Sick leave is related to frequencies of migraine and non-migrainous headache--The HUNT Study.

The aim of this large, cross-sectional, population-based study was to examine the association between sick leave and headache. Between 1995 and 1997, all 92 566 adults in Nord-Trøndelag County in Norway were invited to participate in a health survey. Out of 73 327 invited individuals <67 years old, a total of 38 192 (52%) responded to questions about headache, work situation and sick leave during the past year. Associations between sick leave, headache and migraine included were assessed in multivariate analyses, estimating prevalence odds ratios (ORs) with 95% confidence intervals (CIs). There was an increasing prevalence of sick leave with increasing frequency of migraine and non-migrainous headache. The prevalence of sick leave >8 weeks during the past year was more than three times higher among individuals with headache >14 days per month (20%) compared with those without headache (6%). The results may indicate that better treatment of individuals with chronic headache may have beneficial economic implications.

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.

Modified implanted drop foot stimulator system with graphical user interface for customised stimulation pulse-width profiles.

A modified implanted drop foot stimulator that allows cyclic modulation of the stimulation pulse-width during gait has been developed. Stimulation was on two channels of a four-channel 12 polar cuff electrode. The stimulator allowed modulation of stimulation pulse-width, between 0 and 255 micros, on both channels throughout the swing and stance phases of gait. Stimulation was applied between 17 and 40 Hz. The clinician can specify an infinite range of stimulation profiles on a desktop computer, using a user-friendly LabVIEW interface. The desktop program generated a stimulation profile table of 100 values, which was then downloaded to the drop foot stimulator. As each phase of gait imposed different biomechanical demands on the ankle dorsiflexor muscles, different stimulation intensities were desirable, throughout gait, to match these demands. Moreover, as the gait of each person with hemiplegia is unique, the biomechanical demands imposed throughout the gait cycle for each user of a drop foot stimulator are unique. This stimulator architecture allowed the clinician to, specify stimulation intensities individually, at each phase of the gait cycle for each drop foot stimulator user. The stimulator was evaluated on a male hemiplegic subject. It was used to increase the stimulation pulse-width by 150% at 5% of gait cycle prior to heel strike. The system performed well, with the ankle angle at heel strike increasing by 5 degrees owing to this increased pulse-width.

An instrumented object for evaluation of lateral hand grasp during functional tasks.

We developed an instrumented object for quantitative evaluation of functional tasks performed with lateral hand grasp. The device was instrumented with three force transducers based on metal foil strain gauges. The transducers allowed simultaneous monitoring of the grasp force, the perpendicular force at the tip, and the force in the long axis of the instrumented object. The device was used for evaluation of a simulated eating task performed by able-bodied subjects and a tetraplegic subject instrumented with an FES hand grasp system. Use of the instrumented object will allow us to gain a more thorough understanding of the application of forces on a tool during important functional tasks of daily living. This knowledge will be used to improve the control of a closed-loop FES hand grasp system incorporating natural sensory feedback.

Adaptive fuzzy logic restriction rules for error correction and safe stimulation patterns during functional electrical stimulation.

Adaptive restriction rules based on fuzzy logic have been developed to eliminate errors and to increase stimulation safety in the foot-drop correction application, specifically when using adaptive logic networks to provide a stimulation control signal based on neural activity recorded from peripheral sensory nerve branches. The fuzzy rules were designed to increase flexibility and offer easier customization, compared to earlier versions of restriction rules. The rules developed quantified the duration of swing and stance phases into states of accepting or rejecting new transitions, based on the cyclic nature of gait and statistics on the current gait patterns. The rules were easy to custom design for a specific application, using linguistic terms to model the actions of the rules. The rules were tested using pre-recorded gait data processed through a gait event detector and proved to reduce detection delay and the number of errors, compared to conventional rules.

Signals from skin mechanoreceptors used in control of a hand grasp neuroprosthesis.

We used signals from tactile mechanoreceptors in the skin of the index finger, recorded with an implanted cuff electrode, to automatically control grasp force in a hand grasp neuroprosthesis. Phasic events in the recorded nerve signal, related to mechanical events on the skin, were used to adjust electrical stimulation of hand muscles without any prior knowledge about muscle strength and properties of a held object. A simulated eating task was used to evaluate the hand grasp neuroprosthesis. When using the neuroprosthesis with feedback from natural sensors, the average grasp force could be reduced in comparison to not using feedback. Reducing grasp force is considered a major factor to decrease muscle fatigue, allowing a prolonged use of the hand grasp neuroprosthesis.

Command and control interfaces for advanced neuroprosthetic applications.

Command and control interfaces permit the intention and situation of the user to influence the operation of the neural prosthesis. The wishes of the user are communicated via command interfaces to the neural prosthesis and the situation of the user by feedback control interfaces. Both these interfaces have been reviewed separately and are discussed in light of the current state of the art and projections for the future. It is apparent that as system functional complexity increases, the need for simpler command interfaces will increase. Such systems will demand more information to function effectively in order not to unreasonably increase user attention overhead. This will increase the need for bioelectric and biomechanical signals in a comprehensible form via elegant feedback control interfaces. Implementing such systems will also increase the computational demand on such neural prostheses.

[Improved function of the hand in persons with tetraplegia using electric stimulation via implanted electrodes]. / Forbedret håndfunktion hos tetraplegikere ved elektrisk stimulering via implanterede elektroder.

Functional Electrical Stimulation (FES) is a controlled use of electrical stimulation of muscle contractions to obtain function. FES is utilised today in the treatment of spinal cord injured individuals for diaphragmatic pacing, bladder and bowel management, ejaculation, walking and hand function, as well as conditioning. We present The Freehand System, which consists of implanted electrodes to arm and hand muscles. This system has now been implanted in the first two Nordic tetraplegics. Candidates are tetraplegics with C5-6 lesions. After implantation it may take 6-8 months before the tetraplegic person can expect to use The Freehand System completely in daily life. The tetraplegic individual can choose between two grasps. The Freehand System can for some few very physically disabled tetraplegics be a good aid to increase their level of activities of daily living and independence. Continued development in the coming years may broaden the indications with benefit for more individuals.

Control of FES thumb force using slip information obtained from the cutaneous electroneurogram in quadriplegic man.

A tetraplegic volunteer was implanted with percutaneous intramuscular electrodes in hand and forearm muscles. Furthermore, a sensory nerve cuff electrode was implanted on the volar digital nerve to the radial side of the index finger branching off the median nerve. In laboratory experiments a stimulation system was used to produce a lateral grasp (key grip) while the neural activity was recorded with the cuff electrode. The nerve signal contained information that could be used to detect the occurrence of slips and further to increase stimulation intensity to the thumb flexor/adductor muscles to stop the slip. Thereby the system provided a grasp that could catch an object if it started to slip due to, e.g., decreasing muscle force or changes in load forces tangential to the surface of the object. This method enabled an automatic adjustment of the stimulation intensity to the lowest possible level without loosing the grip and without any prior knowledge about the strength of the muscles and the weight and surface texture of the object.

Adaptive restriction rules provide functional and safe stimulation pattern for foot drop correction.

We report on our advances in sensory feedback data processing and control system design for functional electrical stimulation (FES) assisted correction of foot drop. We have applied 2 methods of signal purification on the bin integrated electroneurogram (i.e., optimized low pass filtering and wavelet denoising) before training adaptive logic networks (ALN). ALN generated stimulation control pulses, which correspond to the swing phase of the impaired leg when dorsal flexion of the foot is necessary to provide safe ground clearance. However, the obtained control signal contained sporadic stimulation spikes in the stance phase, which can collapse the subject, and infrequent broken stimulation pulses in the swing phase, which can result in unpredictable consequences. In this study, we have introduced adaptive restriction rules (ARR), which are initially used as previously reported and then dynamically adapted during the use of the system. Our results suggest that ARR provide a safer and more reliable stimulation pattern than fixed restriction rules.

Interfacing the body's own sensing receptors into neural prosthesis devices.

Functional Electric Stimulation (FES) is today available as a tool in muscle activation used in picking up objects, in standing and walking, in controlling bladder emptying, and for breathing. Despite substantial progress over nearly three decades of development, many challenges remain to provide a more efficient functionality of FES systems. The most important of these is an improved control of the activated muscles. Instead of artificial sensors for feedback, new developments in electrodes to do long-term and reliable recordings from peripheral nerves emphasize the use of the body's own sensors. These are already installed and optimised through millions of years of natural evolution. This paper presents recent results on a system using electrical stimulation of motor nerves to produce movement and using the natural sensors as feedback signals to control the stimulation that can replicate some of the functions of the spinal cord and its communication with the brain. We have used the nerve signal recorded from cutaneous nerves in two different human applications: (1) to replace the external heel switch of a system for correction of spastic drop foot by peroneal stimulation, and (2) to provide an FES system for restoration of hand grasp with sensory feedback from the fingertip. For the bladder function, the sacral root stimulator is a useful control tool in emptying the bladder. To decide when to stimulate, we are at present carrying out experiments on pigs and cats using cuff electrodes on the pelvic nerve and sacral roots to record the neural information from bladder afferents. This information can potentially be used to inhibit unwanted bladder contractions and to trigger the FES system and thereby bladder emptying. Future research will show whether cuffs and other types of electrodes can be used to reliably extract signals from the large number of other receptors in the body to improve and expand on the use of natural sensors in clinical FES systems.

Degeneration and regeneration in rabbit peripheral nerve with long-term nerve cuff electrode implant: a stereological study of myelinated and unmyelinated axons.

Selective and dynamically co-ordinated functional electrical stimulation (FES) of paralysed/paretic limbs in upper motor neuron lesioned people depends on optimal contact at the neural interface. Implanted nerve cuff electrodes may form a stable electrical neural interface, but may also inflict nerve damage. In this study the immediate and long-term effects of cuff implantation on the number and sizes of myelinated and unmyelinated axons have been evaluated with unbiased stereological techniques. Cuff electrodes were implanted in rabbit tibial nerves just below the knee joint, and the stereological analyses were carried out 2 weeks and 16 months after implantation. Myelinated axons were analysed at standardised levels proximal to, underneath, and distal to the cuff; unmyelinated axons underneath the cuff. A 27% loss of myelinated axons was found underneath and distal to the nerve cuff 2 weeks post surgery. All axonal sizes were equally lost except for the very smallest. At 16 months post surgery the number of myelinated axons was restored to control values at both levels. Except for the presence of regenerative sprouts at 2 weeks post surgery, no changes in the number or sizes of unmyelinated axons were revealed at either 2 weeks or 16 months post surgery. Our study demonstrates that implanted cuff electrodes may cause an initial loss of myelinated axons but with subsequent regeneration.

Restoration of lateral hand grasp using natural sensors.

A closed-loop control system for controlling the key grip of a C6 tetraplegic patient was developed. Natural sensors served as the source of the feedback signal. The neural signals from cutaneous receptors were picked up by an implanted cuff electrode placed around the radial branch of the median nerve innervating the lateral part of the index finger. Mechanical stress applied to the skin, like pressure and slips, resulted in an increase in amplitude of the recorded neural signal. The goal of the study was to determine whether the recorded neural signals were able to indicate the slip of an object during lateral grasp and whether the slip could be stopped by increasing the grasp force through functional electrical stimulation of the thumb adductor and flexor.

Neural signals for command control and feedback in functional neuromuscular stimulation: a review.

In current functional neuromuscular stimulation systems (FNS), control and feedback signals are usually provided by external sensors and switches, which pose problems such as donning and calibration time, cosmesis, and mechanical vulnerability. Artificial sensors are difficult to build and are insufficiently biocompatible and reliable for implantation. With the advent of methods for electrical interfacing with nerves and muscles, natural sensors are being considered as an alternative source of feedback and command signals for FNS. Decision making methods for higher level control can perform equally well with natural or artificial sensors. Recording nerve cuff electrodes have been developed and tested in animals and demonstrated to be feasible in humans for control of dorsiflexion in foot-drop and grasp in quadriplegia. Electromyographic signals, being one thousand times larger than electroneurograms, are easier to measure but have not been able to provide reliable indicators (e.g., of muscle fatigue) that would be useful in FNS systems. Animal studies have shown that information about the shape and movement of arm trajectories can be extracted from brain cortical activity, suggesting that FNS may ultimately be directly controllable from the central nervous system.

Natural neural sensing and artificial muscle control in man.

In the intact organism, specialised sensors in the skin, muscles and joints provide sensory feedback information that is normally used by the central nervous system to regulate and update the motor output. Many sensory functions remain intact after spinal cord injury or stroke. Here we demonstrate that natural sensory nerve activity in man can be chronically recorded, and that the recorded neural activity can provide sensory feedback signals for an event-driven artificial reflex control of paralysed muscles.

Short- and long-acting angiotensin-converting enzyme inhibitors: a randomized trial of lisinopril versus captopril in the treatment of congestive heart failure. The Multicenter Lisinopril-Captopril Congestive Heart Failure Study Group.

A randomized, parallel, double-blind study was performed with lisinopril, a long-acting angiotensin-converting enzyme inhibitor, versus captopril, a shorter-acting angiotensin-converting enzyme inhibitor, in the treatment of congestive heart failure. All patients were in New York Heart Association class II, III or IV and had remained symptomatic despite therapy with digoxin and diuretics. After a 4 to 14 day placebo baseline period, patients were randomized to receive either lisinopril, 5 mg orally once per day (n = 94), or captopril, 12.5 mg orally three times per day (n = 95), in addition to continuation of digoxin and diuretics. The dose of study drug could be doubled at 4 week intervals for a total of 12 weeks of double-blind therapy. The maximal dose was 20 mg once per day of lisinopril or 50 mg three times per day of captopril. The addition of either lisinopril or captopril to a regimen of diuretics or digoxin, or both, caused an increase in exercise duration as assessed on a motorized treadmill. When protocol violators were excluded, patients receiving lisinopril had a statistically greater increase in exercise duration than that of patients receiving captopril. In patients with renal impairment (serum creatinine greater than 1.6 mg/dl at baseline), lisinopril was superior to captopril in improving exercise duration. Lisinopril, but not captopril, increased left ventricular ejection fraction in patients with moderately to severely (less than 35%) decreased function (p less than 0.05). Improvement in functional capacity and quality of life, as assessed by the Yale Scale dyspnea/fatigue index, was significantly greater for the lisinopril group.(ABSTRACT TRUNCATED AT 250 WORDS)

A double-blind comparison of lisinopril with captopril in patients with symptomatic congestive heart failure.

Angiotensin-converting enzyme (ACE) inhibition with captopril is accepted therapy for the treatment of symptomatic congestive heart failure. In this trial, we compared the new ACE inhibitor, lisinopril, to captopril during a 12-week randomized double-blind study. One hundred twenty-nine patients with New York Heart Association class II, III, or IV congestive heart failure were randomized to receive either lisinopril 5 mg/day (n = 64) or captopril 37.5 mg/day (n = 65) in 15 centers. Drug doses could be titrated upwards every 4 weeks. The primary measure of drug efficacy was improvement in treadmill exercise time using a modified Naughton protocol. Secondary measures of efficacy and the development of adverse effects were also examined. Lisinopril improved exercise time (following 12 weeks of therapy) more than captopril [from 500 +/- 30 to 682 +/- 34 sec (mean +/- SEM) with lisinopril versus 480 +/- 26 to 600 +/- 35 sec with captopril; difference between groups, p less than 0.05]. Adverse drug effects were unusual and similar in frequency in the two groups, although an increase in blood urea nitrogen was more common with lisinopril than with captopril (p less than 0.05). These results indicate that using the doses and treatment regimens studied, lisinopril is more effective than captopril for the treatment of symptomatic congestive heart failure. Adverse experiences with lisinopril were infrequent and similar in incidence to those observed with captopril.