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Biomedical subjects

T A Perkins

Publications and source records attributed to T A Perkins.

At least 19 recordsLinked to original sources
PubMed2003

Implantable telemeter for long-term electroneurographic recordings in animals and humans.

A system is described that amplifies an electroneurographic signal (ENG) from a tripolar electrode nerve cuff and transmits it from the implanted amplifier to an external drive box. The output was raw ENG, bandpass filtered from 800 to 8000 Hz. The implant was powered by radio-frequency induction and operated for coil-to-coil separations up to 30 mm. The testing and performance of the system is described. The input-referred noise was never more than 1 microV RMS, and, at some positions of the radio-frequency field, was 0.7 microV, close to the expected value for the amplifier used. The common-mode rejection ratio (CMRR) depended on the impedance imbalance from the cuff and the length of input cable. Devices with a short cable and low source impedance had CMRR of 84 dB, but, with 31 cm of cable and a real cuff, the CMRR fell to 66 dB. Recovery from a stimulus artifact took 5 ms. The responses of the cuff to external potential gradients and to common-mode signals are described theoretically or by simulation. The devices are available for use in neuroprosthetic or neurophysiological research.

Animals↗
PubMed2003

Recruitment by motor nerve root stimulators: significance for implant design.

Three paraplegics have been implanted with stimulators of the lumbar anterior roots. Twelve roots were trapped in slots, each with three electrodes, a central cathode and two anodes, but the anodes in all the slots were connected together to reduce the number of wires. Cross-talk between roots was observed at lower levels than expected. Cross-talk was assessed from the ratio of the root's threshold to the threshold of the contralateral response (expected ratio: 72). Two hypothetical reasons for this low ratio were: that the cathode current was not equally shared by the anodes; or that the contralateral responses were reflex. Experiments showed that neither explanation was valid. The ratio of the contralateral to ipsilateral threshold for individual slots (K(1)) was sometimes low because the ipsilateral threshold was high. By taking the ratio of the lowest contralateral response to lowest ipsilateral response, for all roots in each subject (K(2)), the ratio should approach the theoretical value. However, for the two subjects with small slots, it was 7.9 and 15.3, much less than 72, suggesting that the original theory was incorrect. Approximate calculations of the activation function suggest that the reason may be that roots which run close to a slot, but not through it, may pass through a virtual anode region outside the ends of the slots, and that anodal break stimulation in those regions causes the cross-talk. Our estimate is that this cross-talk would be expected to occur at intensities above 5.3 times the cathodal threshold. If the roots are stimulated in pairs, below the levels of cross-talk, experimental results show that the moments obtained in response are additive to within 5%.

Artifacts↗
PubMed2000

FES cycling may promote recovery of leg function after incomplete spinal cord injury.

STUDY DESIGN: Single subject pilot. OBJECTIVES: (i) To see whether strength and endurance for recreational cycling by functional electrical stimulation (FES) are possible following spinal cord injury (SCI). (ii) To develop the equipment for FES-cycling. SETTING: England. METHODS: Near-isometric or cycling exercise was performed by the incomplete SCI subject at home. RESULTS: After training for an average of 21 min per day for 16 months, the stimulated muscles increased in size and the subject was able to cycle for 12 km on the level. Surprisingly, there was a substantial increase in the measured voluntary strength of the knee extensors and the subject reports improved leg function. CONCLUSION: FES-cycling may promote recovery after incomplete spinal cord injury. If so, it offers the possibility of being a convenient method for widespread use.

Bicycling↗
PubMed1999

Apparatus to measure simultaneously 14 isometric leg joint moments. Part 1: Design and calibration of six-axis transducers for the forces and moments at the ankle.

An apparatus has been developed for making isometric measurements of the joint moments corresponding to the 14 degrees of freedom of the legs, in postures ranging between sitting and near full extension. The apparatus is called the multi-moment chair system (MMCS) and is described in the companion paper. This paper describes the most critical components of the MMCS, which are the six-axis transducers for measuring the force and moment components on the plantar-flexion axis of each ankle while the feet are laced into fixed shoes. The transducers are made of steel bars, on which strain gauges are mounted, joined by clamps. The design of the transducer and methods of calibration and error estimation are described. The RMS errors are less than 2 N for the forces and 1 Nm for the moments, but these may be correlated. A method for error reduction that compensates for the finite compliance of the transducer does not reduce the measured errors.

Ankle Joint↗
PubMed1999

Apparatus to measure simultaneously 14 isometric leg joint moments. Part 2: Multi-moment chair system.

An apparatus has been developed that measures isometrically the 14 lower limb joint moments corresponding to the degrees of freedom of the hips, knees and ankles. This is the second of two papers describing the development of the multi-moment chair system (MMCS). It presents the overall design and changes that were implemented to compensate for problems. These were primarily to improve the accuracy of hip joint moments; a compromise between accuracy and practicalities, because of force-moment responses being measured at the ankles. All joint moment errors have been calculated to be of the order of a few newton metres. Since these represent errors of less than 10% when considering peak joint moment responses, this is considered sufficiently accurate for the proposed application. The MMCS is being used in a programme to investigate the restoration of lower limb functions, principally standing, in paraplegics by electrical stimulation of the lumbosacral anterior roots.

Electronics, Medical↗
PubMed1998

Selecting candidates for a lower limb stimulator implant programme: a patient-centred method.

OBJECTIVE: To develop an effective selection procedure for lower limb functional neurostimulation (LLFNS) for standing in paraplegia. DESIGN: The selection procedure and exclusion criteria were based on the previous experience for two clinical centres with experience of LLFNS. SETTING: Two Regional Spinal Injuries units in southern England. SUBJECTS: 254 fully rehabilitated paraplegics living in the community. INTERVENTION: Patients were invited to participate in the programme, and if suitable to subject themselves to a rigorous staged selection procedure from which they could withdraw at any time. OUTCOME MEASURE: Functionally successful home standing using closed-loop surface electrical stimulation. RESULTS: 57/254 patients were suitable on paper and were accessible. 19 of these (CI = 10-28) were interested in the project and attended one of the spinal centres for details. Twelve (CI = 5-19) of these fulfilled the selection criteria and started on the training programme; and 10 of them completed the muscle training programme successfully. Seven patients (CI = 2-12) achieved closed-loop standing in the laboratory and four patients (CI = 1-8) did so at home.

Adult↗
PubMed1997

Apparatus and methods for studying artificial feedback-control of the plantarflexors in paraplegics without interference from the brain.

Apparatus has been built to explore the practical feasibility of using automatic control with electrical stimulation of paralysed legs to restore function. The experiments are performed with paraplegics with the aim of achieving a realistic postural task: to see whether the body may be maintained upright by stimulation of the plantarflexors when the other joints are braced. Significantly, the intact upper body, under natural control of the brain, cannot interfere with the automatic control. The "Wobbler" apparatus allows measurement of the ankle muscle properties in isometric conditions or in sinusoidal motion. Using the biomechanical properties of the body, which are also measured, controllers for stabilising the body can be designed. Controllers can be dynamically tested, imitating anterior-posterior sway, while the body is held upright, before "actual standing" is attempted.

Biomechanical Phenomena↗
PubMed1997

Lumbar root stimulation for restoring leg function: results in paraplegia.

We have implanted an intradural array of 12 tripolar electrodes on the anterior roots L2-S2, left and right, at cauda equina level, in a 33-year-old woman with a complete T9 cord lesion of 3 years' duration. They are driven by an implanted multiplexed stimulator system using radio frequency (RF) power and control signals. All channels generate movements, in patterns that might be predicted from the known anatomy of the cauda equina. In particular, stimulation of L2 and L3 gives hip adduction; L3, L4, and L5 gives quadriceps femoris movements; L5, S1, and S2 gives hamstrings movement; and S1 and S2 give plantar flexion. Stimulation of L5 gives mixed movements at the ankle. Surprisingly, stimulation of the L2 roots has not given strong hip flexion. Responses have been stable. Some thresholds have varied, probably as a result of tissue encapsulation. The moment generated within each degree of freedom of the legs has been measured for each root, using a specially designed multimoment measurement apparatus. For several roots, a movement of lower threshold may be accompanied by a second movement of higher electrical threshold, suggesting that different muscles may have fiber populations that differ in their diameter or their location in the root. The use of stimulus forms that enable selective anodal block may, in the future, enable separation of two distinct movements from a single motor root.

Adult↗
PubMed1997

Lumbar root stimulation for restoring leg function: stimulator and measurement of muscle actions.

We are studying the feasibility of restoring lower limb functions to paraplegics by stimulating their lumbar anterior roots (L2-S2). The potential advantages of placing electrodes at the roots, at the cauda equina, were set out by Rushton (1), and our results so far are in a companion paper by Rushton et al. In this paper, we describe briefly the stimulator system and a special apparatus we call the multimoment chair. The stimulator is a development from an earlier design of an implantable peripheral nerve stimulator (2) and has features that make it easier to use. The multimoment chair enables us to gather simultaneously isometric joint moments for 14 axes of the legs during stimulation while the body is fixed in a posture between sitting and full extension. Such rapid data collection is essential to discover the effects of multiple-root stimulation and its functional possibilities.

Cauda Equina↗
PubMed1996

Fluorescence resonance energy transfer analysis of ribozyme kinetics reveals the mode of action of a facilitator oligonucleotide.

A defining characteristic of catalysts is the rate at which they can process multiple copies of substrate. In the case of synthetic hammerhead ribozymes that cleave an RNA sequence, binding of the ribozyme to the substrate and products is through base-paired duplexes. The kinetics of formation and dissociation of these duplexes can determine the turnover of the ribozyme. We have followed these processes in real time by using fluorescent labels that can interact through fluorescence resonance energy transfer (FRET). This approach has been used to identify the rate-limiting steps for a particular ribozyme and to reveal how turnover was improved by a facilitator oligonucleotide. It was found that dissociation of the ribozyme-substrate complex is faster than cleavage to products. Hence, to undergo cleavage, most substrate molecules must interact with a ribozyme more than once. In the presence of a facilitator oligonucleotide, the complex is stabilized so that cleavage is faster than dissociation. Under these circumstances, cleavage of the substrate becomes the most likely outcome following binding to the ribozyme.

Base Sequence↗
PubMed1994

Implant provision of key, pinch and power grips in a C6 tetraplegic.

An 11-channel multiplexed stimulator of nerves and muscles in the left forearm was implanted for hand control in January 1986 in a 21 year old woman who, after sustaining a C6 spinal lesion 7 years earlier, had voluntary shoulder and elbow movement but paralysed hands, trunk and legs. The patient controls the stimulation via a microcomputer control box and an RF transdermal link. We have investigated the control of her stimulated hand with a joystick under her contralateral hand which she moves from the shoulder and elbow. Since 1986, we have tried a variety of joystick control schemes involving power and key grips. Currently, for grip adjustment, forward and backward joystick movements correspond to thumb extension and abduction, respectively giving in addition both finger and wrist extension, whereas right and left joystick movements yield fist closure and thumb opposition/adduction and flexion, respectively. Useful grasps are available by moving the joystick forward and then left (key grip), by moving the joystick backward and left (pinch grip), or by moving the joystick back and right (power grip). Thus, three distinct grips may be selected using these three quadrants of joystick movement. An additional control mode was found to be desirable to augment the patient's limited voluntary wrist positioning and provide wrist stability while adjusting finger grip.

Adult↗
PubMed1990

Operative treatment of anterior ectopic anus: the efficacy and influence of age on results.

In our experience, anterior ectopic anus (AEA) is a common cause of constipation in children. We have performed 54 anoplasties for AEA in the past 8 years. Seventy-eight percent of the patients were girls. The average age at surgery was 23.8 months and the average stool frequency prior to surgery was once every 3.2 days. Eighty percent of the children had undergone attempts at medical therapy. We compared the functional results of anoplasty in children by age. The children who had surgery prior to the age of 6 months had a significantly better outcome than did older children. These data suggest that patients with AEA have a better response to operative therapy when anoplasty is performed prior to 6 months of age. Early recognition, referral, and surgery is appropriate therapy in this patient group.

Anal Canal↗
PubMed1989

Outpatient bowel preparation in children.

A polyethylene glycol electrolyte solution was evaluated as a mechanical bowel preparation prior to surgery in an outpatient setting. Twelve children underwent outpatient bowel preparation (OPBP) prior to a variety of surgical procedures. The technique was well tolerated and consistently produced a well-prepared intestinal tract. This technique will decrease the overall cost of hospitalization, and it enhances patient and parental acceptance of mechanical bowel preparation.

Electrolytes↗
PubMed1986

Versatile three-channel stimulation controller for restoration of bladder function in paraplegia.

This compact Ni-Cd powered stimulation controller has been designed to operate, by means of appropriate transmitters, a three-channel RF coupled implant for paraplegic bladder control. A wide range of stimulation options may be selected by the use of control lines to CMOS analogue gates. Transdermal transmitters (Hartley oscillators) are driven by power amplifiers of virtually zero quiescent current. Overload protection circuitry which takes account of the pulsatile nature of the output, allows confident use of smaller power transistors than would be required for standard current limit or fold-back protection.

Electric Stimulation Therapy↗
PubMedDate not supplied

Technical note. Estimated electrode operating conditions of the first London Mk V implanted stimulator.

The electrodes of an implanted stimulator must be operated in such a way that the task of converting an electron current in metal to an ion current in tissue is achieved without release of noxious chemical species into the tissue, and without significant corrosion of the electrode metal. Both these effects depend on the charge density at which the electrodes are operated. In bringing a newly designed multichannel stimulator into service, the charge densities can only be known when the operating stimulus strengths have been determined. Even then, unless the stimulator is arranged to telemeter out what it is doing, any charge-density figures obtained have the character of estimates, rather than measurements. The first London Mk. V stimulator is used to enable a paraplegic woman to stand up. This note provides estimates of the average charge density and corrosion rate for the Pt--Ir electrodes used. These fall within limits which we believe to be generally accepted as safe.

Adult↗