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Biomedical subjects

A Scheiner

Publications and source records attributed to A Scheiner.

12 recordsLinked to original sources
PubMed1999

Identification of electrically stimulated quadriceps muscles in paraplegic subjects.

This work establishes a method for the noninvasive in vivo identification of parametric models of electrically stimulated muscle in paralyzed individuals, when significant inertial loads and/or load transitions are present. The method used differs from earlier work, in that both the pulse width and stimulus period (interpulse interval) modulation are considered. A Hill-type time series model, in which the output is the product of two factors (activation and torque-angle) is used. In this coupled model, the activation dynamics depend upon velocity. Sequential nonlinear least squares methods are used in the parameter identification. The ability of the model, using identified time-varying parameters, to accurately predict muscle torque outputs is evaluated, along with the variability of the identified parameters. This technique can be used to determine muscle parameter models for biomechanical computer simulations, and for real-time adaptive control and monitoring of muscle response variations such as fatigue.

Algorithms↗
PubMed1996

Implanted Functional Neuromuscular Stimulation systems for individuals with cervical spinal cord injuries: clinical case reports.

OBJECTIVE: To determine the feasibility of providing the ability to stand and to facilitate the performance of standing transfers to individuals with cervical-level spinal cord injuries via functional neuromuscular stimulation (FNS). The applicability of implantable technology to this population was investigated, and the characteristics of the potential system users were explored. The effects of FNS on the effort and assistance required to stand and complete standing transfers were examined. SETTING: Institutional rehabilitation practice. DESIGN: Nonrandomized controlled trial. PATIENTS: Twenty-four individuals with low cervical spinal cord injuries were evaluated for inclusion in a program of lower extremity FNS, four of whom received the intervention. INTERVENTION: Chronically indwelling percutaneous intramuscular electrodes were used to exercise the hip, knee, and trunk extensors and develop activation patterns to produce standing function. These temporary systems were then replaced with silicone-enclosed helical wire electrodes suitable for eventual use with an eight-channel implantable receiver/stimulator. MAIN OUTCOME MEASURES: Full sensory and motor evaluations were performed and physical contraindications to stimulation were catalogued. For active subjects, American Spinal Injury Association Total Motor Scores with and without FNS were recorded, along with quadriceps strength and ability to complete exercise, standing, controlled sitting, and standing transfer maneuvers. Performances of implanted electrodes were determined by the stability of recruitment properties, impedances or surface potentials, and serial radiographs. RESULTS: Motor scores increased an average of nine points with stimulation over baseline volitional values. With FNS, all four volunteers were able to exercise, stand, and sit independently or with minimal assistance. Although they required varying degrees of assistance with the pivot phase of the transfer maneuver, all were able to raise and lower their body weight independently with stimulation and to use the system to facilitate standing transfers. One participant received the implantable receiver/stimulator, which remains operational at follow-up more than 3 years later. CONCLUSION: FNS can provide the ability to exercise, stand, and transfer to individuals with tetraplegia, even in the presence of medical complications and upper extremity impairment. FNS facilitates standing transfers by eliminating the heavy lifting usually required by a caregiver, thus decreasing the effort and assistance necessary to gain access to places impossible to approach with conventional sliding transfers.

Adult↗
PubMed1996

Estimating mechanical parameters of leg segments in individuals with and without physical disabilities.

Methods are described for estimating the inertia, viscosity, and stiffness of the lower leg around the knee and of the whole leg around the hip that are applicable even to persons with considerable spasticity. These involve: 1) a "pull" test in which the limb is slowly moved throughout its range of motion while measuring angles (with an electrogoniometer) and torques (with a hand-held dynamometer) to determine passive stiffness and 2) a "pendulum" test in which the limb is moved against gravity and then dropped, while again measuring angles and torques. By limiting the extent of the movement and choosing a direction (flexion or extension) that minimizes reflex responses, the mechanical parameters can be determined accurately and efficiently using computer programs. In the sample of subjects studied (nine with disability related to spinal cord injury, head injury, or stroke, and nine with no neurological disability), the inertia of the lower leg was significantly reduced in the subjects with disability (p < 0.05) as a result of atrophy, but the stiffness and viscosity were within normal limits. The values of inertia were also compared with anthropometric data in the literature. The identification of these passive parameters is particularly important in designing systems for functional electrical stimulation of paralyzed muscles, but the methods may be widely applicable in rehabilitation medicine.

Adult↗
PubMed1994

Augmentation of transfers for a quadriplegic patient using an implanted FNS system. Case report.

A 22 year old man with incomplete quadriplegia (C6-7) was unable to perform either a sliding or a pivot transfer. He was instrumented with an implanted functional neuromuscular stimulation (FNS) system, radio frequency-linked to a belt-worn controller. The system activated eight muscles selected from among quadriceps, hamstrings, posterior portion of the adductor magnus, gluteus maximus, and erector spinae, bilaterally. The two-stage implantation procedure included electrode implantation with percutaneous leads followed by stimulator implantation and removal of the percutaneous leads. All implants were well tolerated with no adverse effects. The subject was able independently to put on the external controller portion of the system and to perform a standing pivot transfer with only standby assistance. An unexpected outcome of the FNS system use was increased voluntary upper body strength that resulted in improvement of the sliding transfer from 'inability' to 'independent'.

Adult↗
PubMed1994

Design and clinical application of a double helix electrode for functional electrical stimulation.

An electrode, designed to be implanted without a surgical incision, was developed for skeletal muscle stimulation. Stainless steel, Teflon-insulated wire was wound into a helical lead around a polypropylene core and then rewound into a double helix configuration for stress relief during muscle contractions. The electrode tip was augmented with stainless steel barbs to increase anchoring strength. Electrodes were implanted with the help of specially modified hypodermic needles, sheaths, and passing tubes. 775 electrodes were implanted in a five year period in 22 subjects; accumulated implant time was 1,080 electrode years. 453 electrodes (65%) continue to produce strong, stable, muscle contractions. Electrode longevity varied with the location of implant. Electrodes were removed because of (1) inability to locate and properly place the electrode in a suitable site for stimulation during surgery (28.4%), (2) unwanted changes in muscle response to stimulation (91, 12%; one-third occurring during the first six weeks post implant), (3) increase in electrode impedance (74, 10%; assumed breakage, mostly occurring during the first year after implant), (4) intolerable pain during stimulation (8, 1%), and (5) infection (4, 0.5%). 67 (8%) electrodes were removed by accident or when the subjects left the program. This double helix electrode design has proven practical for achieving chronic stimulation of selected muscles in hemiplegic, paraplegic, stroke and brain-injured subjects with minimally invasive surgery.

Animals↗
PubMed1992

Augmentation of the accuracy of percutaneous electrode implantation by using a modified arthroscope to guide insertion.

Using a clear polyvinyl fluoride sheath over an arthroscope, inserted through a 1-cm stab incision, we have demonstrated the feasibility of visualizing the sciatic nerve and its branches in the feline model. The purpose of this technique is to allow visual control, without a large surgical incision, of the exact site of implantation of electrodes used for functional neuromuscular stimulation. Currently, we determine the optimum site for percutaneous electrode implantation by stimulating the target nerve or muscle with a 26-gauge probe needle until maximal response is obtained. This method lacks accuracy because there is no direct visualization of the location of the tip of the probe or the electrode. With the new technique, we identified nerves by their distinctive vascular markings and we followed the nerves with minimal disruption of the soft tissues. In this way, individual branches were identified and targeted for instrumentation, allowing selective stimulation of specific muscle groups.

Animals↗
PubMed1991

A study of the fatigue properties of small diameter wires used in intramuscular electrodes.

Single and multi-strand stainless steel and cobalt-nickel alloy wires, with strand diameters from 26 to 46 microns, were fatigue tested using a modified rotating bending test to determine what factors are most important in controlling fatigue life. The relation between cyclic strain and cyclic life was determined for each material by cyclically straining test specimens at various strain ranges and recording the number of cycles to failure. The results show that (a) the fatigue curves of the 316LVM, MP35N, DBS, and Syntacoben wires are very similar and have many of the same fatigue characteristics of specimens of large cross section. (b) Multi-stranded wires have the same average fatigue life as their individual constituent strands, but the variance of that life is smaller. (c) Deformities in the wire, which are created during the manufacturing, appear to have the effect of shortening the fatigue life of these small section wires. (d) Observation of wire fracture surfaces show a relatively small crack propagation zone and a large fast fracture zone suggesting that most of the fatigue life of these small wires is in the original crack formation, which creates a large stress concentration and quickly leads to wire failure. (e) The size of the wire cross sectional area is of secondary importance compared to the amplitude of the maximum cyclic strain of the individual strands in determining fatigue life of the cable. To maximize the fatigue life of electrodes in vivo, the highest fatigue life for a given bending radius of curvature is desired. This suggests wire strands should be manufactured at the smallest diameter possible (without introducing structural flaws) to maximize service life.

Electrodes, Implanted↗
PubMed1990

Imbalanced biphasic electrical stimulation: muscle tissue damage.

The effects of imbalanced biphasic stimulation were studied on cat skeletal muscle to determine if greater charge densities can be safely used than with balanced or monophasic stimulation. The results of the study indicate that imbalanced biphasic stimulation can be tolerated safely by tissue at or below a net dc current density of 35 microA/mm2 and not safely tolerated at or above a net dc current of 50 microA/mm2. Monophasic stimulation has been shown to be safe at or below net dc current levels of 10 microA/mm2 and in these studies we found it was not safe at or above net dc current levels of 20 microA/mm2. Stimuli were applied to muscles via coiled wire intramuscular electrodes using a regulated current source. Since the safe average current density was higher for imbalanced biphasic stimulation than for monophasic stimulation, this suggests that: (a) pH change is not the primary reaction causing tissue damage and (b) the damaging electrochemical process that takes place during a cathodic stimulation pulse can be reversed by an anodic pulse having substantially less charge than its companion cathodic pulse. We conclude that greater cathodic charge densities can be safely employed with imbalanced biphasic stimulation than with either monophasic stimulation or balanced charge biphasic stimulation.

Animals↗
PubMedDate not supplied

Performance of an intramuscular electrode during functional neuromuscular stimulation for gait training post stroke.

The goal of rehabilitation for stroke patients in this research was to improve the volitional coordination of the swing phase and stance phases of gait. Functional neuromuscular stimulation (FNS) is a promising rehabilitation tool for restoring motor control. For our gait training protocols, FNS systems with surface electrodes were impractical. For the rehabilitation protocols that we defined, available implantable electrode designs did not meet desired criteria regarding fracture rate, invasiveness of placement procedures, and maintenance of position at the motor point. The criteria for the new intramuscular (IM) electrode design included minimally invasive electrode placement technique, accurate placement of electrodes, good muscle selectivity, consistency of muscle activation, good position maintenance of the electrode at the motor point, comfortable stimulus, and practical donning time for the system. A percutaneous electrode was designed for placement beneath the skin at the motor point of seven paralyzed or paretic muscles in the lower limb. A single-helical coil lead, a double-helical coil electrode, and fine wire barbs were design features that enhanced the anchoring capability of the electrode. A polypropylene core enhanced electrode durability. Implantation tools were custom-designed to enable accurate electrode placement without incision. We studied 17 subjects with a total of 124 electrodes. With the use of IM electrodes, FNS was provided for 1,413.8 electrode months. During this time, no instances of infection occurred. The measure of electrode integrity showed a 99% electrode survival rate. Throughout the treatment protocols, 93% of the electrodes delivered a good muscle response; 7% (nine electrodes) moved from the motor point and delivered a poor muscle response during the treatment protocol. Anchoring performance was higher for electrodes implanted in muscles that moved the hip (96.0%) and ankle joints (97.45%) compared with electrodes implanted in muscles that moved the knee joint (88.5%). Ninety-seven percent of the electrodes delivered a comfortable stimulus. Three percent delivered a stimulus that was uncomfortable at therapeutic levels and therefore were not used. We achieved gains in subject impairment and disability measures. The system proved to be practical for use in both clinical and home environments.

Aged↗