Mechanical fatigue resistance of an implantable branched lead system for a distributed set of longitudinal intrafascicular electrodes.

OBJECTIVE: A neural interface system has been developed that consists of an implantable stimulator/recorder can with a 15-electrode lead that trifurcates into three bundles of five individual wire longitudinal intrafascicular electrodes. This work evaluated the mechanical fatigue resistance of the branched lead and distributed electrode system under conditions designed to mimic anticipated strain profiles that would be observed after implantation in the human upper arm. APPROACH: Custom test setups and procedures were developed to apply linear or angular strain at four critical stress riser points on the lead and electrode system. Each test was performed to evaluate fatigue under a high repetition/low amplitude paradigm designed to test the effects of arm movement on the leads during activities such as walking, or under a low repetition/high amplitude paradigm designed to test the effects of more strenuous upper arm activities. The tests were performed on representative samples of the implantable lead system for human use. The specimens were fabricated using procedures equivalent to those that will be used during production of human-use implants. Electrical and visual inspections of all test specimens were performed before and after the testing procedures to assess lead integrity. MAIN RESULTS: Measurements obtained before and after applying repetitive strain indicated that all test specimens retained electrical continuity and that electrical impedance remained well below pre-specified thresholds for detection of breakage. Visual inspection under a microscope at 10× magnification did not reveal any signs of damage to the wires or silicone sheathing at the stress riser points. SIGNIFICANCE: These results demonstrate that the branched lead of this implantable neural interface system has sufficient mechanical fatigue resistance to withstand strain profiles anticipated when the system is implanted in an arm. The novel test setups and paradigms may be useful in testing other lead systems.

[Selected aspects of citizen and patient orientation in Germany. Assessment from the point of view of users]. / Ausgewählte Aspekte einer Bürger- und Patientenorientierung in Deutschland. Die Beurteilung aus der Sicht der Nutzer.

The growing citizen and patient orientation of the German healthcare system reflects a health policy process which aims to achieve more individual and social responsibility as well as more autonomy on the part of healthcare users. At the same time the process is regarded as an essential component of a future oriented quality development involving raising transparency, developing competence, strengthening patient rights and improving complaints management. Representative data on these parameters and on people's level of satisfaction with their most recent contact with the healthcare service were collected in the 2009 GEDA survey 'Information Behaviour and Self-determination of Citizens and Patients' by the Robert Koch Institute. It reveals knowledge deficits in the population relating to selected areas of the healthcare service and there are also deficits in people's knowledge and assertion of their rights and in the way complaints are handled. These deficits vary according to demographic and socio-economic criteria (age, sex, educational and social status, status vis à vis health insurance companies). It emerges that different population groups have different needs, which can be used for a target group orientation in the communication of knowledge and the development of competencies.

[Evaluating the health target "Increasing health competence, strengthening patient sovereignty"]. / Ansätze zur Evaluation des Gesundheitsziels "Gesundheitliche Kompetenz erhöhen, Patient(inn)en-souveränität stärken".

Establishing citizen and patient orientation is a national objective of German health policy. The cooperation network gesundheitsziele.de has defined the target area "Increasing health competence, strengthening patient sovereignty", and its Working Group 8, which bears the same name, has identified four key areas for action: increasing transparency, developing competence, strengthening patients' rights, and improving complaint management. As in the case of all the other targets defined by gesundheitsziele.de, attention is drawn to the need to evaluate the effects and success of the targets and related measures. A group of experts was given the task of developing an evaluation strategy, defining success indicators, and examining the availability of data sources for evaluation. With regard to the health target "Increasing health competence, strengthening patient sovereignty", the evaluation is focusing on what effect the corresponding targets and measures are having on users and how they are perceived (summative evaluation), i.e., primarily on measuring outcomes at the population level. An examination of available studies and surveys shows that to date little is known about the expectations and assessments of health-service users. At the same time, the analysis makes it clear that priority should be given to using continuous data in order to arrive at a continuous and systematic evaluation of the "Increasing health competence, strengthening patient sovereignty" health target and the implementation of citizen and patient orientation in healthcare in general. It would also be useful to include all hitherto underrepresented indicator questions in these surveys and to also examine the implementation of the health target among vulnerable population groups, e.g., elderly people in nursing homes.

[People's interest in health information]. / Nutzung von Gesundheitsinformationen.

Well-informed citizens and patients regard health policy innovations as a key element when it comes to reforms in the health service--both in health economics and with regard to prevention issues. We evaluated the data provided by the 2003 Telephone Health Survey (GSTel03) to examine demographic and social distinctions in the use of different information sources. At the same time we examined whether there are any population-related differences in people's interest in health information depending on their levels of health awareness, attitudes to prevention and related modes of behaviour. The data generated by the survey show that there is considerable interest in health-related topics. Only 2% of the people questioned used no information sources for this purpose. In addition to more traditional media (books, newspapers, information from pharmacies), information provided by health insurance companies and via the Internet is becoming increasingly important. With the exception of the Internet, all other sources of information are used more frequently by women than by men, and demand for most of the information media increases with age. The frequency of information use and the number of different media used increase from the lower to the upper strata of society. As far as selected variables of health-related behaviour are concerned (smoking, sport, alcohol), the results show a link between a more positive attitude to health and a greater interest in information.

Effects of short-term training on sensory and motor function in severed nerves of long-term human amputees.

Much has been studied and written about plastic changes in the CNS of humans triggered by events such as limb amputation. However, little is known about the extent to which the original pathways retain residual function after peripheral amputation. Our earlier, acute study on long-term amputees indicated that central pathways associated with amputated peripheral nerves retain at least some sensory and motor function. The purpose of the present study was to determine if these functional connections would be strengthened or improved with experience and training over several days time. To do this, electrodes were implanted within fascicles of severed nerves of long-term human amputees to evaluate the changes in electrically evoked sensations and volitional motor neuron activity associated with attempted phantom limb movements. Nerve stimulation consistently resulted in discrete, unitary, graded sensations of touch/pressure and joint-position sense. There was no significant change in the values of stimulation parameters required to produce these sensations over time. Similarly, while the amputees were able to improve volitional control of motor neuron activity, the rate and pattern of change was similar to that seen with practice in normal individuals on motor tasks. We conclude that the central plasticity seen after amputation is most likely primarily due to unmasking, rather than replacement, of existing synaptic connections. These results also have implications for neural control of prosthetic limbs.

Experience with the first three years of an accelerated dual-degree program in biomedical engineering.

Our Department of Bioengineering has instituted a pilot program aimed at helping a select group of highly qualified students obtain both bachelor's and master's degrees in an accelerated timeframe - approximately four years from the beginning of their university studies. A key element of this program is the introduction of the students to research in their second year of studies via a directed and closely supervised cohort mechanism. These students also come to the university with substantial AP credit and spend two summers fulfilling some general education requirements of the university. Our first three years with the program have shown positive results, with most students on track in both academics and research. There have been some challenges, however, with regard to tight scheduling, leaves for religious missions, and continued student stipend funding.

Evidence for a two pigment visual system in the fiddler crab, Uca thayeri.

Intraocular recordings were made from the eyestalks of dark-adapted fiddler crabs (Uca thayeri) during presentation of monochromatic light flashes of different wavelengths and intensities. Two types of signals were recorded in different experiments: slow potentials (electroretinogram) and fast potentials (spikes). The latter were also recorded in the presence of a continuous green or red adapting light. The resulting visual spectral-sensitivity curves, when fitted to rhodopsin-based visual pigment absorption spectra (from Dartnall nomograms), indicated the presence of two visual pigments, one with an absorption maximum near 430 nm, and the other with a peak absorption between 500 nm and 540 nm. The data also provided evidence for some differential bleaching of the pigments in the presence of a colored adapting light, but most of the adaptation effect was probably due to changes in screening pigment and neural desensitization or inhibition. These two observations suggest that an adequate substrate for color vision may exist in this and other species of fiddler crabs. The electroretinogram and spike-recording methods produced similar visual-sensitivity data, suggesting that latter technique, a much more efficient way of collecting data that is physiologically relevant, may be the method of choice for determining spectral sensitivity in crustaceans.

Formative research activities to provide Web-based nutrition education to adults in the Upper Rio Grande Valley.

The Internet is a promising new tool for disseminating cancer prevention information. Barriers to full implementation include disparities in access and skill and availability of information relevant at the local level. A nutrition education Web site to promote fruit and vegetable intake is being produced for a tri-ethnic adult population in Colorado and New Mexico. Development is guided by findings from formative research including focus groups with local residents, a survey on computer and Internet use with 200 adults in 1998, an assessment of public access computer sites, and in-depth discussion with local community computer skills trainers.

Electrical resistivity of the upper arm and leg yields good estimates of whole body fat.

Single frequency bioelectrical impedance analysis is an inexpensive, quick and painless means of estimating body composition. However, current approaches to estimating body composition from segment resistivity have some drawbacks. The purpose of this study was to overcome these limitations by developing a better model of the relationship between resistivity and body composition. A three-compartment model of body mass and body segment resistivity is presented and calibrated to predict %Fat estimated by underwater weighing. The subject population from which the data were obtained was heterogeneous. Both sexes were represented, as were a range of ages (21-44 years), ethnic backgrounds, body masses (47.0-129.0 kg) and body compositions (%Fat = 8.7-50.7%). Based on resistivity measurements from the upper arm and upper leg, and measurements of subject height and weight, the model predicted %Fat with errors comparable to those reported for other methods based on segmental resistivity. All the terms in the calibrated model represented a physical component of the body and show reasonable agreement with resistivity measured in tissue samples. In short, predicting %Fat from resistivity of the proximal arm and leg segments compares favourably with other methods based on segment resistivity.

Acoustic detection and communication by decapod crustaceans.

This paper reviews behavioral, physiological, anatomical, and ecological aspects of sound and vibration detection by decapod crustaceans. Our intent is to demonstrate that despite very limited work in this area in the past 20 years, evidence suggests that at least some decapod crustaceans are able to detect and use sounds in ways that parallel detection and processing mechanisms in aquatic and terrestrial vertebrates. Some aquatic decapod crustaceans produce sounds, and many are able to detect substrate vibration at sensitivities sufficient to tell of the proximity of mates, competitors, or predators. Some semi-terrestrial crabs produce and use sounds for communication. These species detect acoustic stimuli as either air- or substrate-borne energies, socially interact in acoustic "choruses," and probably use "calls" to attract mates.

Selective activation of muscle groups in the feline hindlimb through electrical microstimulation of the ventral lumbo-sacral spinal cord.

Selective activation of muscle groups in the feline hindlimb by electrical stimulation of the ventral lumbo-sacral spinal cord was investigated. Spinal cord segments L5 to S1 were mapped using a penetrating tungsten needle electrode. Locations that produced isolated contraction of quadriceps, tibialis anterior or triceps surae/plantaris muscles when stimulated with a current of 40 microA or less, and in which spread of activity to other muscles was not detected after increasing the stimulus to at least twice the threshold level, were defined as belonging to the target muscle's "activation pool." The quadriceps activation pool was found to extend from the beginning of L5 to the middle of L6. The tibialis anterior activation pool extended from the beginning of L6 to the middle of L7, and the triceps surae/plantaris activation pool extended from the caudal end of L6 to the beginning of S1. The three activation pools were located in Rexed motor lamina IX and their spatial organization was found to correspond well with that of the anatomically defined motor pools innervating the same muscles. The spatial and functional segregation of motor pools manifested at the spinal cord level can have direct applications in the areas of functional electrical stimulation and motor control.

Muscle recruitment through electrical stimulation of the lumbo-sacral spinal cord.

The goal of this study was to determine the feasibility of producing graded muscle contraction in individual muscles or muscle groups by electrically stimulating motor neurons in the lumbo-sacral spinal cord. Recruitment curves were obtained for quadriceps, tibialis anterior and triceps surae/plantaris by stimulating their activation pools in the ventral horn of the feline spinal cord. Mean twitch times-to-peak for quadriceps, tibialis anterior and triceps surae/plantaris were 33.0, 41.0, and 36.0 ms, respectively. Twitch duration as a function of stimulus strength demonstrated a mixed motor unit recruitment order, distinctively different from the inverse recruitment order exhibited by conventional methods of electrical stimulation of peripheral nerve. The recruitment curve slopes (expressed as a percentage of maximum force per nanocurrent of delivered charge) were shallow: 7.9 for quadriceps, 2.6 for tibialis anterior and 8.5 for triceps surae/plantaris. These results show that graded control of force in individual muscles or muscle groups can be obtained through spinal cord stimulation, and suggest that spinal cord stimulation could be used for functional neuromuscular stimulation applications.

Biomechanical model predicts directional tuning of spindles in finger muscles facilitates precision pinch and power grasp.

Humans have a sense of static limb position derived primarily from the output of secondary muscle spindle endings. The features of finger pose these proprioceptors signal best were predicted by singular value decomposition of a kinematic model of the human long finger and the six muscles that actuate it. The analysis indicated that muscle spindles signal the location of the fingertip with less error than they signal angles of individual finger joints. The fingertip displacements for which proprioceptors have greatest sensitivity were also predicted. These fingertip displacements seem to correspond to the fine positioning of an object pinched between the fingertip and distal phalanx of the thumb. The analysis also predicted the directions in which subjects can displace the fingertip most rapidly. The directions seem to correspond to rapid closure of precision pinch or power grasp.

Extrinsic muscles of the hand signal fingertip location more precisely than they signal the angles of individual finger joints.

Studies have demonstrated that muscle spindle organs provide the majority of the proprioceptive information available to the nervous system about limb position. Other studies suggest that a sense of position may be lacking in the fingers, as subjects were unaware of rather large excursions of finger joints if the excursions were made slowly enough. We sought to investigate the basis for this unexpected finding with a biomechanical model of the human long finger and the forearm muscles which actuate it, in order to study potential contributions of spindle organs in the extrinsic muscles of the hand to a sense of position of the finger. The model, based on cadaver data, allowed us to determine how precisely estimates of the lengths of the extrinsic finger muscles can be transformed into estimates of: (1) the flexion/extension angles of the individual finger joints, and (2) the location of the fingertip in the flexion/extension plane. We found that, for some finger positions, length information from all three extrinsic muscles was not sufficient to precisely estimate the flexion angles of all finger joints. Precision of joint angle estimates could be as poor as +/- 18% of joint range of motion. However, length information from just two of the extrinsic muscles taken together could always provide information sufficient to estimate the location of the fingertip relative to the metacarpophalangeal joint within a reasonably small tolerance (+/- one-half thickness of the fingertip). Furthermore, it was possible to make this estimate without determining any of the finger joint angles. These results suggest that spindles in the extrinsic muscles alone can signal fingertip location, even though they may not provide sufficient information to estimate the individual joint angles that set the position of the fingertip. Thus, an absence of position sense for individual joints (the sense many studies have tried to measure) may say little about a sense of location of the tip of the finger.

A three-dimensional kinematic model of the human long finger and the muscles that actuate it.

A kinematic model of the human long finger and the six muscles that actuate it is presented. The model transforms finger pose into estimates of muscle excursions and fingertip location. The effects of abduction/adduction about the metacarpo-phalangeal joint are accounted for, as are the effects of flexion of the three finger joints. A set of parameters are provided which approximate kinematics of the segments and muscles of a cadaver finger over the range of finger poses humans normally assume.

Recording properties and biocompatibility of chronically implanted polymer-based intrafascicular electrodes.

We implanted polymer-based longitudinal intrafascicular electrodes (polyLIFEs) in feline dorsal rootlets acutely and for periods of two to six months to evaluate their electrical properties and biocompatibility. A total of 38 implanted electrodes were analyzed. Some 25 of the 38 electrodes were implanted with an insulative flexible polymer cuff, which was required for recording of afferent activity in situ. Electrode impedances remained stable for the duration of the experiments. The distributions of axons were measured at three levels of the implanted rootlets: the implant level, 1-2 mm proximal to the implant with respect to the cell body, and 1-2 mm distal to the implant with respect to the cell body. Similar measurements were made in five samples of fascicles neighboring an implant and six samples of control tissue from animals in which no implants were placed. The polyLIFEs demonstrated a high degree of biocompatibility, as no adverse effects on axon size were observed in either the implanted fascicle or neighboring neural tissue. However, the insulative cuffs were found to be a source of compression, resulting in necrosis of the neural tissue.

Proposed specifications for a lumbar spinal cord electrode array for control of lower extremities in paraplegia.

The goal of the study was to provide specifications for a stimulating electrode array to be implanted in the lumbosacral spinal cord as part of a functional neuromuscular stimulation (FNS) system for control of lower extremity muscles in paralyzed individuals. Dual channel stimulation of the quadriceps activation pool in the feline ventral lumbo-sacral spinal cord was performed to measure electrode interactions and to explore the effect of various stimulation paradigms on muscle fatigue. There was no measurable overlap in the populations of motor neurons activated from two different electrodes for spacings > or = 1 mm with currents below 100 microA. However, a statistically significant increase in the population of activated fibers due to current summation was observed when stimuli > or = 70 microA were simultaneously presented through pairs of electrodes within 3 mm of each other. Fatigue effects were studied with three paradigms: 1) stimuli were delivered through a single electrode, 2) stimuli were delivered through two electrodes with the stimulus to the second electrode presented during the refractory period of fibers stimulated by the first electrode, and 3) stimuli were interleaved between the two electrodes such that the stimulus to one electrode was presented midway between stimuli to the other electrode, and the rate of stimulation through a single electrode was half that used in the first two paradigms. Dual channel refractory and single channel stimulation did not differ from each other in the rate at which the muscle fatigued, in both cases the force decayed to 30% of its initial level within 2 min of the initiation of the stimulation regime, whereas the force with interleaved stimulation was still above the initial force at this time due to strong potentiation. Based on these results and on and activation pool dimensions obtained in an earlier study, preliminary specifications are presented for an electrode array to be implanted in the human spinal cord for functional neuromuscular stimulation.

Recognition of temporally changing action potentials in multiunit neural recordings.

We present a method to iteratively train an artificial neural network (ANN) or other supervised pattern classifier in order to adaptively recognize and track temporally changing patterns. This method uses recently acquired data and the existing classifier to create new training sets, from which a new classifier is then trained. The procedure is repeated periodically using the most recently trained classifier. This scheme was evaluated by applying it to simulated situations that arise in chronic recordings of multiunit neural activity from peripheral nerves. The method was able to track the changes in these simulated chronic recordings and to provide better unit recognition rates than an unsupervised clustering method suited to this problem.

Metallized polymer fibers as leadwires and intrafascicular microelectrodes.

We have developed a process for producing fine, very flexible microwires suitable for use as small signal leadwires or nerve electrodes. The process incorporates metallization of high-performance monofilament polymer fibers to yield electrically conductive fibers with greatly improved flexibility over solid metal wires of similar strength. The metallization layers are produced by serial vacuum deposition of a 0.3 micron thick coating of three metals, titanium-tungsten (Ti/W), gold (Au), and platinum (Pt), onto monofilament, poly-p-phenyl-terephthalate aramid fibers (Kevlar). The metallized fibers are then insulated with an approx. 1 micron thick layer of silicone elastomer. The result is a microlead with high electrical conductivity (linear resistance = 30 omega/cm), desirable interfacial properties, excellent mechanical stability and extremely high flexibility. These physical characteristics are appropriate for application as signal leadwires or recording/stimulating electrodes where small size and high flexibility are paramount. In this paper we report on the electrical and mechanical properties of these metallized fibers and demonstrate their use as intrafascicular electrodes for recording multi-unit neural activity in feline peripheral nerves.