Surface EMG analysis on normal subjects based on isometric voluntary contraction.

The objective of this study was to compute reference SEMG values for normal subjects of 13 parameters extracted in the time, frequency and bispectrum domain, from the Biceps Brachii (BB) muscle generated under isometric voluntary contraction (IVC). SEMG signals were recorded from 94 subjects for 5s at 10, 30, 50, 70 and 100% of maximum voluntary contraction (MVC). The Wilcoxon signed rank test was applied to detect significant differences or not at p<0.05 between force levels for each of the 13 parameters. The main findings of this study can be summarized as follows: (i) The time domain parameters turns per second and number of zero crossings per second increase significantly with force level. (ii) The power spectrum median frequency parameter decreases significantly with force level, whereas maximum power and total power increase significantly with force level. (iii) The bispectrum parameter, maximum amplitude, increases significantly with force level with the exception the transition from 30% to 50% MVC. Although, the tests for Gaussianity and linearity show no significant difference with force level, the SEMG signal exhibits a more Gaussian distribution with increase of force up to 70% MVC. The SEMG linearity test, which is a measure of how constant the bicoherence index is in the bi-frequency domain, shows that the signal's bicoherence index is less constant (hence, the signal is less linear) at 70% of MVC compared to 10, 30, 50 and 100% MVC. (iv) The time domain parameters have good correlation between them as well as, between each one of them and maximum and total power. The median frequency has a good (negative) correlation with the bispectrum peak amplitude. (v) No significant differences exist between values based on gender or age. The findings of this study can further be used for the assessment of subjects suffering with neuromuscular disorders, or in the rehabilitation laboratory for monitoring the elderly or the disabled, or in the occupational medicine laboratory.

Development of educational image databases and e-books for medical physics training.

Medical physics education and training requires the use of extensive imaging material and specific explanations. These requirements provide an excellent background for application of e-Learning. The EU projects Consortia EMERALD and EMIT developed five volumes of such materials, now used in 65 countries. EMERALD developed e-Learning materials in three areas of medical physics (X-ray diagnostic radiology, nuclear medicine and radiotherapy). EMIT developed e-Learning materials in two further areas: ultrasound and magnetic resonance imaging. This paper describes the development of these e-Learning materials (consisting of e-books and educational image databases). The e-books include tasks helping studying of various equipment and methods. The text of these PDF e-books is hyperlinked with respective images. The e-books are used through the readers' own Internet browser. Each Image Database (IDB) includes a browser, which displays hundreds of images of equipment, block diagrams and graphs, image quality examples, artefacts, etc. Both the e-books and IDB are engraved on five separate CD-ROMs. Demo of these materials can be taken from www.emerald2.net.

A combined ultrasonic linear array scanner and pulsed Doppler velocimeter for the estimation of blood flow in the foetus and adult abdomen--I: Technical aspects.

A method is proposed for estimating the volume blood flow of deep lying vessels in the foetus and in adult portal vein and renal vessels. The equipment combines a 3.5 MHz linear array scanner with a 2 or 4 MHz pulsed Doppler. The pulsed Doppler tranducer is connected to the linear array by two movable arms. A real time spectrum analyser is used to process the Doppler signals. A water bath was used to perform an in vitro calibration of the complete system and to adjust the registration of the Doppler sample volume with the echo picture. Several possible inaccuracies in vessel diameter measurement are discussed and the mean of several caliper measurements described by Eik-Ness (1982) is used. Time Motion is thought to be the better method but is more complicated in practice.

The computer as a tool in the diagnosis and treatment of peripheral vascular disease.

The application of a mini computer to a routine diagnostic vascular laboratory has been assessed in over 4,500 patients over a period of 5 years. The laboratory functions to provide diagnosis of peripheral vascular disease. The computer functions are: scientific, in which it is used for modelling the arterial system and for applying diagnostic algorithms using haemodynamic signals re-input data, data base management, in which it is used to store clinical histories, the results of haemodynamic tests, and data for reconstructive surgery, and administrative, in which it is used for laboratory booking, report generation and management and workload statistics.

Detection of early atherosclerosis by analysis of ultrasonic Doppler signals produced by mural flow disturbances.

The paper describes an in vitro study using a multi-gate Doppler ultrasound system to investigate flow disturbances in a blood analogue caused by small stenoses (2-25% cross-sectional area reduction), using steady flow (100-600 ml min-1) in a 6 mm diameter rigid artery model. The results indicate that stenoses greater than 5% were detectable.

Triaxial force transducer for investigating stresses at the stump/socket interface.

Although normal pressures at the stump socket interface of the lower-limb amputee have been investigated, little is known about the shear stresses that also occur. Studies suggest that the combination of both shear and normal stresses significantly exacerbates discomfort and vascular and tissue damage. A means of simultaneously measuring normal and shear stresses will aid in the investigation and improvement of prosthetic fit. A miniature triaxial force transducer (4.9 x 16 mm diameter) has been developed which can be recessed into the socket wall. The principle of operation, construction, performance and limitations of the device are described. Preliminary measurements of the interface stress variations over the gait cycle in a supra-condylar PTB socket are presented. These show clear differences in the stress patterns present when two different prosthetic feet are used.

Deceleration vs. acceleration: a haemodynamic parameter in the assessment of vascular reactivity. A preliminary study.

The parameter deceleration vs. acceleration (dc/ac) as derived from the instantaneous peak velocity is obtained by dividing the descending and ascending slopes of plotted velocity curves. Blood velocities were recorded with a specially designed continuous-wave ultrasonic Doppler unit which provides: the instantaneous peak velocity, the instantaneous mean velocity, the acceleration, and an indication of volume flow. A physical meaning to the dc/ac parameter is given through an analysis, based on an electrical model, of a small portion of an artery. This gives a simple relationship which only takes account of the assumed vascular resistances. Measurements were performed in 67 male subjects; 39 were normotensive control subjects and 28 had established moderate hypertension. In both groups there was an increase of dc/ac in passing from the supine to the erect position, the increase being more accentuated by hypertension. The variation of dc/ac with age was significantly different in both groups. The results suggest that this parameter is a sensitive indicator of variations in vascular reactivity and as an indicator of structural changes in the arterial wall.

Finite element modelling of a residual lower-limb in a prosthetic socket: a survey of the development in the first decade.

A review is presented of the existing finite element models developed from 1987 to 1996 for the biomechanics of lower-limb prostheses. Finite element analysis can be a useful tool in investigating the mechanical interaction between the residual limb and its prosthetic socket, and in computer-aided design and computer-aided manufacturing of prosthetic sockets. Various assumptions and simplifications are made in these models to simplify the actual problem with complex geometry, material properties, boundary and interfacial conditions, as well as loading situations. The analyses can provide the information on the stress distribution at the stump/socket interface and within the residual limb tissues. More recently, nonlinear models have been developed taking into consideration the process of socket rectifications, the slip/friction conditions and material large deformation. The models so far developed have provided some basic understanding of the biomechanics. Comparison of the predictions of these models with experimental measurements indicated that the predicted stresses were within the ranges measured, although one-to-one correspondence was difficult to achieve. Further research is still required in order to improve these models to obtain higher precision in the results taking into account nonlinear and dynamic effects.

Development of a non-linear finite element modelling of the below-knee prosthetic socket interface.

A non-linear finite element model has been established to predict the pressure and shear stress distribution at the limb-socket interface in below-knee amputees with consideration of the skin-liner interface friction and slip. In this model, the limb tissue and socket liner were respectively meshed into 954 and 450 three-dimensional eight-node isoparametric brick elements, based on measurements of an individual's amputated limb surface; the bone was meshed into three-dimensional six-node triangular prism elements, based on radiographic measurements of the individual's residual limb. The socket shell was assumed to be a rigid boundary. An important feature of this model is the use of 450 interface elements (ABAQUS INTER4) which mimic the interface friction condition. The results indicate that a maximum pressure of 226 kPa, shear stress of 53 kPa and less than 4 mm slip exist at the skin-liner interface when the full body weight of 800 N is applied to the limb. The results also show that the coefficient of friction is a very sensitive parameter in determining the interface pressures, shear stresses and slip. With the growth of coefficient of friction, the shear stresses will increase, while the pressure and slip will decrease.

Clinical investigation of the pressure and shear stress on the trans-tibial stump with a prosthesis.

A system for measuring pressures and bi-axial shear stresses at the body support interfaces has been developed. This system has been used, in five unilateral trans-tibial amputees, to investigate the stresses at multiple points on the residual limb and prosthetic socket interface during standing and walking. The subjects investigated regularly used a patellar-tendon-bearing socket. The maximum peak pressure at the measured points was 320 kPa over the popliteal area during walking. The maximum shear stress was 61 kPa over the medial tibia area. Variable wave-forms of stress during walking were observed at the different measured points. The influence of the angular alignment on the stresses was investigated on one subject. It was found that a miss-alignment of +/- 8 degrees produced a change in peak longitudinal shear stress of between 8% and 11.5%.

Frictional action at lower limb/prosthetic socket interface.

The frictional action at stump/socket interface is discussed by a simplified model and finite element model analyses and clinical pressure measurements. The friction applied to the stump skin produces stresses within tissue and these stresses may damage the tissues and affect their normal functions. The combination of normal and shear stresses is considered to be a critical factor leading to amputee's discomfort and tissue damage. However, friction at the stump/socket interface has a beneficial action. A simplified residual limb model and a finite element model using real geometry have been developed to analyse the support action of friction. Both results show that the friction plays a critical role both in supporting the load of the amputee's body during the support phase of the gait cycle and in preventing the prosthesis from slipping off the limb during swing phase. Pressure at the below-knee socket during walking were measured with conditions of different friction. The results reveal that a larger pressures was produced at the lubricated interface than at the normal interface. A proper choice of coefficient of friction will balance the requirements of relief of load stress and reduction of slip with the general ability to support loads.

A transputer-based physiological signal processing system. Part 1--System design.

This paper, the first of two, details the design and in-vitro testing of a transputer-based physiological signal processing system. The heart of the system is a transputer-based digital signal processing (DSP) board which can act as a stand-alone spectrum analyser, designed to operate in the audio-frequency band up to 25 kHz. The board comprises a T800 processor, two A100 transversal filters, 12 bit A-D circuitry capable of sampling up to 48 kHz, memory and address mapper. The initial application of the system is for the detection of early arterial disease. For this the DSP board is harnessed to the front end of a multigate pulsed Doppler ultrasound scanner operating at 4.8 MHz insonation frequency and incorporating a vessel wall tracking unit. The complete system performs a Fourier transform on the backscattered signals, providing spectral information on discrete areas of flow (0.6 mm3) across the vessel lumen in real time. This first paper describes the hardware, and the second describes the performance testing of the system on the bench and an assessment of its ability to detect low grade stenoses during steady flow.

A transputer-based physiological signal processing system. Part 2--System testing and investigation of flow through models of very small arterial stenoses.

This paper describes the performance testing of a novel transputer-based physiological digital signal processing (DSP) unit and its application in the interpretation of pulsed Doppler ultrasound signals, obtained from models of arterial stenoses. The first test used the DSP unit as a stand-alone spectrum analyser using (1) sinusoidal frequencies (50 Hz to 10 kHz) and (2) filtered white noise (centre frequency 3 kHz, bandwidth 2.5 kHz). For the second test, the DSP unit was attached to a 30-channel multi-gate Doppler ultrasound scanner (transmitting a 4.8 MHz pulse with a repetition frequency of 4.8 kHz) and a vessel tracking unit. The Doppler ultrasound signals obtained from steady flow (100-600 ml/min) in a rigid acrylic tube (internal diameter 6 mm) were then analyzed by the DSP unit and a commercially available system. Lastly, an in vitro investigation into the flow disturbances around very small stenoses (2-25% cross-sectional area reduction), using steady flow (100-600 ml/min), was undertaken. The results indicated that the system was capable of detecting stenoses as small as 5% cross-sectional area reduction.

Phase-locked loop techniques applied to ultrasonic Doppler signal processing.

A new method of measuring blood flow velocity and acceleration using analogue and phase locked loop techniques is described. Instantaneous peak velocity, instantaneous mean velocity and acceleration can be obtained on-line and displayed on simple recording systems.

Evaluation of introducing the team approach to the care of the amputee: the Dulwich study.

The effects of introducing the Team Approach to the management of the lower limb amputee has been assessed in a consecutive series of 233 patients over a five year period. During the first year, baseline data was collected and during the subsequent yearly phases the effects of introducing a physiotherapist co-ordinator, visiting prosthetist and medical officer from the local Artificial Limb and Appliance Centre (ALAC), and finally trained surgeons were studied. During the final phases of the study, the effects of changing team staff were monitored. The results have shown that only when the full Team Approach is adopted are the best results achieved, but that, once this approach is established, staff changes can be made without serious reductions in effectiveness. The study has shown that the team can reduce in-patient stay by 20 days; reduce the need for post-discharge physiotherapy by 94%; increase the proportion of patients discharged with a prosthesis more than fivefold and increase the effectiveness of long term rehabilitation threefold.

The effect of footwear mass on the gait patterns of unilateral below-knee amputees.

This study reports an investigation into the effect of shoe mass on the gait patterns of below-knee (BK) amputees. Ten established unilateral BK, patellar-tendon-bearing prosthesis wearers were assessed using a VICON system of gait analysis. Incremental masses of 50g (up to 200g) were added to the subjects' shoes and data captured as they walked along a 15m measurement field. Coefficients of symmetry of various parameters of the swing phase (knee frequency symmetry, swing time symmetry) were measured and their correlation was tested with the patient's preferred shoe mass and also their own shoe mass, all expressed as a proportion of body mass. The subjects' 'preferred' shoe mass (139-318g) showed the greatest symmetry in all the parameters examined (correlations 0.78-0.81 p less than 0.01 and less than 0.005), whereas there was no correlation between the subjects' own shoe mass (121-325g) and the symmetry coefficients measured.

The effect of adjuvant oxygen therapy on transcutaneous pO2 and healing in the below-knee amputee.

The effects on tissue oxygenation of postoperative adjuvant oxygen have been studied in a group of 20 patients undergoing below-knee (BK) amputation for vascular disease. Ten patients received no therapy, the remainder receiving 28% oxygen for 48 hours following surgery. The results showed that the transcutaneous pO2 in the amputation flaps fell significantly by some 20 mmHg (p less than 0.01) following surgery and that this fall was prevented by the use of adjuvant oxygen. The fall was not observed in the non-amputated limbs. TcpO2 took almost two weeks to reach its pre-operative levels in the amputated limbs. The effect on stump healing of adjuvant oxygen therapy was investigated in a randomized controlled trial in a series of 39 patients undergoing BK amputation. There were 22 patients in the control (untreated) group and 17 in the treated group (adjuvant oxygen for 48 hours). In the treated group 14 patients healed primarily and three amputations failed. In the untreated group 14 limbs healed primarily, one secondarily and there were 7 failures. The pre-operative transcutaneous values in the stumps which failed (26 mmHg +/- 14) was significantly lower (p less than 0.005) than in those which healed (40 mmHg +/- 9). The mean pre-operative TcpO2 in the patients in whom healing occurred in the treated group (35 mmHg +/- 10) was significantly lower (p less than 0.001) than the mean pressure observed in the untreated group (44 mmHg +/- 9).

Limb perfusion in the lower limb amputee--a comparative study using a laser Doppler flowmeter and a transcutaneous oxygen electrode.

Accurate and objective assessment of amputation level in the lower limb plays an important role in patient management. Laser Doppler flowmetry (LDF) is a new and noninvasive technique for skin blood flow measurement and has been used pre-operatively in 25 patients undergoing amputation for vascular disease and in five normal controls. Baseline flux measurements were made at room temperature on the medial aspect of legs and then again after local heating of the skin for five minutes. Transcutaneous oxygen measurements were made at the same site for comparison and amputation level in patients selected on this basis. Significant differences (p less than 0.001) in TcPO2 values were found between controls (10.9 +/- 0.5 kPa), below-knee (BK) amputees (6.0 +/- 1.5 kPa) and above-knee (AK) amputees (1.5 +/- 0.6 kPa). Baseline LDF flux did not differ significantly between any group. Heated flux values did however show a significant difference (p less than 0.005) between controls (52.4 +/- 23.5) and both BK (20.6 +/- 9.2) and AK groups (8.1 +/- 7.7) and also between the amputee groups. The relative increase in flux (heated flux/baseline flux) differed significantly between the BK (3.3 +/- 1.5) and AK (1.2 +/- 0.3) groups (p less than 0.001) and between these two and the controls (11.2 +/- 5.4) (p less than 0.001). The correlation between relative increase in flux and TcPO2 was 0.7 (p less than 0.001). It is concluded that laser Doppler flowmetry used in conjunction with thermal stressing could provide a quick, simple and non-invasive method for objectively determining amputation level in the lower limb.