Biomedical subjects
R N Scott
Publications and source records attributed to R N Scott.
Melphalan concentration and distribution in the tissues of tumour-bearing limbs treated by isolated limb perfusion.
Levels of melphalan (L-phenylalanine mustard) were measured in the tissues of tumour-bearing limbs treated by isolated limb perfusion (ILP). 41 samples of melanoma tissue, normal fat and skin were excised from 15 patients during ILP. A high performance liquid chromatography assay was used to measure melphalan concentrations. Levels of melphalan were higher in tumour than in fat (P < 0.01, Wilcoxon signed-ranks test), and not significantly different from levels in adjacent skin. In 2 cases there was significant regional toxicity in the treated limb, but this was not related to the levels of melphalan measured in the tissues of the limb. It is encouraging that the concentrations of melphalan which were achieved in large necrotic nodules by ILP were similar to those in well-perfused normal skin.
The pharmacokinetic advantages of isolated limb perfusion with melphalan for malignant melanoma.
We describe melphalan pharmacokinetics in 26 patients treated by isolated limb perfusion (ILP). Group A (n = 11) were treated with a bolus of melphalan (1.5 mg kg-1), and in a phase I study the dose was increased to 1.75 mg kg-1. The higher dose was given as a bolus to Group B (n = 9), and by divided dose to Group C (n = 6). Using high performance liquid chromatography (HPLC) the concentrations of melphalan in the arterial and venous perfusate (during ILP) and in the systemic circulation (during and after ILP) were measured. Areas under the concentration time curves for perfusate (AUCa, AUCv) and systemic (AUCs) data were calculated. In all three groups the peak concentrations of melphalan were much higher in the perfusate than in the systemic circulation. The pharmacokinetic advantages of ILP can be quantified by the ratio of AUCa/AUCs, median value 37.8 (2.1-131). AUCa and AUCv were both significantly greater in Group B than in Group A (P values less than 0.01, Mann-Whitney). In Groups B and C acceptable 'toxic' reactions occurred but were not simply related to melphalan levels. Our phase I study has allowed us to increase the dose of melphalan to 1.75 mg kg-1, but we found no pharmacokinetic advantage from divided dose administration.
Pilonidal abscess of the penis.
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Psychological morbidity in the first year after breast surgery.
In this prospective study, the psychological morbidity associated with the treatment of breast cancer was assessed. The study population comprised all patients referred to one centre with a recently diagnosed breast lump, who were to undergo surgery. Psychological morbidity was assessed preoperatively and at 6 and 12 months postoperatively by modified Rotterdam Symptom Checklist. Three hundred and twenty patients completed all three questionnaires: 93 women undergoing mastectomy, 73 women having conservation therapy for breast cancer and 156 women having biopsy for benign breast disease. Patients with a breast malignancy smaller than 4 cm in diameter were treated by lumpectomy and radiotherapy, anti-oestrogen therapy or chemotherapy alone or in combination. Psychological morbidity among patients with malignant disease was significantly greater than that seen in the group with benign disease. Among cancer patients, a significant decrease in anxiety and depression occurred during the year following surgery. The study failed to demonstrate any psychological advantage associated with breast conservation.
Noise characteristics of stainless-steel surface electrodes.
Bioelectric events measured with surface electrodes are subject to noise components which may be significant in comparison with low-level biological signals such as evoked neuroelectric potentials, and myoelectric potentials. In an effort to better understand noise arising from these electrodes, electrode and measurement system noise is modelled. The effect of electrode surface area on electrode impedance and noise is studied using circular stainless-steel electrodes of varying diameters. The main contributions of the work are the development of a model for stainless-steel electrode noise as a function of electrode area, and demonstrating that, for the band-width of interest to evoked neuroelectric and myoelectric signals (8-10,000 Hz), the primary noise components are thermal and amplifier current generated. The magnitudes of both of these depend on the electrode impedance magnitude. Electrode impedance is shown to be a power function of both electrode diameter and frequency, consistent with a capacitive electrode model.
Control performance characteristics of myoelectric signal with additive interference.
Myoelectric signal is an important source of control information for powered prostheses. A commonly used performance measure for the signal processors of such control systems is the ratio of processor output mean to variance. This ratio (SNR) is a function of a number of factors including physiological parameters and additive interference. The paper investigates the effects of motor unit physiological parameters and interference on control performance, with particular reference to SNR. Performance equations are derived and verified with in vivo experiments. The results show a complex interaction among the physiological parameters and interference. A particular point of interest is the misleading SNR values that can occur under certain recruitment and interference conditions.
Study of the effects of motor unit recruitment and firing statistics on the signal-to-noise ratio of a myoelectric control channel.
An important measure of the performance of a myoelectric control channel for powered artificial limbs is the myoelectric signal processor output signal-to-noise ratio (SNR). The signal and noise in this context are, respectively, the mean and variance of the estimate of some signal parameter to be used for control purposes. These quantities are determined by the signal processor, motor unit recruitment and motor unit firing statistics. The paper investigates, through analytical, simulation and experimental work, the role and significance of recruitment and firing statistics in channel performance. Equations are derived which express, for the single and multi-unit cases, channel SNR as a function of the number of active units, firing rates, action potential amplitude variation and action potential moments. A computer-simulated myoelectric signal is generated in which these variables can be controlled and SNR measured. The simulation results are compared with the theoretical and found to agree very well. Limited experiments with wire intramuscular electrodes and surface electrodes are performed to measure in vivo SNR from the biceps brachii muscle. The results of the experiments agree well with those of the simulation and theoretical work. The significance of this work is that it provides insight into the roles of important physiological parameters in myoelectric channel performance. It will also provide data necessary for the development of SNR enhancement techniques.
The application of neural networks to myoelectric signal analysis: a preliminary study.
Two neural network implementations are applied to myoelectric signal (MES) analysis tasks. The motivation behind this research is to explore more reliable methods of deriving control for multidegree of freedom arm prostheses. A discrete Hopfield network is used to calculate the time series parameters for a moving average MES model. It is demonstrated that the Hopfield network is capable of generating the same time series parameters as those produced by the conventional sequential least squares (SLS) algorithm. Furthermore, it can be extended to applications utilizing larger amounts of data, and possibly to higher order time series models, without significant degradation in computational efficiency. The second neural network implementation involves using a two-layer perceptron for classifying a single site MES based on two features, specifically the first time series parameter, and the signal power. Using these features, the perceptron is trained to distinguish between four separate arm functions. The two-dimensional decision boundaries used by the perceptron classifier are delineated. It is also demonstrated that the perceptron is able to rapidly compensate for variations when new data are incorporated into the training set. This adaptive quality suggests that perceptrons may provide a useful tool for future MES analysis.
Operator performance in myoelectric control of a multifunction prosthesis stimulator.
In this paper, a microcomputer-based system is described which facilitates the evaluation of different myoelectric control strategies. The system is based on an IBM-PC/AT microcomputer which generates and develops tracking targets, processes and displays the operator's response, and computes tracking performance. The dynamics of the prosthetic elbow, hand, and forearm are simulated in software which drives a stick figure in response to the operator's input. Performance is measured in terms of integral absolute error in target-response match. Control strategies to simulate different systems are easily modified through software and are evaluated under identical conditions. As a test of this evaluation system and to obtain some comparative data on control strategies, four strategies which are either in use or proposed for use are evaluated. The test procedure is divided into a control training session and a control evaluation session. Data collected from groups of three normally-limbed subjects per strategy over a period of five control evaluation sessions are presented. The results of this evaluation are discussed and improvements in the evaluation system suggested.
Myoelectric control systems research at the Bio-Engineering Institute, University of New Brunswick.
Myoelectric controls research began at the University of New Brunswick in 1960, and has continued without interruption since that time. The Bio-Engineering Institute has emphasized control systems which meet special clinical needs. These have included systems for amputees with only a single muscle remnant with which to control a prosthesis and, more recently, systems which provide the best possible appearance for children and for infants as young as 15 months of age. Throughout this work, however, the Institute has maintained a fundamental interest in the problem of control of complex multifunction prostheses. With recent developments in electromechanical systems this more advanced controls research will find clinical application shortly.
Feedback in myoelectric prostheses.
This article briefly reviews the history of the use of feedback in artificial limbs. It suggests that researchers have concentrated unduly upon the use of feedback to control prehensile force or joint angle and advocates a broader perspective. In that context, the article presents a comprehensive view of the need for feedback in myoelectric prostheses. The difficulties of designing transducers to meet the stringent demands of prosthetics applications are considered, and problems inherent in several alternatives are identified. Various means of conveying feedback information to the amputee are reviewed in some detail. The concept of feedback in control systems is introduced in the context of closed-loop control of a prosthesis. The surprisingly good performance of skilled users of myoelectric prostheses is noteworthy implying that the distinction between sensory and proprioceptive feedback may be somewhat artificial. By integrating these two feedback types a satisfactory feedback system may become an attainable goal.
Do artificial limbs become part of the user? New evidence.
This paper provides evidence that limb-deficient subjects who wear artificial arms tend to overestimate the perceived length of their residual limb. It is proposed that this "perceptual error" may provide a useful and possibly more valid alternative to existing methods of determining prosthetic acceptance. The degree of overestimation is substantial for most subjects with amputations, and typically represents 20 percent of the length of the prosthetic arm. The effect is considerably reduced when the prosthetic limb is removed. Comparisons are made with normal-limbed subjects of various ages. For the most part, their errors are small and typically are underestimates of actual limb length. This research is compared with the work of Fraser (1984), who found similarities in reaching trajectories for normal and artificial arms. Further investigation is required to determine if this effect may serve as an index of adjustment to a prosthesis and, additionally, if prosthetics training programs might benefit from including techniques for enhancing perceptual adaptations to artificial limbs.
A biphasic pulse burst generator for afferent nerve stimulation.
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Characterization and processing of surface recorded spinal somatosensory evoked potentials.
Somatosensory evoked potentials were recorded from the skin surface overlying the spinal cord, from the lower lumbar to the lower cervical regions. The recorded responses did not vary over time in any one individual and at each level a consistent wave shape was obtained across all individuals tested. Since the initial signal-to-noise ratio (SNR) for the evoked response recorded at any cord level is very low, the signal data must be processed. In this study, bandpass filtering or matched filtering was used together with ensemble averaging to obtain a usable signal in a reasonable processing time. SNR was improved approximately 1.5 X with bandpass filtering and 2 X with matched filtering. Although the output of the matched filter is a distorted version of the input signal, detection of information is enhanced and processing time using the matched filter and ensemble averaging can be reduced to 1/4 that required for ensemble averaging alone.
Split power rails for battery operated equipment--design alternatives.
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Improved battery saving device for use with myoelectric control systems.
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Epoxy moulding system for the encapsulation of microelectronic devices suitable for implantation.
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