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V C Roberts

Publications and source records attributed to V C Roberts.

At least 19 recordsLinked to original sources
PubMed1998

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%.

Adult↗
PubMed1998

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.

Artificial Limbs↗
PubMed1996

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.

Arteries↗
PubMed1996

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.

Amputation Stumps↗
PubMed1995

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.

Arteries↗
PubMed1995

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.

Artificial Limbs↗
PubMed1995

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.

Adolescent↗
PubMed1994

Raynaud's phenomenon and cold stress testing: a new approach.

There are a number of methods of evaluating digital blood flow in the vascular laboratory but none fulfills the criteria of providing a quick and reproducible diagnostic test for Raynaud's phenomenon. We present our experience with the use of high frequency ultrasound to provide direct real time imaging of the digital arteries. Using this method and a standardised cold challenge test, consisting of exposure of the hand to a temperature of 10 degrees C for 5 minutes, it is possible to distinguish patients with Raynaud's phenomenon from normal controls on the basis of extent of digital artery closure. The mean fall in digital artery diameter on cold challenge, expressed as a percentage of the original diameter, was 92.4% (S.D. = 16.4, S.E.M. = 2.1) in patients with Raynaud's phenomenon as against 8.7% (S.D. = 11.5, S.E.M. = 2.5) in a group of normal volunteers. Using a 45% fall in digital artery diameter as the diagnostic cut-off point, the test has a specificity of 100% and a sensitivity of 96.6% in differentiating patients with Raynaud's phenomenon from controls. It is suggested that the test could be used as objective confirmation of a clinical diagnosis and to assess the efficacy of therapeutic interventions.

Adolescent↗
PubMed1993

The effect of shear forces externally applied to skin surface on underlying tissues.

The effects of shear forces externally applied to the skin surface on the underlying tissues have been investigated. An analysis of the internal stresses and strains was conducted using a simplified model incorporating elasticity theory. Skin blood flow was measured using laser Doppler flowmetry while variable shear forces over a range of 0-250 g were applied to the skin surface. The theoretical model predicts that the application of surface shear forces alters the internal stress distribution and makes the shear and compressive components of stresses increase ahead of the surface force application point. The force resulting from concomitant application of shear and normal force determines the internal maximum stress and strain. Theoretically, the shear force should have the same effects on the underlying tissues as normal force. The experimental investigations revealed that the skin blood flow decreased roughly linearly with the increase of shear forces. When a shear force equal to the normal force was applied, the flux decreased by 45%, nearly equal to the increasing magnitude (41%) of resultant of normal and shear forces.

Adult↗
PubMed1992

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.

Amputation Stumps↗
PubMed1991

Accuracy of colour Doppler ultrasound velocity measurements in small vessels.

Colour Doppler ultrasound offers the possibility of imaging small vessels not visible by B-mode alone. The colour Doppler image of velocities allows the course of small vessels to be imaged in the X-Y plane of the scan provided the Doppler frequency shift is of sufficient magnitude. This permits alignments of the Doppler cursor, allowing angle correction to provide true velocity measurements from the Doppler shift obtained. Before attempting to make velocity measurements, however, it is essential to be aware of the possible error in the Z plane caused by the thickness of the Doppler sample volume. To quantify this source of error, hydrophone and flow-rig measurements were performed on an Acuson 128 colour Doppler scanner with both 5 MHz linear-array and 3.5 MHz phased-array transducers. Measurements of the transmitted pulses using a point hydrophone showed that both probes employ approximately 3.5 MHz Doppler pulses (in both colour and pulsed Doppler modes). The two transducers have the same axial resolution. In colour Doppler mode the axial length of the sample volume increases automatically with depth by up to 0.5 mm. Measurements of colour and pulsed Doppler signal strength were obtained in a controlled flow rig. Both transducers produced accurate colour flow images of the phantom at their optimum depths; flow velocity errors due to Z-plane thickness are less than 5%. There was, however, substantial error outside these optimum conditions (up to 20%).

Arteries↗
PubMed1991

Digital artery calibre measurement--a new technique of assessing Raynaud's phenomenon.

This study evaluated the use of a high frequency A-mode ultrasound scanner (CUTECH DM70) for monitoring the digital artery vasospasm of Raynaud's Phenomenon (RP). The technique was evaluated on 12 RP patients and 12 age and sex matched controls. The diameter of a single digital artery was measured in these subjects over a range of finger temperatures between 14-35 degrees C. The reproducibility of the measurements was assessed by repeating the procedure in two subjects (a control and an RP patient) on 5 separate days. The results confirmed that the technique is reproducible and monitored vasospasm occurring in all 12 RP patients. In the temperature range tested, none of the controls developed digital artery vasospasm. At finger temperatures greater than 25 degrees C the response to thermal stimuli of the digital arteries in RP patients and controls was similar. However, at temperatures less than 25 degrees C a marked vasoconstriction leading to complete digital artery closure was seen in the RP patients and not in the controls. This technique may prove useful in monitoring RP patients.

Adult↗
PubMed1990

Ultrasound imaging of digital arteries.

This study assessed the use of high frequency ultrasound (CUTECH DM70) in the measurement of digital artery diameters. The accuracy of the technique was assessed using a model. Four silicone tubes of different diameters were embedded in opaque agar. Three independent observers measured the diameter of the tubes using the CUTECH DM70 and the measurements obtained were compared with those obtained using a travelling light microscope. The technique was then evaluated on digital arteries. Ten recordings of digital artery diameter were made at a fixed point on the index finger in two subjects at 20 degrees C and at 30 degrees C. There was no statistical difference between the mean diameters obtained by the three observers using the CUTECH DM70 on the model. No statistical difference was noted when the mean diameters measured using the travelling microscope were compared with those obtained by the three observers. The diameter differences between the tubes were all highly significant (P less than 0.001 Mann Witney). The variability in the recordings of digital artery diameter in the two subjects was very low (maximum coefficient of variance less than 4%). A significant difference in the mean measured vessel diameter at the two different temperatures was obtained (P less than 0.001 Mann Witney). We conclude that digital artery diameter can be measured using the CUTECH DM70.

Arteries↗
PubMed1989

Detection of breast cancer by measuring areolar blood flow--a pilot study.

Regional blood flow in the areola was measured by using the non-invasive transient thermal clearance method in normal breasts and in breasts involved with cancer. Areolar blood flow (ABF) in normal breasts was almost constant for women in the age range 20-60y, but decreased at higher ages. ABF in breasts involved with cancer was higher than that in the contralateral breast, and higher than the average normal ABF in the corresponding age group. The effect was more prominent in the left breast. The transient thermal clearance method provides a potential non-invasive means for detection of breast cancer.

Adult↗
PubMed1989

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.

Amputation, Surgical↗
PubMed1989

Wound hematoma: prophylaxis with topical thrombin.

We studied 123 patients having elective exploratory laparotomy through a midline vertical incision for gynecologic disease; patients were randomized to receive wound irrigation with either saline or topical thrombin before closure of the incision. Seven patients were not evaluable. No patient received low-dose heparin therapy perioperatively. No patient in either group had a clinically significant wound hematoma or disruption. Minor wound hematomas were more common in the saline group, a finding that approached statistical significance. Blood coagulation profiles were not different in the two groups either preoperatively or postoperatively. Topical thrombin is probably not clinically useful in preventing wound hematomas in patients who do not receive perioperative treatment with low-dose heparin; however, it seems to be safe for application to open wounds.

Administration, Topical↗