optics and optical sensors in medicine.

Abstract: A number of new optical techniques for both thein vivo identification of blood analytes and the measurement of physical properties of interest to the clinician have recently been developed. These optical transducers are based on glass or plastic fibres, fractions of a millimetre (100–250 μm) in diameter, as found in fibre-optic communication systems. These sensors offer a number of advantages for physiological applications over their conventional electrical counterpart, the most important of which are: their non-electrical nature; the operating optical signal is not subject to electrical interference; the fibre allows a high degree of mechanical flexibility combined with very small size and low-cost disposable construction; materials suitable for long-term implantation, e.g. plastics, may be used in their construction. Optical sensors fall into three categories: (a) the photometric or bare-ended fibre; (b) the physical sensor which is used to measure temperature and pressure; and (c) the chemical sensors or ‘optrodes’ based on the immobilisation of a reagent phase on the end of the fibre. Clinical sensors based on fibre-optics, although clearly attractive in concept, are mostly in the developmental stage. However, the devices developed to date already illustrate the potential systems that are possible with this expanding technology.

Effect of stenotic geometry on flow behaviour across stenotic models

Abstract: In the study the influence of the geometry of stenoses on poststenotic flow characteristics such as faminar flow, separation, flow instabilities and local turbulences were assessed. Stenoses were represented by 12 rigid-walled models. The different geometric characteristics were length, percentage lumen area reduction, exit angle and eccentric location of the residual lumen. The flow characteristics were investigated by visualising the flow pattern with a birefringent solution and by measuring the flow and the pressure drop along the stenoses. All data were obtained under steady flow conditions for Reynolds numbers varying from approximately 1 to 500. In stenoses with short and concentric shapes local turbulence develops at Reynolds numbers well below the corresponding Reynolds numbers obtained in stenoses with the same percent lumen area reduction but with a long and eccentric shape. The results indicate that the photoelastic technique is a suitable method of obtaining a picture of the overall flow field downstream of a constriction.

Computerised analysis of ST segment changes in ambulatory electrocardiograms.

Abstract: The TELAVIV system for computerised arrhythmia detection and identification in ambulatory ECGs has been extended to include a reliable and rapid computerised method for ST-segment analysis. It now incorporates self-learning analysis and classification of ST-segment changes. Some advantages for ST-segment analysis present in this algorithm are: (a) it analyses three channels simultaneously instead of one or two in other systems; (b) it includes a larger number of parameters describing the ST-segment changes; (c) the measurements are detected from a noise-free template, averaged over 20 beats; (d) isoelectric and J-points are detected by a self-learning process; (e) a scoring system has been added; and (f) it now has the capability to detect and classify arrhythmias and ST-segment changes simultaneously. The system was tested on three types of recordings: 30 1 h recordings in which ST-changes were observed in the quick summary plot produced by the TELAVIV system; 12 recordings taken during submaximal effort; and 13 recordings made during conventional ergometry. The results indicated a high level of sensitivity and specificity of the program.

Clinically relevant computer model of cardiac rhythm and pacemaker/heart interaction.

Abstract: A computer simulation model of cardiac rhythm disturbances and of the heart/pacemaker interaction has been created and implemented on a NORD-100 minicomputer. The model incorporates important properties including cycle length dependence of the refractory periods of different parts of the heart and of the atrioventricular nodal conduction speed. Computational experiments produce an explicit timetable of polarisation changes, a simulated one-channel electrocardiographic record and a pacemaker marker channel. The simulation program is written infortran and uses discrete event simulation techniques. The heart is modelled using instances of nine simulation process prototypes. The paper presents and discusses several examples in the form of simulated electrocardiographic records and the results show that the model is clinically relevant. Included in the examples are the modelling of rhythm disturbances, pacemaker actions, pacing for tachycardia prophylaxis and atrioventricular nodal conduction disorders.

Quasi-steady-state compartmental model of intracranial fluid dynamics.

Abstract: A lumped-parameter compartmental model for the cerebrovascular fluid system is constructed and solved for quasi-steady-state flow. The model predicts the pressure waves in the various compartments of the intracranial region in response to changes in the arterial pressure.

Dual-channel self-balancing electrodermal impedance reactometer for autonomic response studies.

Abstract: A self-balancing two-channel electrodermal impedance reactometer is described. It uses a phase-sensitive detector and incorporates feedback loops to achieve rapid automatic balancing of both resistive and capacitive components of skin impedance. The calibrated output which is produced is proportional to the skin electrical resistance and relative capacitance variation values and latency of the electrodermal response. The results of preliminary investigations on diabetics and nondiabetics are presented illustrating its application for the measurement of the electrodermal response to an external acoustic stimulus as a variation of the skin electrical resistance ΔR/R and latency in the appearance of the response. The results obtained show the electrodermal impedance reactometer to be highly technical, non-invasive, easy to handle and sensitive for evaluating autonomic dysfunction in diabetic neuropathy.

Real-time measurement of muscle fatigue related changes in surface EMG

Abstract: A muscle fatigue indicating parameter is proposed, which can be computed from the surface EMG in real time by a simple analogue device. It is compared with the well known offline algorithms that are currently in use. It is fairly robust and a relatively good indicator.

Turbulence downstream from the Ionescu-Shiley bioprosthesis in steady and pulsatile flow

Abstract: The turbulence generated downstream from an aortic Ionescu-Shiley bioprosthesis has been investigated in vitro with both steady and pulsatile flow; Instantaneous point velocities were measured using laser-Doppler anemometry (LDA) at numerous preselected locations in the flow. The mean and RMS velocities from these data at each location were then used to estimate the laminar and turbulent shear in the bulk flow as a function of radial position on a cross-section of the flow system downstream from the mounted prosthesis. Estimated total shear stresses were found in the bulk flow that were of sufficient magnitude to possibly cause haemolysis and initiate platelet chemical-release reactions. For steady flow and at peak pulsatile flow, maximum total shear stresses were estimated to be 120 N m−2 and 100 N m−2, respectively, over more than 5 per cent of the flow cross-section. The spatial distribution of the elevated shear stresses correlates well with the valve superstructure. It is concluded that these elevated stresses are a direct consequence of the notable flow constriction generated by the valve’s fully opened leaflets.