Biomedical subjects

Thomas Sinkjaer

Publications and source records attributed to Thomas Sinkjaer.

28 records · Page 2Linked to original sources

PubMed2002

A task dependent change in the medium latency component of the soleus stretch reflex.

In comparison to the H-reflex, the task dependency of the human stretch reflex during locomotive and postural tasks has not received a great deal of attention in the literature. The few studies on reflex task dependency that have been performed to date have concentrated on either the group Ia mediated H-reflex or the short latency stretch reflex. In the present study the medium latency component of a mechanically evoked stretch reflex is investigated during walking, pedalling, and sitting. Stretch reflexes were evoked in the soleus muscle using dorsiflexion perturbations generated with a portable stretching device. Perturbations of equal amplitude and velocity (8 deg, 300 deg/s) were presented to 16 healthy subjects while they walked on a treadmill and pedalled a cycle ergometer. For eight of these subjects, an additional set of data was collected as they sat on the ergometer holding a steady posture. Perturbations were presented in the early to mid stance phase of walking and the downstroke of the pedal cycle. During all three conditions, the background soleus muscle activity was matched. The short (SLR) and medium (MLR) components of the soleus reflex responses were quantified by calculating the area of each burst in a 15-ms window centred on the peak of the respective burst. In addition, the stretch velocity-stretch reflex input-output curve was examined for the two locomotion tasks over a range of velocities from 100 to 400 deg/s. Peak latencies for the two reflex responses were observed at 52+/-5/77+/-6 ms (SLR/MLR) for walking, 51+/-3/76+/-6 ms (SLR/MLR) for pedalling, and 50+/-3/76+/-7 ms for sitting. A statistically significant increase in the magnitude of the MLR was observed during walking compared with pedalling and sitting ( P=0.007), whereas no difference in magnitude was observed between the three tasks for the SLR ( P=0.616). Furthermore, no difference was observed in the stretch velocity-stretch reflex input-output relationship between walking and pedalling. It is suggested that the medium component of the stretch reflex response is modulated to provide increased control for the postural demands of walking.

Adult↗

PubMed2002

Long-term biocompatibility of implanted polymer-based intrafascicular electrodes.

Polymer-based longitudinal intrafascicular electrodes (polyLIFEs) were chronically implanted into the sciatic nerve of white New Zealand rabbits (n=8) for a period of 6 months (hereafter referred to as the long-term group). The impact of the implantation procedure, as observed 6 months post surgery, was evaluated in a sham-treated control group (n=9). The contralateral sciatic nerve served as the control for each animal. Nerve-fiber counts, fiber diameters, and myelin thickness were estimated at the level of the implant site, 1.5 cm proximally, and 1.5 cm distally for both nerves in sham-treated and long-term groups. Implantation of polyLIFEs had no significant effect on fiber counts, nerve-fiber diameter, or myelin thickness. A slight increase in connective tissue in the vicinity of the implant site was evident in the long-term group, including a thin but dense capsule immediately surrounding the implanted electrode.

Animals↗

PubMed2002

Plantar flexor stretch reflex responses to whole body loading/unloading during human walking.

Numerous animal and human studies have shown that afferent information from the periphery contributes to the control of walking. In particular, recent studies have consistently shown that load receptor input is an important element of the locomotion control mechanism. The objective of this study was to investigate the contribution of load receptor feedback to the compensatory stretch reflex response. We examined the contribution of load receptor feedback to the magnitude of the short and medium latency components of the ankle plantar flexor stretch reflex responses following an unexpected dorsiflexion perturbation during human walking. Three body load conditions were investigated: normal body load, a 30% increase in body load, and a 30% decrease in body load. Healthy subjects walked on a treadmill at approximately 3.6 km/h with the left ankle attached to a portable stretching device. Dorsiflexion perturbations (8 degrees; 350-425 degrees/s) were generated during the late stance phase of gate (approximately 400 ms following heel contact). Electromyographic activity was recorded from the soleus, tibialis anterior, medial gastrocnemius, rectus femoris, and biceps femoris muscles using bipolar surface electrodes. Stretch reflex responses were observed in the soleus and gastrocnemius muscles for all of the body load conditions; however, increasing or decreasing the body load did not affect the timing and magnitude of the responses. This study provides evidence that load receptor input does not contribute strongly to the corrective response of the stretch reflex in the plantar flexor muscles during walking.

Adult↗

PubMed2002

Restitution of reaching and grasping promoted by functional electrical therapy.

Functional electrical therapy (FET) is a new term describing a combination of functional electrical stimulation that generates life-like movement and intensive exercise in humans with central nervous system lesions. We hypothesized that FET can promote a significant recovery of functioning if applied in subacute stroke subjects. The study included 16 stroke subjects divided into a low functioning group (LFG) and a high functioning group (HFG) based on their ability to control wrist and fingers and randomly associated into FET and controls. The FET consisted of 30 min daily sessions during 3 weeks. The exercise comprised functional use of daily necessary activities (e.g., writing, using a telephone receiver, and drinking from a can). The outcome presented in this article is the upper-extremity function test performed before and after the therapy. The change in performance of the HFG group was significant. The number of successful repetitive movements in 2 min was doubled and 1.6 times increased for controls, and the time to perform the movement was decreased by 71% percent and by 36% in controls. In the LFG FET group, the difference in performance was the following. First, the number of tasks was increased from 0 to 6 (total of 11 tasks). Second, the averaged number of successful repetitive movements was increased from 0 to 3. The functional improvement in the FET LFG is probably not sufficient to make the more affected arm/hand effective for daily necessities; thus, the FET effects could deteriorate over a longer time. The subjects from the control LFG made only a marginal improvement. The follow-up for each subject will continue for 12 months after the beginning of the treatment.

Adult↗

PubMed2002

Improving signal reliability for on-line joint angle estimation from nerve cuff recordings of muscle afferents.

Closed-loop functional electrical stimulation (FES) applications depend on sensory feedback, thus, it is important to continuously investigate new methods to obtain reliable feedback signals. The objective of the present paper was to examine the feasibility of using an artificial neural network (ANN) to predict joint angle from whole nerve cuff recordings of muscle afferent activity within a physiological range of motion. Furthermore, we estimated how small changes in joint angle that can be detected from the nerve cuff recordings. Neural networks were tested with data obtained from ten acute rabbit experiments in simulated, on-line experiments. The electroneurograms (ENG) of the tibial and peroneal nerves were recorded during passive ankle joint rotation. To decrease the joint angle prediction error with new rabbit data, we attempted to pretune the nerve signals and re-trained the ANNs with the pretuned data. With these procedures we were able to compensate for interrabbit variability. On average the mean prediction errors were less than 2.0 degrees (a total excursion of 20 degrees) and we were able to predict joint angles from muscle afferent activity with accuracy close to the best-estimated angular resolution. The angular resolution was found to depend on the initial joint angle and the actual step size taken and we found that there was a low probability of detecting joint angle changes less than 1.5 degrees. We thus suggest that muscle afferent activity is applicable as feedback in real-time closed-loop control, when the motion speed is restricted and when the movement is limited to a portion of the joint's physiological range.

Animals↗

PubMed2002

A review of portable FES-based neural orthoses for the correction of drop foot.

This paper reviews the technological developments in neural orthoses for the correction of upper motor neurone drop foot since 1961, when the technique was first proposed by Liberson and his co-workers. Drop foot stimulator (DFS) developments are reviewed starting with hard-wired single-channel and multichannel surface functional electrical stimulation (FES) systems, followed by implanted drop foot stimulators, and then continuing with microprocessor-based surface and implanted drop foot stimulators. The review examines the role of artificial and "natural" sensors as replacements for the foot-switch as the primary control sensor in drop foot stimulators. DFS systems incorporating real-time control of FES and completely implanted DFS systems finish the review.

Electric Stimulation Therapy↗

PubMed2002

Reflex excitation of muscles during human walking.

Sensory activity may contribute to the control of human walking in two different ways. It may contribute to the pre-programmed drive to the motoneurones and to the reactions to unexpected external perturbations. Some recent findings in relation to these two different roles of sensory activity will be reviewed. When unloading the ankle plantarflexors in the stance phase of walking a drop in the soleus EMG activity is seen at a latency of around 60 ms. This drop is likely caused by the removal of the contribution of Gp II afferents from the ankle plantarflexors to the motoneuronal drive. When stretching plantarflexor muscles in the stance phase three reflex responses are generally observed. These responses may be caused by the spinal monosynaptic Ia reflex pathway, a spinal Gp II pathway and a transcortical reflex pathway, respectively. The reflex responses are modulated with the background EMG activity and may not be evoked in the swing phase when the plantarflexors are not active. In contrast, stretch of the ankle dorsiflexor muscles evoke relatively small responses in the swing phase when these muscles are active, but very large responses in the stance phase when the muscles are silent. Part of these responses may have a transcortical nature. These findings illustrate the complexity with which sensory input may contribute to the ongoing muscle activity during walking and may also mediate adequate responses to sudden external perturbations.

Feedback↗

PubMedDate not supplied

Therapy of paretic arm in hemiplegic subjects augmented with a neural prosthesis: a cross-over study.

There are indications that both intensive exercise and electrical stimulation have a beneficial effect on arm function in post-stroke hemiplegic patients. We recommend the use of Functional Electrical Therapy (FET), which combines electrical stimulation of the paretic arm and intensive voluntary movement of the arm to exercise daily functions. FET was applied 30 min daily for 3 weeks. Forty-one acute hemiplegics volunteered in the 18-months single blinded cross-over study (CoS). Nineteen patients (Group A) participated in FET during their acute hemiplegia, and 22 patients (Group B) participated in FET during their chronic phase of hemiplegia. Group B patients were controls during FET in acute hemiplegia, and Group A patients were controls during the FET in chronic hemiplegia. Thirty-two patients completed the study. The outcomes of the Upper Extremity Function Test (UEFT) were used to assess the ability of patients to functionally use objects, as were the Drawing Test (DT) (used to assess the coordination of the arm), the Modified Ashworth Scale, the range of movement, and the questionnaire estimating the patients' satisfaction with the usage of the paretic arm. Patients who participated in the FET during the acute phase of hemiplegia (Group A) reached functionality of the paretic arm, on average, in less than 6 weeks, and maintained this near-normal use of the arm and hand throughout the follow-up. The gains in all outcome scores were significantly larger in Group A after FET and at all follow-ups compared with the scores before the treatment. The gains in patients who participated in the FET in the chronic phase of hemiplegia (Group B) were measurable, yet not significant. The speed of recovery was larger during the period of the FET compared with the follow-up period. The gains in Group A were significantly larger compared with the gains in Group B. The FET greatly promotes the recovery of the paretic arm if applied during the acute phase of post-stroke hemiplegia.

Acute Disease↗

PubMedDate not supplied

Ankle extensor proprioceptors contribute to the enhancement of the soleus EMG during the stance phase of human walking.

A rapid plantar flexion perturbation applied to the ankle during the stance phase of the step cycle during human walking unloads the ankle extensors and produces a marked decline in the soleus EMG. This demonstrates that sensory activity contributes importantly to the enhancement of the ankle extensor muscle activation during human walking. On average, the EMG begins to decline approximately 52 ms after the perturbation. In contrast, a rapid dorsi flex ion perturbation produces a group Ia mediated short-latency stretch reflex burst with an onset latency of approximately 36 ms. The transmission of sensory traffic from the foot and ankle was suppressed in 10 subjects by an anaesthetic nerve block produced with local injections of lidocaine hydrochloride. The anaesthetic block had no effect on the stance phase soleus EMG, the latencies of the EMG responses, or the magnitude of the EMG decline following the plantar flexion perturbation. Therefore, it is more likely that proprioceptive afferents, rather than cutaneous afferents, contribute to the background soleus EMG during the late stance phase of the step cycle. The large difference in onset latencies between the short-latency reflex and unload responses suggests that the largest of the active group Ia afferents might not contribute strongly to the background soleus EMG, although it remains to be determined which of the proprioceptive pathways provide the more important contributions.

Adult↗

PubMedDate not supplied

Clinical evaluation of Functional Electrical Therapy in acute hemiplegic subjects.

This paper describes a clinical randomized single-blinded study of the effects of Functional Electrical Therapy (FET) on the paretic arms of subjects with acute hemiplegia caused by strokes. FET is an exercise program that comprises voluntary arm movements and opening, closing, holding, and releasing of objects that are assisted by a neural prosthesis (electrical stimulation). FET consisted of a 30 min everyday exercise for 3 consecutive weeks in addition to conventional therapy. Twenty-eight acute hemiplegic subjects participated in a 6 mo study. The subjects were divided into lower functioning groups (LFGs) and higher functioning groups (HFGs) based on their capacity to voluntarily extend the wrist and fingers against the gravity, and were randomly assigned to controls or FET groups. The outcomes included the Upper Extremity Function Test, the coordination of elbow and shoulder movements, spasticity of key muscles of the paretic arm, and Reduced Upper Extremity Motor Activity Log. FET and control groups showed a recovery trend in all outcome measures. The gains in FET groups were much larger compared with the gains in control groups. The speed of recovery in FET groups was substantially faster compared with the recovery rate in control groups during the first 3 weeks (treatment). The LFG subjects showed less improvement than the HFG in both the FET and control groups.

Adult↗