Medical Engineering & Physics (MED ENG PHYS )

Publisher: Institute of Physics and Engineering in Medicine (Great Britain), Elsevier


Medical Engineering & Physics provides a forum for the publication of the latest developments in biomedical engineering, and reflects the essential multidisciplinary nature of the subject. The journal publishes in-depth critical reviews, scientific papers and communications of work which is at an earlier stage of development. Topics covered include clinical engineering, biomedical computing, biological systems, instrumentation, medical imaging technology, biomaterials, biomechanics and rehabilitation. Medical Engineering & Physics keeps both medical engineers and clinicians abreast of the latest applications of technology to health care.Months of publication: February, March, May, June, August, September, November, December.Index bound in last issue of calendar year.

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    Medical engineering & physics (Online), Medical engineering and physics
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    • Publisher last contacted on 18/10/2013
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Publications in this journal

  • [Show abstract] [Hide abstract]
    ABSTRACT: One of the less desirable features about technological advances in medicine is that individuals working with sophisticated monitoring equipment are often bombarded by warning sounds and signals. However, there are some basic cognitive psychological principles which suggest that the over-use of auditory warnings in such circumstances may be counter-productive. This review highlights some of these principles, arguing that future systems should place more emphasis upon cognitive capabilities and predispositions in their design. Upcoming alarms standards where issues such as the number of alarms, their recognizability, and the principle of 'urgency mapping' are discussed with relation to the cognitive psychology of sound.
    Medical Engineering & Physics 12/1994; 16(6):445-9.
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    ABSTRACT: A microcomputer-based system developed for the automated analysis of the electromyogram (EMG) recorded from respiratory muscles in a variety of situations is described. In addition, an assessment of the performance of the system is presented, along with data relating intercostal EMG activity to ribcage movement in seated subjects. Studies were performed on sixteen normal subjects--non smokers, mean (+/- SD) age 31 (+/- 6) years, mean (+/- SD) mass 78 (+/- 8) kg--of which fifteen studies proved suitable for analysis. Each study lasted for a period of five minutes, during which time recordings of intercostal EMG, ribcage postero-anterior displacement (RCPA) and airflow were made. For every breath taken by each of the subjects, the peak integrated EMG activity (iEMGpeak) was measured both by hand and by the automated system. The automated and manual measurements of iEMGpeak, which ranged from 0.0 to 91.3 microV, differed by only -0.82 +/- 3.34 microV (mean +/- SD). The index iEMGpeak and two additional indices of iEMG activity (iEMGmean, iEMGarea) were evaluated with respect to RCPA, a measure of overall respiratory activity. The indices of iEMG were observed to show an exponential dependence on RCPAamp, the amplitude of ribcage motion. Following a log transformation to linearise the relationship, the correlation of each index with RCPAamp was evaluated; iEMGpeak and iEMGarea correlated similarly with RCPAamp (no significant difference at 5% level), but iEMGmean was found to be a significantly different (p < 0.001) and poorer correlate. We conclude that the automated analysis of respiratory iEMG as described in this paper can provide results showing consistency with manual measurement.(ABSTRACT TRUNCATED AT 250 WORDS)
    Medical Engineering & Physics 12/1994; 16(6):477-83.
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    ABSTRACT: In a project on the mapping of body surface potentials evoked by implanted spinal cord stimulators and transcutaneous electrostimulators, a simple device was developed for use in polyclinical practice for easy checking of the function of these stimulators. The device is an electrical stethoscope and consists of an instrumentation amplifier, bandpass filter, a distortion circuit and a headphone. In vivo measurements demonstrate the generation of an amplitude-dependent tone by the distortion circuit. The apparatus is in many aspects similar to a stethoscope: simple to understand and a practical tool for a fast Go/No-Go test. The device can be optionally connected with a PC and enables body surface mapping documentation within a few minutes.
    Medical Engineering & Physics 12/1994; 16(6):492-5.
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    ABSTRACT: In this study, human umbilical vein and human saphenous vein endothelial cells were seeded on glass and exposed to fluid shear in a parallel-plate flow chamber. Cell retention, morphology and migration were studied as a function of shear stress and of adhesion time prior to exposure to shear. Three-hour and 24-h adhesion times gave rise to comparable cell retention values after 2 h of flow for both cell types. Cell retention decreased from 85 to 20% as shear stress increased from 88 to 264 dynes cm-2 (8.8 to 26 Pa). Mean spreading areas decreased after the onset of flow, but subsequently stabilized to plateau values, which were smaller at higher shear stresses. Shape factors increased faster to higher values as cells were exposed to higher shear stresses, without any obvious preference in orientation of the cells with respect to the direction of flow. Migration was unidirectional with flow and linear with time. Migration was faster for cells which had adhered for 24 h than for cells which had adhered for 3 h and was accompanied by the presence of fibrillar structures left behind on the surface upstream of migrating cells. It is concluded that after 3 h adhesion to glass, cells have adhered with an adhesion strength that does not substantially increase during the next 21 h. However, during this time changes in cell-substratum interactions seem to occur judging by the differences in, e.g., migration rates.
    Medical Engineering & Physics 12/1994; 16(6):506-12.
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    ABSTRACT: A new geometry for the design of polyurethane leaflet heart valves has been investigated. The geometry termed the 'alpharabola' has a radius of curvature that increases from the centre of the leaflet at the free edge towards the base of the valve and perimeter of the leaflet. The hydrodynamic function and leaflet opening characteristics of the new valve design have been compared to a valve with a spherical leaflet geometry using the same material. The pressure and flow required to open alpharabola leaflets in steady flow tests was markedly lower than for spherical leaflets. Under pulsatile flow conditions with the valve leaflets fully open, the pressure drop across the alpharabola and spherical leaflets was similar, but much lower than in a porcine bioprosthesis. High speed photography showed that the alpharabola leaflets opened in less than 30 ms with the leaflet opening initiating in the base of the leaflet where the radius of curvature was larger. The synthetic leaflet valve has demonstrated short term durability in accelerated fatigue tests to 100 million cycles.
    Medical Engineering & Physics 12/1994; 16(6):470-6.
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    ABSTRACT: This paper investigates the possibility of characterizing the differences between normal- and high-risk postoperative cardiac patients on the basis of four parameters related to a simple linear model of cardiorespiratory performances. The model comprises three subsystems representing cardiac, vascular and respiratory functions, respectively. These parameters, determined from physiological variables measured in the Intensive Care Unit, seem useful for clinical evaluation of patient status. In fact, their values quantify the improved cardiovascular and respiratory response that normal-risk patients exhibit to increasing metabolic needs after hypothermic treatment, with less utilization of blood oxygen reserve. In addition, a set of three parameters derived from the proposed four allows a prediction of patient class membership with an error lower than 7% when used with a Bayes quadratic classifier.
    Medical Engineering & Physics 12/1994; 16(6):484-91.
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    ABSTRACT: A mathematical model is developed to investigate the coupled electrochemical processes of nerve-pulse transmission via adrenergic synapse. Based on pharmacological and morphophysiological data, the model describes the dynamics of the propagation of the electric signal along the unmyelinated geometrically non-uniform axon of the neuron and the chemical mechanisms of the transformation of the electrical signal in the synaptic zone into the post-synaptic output. The combined nonlinear system of partial and ordinary differential equations has been obtained and solved numerically. The results of computer simulation of the function of the idealized adrenergic neuron quantitatively and qualitatively describe the dynamics of Ca2+ ion influx into the terminal, noradrenaline release from the free 'releasable' store, its diffusion into the synaptic cleft, binding with the adrenoceptors on the pre- and post-synaptic structures with the generation of the inhibitory post-synaptic potential, and utilization of noradrenaline by neuronal and non-neuronal capture mechanisms.
    Medical Engineering & Physics 12/1994; 16(6):450-7.
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    ABSTRACT: Rate and rate variation algorithms used by implantable devices designed for management of life-threatening arrhythmias have major limitations in separating physiologic sinus tachycardia (ST) from pathologic ventricular tachycardia (VT) requiring therapy. These algorithms presently utilize criteria such as simple heart rate, stability of rate, or derivative of rate (sudden onset) which assumes a gradual onset for ST and an abrupt onset for VT. An alternative method employing median filtering was designed, tested, and compared to a previously published sudden onset rate algorithm using the same data set for analysis of performance. In 50 patients, the onset of ST during exercise and onset of VT were analysed. To accommodate occasional outlying intervals which might affect rate derived by averaging, a five-cycle median filter was used to smooth heart rate. Results from using a 'fixed-interval' or a 'percent' change in the median gave better discrimination of ST and VT than previously published 'fixed-interval' or 'percent' change algorithms. The superiority of median filtering performance was validated by statistical measures.
    Medical Engineering & Physics 12/1994; 16(6):513-7.
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    ABSTRACT: A large number of spatial coordinates were directly measured on two wet anatomical muscle specimens with a measuring device specifically designed to collect cylindrical coordinates. Three-dimensional coordinates of muscle attachment circumferences, joint centres and bone landmarks were collected. All the measured points of a segment, including the adjacent joint centres, were referred to a reference system defined by three marked screw heads at the femur and tibia. The points of the pelvic segment were referred to three marks on a lumbar mounting plate. This approach allows one to define and to transform the data to any reference frame.
    Medical Engineering & Physics 12/1994; 16(6):518-25.
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    ABSTRACT: The closing motion of the occluder leaflets in bileaflet type mechanical heart valves (MHV) was monitored with a laser sweeping technique. The angular displacements of the leaflets were registered with precision of 0.2 microsecond steps. Experimental measurements were made using five 29 mm Edwards-Duromedics including three original specification (EDOS) and two modified specification (EDMS), and two 29 mm St Jude Medical MHVs. The testing valve was installed in the mitral position of a physiologic pulsatile mock circulatory flow loop using water-glycerine solution as the testing fluid. Each valve was tested by: (1) direct mounting the valve on metal washers, and (2) mounting the valve with its sewing ring. Experiments were carried out at pulse rates of 70, 90, and 120 beats min-1, with the corresponding cardiac output of 5, 6, and 7.5 litres min-1, and maximum left ventricular pressure gradients (dp/dt) of 1,800, 3,000 and 5,600 mm Hg s-1, respectively. The maximum leaflet closing velocity of each of the tested valve types are presented. The difference in leaflet closing movements between the direct rigid mounting and the sewing ring mounting are discussed. The details of the laser sweeping technique are presented.
    Medical Engineering & Physics 12/1994; 16(6):458-64.
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    ABSTRACT: A much smaller percentage of thickened leaflets of the aortic valve have been found in the right or left coronary leaflet than in the noncoronary leaflet. This study investigated the pressure loading transferring to the leaflets of the aortic valve and their effects on the valvular thickening. A simple ascending aorta model was established, and a simulation was made. The pressure loading in the coronary and noncoronary leaflets then were estimated. The simulation results showed that 5.8% to 17.% percentage of pressure loading to the coronary leaflet may be decreased by the coronary perfusion in diastole. The coronary arteries play an important role on pressures in the sinuses of Valsalva. The smaller pressure loading transferring to the coronary leaflet than that to the noncoronary leaflet is one reasonable explanation related to the thickened leaflets of the aortic valve.
    Medical Engineering & Physics 12/1994; 16(6):465-9.
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    ABSTRACT: A biomechanical model and results of numerical simulation of the propagation of electromechanical waves of deformation along the small bowel are presented. The organ is modelled as a soft orthotropic cylindrical biological shell reinforced by orthogonally interwoven smooth muscle elements, embedded in a connective tissue network. The dynamic reaction starts as a response to the propagation of a depolarization wave along the smooth muscle layers. The muscle layers contract independently but in a coordinated way with the generation of active forces. The mechanical properties of the wall are assumed to be nonlinear. Deformations of the bioshell are finite. The governing system of equations is obtained and solved numerically. The finite-difference method of the second order accuracy over the time and space variables was used. The dynamics of strain distribution in the biological shell and shape changes are analysed.
    Medical Engineering & Physics 10/1994; 16(5):406-15.
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    ABSTRACT: Knowledge of the fundamental frequency of transverse vibrations of bones is of interest in bioengineering applications. The finite method is probably the best tool for the numerical determination of natural frequencies and mode shapes of any type of structural system. The present study proposes a simple approach based on the optimized Rayleigh-Ritz method which yields satisfactory answers for many practical applications.
    Medical Engineering & Physics 10/1994; 16(5):422-4.
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    ABSTRACT: Event-related potentials (ERPs) are responses related to the recognition of certain stimuli. P300 is the most important positive component in the ERP and appears around 300 ms after the target stimulus in the oddball paradigm. In our previous work, we proposed a method for the automatic detection of the P300 waveform in single-sweep records by using a correlation technique. However, determination of the threshold values of the P300 waveform for the correlation study was not an easy task. In skirting this problem, we developed an automatic method of detecting a single-sweep P300 waveform by using an artificial neural network. We selected appropriate characteristic parameters of positive peaks as input signals for the input layer units, and the weights between the layers were determined by using the back-propagation algorithm. The neural network for P300 detection was obtained automatically, based on the data of ERPs obtained from 11 healthy males, and gave substantial accuracy for P300 detection. Furthermore, by using this neural network we clarified the way in which the P300 waveform is judged visually by each inspector.
    Medical Engineering & Physics 10/1994; 16(5):425-9.
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    ABSTRACT: Intense interest in knee joint mechanics has resulted in the development of numerous models to predict forces acting at the knee. However, few models have accounted for the unique geometric characteristics of the knee joint's articular surfaces when predicting the mechanical response of the joint. The purpose of this study was to stimulate accurately the complex geometric characteristics of the tibiofemoral joint for input into a finite element model representing the knee joint of athletic females. The right knee of an athletic female with no history of knee joint trauma was imaged using a 0.5 T magnetic resonance imaging (MRI) unit. Twelve cross-sectional slices of the knee were scanned in each of three orthogonal planes (coronal, sagittal and axial) at slice intervals of 6 mm, 7 m, and 8 mm respectively. A scan plan (two coronal images and an axial image) was also generated to enable calculation of the orthogonal scans with respect to one another. Select anatomical reference points representing cancellous and compact bone, major ligament attachment areas, and articular cartilage of the distal femur and proximal tibia were digitized from the processed shadowgraphs. The processed digitized data were input into a computer graphics program which was the pre- and post-processing software for the finite element analysis package. Contours of the cancellous and compact bone of the tibial and femoral condyles were generated using beta and cubic spline curves. Bezier quadratic and cubic polynomials were used to reconstruct the tibial and femoral shafts.(ABSTRACT TRUNCATED AT 250 WORDS)
    Medical Engineering & Physics 10/1994; 16(5):363-9.
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    ABSTRACT: The results of Hert et al. have been re-examined using an external pin fixation technique involving New Zealand White rabbits. New bone formation was assessed with tetracycline epifluorescence in 49 animals. The animals were operated upon using inhalational anaesthesia, and pins were placed at opposite ends of the tibia of both hind limbs. Following recovery, oxytetracycline was given at a dosage of 25 mg kg-1 body weight intraperitoneally on the day of loading and on the fourteenth day of the loading regimen. The bones were loaded for 45 min per 24 h. Undemineralized specimens were sectioned and standardized photographs produced. The area of new bone was determined by a planimeter and by digitization. In dynamic loading the shape of the force/time curve is of little significance; the response is frequency dependent and for higher frequencies the response is greater than that from continuous loading; there was no statistical significance between the rapid relief loading regimens. For continuous loading the response is a function of the load value. In all cases more bone is laid down in immature subjects than in adults. With regard to osteoclastic activity, all loading increased the areas of resorption irrespective of character, in all adult animals intermittent loads produced a greater area of ostoeclastic resorption than static loads and produced a greater change as the number of load cycles per minute increased. The adult control animals had more resorptive activity than the immature animals although there was no statistical significance. Loading, irrespective of its character, led to a net increase of bone, the osteoblastic effects thus outweighing the osteoclastic effects.
    Medical Engineering & Physics 10/1994; 16(5):384-97.
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    ABSTRACT: This paper contains the details of a new technique for measuring the mechanical phase constants of transverse waves in human tibia, in vivo. The measurements are made in the frequency range from 100 to 1000 Hz. The importance of these measurements is that healthy tibia has quite small phase delays along the bone at these frequencies. On the other hand, a fractured tibia has a large phase delay at the fracture site. This paper establishes a set of typical phase delays for a range of tibia so that subsequent measurements on fractured patients can be interpreted. It contains a description of the method of measuring the phase delay and a detailed analysis of errors. In particular, it includes an account of the phase delay through the soft tissues as well as the bone and how the former can be eliminated. It is not an exhaustive account of this topic but contains sufficient results to show that the measurements can be made relatively easily. Finally, there is a theoretical model which can be used to predict the phase shift. However, in order to use the model various other measurements are necessary and a direct measurement of phase is easier than using a model.
    Medical Engineering & Physics 10/1994; 16(5):379-83.
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    ABSTRACT: The management of dysphagia presents a major problem in the comprehensive rehabilitation of stroke and head injury patients. Dysphagia is a disorder of the swallowing process. Oral dysphagia refers to abnormalities in the oral phase of the swallowing mechanism. The oral phase of the swallowing mechanism is important for the proper triggering of the swallowing reflex. Current techniques in oral dysphagia rehabilitation include oro-motor exercises using tongue depressors and mouth-care swabs. There is thus a need for a better therapeutic method for oral dysphagia. The purpose of this paper is to report the development of audio-visual biofeedback devices for treating oral dysphagia. Portable biofeedback devices rendering feedback of biomechanical parameters characterizing the oral phase were developed and evaluated in preliminary clinical trials. A patient progress index (PPI) was developed and used to quantify the overall patient progress. The devices demonstrated good patient acceptability.
    Medical Engineering & Physics 10/1994; 16(5):430-5.