Showing papers in "Medical & Biological Engineering & Computing in 1984"

Software QRS detection in ambulatory monitoring--a review.

Abstract: The QRS detection algorithm is an essential part of any computer-based system for the analysis of ambulatory ECG recordings. This review asserts that most one-channel QRS detectors described in the literature can be considered as having the same basic structure. A discussion of some of the current detection schemes is presented with regard to this structure. Some additional features of QRS detectors are mentioned. The evaluation of performance and the problem of multichannel detection, which is now gaining importance, are also briefly treated.

Signal processor for laser Doppler tissue flowmeters.

Abstract: Laser Doppler flowmeter for the assessment of tissue blood flow are generally equipped with a signal processor which generates the first moment of the unnormalised power spectral density as a continuous output signal. This signal is related to blood flow for low and moderate flow rates. At higher flow rates the interpretation of the output signal becomes ambiguous as a consequence of the multiple scattering in moving blood cells and the homodyne mixing of waves on the detector surface. The paper describes a new signal processor which takes these effects into account and establishes a linear relationship between the flowmeter output signal and blood flow for all flow rates. The performance of the signal processor was evaluated by an experimental fluid model which optically resembled the blood flow through the microvasculature. The transiently high blood flow in the initial phase of reactive hyperaemia, recorded from palmar skin, gave peak values which were almost double those recorded with the original signal processor of the flowmeter. In conjunction with these high peak values a high concentration of moving blood cells was recorded, indicating that the initially high flow rate is produced by an increased number of moving blood cells due to vasodulation rather than by a change in average velocity.

Electrical conductivity of skeletal muscle tissue: Experimental results from different musclesin vivo

Abstract: For a quantitative EMG analysis reliable and unique values of the electrical conductivities of skeletal muscle tissuein vivo are indispensable. Literature values do not satisfy these criteria. In the paper experimental results of conductivity measurements (four-electrode technique) on musclesin vivo on which quantitative EMG experiments are also carried out are reported. Depending on the interelectrode distance (IED) in the four-electrode technique the results appear to be either frequency dependent (IED=0·5 mm) or frequency independent (IED=3·0 mm). The anisotropy value obtained with an IED of 0·5 mm is frequency dependentin the frequency range of EMG signals. Experimental results of different muscle types (white muscle, EDL rat and red muscle, soleus rat) appear to be significantly different.

Analysis of gaseous exchange in open-circuit indirect calorimetry.

Abstract: A method is described for determining rapid changes in gaseous exchange between a subject and the environment, while living in a whole body opencircuit calorimeter. The formulae which must be applied to standard estimates of oxygen consumption are derived the computation of rates of change of gas concentration is discussed the sensitivity of estimated heat production to errors in gas concentration is determined and heat production shown to be largely independent of CO2 measurements; and examples of veritication of the method for known rates of gas injection, and of its use with human subjects, are given. The method is of particular value in assessing the rapid changes in metabolic rate which occur as a result of changes in activity, nutritional state, environmental temperature and the administration of drugs. Such changes are monitored in an unrestrained subject living in a whole-body calorimeter rather than in a subject living with the restrictions imposed by a face-mask or ventilated hood.

Effects of multiple scattering and peripheral circulation on arterial oxygen saturation measured with a pulse-type oximeter.

Abstract: NONINVASIVE monitoring of arterial oxygenation is essential for the management of patients with respiratory insufficiency. We previously developed a pulse-type oximeter which estimates the absolute value of oxygen saturation (YOSHIYA et al., 1980). The determination is performed by considering just the change in the attenuation of light caused by the inflow of arterial blood into the fingertip. However, SARNQU[ST et al. (1980) recently reported that the device overestimates arterial oxygen saturations below 90 per cent. If this is the case, there would be serious limitations in its use as a monitoring device for hypoxaemic patients. We re-evaluated the device and found similar overestimation. We then performed an in vitro study to clarify the possible contribution of multiple scattering on the saturation measurement. We also evaluated the effects of an impaired peripheral circulation on the arterial oxygen saturation values of the pulse-type oximeter.

What does photoplethysmography measure

Abstract: mograph (GILTVEDT et al., MBEC, 22, 212-215) would seem to be a major step in exploring the interactions between optical radiation and the skin. However, the clinical usefulness of such instruments will remain limited until the nature and source of the signal they produce is accurately determined at each site they are used. The degree of attenuation of either transmitted or reflected light is related not only to the light frequency as has been shown by Giltvedt et al. but also to the amount of blood in the tissue under scrutiny, the orientation, concentration and packing of erythrocytes, the erythrocyte oxygenation and the reflective properties of the blood vessel wall (WEINMAN e t al., 1977). Moreover, photodetector output is markedly affected by the local blood velocity and the light-source/detector separation (ROBERTS, 1982), although Giltvedt and his colleagues give no information on this latter parameter. Despite such uncertainties, tracings obtained with such devices bear a remarkable resemblance to those obtained using more conventional strain-gauge or displacement instruments, particularly when used on the finger pulp. Waveforms obtained from this Site consist of two components: one pulsatile component at the same frequency as the heart rate, often referred to as the 'pulse volume', and a less oscillatory remittance signal, often referred to as the total 'blood volume'. When measuring tissue blood flow changes qualitatively with other volumetric methods, the value of the 'blood volume' signal is limited since it is altered by venous capacitance; the amplitude of the 'pulse volume' being considered more reliable. It has been stated (CHALLONER, 1979), although not proved, that the same constraints apply to photoplethysmography, but it may be erroneous to draw comparisons between two conceptually different techniques. To test the validity of this comparison we have conducted an experiment in which absolute blood flow to the finger is correlated

External recording and processing of fast electrical activity of the uterus in human parturition.

Abstract: The fast uterine electrical activity during parturition is analysed through two signals recorded on the abdominal wall. After differential amplification and filtration the fast activity is numerically processed to obtain quantified information for monitoring labour progress. Through parametric modelling, the necessary data for the study of the EMG signal at each contraction is reduced to six. Moreover, an attempt was made to measure the velocity of electrical wave propagation across the uterus from the delay of the cross-correlation function maximum of the two signals.

Capacitive transducer for continuous measurement of vertical foot force.

Abstract: A capacitive transducer is developed which continuously measures the vertical component of foot forces during walking. The transducer is shaped like an insole and consists of two subtransducer units, the front and rear. The outputs of the two units are summed to give the total force exerted by the foot. Each unit has a multilayered structure. The basic layer is a 2 mm Neoprene sponge sheet sandwiched by two 50 μm copper foils. They as a whole form a capacitor. The other two layers are a driving shield and static shield, which minimise the effect of stray capacitance and power-line noise, respectively. The transducer is thin (3·8 mm), light (90 g) and flexible and so does not hinder the natural gait pattern. It can be attached to the sale of the shoe easily by elastic bands and Velcro straps. The accuracy of the transducer is well within ±10 per cent of the full scale. An error analysis is made to clarify the change in sensitivity owing to a localised foad. The results are used to compensate for the inherent nonlinearity of the transducer units.

The recording of heart vibrations: a problem of vibration measurement on soft tissue

Abstract: The determination of the effect of loading of the chest wall exerted by a contact phonocardiographic microphone, has been attempted in earlier investigations by the measurement of the mechanical properties of the microphone and the chest wall in combination with mechanical models describing the coupling phenomenon (method 1). For computing the acceleration response of the microphone applied to the chest wall a number of unverified assumptions were made. In the paper a method is described for experimental determination of the coupling characteristic. A specially designed ultralight pick-up (1 g) was applied for recording the quasi-unloaded vibrations and the average amplitude spectrum was calculated. The procedure was repeated at the same site, the chest wall successively being loaded with different masses and two commercial microphones (method 2). Logarithmic transfer functions of the loaded to unloaded situations have been computed. The experiments were performed on six healthy persons. The results of method 1 appeared to be very similar to those obtained with method 2 when a Verburg model was assumed. In this manner we determined the acceleration response of microphones applied to the chest wall, which is both of interest for standardised and quantitative phonocardiography.

Dynamics of spastic knee joint.

Abstract: Goniometric records of a swinging lower leg (pendulum test) provide useful information in assessing the level of hypertonia in normals, spinal cord injured (SCI) patients and hemiparetic patients. A linearised second-order dynamic model without forcing function is proposed for a normal and hypotonic paraplegic leg Forces which appear in the quadriceps muscle in spastic patients are simulated with hypertonia torquest Th. A combined biomechanical and neural model is proposed to facilitate qualitative discussion of the observed phenomena. Large variability of goniograms in spastic patients as well as lack of detailed knowledge regarding the neurophysiology of spasticity prevents further development of realistic models which should be time varying and nonlinear.

Pulsed multifrequency photoplethysmograph.

Abstract: A technical description of a pulsed, multifrequency photoplethysmograph is given. It has four channels, thus featuring two probes, each with two different wavelengths. In this study 950 and 560 nm are used. The penetration depth of light in skin is wavelength dependent, thus making it theoretically possible to record vascular changes in different layers of the skin. Results from skin blood-pressure measurements and rest recordings are presented.

In-Vivo Experiments with a pH-ISFET Electrode

Abstract: Thein vivo stability and pH sensitivity of 19 intravascular pH electrodes for continuous monitoring have been investigated. The sensors were mounted in indwelling vascular catheters (7F) which were inserted into the arteries of seven anaesthetised and mechanically ventilated dogs. Variations in arterial pH, ranging from 6·82 to 7·72, were obtained by infusion of sodium bicarbonate and hydrochloric acid and by hyper/ hypoventilation with various volume fractions of carbon dioxide in the inspiratory gas mixture. The pH sensor output potential was compared within vitro pH determinations of arterial blood samples. After an initial stabilisation period following their introduction into the arterial blood, the electrodes showed an average long-term drift of 2·3 mVh−1. When this drift was taken into account, a typical pH sensitivity of 50 mV per pH was found. The relationship between the electrode potentials and thein vitro pH values was linear and in almost all cases the correlation coefficient (r) was above 0·9. The electrodes responded rapidly enough to reflect breath-to-breath oscillations in pH.

Estimation of muscle force from intramuscular total pressure

Abstract: Estimation of muscle force from the root mean square value of the myoelectric signal is limited to nonfatiguing contractions because of the change in the signal value that occurs with fatigue. In this paper the total intramuscular pressure is proposed as a muscle force estimator. Using a catheter, intramuscular pressure was measured for isometric time-varying force contractions and compared with the myoelectric signal mean absolute value. Results show that the pressure provides a linear estimator for load with an estimation error which is less than that obtained from the myoelectric signal. The myoelectric load estimator changes with fatigue but there is no significant change in the pressure load estimator.

Design, implementation, and evaluation of a microcomputer-based portable arrhythmia monitor.

Abstract: The design of a portable, battery-operated microcomputer-based monitor for ambulatory ECG recording and analysis is described. Designed for real-time cardiac arrhythmia analysis, it is suitable for use on ambulator, patients for several weeks, and is about the size and weight of a Holter recorder. The device differs from a Holter recorder in that is does not store normal complexes but recognises and alarms on significant arrhythmias. It sotres 16 s of the arrhythmic event, which it can transmit by telephone to a central receiving station for immediate appraisal by a cardiologist. The monitor uses a CMOS microcomputer and has 2kbytes of program memory and 2kbytes of data memory. The arrhythmia monitor program recognises tachycardia, bradycardia, asystole, dropped beats, and PVCs. The alarm limits are physician programmable. The performance of the monitor was evaluated with standard annotated ECG tapes provided by MIT/BIH. This device should be useful for applications such as antiarrhythmic drug studies, for pacemaker and postsurgery evaluations, and for detecting premonitory as well as life-threatening arrhythmias.

Factors affecting the measurement of bone impedance

Abstract: Factors which affect the measurement of the electrical properties of bone were examined. Environmental conditions such as the pH of the preserving solution and time of exposure of the sample to air, which controls the moisture content of the specimen, significantly affected the bone impedance. A change in pH of ×2 from the neutral solution (pH=7) caused a change in the resistance R. conductance β and capacitance C values of 70 per cent, 125 per cent and 190 per cent respectively. A 5 min exposure to air increased the resistance by 92 per cent and reduced the capacitance by 35 per cent of their original values. A loss of 8 per cent moisture content by weight resulted in 400 per cent increase in R and 65 per cent decrease in C. Significant errors were introduced in the measurement of bone impedance owing to stray and wiring capacitances; these were avoided by using a differential impedance measurement technique. Further, it is shown that it is essential to measure the phase angle while measuring the bone impedance. Finally, it is illustrated that when normalising for different sized bone specimens, both the resistive component and capacitive component have to be considered while computing the impedance per unit volume.

Leg exerciser for training of paralysed muscle by closed-loop control.

Abstract: An exercise device which can be used to stimulate either paralysed or nonparalysed muscles is described. The device uses sequential activation of muscles to elicit either isometric or isotonic contractions. Feedback sensors provide the relative position of the joints of the leg to a computer-controlled two-channel sequential stimulatior which regulates the activity of the muscles. The computer can be programmed to preprogram workouts so that the muscle can move throught patterns of activity requiring either isometric exeroise, isokinetic exercise or isotonic exercise. In all cases the computer controls the entire exercise program and automatically terminates when the muscle is fatigued. THis device could be used for any type of physical therapy involving active stimulation of muscle.

Methods of data smoothing for instantaneous centre of rotation measurements.

Abstract: Description d'une methode simple pour definir et trouver le centre de rotation instantane des mouvements articulaires

A low noise isolated amplifier system for electrophysiological measurements: basic considerations and design

Abstract: An instrumentation amplifier for medical and biological research applications is described. It consists of an isolated preamplifier with a high signal/ noise ratio and a computer or microprocessor controlled main amplifier that incorporates variable highpass and lowpass filtering. The preamplifier includes an input stage, a compensation circuit for electrode offset voltage and an isolation amplifier. Recently introduced ultra low noise operational amplifiers used in the input stage ensure good noise behaviour. Isolation is obtained with an inductive isolation amplifier, which also delivers the supply voltages for the input stage. Accordingly, battery power is not needed, in contrast with optically isolated amplifiers. The main amplifier has computer control for gain, lowpass cut-off frequency and highpass cut-off frequency settings. This features dynamic changes in signal conditioning and data acquisition by the same computer that collects the data. Data acquisition and noise behaviour are discussed. The filter configuration is designed in such a way that several user-defined options can be implemented on the same circuit board. The trade-off between the order of the lowpass filters, their roll-off, and the sampling rate which is used in the subsequent computing system, are of major importance and will be discussed. The amplifier system is at present in sue in laboratories of neurology (BEP, EEG), opthalmology (VEP, EOG, ERG) and cardiology (noninvasive His bundle recordings) from which some results will be presented. The amplifiers form a part of a microprocessor-controlled data acquisition system.

Blood flow and blood velocity measurement in vivo by electromagnetic induction.

Abstract: The application of electromagnetic induction to the measurement of blood flow and blood velocityin vivo is reviewed. The electronics requirements are discussed and the associated problems are surveyed. An account is given of Bevir's virtual-current theory and its application to various flow and velocity measuring devices. The devices at present known to be in use or under development are reviewed under the following headings: invasive local-magnetic-field devices, which include cannular and perivascular flowmeters; intravascular velometers and flowmeters, invasive extracorporeal field perivascular and intravascular flowmeters; and noninvasive systems which either utilise skin electrodes and a separate extracorporeal magnet or comprise an integral extracorporeal flowmeter. There is a brief discussion of the present state of development

Quantification of Gait Abnormalities on the Basis of Continuous Foot-Force Measurement: -Correlation between Quantitative Indices and Visual Rating

Abstract: Although various methods have been proposed for quantitative evaluation of pathological gait, they are not yet widely used as routine clinical tools. The reasons are that measuring systems are too expensive and complicated and that the validity of the methods has not been fully examined in a statistical manner. In this paper, the validity of a new evaluation method based on a simple foot-force measuring device is investigated in terms of the correlation between quantitative indices and visually-rated grades. Forty-eight hemiparetic patients secondary to cerebral vascular accident walked on a 15 m straight level floor. Four people independently evaluated each subject in eight gait characteristics or items on a scale of 1–4 grades on the basis of visual inspection. These items include symmetry, variation, fluctuation, and dependence on the cane. At the same time, the vertical ground-reaction forces exerted on the right and left feet and on the cane were measured, and then quantitative indices representing these eight items were derived. All but one index shows a reasonably good correlation with the mean of the grades of the four observers. Thus, the feasibility of these indices is demonstrated. Statistical analysis also reveals several problems inherent in visual rating, such as inconsistency in the interpretation of evaluation criteria among observers, and a degradation of the independence of items owing to the observer’s subjectivity.

Computer studies of systemic and regional blood flow mechanisms during cardiopulmonary resuscitation.

Abstract: Based on the new concept that intrathoracic and abdominal pressure variations cause blood flow in most of the cardiopulmonary resuscitation (CPR) techniques, two mathematical models were developed to explore related mechanisms of blood flow The models were based on a representation of the cardiovascular system by resistive, capacitive and inductive elements, and the existence of venous and cardiac unidirectional valves Cyclic intrathoracic and abdominal pressure variations were simulated by modulating the pressure within the corresponding vessels It was found that blood flow during CPR is highly dependent on venous valving and aortic valve competence The systemic blood flow was calculated to be between 10 and 20 per cent of its normal value The maximum flow under a cyclic pressure of 50 mmHg was 663 m/min−1, which was achieved with a pulse rate of 115 cycles per min and a duty cycle (ratio of artificial systole to cycle duration) of 58 per cent The coronary blood flow was found to occur only during artificial diastole and was actually reversed during the compression phase The systemic blood flow increased when pressure variations were delivered to the chest alone or when some phase lag was introduced between the thoracic and abdominal pressure waves The mathematical model presented provided a tool to study the effect of thoracic and abdominal pressure waves on the circulation in CPR The information derived from the model can be used to design better methods for CPR

Radial decline of the extracellular action potential.

Abstract: A modified line source model presented earlier has been used to study the decline of the extracellular single muscle fibre action potential. The muscle tissue is modelled as a low-pass filter. The transfer function of the filter declines more slowly than a first order low-pass filter at low frequencies, but much faster at high frequencies. The cutoff frequency of the filter increases when the anisotropy of the muscle decreases. It also increases proportionally with the propagation velocity of the action potential. The decline of different frequency components obtained from the modified line source volume conductor and a filter model derived from experimental measurements are compared and their differences explained. The modified line source model was found to be identical to the volume conductor model in terms of results and at the same time conceptually simple for applications.

Analysis of posturographic measurements on children.

Abstract: To evaluate the relationship between the statokinesogram and age postural measurements were taken on a group of normal children aged between 6 and 13. From these measurements, 40 parameters representing different aspects of the statokineso gram were computed. The regression coefficients for the linear equations, describing stability as a function of age, were different for boys and girls. After the parameters were corrected for age no further dependency on weight and height was found.

Dielectric analysis of blood by means of a raster-electrode technique

Abstract: Dielectric measurements were made on blood samples containing erythrocytes of varying diameter D and percentage p. For effective measurements of the conductivity γ and the dielectric constant e, in the frequency range f=10–100 kHz electrode effects were corrected by means of a raster-electrode technique, which is based on the automatic variation of the effective electrode area. The results, which proved to be independent of f, indicate that an increase of haematocrit p is linked with a strong decrease of γ, being essentially independent of D. For low and medium p an increase of e, resulted from increasing p. For physiological values of p close to 40 per cent, a strong increase of e, was found with increasing D, indicating possibilities of using the method for rapid determination of D in addition to p. For very high values of p (>60 per cent) e, showed a distinct decrease. This finding is discussed using a cube model for the particle suspension.

Technology and the diabetic patient.

Abstract: Diabetes is conventionally treated by one or two daily subcutaneous injections of insulin. Although controlling the acute symptoms of the disease, this regimen is unable to achieve and maintain long term metabolic near normalisation. It is this chronic metabolic disorder which is probably the cause of the several serious tissue complications affecting the eyes kidney's nerves and blood vessels of long standing diabetic patients. To improve blood glucose and intermediary metabolite control in diabetics newer insulin delivery systems are being developed which seek more closely to mimic nondiabetic insulin secretion patterns. Continuous infusion of insulin from a pump is a key strategy which allows constant but variable dosage rates either in open-foop mode with pre-set basaf levels and prandial boosts activated by the patient, or with continuous automatic glucose sensing and feedback control of insulin or glucose infusion rates (the artificial endocrine pancreas). The intravenous, intramuscular and intraperitoneal routes of insulin delivery are being explored but most clinical and experimental experience has been with open loop continuous subcutaneous insulin infusion (CSII) using a portable pump worn outside the body. Torally implantable infusion pumps are at an early stage of clinical testing. A reliable implantable glucose sensor is not yet available but several approaches to the problem are under active investigation.

Interpretation of venous occlusion plethysmographic measurements using a simple model.

Abstract: A model is developed to interpret changes in limb volume measured during venous occlusion plethysmography. The parameters of the model are chosen to represent, as closely as possible, physiological variables related to blood flow within the limb. These parameters are shown to be related to various parameters derived by other investigators for interpreting the same measurements. An experiment is reported in which these changes in volume are inferred from measurements of the electrical resistance of limbs. It is shown that the model can accurately represent such changes in volume. A further experiment is reported which demonstrates how changes in the model parameters are related to changes in the circulatory system within a laboratory model of a limb.

Efficacy and safety of the reciprocal pulse defibrillator current waveform.

Abstract: The efficacy and safety of a new defibrillating current waveform, consisting of a low-tilt 5 ms trapezoidal pulse followed closely by a second identical pulse of opposite polarity, was tested in seven isolated, perfused, working canine hearts suspended in an isoresistive, isotonic shock bath at 37°C. The efficacy and safety of the reciprocal pulse was compared with a single 5 ms pulse, a single 10 ms pulse, and a dual (unidirectional) 5ms pulse waveform. The mean threshold average current densities for the 5 ms single pulse, 10 ms single pulse, dual 5 ms pulse, and reciprocal pulse (absolute values) were 40, 38, 36 and 37 mA cm−2, respectively. The corresponding mean threshold energy densities in the shock bath were 2·8, 2·9 and 3·1 mJ cm−3. Despite the differences in threshold current density among the waveforms, no differences in safety factor (shock strength for 50 per cent postshock depression divided by threshold shock strength) were found among the waveforms. The current safety factors were 5·4, 5·4, 5·6 and 5·5 for the 5 ms single pulse, 10ms single pulse, dual unidirectional pulse and reciprocal pulse, respectively. The corresponding energy density safety factors were 25, 27, 29 and 27. Thus the use of this reciprocal pulse waveform provides no advantage in efficacy or safety over waveforms of the same total duration.