Motor response of the leg muscles produced by position-selective stimulation of spinal nerve roots.

OBJECTIVE: To define and measure motor responses of the leg muscles in the ankle associated with position-selective and tetanic stimulation of spinal nerve roots L3-S1. METHODS: Sixteen lumbosacral spinal nerve roots in 14 subjects were stimulated intraoperatively after surgical exposure and decompression for a herniated disc. Each contact of a spiral cuff multielectrode was wrapped around the root and used to excite a spatially defined population of axons beneath the electrode. The motor response from each stimulated position was evaluated in terms of three-dimensional vector torque in the ankle. RESULTS: Each position at which the stimulating electrode was placed around the root exhibited the same vector torque qualitatively, but at different thresholds. The root was most excitable ventrally. The S1 roots responded with a uniform three-dimensional torque pattern: plantar flexion plus lateral leg and foot rotation plus inversion. All L5 roots responded by plantar flexion. Dorsiflexion torque was possible only with stimulation of the L3 and L4 roots. Eversion was not possible with stimulation of the S1 roots or with most of the L5 roots. CONCLUSION: Position-selective stimulation of the extrathecal spinal nerve roots influences the threshold of the biomechanical response, the torque recruitment dynamics, and the magnitude of three-dimensional vector torque. Selective activation of some leg muscles or agonist muscle groups with stimulation of a single nerve root could not be achieved owing to the low spatial selectivity of the stimulation design and/or the low muscle specificity of motor fascicles in the root. Direct extrathecal stimulation of spinal nerve roots has some hypothetical advantages over stimulation of other sites along the peripheral nerves, owing to their unique anatomy, and may contribute to functional electrical stimulation of the lower extremities. Further investigation with a more selective multielectrode configuration and the use of multiple root stimulation is suggested.

Biomechanical response in the ankle to stimulation of lumbosacral nerve roots with spiral cuff multielectrode--preliminary study.

Biomechanical response in the ankle to tetanic stimulation of the lumbosacral root was investigated to assess the potential for lower limb functional neurostimulation. Myotomal response in the leg was measured as the three-dimensional isometric torque in the ankle after extradural tetanic stimulation of the L3-S1 roots exposed surgically for herniated disc removal in five patients. The cuff multielectrode was employed to investigate functional topography of the roots by monopolar, bipolar, and tripolar electrode configurations. Four response patterns in the direction of three-dimensional torque vectors were observed. The L-5 and S-1 roots had the same response pattern, but S-1 roots produced stronger torques. Dorsiflexion torque was not obtained by stimulation of L-5 roots despite coactivation of the tibial anterior and peroneal muscles. Dorsiflexion torques were produced only by stimulating the L-4 roots. More selective bipolar and tripolar stimulations recruited force at higher thresholds and less gain. Additionally, some muscles were not activated by tripolar stimulation of the same root. In one L-4 root, the torque at lower electrical threshold was replaced by inverse torque at higher threshold, providing indirect evidence that different muscles may have motoneuron populations that differ in diameter or location within the root. Although dorsiflexion and plantarflexion torques are functional per se, they are accompanied by foot inversion and leg rotation torques (as well as proximal muscle contractions). Further experimental investigations on direct extradural stimulation of lumbosacral roots, either single or in combination, are recommended to explore the potential of lumbosacral nerve root stimulation for restoration of leg function.

Problems associated with FES-standing in paraplegia.

Prolonged immobilization, such as occurs after the spinal cord injury (SCI), results in several physiological problems. It has been demonstrated that the standing posture can ameliorate many of these problems. Standing exercise can be efficiently performed by the help of functional electrical stimulation (FES). The first application of FES to a paraplegic patient was reported by Kantrowitz in 1963. It was later shown by our group that standing for therapeutic purposes can be achieved by a minimum of two channels of FES delivered to both knee extensors. The properties of the stimulated knee extensors (maximal isometric joint torque, fatiguing, and spasticity) were not found as sufficient conditions for efficient standing exercise. According to our studies, the ankle joint torque during standing is the only parameter which is well correlated to the duration of FES assisted standing. For good standing low values of the ankle joint torque are required. To minimize the ankle joint torque the lever belonging to the vertical reaction force must be decreased. Adequate alignment of the posture appears to be the prerequisite for efficient FES assisted and arm supported standing exercise. Some patients are able to assume such posture by themselves, while many must be aided by additional measures. At present, surface stimulation of knee extensors combined with some appropriately "compliant shoes" looks to be adequate choice.

Use of functional electrical stimulation in the lower extremities of incomplete spinal cord injured patients.

After a program of therapeutic electrical stimulation, 3 groups of incomplete spinal cord injured (SCI) patients were identified, those in whom an improvement of both voluntary and stimulated muscle force was observed, those with an increase in stimulation response only, and patients in whom no effect of electrical stimulation training could be recorded. As it is difficult to predict the outcome of the electrical stimulation rehabilitation process, a diagnostic procedure was developed to predict soon after accidents which incomplete SCI patients are candidates for permanent use of a functional electrical stimulation (FES) orthotic aid. The candidates for chronic use of FES are patients with weak ankle dorsiflexors and sufficiently strong knee extensors. These patients are equipped with a single channel peroneal stimulator augmenting dorsiflexion and knee and hip flexion in a total lower limb flexion response. By applying FES to the ankle plantar flexors, the swing phase of walking can be significantly shortened and faster walking obtained.

Functional electrical stimulation and arm supported sit-to-stand transfer after paraplegia: a study of kinetic parameters.

The sit-to-stand transfer of paraplegic patients using functional electrical stimulation (FES) of the knee extensors and arm support was analyzed in the study. In a group of 8 completely paralyzed subjects who were trained FES users, kinematic and dynamic parameters were recorded during standing up trials. A contactless optical system was used to assess the human body motion. The forces acting on the human body were measured by multi-axis force transducers. On the basis of recursive Newton-Euler inverse dynamic analysis, the forces and torques acting on the body joints were calculated. The joint moments in the lower and upper extremities during the sit-to stand task are presented in this paper. The influences of the patient's strength, FES training duration, and rising strategy on the joint loading are discussed.

Stability and velocity in incomplete spinal cord injured subject gaits.

We have defined 2 indices describing gait kinematic and dynamic stability. We assessed their values in the gaits of 5 different paraparetic subjects. The indices are correlated to the gait velocity to prove the close relationship between overall gate velocity and stability. Based on stability analysis and certain kinematic parameters, some possible ways of increasing the average gait velocity are explained.

Effects of respiratory muscle training and electrical stimulation of abdominal muscles on respiratory capabilities in tetraplegic patients.

Thirteen tetraplegic patients were included in the study of the effects of respiratory muscle training and of electrical stimulation of the abdominal muscles on their respiratory capabilities. Each patient was subjected for three 1 month lasting periods of the study: for inspiratory muscle training, expiratory muscle training and for a period without training. The sequence of these three periods was random for each patient. Respiratory tests (RT) measuring forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) were conducted before and following each monthly period. Measurements were taken under four sets of conditions: the patients' unassisted efforts, their efforts combined with pressure manually applied by a therapist to the upper part of their abdomen, and their efforts accompanied by electrical stimulation (ES) of the abdominal muscles during the early phase of expirium, once triggered by the therapist and once by the patients themselves. RT values were increasing following respiratory muscle training and inspiratory training apparently had a slightly greater effect than its expiratory counterpart. The increments of values of RT were statistically significant (P < 0.05) after the inspiratory muscle training. RT measurements were greater when the patient's voluntary effort was combined with ES of abdominal muscles than when it was not. This study concludes that respiratory muscle training is a potentially effective approach and that ES of the abdominal muscles has potentials to improve coughing in tetraplegic patients.

Improvement in step clearance via calf muscle stimulation.

The aim is to study the influence of electrically stimulated calf muscles on the effectiveness of the swinging leg movement. The study is carried out with a group of patients with incomplete spinal cord injuries both under stationary conditions and during crutch-assisted walking. Before stimulation is applied to the ankle plantar flexors, the knee extensors are inactivated. In each cycle, after ankle plantar flexor stimulation, peroneal stimulation is started, triggering the flexion reflex. From a biomechanical point of view, functional electrical stimulation (FES) of the ankle plantar flexors results in increased ground clearance of the lower extremity. Additionally, the FES-assisted lifting of the heel results in the elimination of extensor tone and thus shortens the swing time.

Influence of electrically stimulated ankle plantar flexors on the swinging leg.

The influence of functional electrically stimulated ankle plantar flexors on the swinging lower extremity was studied in incomplete spinal cord injured persons. Stimulation sequences with different time and frequency parameters were delivered to ankle plantar flexors and knee extensors and to the peroneal nerve. The results of kinematic assessment showed that stimulated calf muscles provide noticeable forward and upward propulsion to the swinging leg.

Stability and energy criteria in healthy and paraplegic subject gait.

The functional electrical stimulation (FES) assisted gait of paraplegic patients is inferior to that of healthy subjects. The difference can be observed in terms of speed, upright balance, biomechanical energy consumption, and generation of propulsion forces in the direction of walking. The biomechanical structure of paraplegic subjects is the same as that of normal ones; however, the mode of walking differs significantly because of the reduced number of activated muscles and primitive control. The healthy subject is utilizing a 2-point dynamically stable gait. The paraplegic patient is using 4-channel FES and utilizing a 4-point statically stable gait. We believe that the FES gait can be improved if converted into a semidynamically or dynamically stable gait. The gait is considered statically stable if the center of gravity (COG) projection on the ground (PCOG) is inside the supporting area. For a quadruped, this is only possible if it is utilizing a creeping crawl gait. In this paper, the relationship between PCOG and the supporting area are discussed as a criterion for dynamic stability assessment. Results are shown for 3 different modes of 2-point and 4-point gaits.

Wireless control of functional electrical stimulation systems.

With the assistance of crutches and functional electrical stimulation (FES), we are able to restore standing and simple gait in some spinal cord injured (SCI) patients. In present rehabilitative systems, the patient divides the gait cycle into stance and swing phases via pushbuttons mounted on the handles of the crutches, which are hardwired to the functional electrical stimulator. The surface-mount technology based telemetry system, which makes use of the radiofrequency medium at 40 MHz, was developed to provide wireless control of the FES system. Signals from crutch pushbuttons were coded and transferred from the transmitter to the receiver. The receiver was firmly attached to the patient's waist and was connected to the stimulator.

Modelling muscle activity in standing with considerations for bone safety.

The functional use of electrical stimulation (FES) for the restoration of movement to paraplegics has been improved in the last decade but questions about the mechanical effect of stimulation on the skeleton have arisen. In intact people, neuromuscular activity not only controls movement, but also minimizes bone and joint tissue loading. Current FES systems do not use feedback and do not even use average natural patterns of muscle activation. FES systems would be safer if muscle activation patterns were synthesized so as to minimize bending in the long bones. By modelling, we have verified that appropriate muscular activity reduces bone bending stresses, an approach we named active unloading of the skeleton. Using this criterion for control is novel. The muscle activation was calculated using measurements from intact people in different postures, and later modelling of the musculoskeletal system. The two-dimensional model of the lower limb includes 23 muscles relevant primarily for movement in the sagittal plane. The muscle model for constraint calculation is divided into first-order activation dynamics and first-order contraction dynamics. Optimization, which includes minimization of net bending moment calculated along the long bones, is static because changes in the observed postures are slow. In the calculated muscle activity patterns, muscle coactivation and cocontraction yield very uniform and low bone loading. Net bending moment values were fairly stable as the posture varies. The moment distribution in the femur was found to be U-shaped, while in the tibia it is sometimes V-shaped. The bones are naturally thicker at the points of peak moment.

Voluntary telemetry control of functional electrical stimulators.

With the assistance of crutches and functional electrical stimulation (FES) we are able to restore standing and simple gait in some spinal cord injured (SCI) patients. In the present rehabilitative systems the patient divides the gait cycle into 'stance' and 'swing' phase by using pushbuttons mounted in the handles of the crutches. These are then hard wired to the functional electrical stimulator. We present the development and evaluation of a surface mount technology based telemetry system that provides reliable and interference resistant wireless control of FES assisted walking. The system makes use of radio frequency carriers operating at a frequency of 40 MHz. Crutch pushbutton signals are coded and transferred from the transmitter placed in the crutch to the receiver which is firmly attached to the patient's waist and connected to the stimulator. The telemetry system was found to be of special importance for both complete and incomplete SCI subjects and is currently in use at the Rehabilitation Institute of the Republic of Slovenia.

[Flow cytometry identification of CD34-positive cells]. / Flowzytometrische Identifizierung von CD34-positiven Zellen.

In the present study three clinical applications of flow-cytometric quantification of CD34-positive cells in the field of blood and marrow transplantation are evaluated. By daily determination of CD34-positive cells in the peripheral blood after mobilization of stem cells with chemotherapy or growth-factors it is possible to set the optimal time for collection of the transplant material. Thereafter the yield of CD34-positive cells within the harvested material is determined. Finally, the efficacy of positive CD34 selection using a biotin-avidin column is evaluated. Initial experience is presented here.

Enhancement of hemiplegic patient rehabilitation by means of functional electrical stimulation.

This presentation will review briefly the current practice and state of the art in functional electrical stimulation (FES) as applied to stroke, head injured or brain tumour operated patients. A similar application is used in paretic patients following trauma or other aetiology. Over 20 years experience in the application of FES, as practised in Ljubljana, will be highlighted and the devices currently in use will be described. The statistics show the results obtained on 2,500 hemiplegic patients examined for FES application during the last 10 years. The statistics and results of the Slovenian population indicate 0.15-0.20% new cases annually or 1,500 new cases per million inhabitants. Up to 63% of annual cases are candidates for an FES based therapeutic locomotion rehabilitation programme. Experience indicates that 60% of hemiplegic patients received single-channel stimulation to correct equinovarus or foot drop, 30% obtained dual or even three channel stimulation treatment and only 10% of patients were involved in multichannel FES of four to six or even eight channels of stimulation. The benefits and outcome of rehabilitation will be presented and discussed in regard to current trends in the field of FES for hemiplegic and paretic patients. The partly inactive but very important field of FES application to the upper extremity in hemiplegic and paretic patients will be discussed and the relatively modest achievements presented. Future developments will be presented together with advances foreseen by steadily improving technology.

Unstable states in four-point walking.

The presently utilized walking patterns in paraplegic subjects with complete spinal cord injury (SCI) are compared by the help of graphic representations. Improved four-point gait assisted by functional electrical stimulation (FES) and crutches is proposed by introducing unstable states into the walking sequence. The unstable states are defined as passive phases of walking where the centre of mass (COM) is gravity driven in the direction of progression. The unstable state is described by a simple inverted pendulum model. Kinematic measurements of the unstable state were performed in normal and paraplegic subjects.

FES gait restoration and balance control in spinal cord-injured patients.

The status of gait restoration in spinal cord-injured patients by means of FES is reviewed and the main aspects are discussed. This introduction highlights the issues of balance control, stimulation sequence synthesis, and control of enhanced gait modes containing unbalancing. The use of statically unstable dynamic weight-transfer phases is important for enhanced gait modes. To show how this phase can be employed the mode of static balance currently used for FES-assisted four-point gait in paraplegic patients is discussed, and how this mode of gait can be converted to a semi-dynamic gait mode is described. The possibilities and consequences of such an approach are briefly discussed.

Bending moments in lower extremity bones for two standing postures.

The goal of this paper is to study how external gravitational forces stress the lower extremity bones and to ascertain and study how muscle activation compensates for the external load. For these purposes relatively accurate anatomical and biomechanical modelling is necessary. For a comparison of the calculated results to the naturally occurring muscular activity, seven-channel surface EMG activity was recorded. For simplicity a two-dimensional model was developed for the sagittal plane including 19 lower extremity muscles relevant to human standing and walking. In the calculation procedure of muscle forces an optimization procedure is also included. The results give rise to the expected assumption that muscle action is covered by two main requirements: first, to stabilize the joint actively (moment equilibrium) and, second, to compensate efficiently for bending moments produced by gravitational and external forces.

Symmetry of FES responses in the lower extremities of paraplegic patients.

Due to natural or artificial obstacles, gait is a less automatic and periodic process than it would appear when studying normal walking on the level. Pre-programmed functional electrical stimulation (FES) sequences, therefore, do not appear to be a suitable approach to the control of multichannel electrical stimulators in the restoration of paraplegic walking. Walking in paraplegic subjects must be, to a large extent, under voluntary control. To lessen the burden of this control, the symmetry of walking can be taken into account. Symmetric motion of the legs requires symmetric FES actuation. Symmetry of FES responses was studied in a group of 10 paraplegic subjects who had all undergone the FES training program. Recruitment curve, fatigue index and twitch delay were assessed. An average 80% symmetry was found in all parameters measured, thus allowing a reduction of complexity of control approach for FES locomotor aids.