Biomedical subjects

T Sinkjaer

Publications and source records attributed to T Sinkjaer.

At least 37 records · Page 2Linked to original sources

PubMed2001

Cerebral functional anatomy of voluntary contractions of ankle muscles in man.

1. Cerebral activation elicited by right-sided voluntary ankle muscle contraction was investigated by positron emission tomography measurements of regional cerebral blood flow. Two studies with eight subjects in each were carried out. Tonic isometric plantar and dorsiflexion and co-contraction of the antagonist muscles were investigated in study 1. Tonic contraction was compared with dynamic ramp-and-hold contractions in study 2. 2. All types of contraction elicited activation of the left primary motor cortex (M1). The distance between the M1 peak activation locations for tonic isometric dorsi- and plantar flexion was 17 mm. Co-contraction elicited activation of a larger area of M1 mainly located in between but partially overlapping the M1 areas activated during isolated dorsi-/plantar flexion. 3. A voxel-by-voxel correlation analysis corrected for subject covariance showed for dorsiflexion a significant correlation between tibialis anterior EMG level and cerebral blood flow activation in the cerebellum and the M1 of the medial frontal cortex. For plantar flexion a significant correlation was found between soleus EMG and cerebral activation in the left medial S1 and M1, left thalamus and right cerebellum. 4. The activation during dynamic isotonic and isometric dorsi- and plantar flexion was significantly more extensive than during tonic contractions. In addition to M1, activation was seen in the contralateral supplementary motor area and bilaterally in the premotor and parietal cortices. Isotonic and isometric contractions did not differ except in a small area in the primary somatosensory cortex. 5. One possible explanation of the different cerebral activation during co-contraction compared to that during plantar/dorsiflexion is that slightly different populations of cortical neurones are involved. The more extensive activation during dynamic compared with tonic contractions may reflect a larger cortical drive necessary to initiate and accelerate movements.

Adult↗

PubMed2001

Group II muscle afferents probably contribute to the medium latency soleus stretch reflex during walking in humans.

1. The objective of this study was to determine which afferents contribute to the medium latency response of the soleus stretch reflex resulting from an unexpected perturbation during human walking. 2. Fourteen healthy subjects walked on a treadmill at approximately 3.5 km h(-1) with the left ankle attached to a portable stretching device. The soleus stretch reflex was elicited by applying small amplitude (approximately 8 deg) dorsiflexion perturbations 200 ms after heel contact. 3. Short and medium latency responses were observed with latencies of 55 +/- 5 and 78 +/- 6 ms, respectively. The short latency response was velocity sensitive (P < 0.001), while the medium latency response was not (P = 0.725). 4. Nerve cooling increased the delay of the medium latency component to a greater extent than that of the short latency component (P < 0.005). 5. Ischaemia strongly decreased the short latency component (P = 0.004), whereas the medium latency component was unchanged (P = 0.437). 6. Two hours after the ingestion of tizanidine, an alpha(2)-adrenergic receptor agonist known to selectively depress the transmission in the group II afferent pathway, the medium latency reflex was strongly depressed (P = 0.007), whereas the short latency component was unchanged (P = 0.653). 7. An ankle block with lidocaine hydrochloride was performed to suppress the cutaneous afferents of the foot and ankle. Neither the short (P = 0.453) nor medium (P = 0.310) latency reflexes were changed. 8. Our results support the hypothesis that, during walking the medium latency component of the stretch reflex resulting from an unexpected perturbation is contributed to by group II muscle afferents.

Adrenergic alpha-Agonists↗

PubMed2001

Transcranial magnetic stimulation and stretch reflexes in the tibialis anterior muscle during human walking.

Stretch of the ankle dorsiflexors was applied at different times of the walking cycle in 17 human subjects. When the stretch was applied in the swing phase, only small and variable reflex responses were observed in the active tibialis anterior (TA) muscle. Two of the reflex responses that could be distinguished had latencies which were comparable with the early (M1) and late (M3)components of the three reflex responses (M1, M2 and M3) observed during tonic dorsiflexion in sitting subjects. In the stance phase a single very large response was consistently observed in the inactive TA muscle. The peak of this response had the same latency as the peak of M3, but in the majority of subjects the onset latency was shorter than that of M3. The TA reflex response in the stance phase was abolished by ischaemia of the lower leg at the same time as the soleus H-reflex, suggesting that large muscle afferents were involved in the generation of the response. Motor-evoked potentials (MEPs) elicited in the TA by transcranial magnetic stimulation (TMS) were strongly facilitated corresponding to the peak of the stretch response in the stance phase and the late reflex response in the swing phase. A similar facilitation was not observed corresponding to the earlier responses in the swing phase and the initial part of the response in stance. Prior stretch did not facilitate MEPs evoked by transcranial electrical stimulation in the swing phase of walking. However, in the stance phase MEPs elicited by strong electrical stimulation were facilitated by prior stretch to the same extent as the MEPs evoked by TMS. The large responses to stretch seen in the stance phase are consistent with the idea that stretch reflexes are mainly involved in securing the stability of the supporting leg during walking. It is suggested that a transcortical reflex pathway may be partly involved in the generation of the TA stretch responses during walking.

Adult↗

PubMed2001

Detection and inhibition of hyperreflexia-like bladder contractions in the cat by sacral nerve root recording and electrical stimulation.

Detection of bladder volume and hyperreflexive bladder contractions would be useful in individuals with overactive bladders. We sought to determine whether bladder filling and/or reflex bladder contractions could be detected by electrical recording from the sacral nerve roots, and whether bladder contractions could be inhibited by stimulation of sacral afferents. Six male cats were anesthetized with alpha-chloralose and bipolar cuff electrodes were used to measure sacral nerve root electroneurograms (ENG) during slow bladder filling, during rapid injections of fluid into the bladder, and during hyperreflexia-like bladder contractions. The rectified and time-averaged activity of the S1 extradural root increased by 0-5 % above the baseline during bladder filling. Rapid injections caused a sudden increase in bladder pressure, and a 3-36 % increase over baseline in the S1 nerve activity. Withdrawal of the same volume caused a reduction in pressure and a decrease in recorded activity (4-14 %). At the onset of a bladder contraction, there was a 7-38 % increase over baseline in the S1 nerve activity. This activity increase was sustained for the duration of the contraction and decreased during bladder relaxation. The onset and duration of bladder contractions could be detected consistently from these nerve activity changes. Recording only afferent activity showed that the increased nerve activity was due to S1 sensory rather than motor fibers. In two cats, it was demonstrated that an ongoing bladder contraction could be inhibited by rectal distension. In one cat, the contractions could be terminated by electrical stimulation of the S1 dorsal root. The results demonstrate that afferent sacral root nerve activity can be used to detect hyperreflexive bladder contractions at low bladder pressures. Such a signal might be used to trigger bladder inhibition via electrical stimulation of specific sacral afferents.

Animals↗

PubMed2001

Functional postural responses after perturbations in multiple directions in a standing man: a principle of decoupled control.

The objective of this study was to assess functional postural responses by analyzing the net joint torques (NJT) in the ankles and the hips resulting from perturbations delivered in multiple directions to subjects standing quietly. A total of eight subjects were standing on two force platforms while an apparatus randomly delivered controlled perturbations at the level of the pelvis in eight directions: anterio-posterior (AP), medio-lateral (ML), and four combinations of these principal directions. Perturbations were repeated five times in each direction for six conditions (i.e., three different perturbation strengths and three different feet orientations). The comparison of the averaged ankle sum NJT (AP) responses showed that the time courses of the responses elicited by a perturbation acting only in the AP direction were identical to those elicited by a combination of two corresponding AP and ML perturbations. In contrast the observed averaged ankle NJT (ML) responses did not follow the same similarity. The comparison of the averaged ankle and hip sum NJT (ML) responses revealed that the time courses of the responses elicited by a perturbation acting only in the ML direction were identical to those elicited by a combination of two corresponding AP and ML perturbations. These findings were invariable of the experimental conditions and were consistent among all the eight subjects. Thereby, we conclude that the ankle sum NJT (AP) and the ankle and hip sum NJT (ML) are the global variables being controlled. This shows that CNS controls the recovery from the multiple direction perturbations of moderate strength by decoupling the AP-ML postural space into two orthogonal directions (AP and ML).

Adult↗

PubMed2001

Neuro-fuzzy extraction of angular information from muscle afferents for ankle control during standing in paraplegic subjects: an animal model.

This paper is part of a project whose aim is the implementation of closed-loop control of ankle angular position during functional electrical stimulation (FES) assisted standing in paraplegic subjects using natural sensory information. In this paper, a neural fuzzy (NF) model is implemented to extract angular position information from the electroneurographic signals recorded from muscle afferents using cuff electrodes in an animal model. The NF model, named dynamic nonsingleton fuzzy logic system is a Mamdani-like fuzzy system, implemented in the framework of recurrent neural networks. The fuzzification procedure implemented was the nonsingleton technique which has been shown in previous works to be able to take into account the uncertainty in the data. The proposed algorithm was tested in different situations and was able to predict reasonably well the ankle angular trajectories especially for small excursions (as during standing) and when the stimulation sites are far from the registration sites. This suggests it may be possible to use activity from muscle afferents recorded with cuff electrodes for FES closed-loop control of ankle position during quite standing.

Algorithms↗

PubMed2001

Effect of initial joint position on nerve-cuff recordings of muscle afferents in rabbits.

The objective was to characterize nerve-cuff recordings of muscle afferents to joint rotation over a large part of the physiological joint range. This information is needed to develop control strategies for functional electrical stimulation (FES) systems using muscle afferent signals for sensory feedback. Five acute rabbit experiments were performed. Tripolar cuff electrodes were implanted around the tibial and peroneal divisions of the sciatic nerve in the rabbit's left leg. The electroneurograms (ENG) were recorded during passive ankle rotation, using a ramp-and-hold profile starting at seven different joint positions (excursion = 5 degrees, velocity = 10 degrees/s, initial positions 60 degrees, 70 degrees, 80 degrees, 90 degrees, 100%, 110 , and 120 ). The amplitude of the afferent activity was dependent on the initial joint position. The steady-state sensitivity of both nerve responses increased with increasing joint flexion, whereas the dynamic sensitivity increased initially but then decreased. The results indicate that recordings of the muscle afferents may provide reliable information over only a part of the physiological joint range. Despite this limitation, muscle afferent activity may be useful for motion feedback if the movement to be controlled is within a narrow joint range such as postural sway.

Afferent Pathways↗

PubMed2001

Soleus stretch reflex during cycling.

The modulation and strength of the human soleus short latency stretch reflex was investigated by mechanically perturbing the ankle during an unconstrained pedaling task. Eight subjects pedaled at 60 rpm against a preload of 10 Nm. A torque pulse was applied to the crank at various positions during the crank cycle, producing ankle dorsiflexion perturbations of similar trajectory. The stretch reflex was greatest during the power phase of the crank cycle and was decreased to the level of background EMG during recovery. Matched perturbations were induced under static conditions at the same crank angle and background soleus EMG as recorded during the power phase of active pedaling. The magnitude of the stretch reflex was not statistically different from that during the static condition throughout the power phase of the movement. The results of this study indicate that the stretch reflex is not depressed during active cycling as has been shown with the H-reflex. This lack of depression may reflect a decreased susceptibility of the stretch reflex to inhibition, possibly originating from presynaptic mechanisms.

Adult↗

PubMed2001

Neural network classification of nerve activity recorded in a mixed nerve.

Whole-nerve cuff electrodes can be used to record electrical nerve activity in peripheral nerves and are suitable for chronic implantation in animals or humans. If the whole nerve innervates multiple target organs or muscles then the recorded activity will be the superposition of the activity of different nerve fibers innervating these organs. In certain cases it is desirable to monitor mixed nerve activity and to determine the origin (modality) of the recorded activity. A method using the autocorrelation function of recorded nerve activity and an artificial neural network was developed to classify the modality of nerve signals. The method works in cases where different end organs are innervated by nerve fibers having different diameter distributions. The electrical activity in the cat S1 sacral spinal root was recorded using a cuff electrode during the activation of cutaneous, bladder, and rectal mechanoreceptors. Using the classification method, 87.5% of nerve signals were correctly classified. This result demonstrates the effectiveness of the neural network classification method to determine the modality of the nerve activity arising from activation of different receptors.

Action Potentials↗

PubMed2000

[Improved function of the hand in persons with tetraplegia using electric stimulation via implanted electrodes].

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.

Activities of Daily Living↗

PubMed2000

Major role for sensory feedback in soleus EMG activity in the stance phase of walking in man.

1. Sensory feedback plays a major role in the regulation of the spinal neural locomotor circuitry in cats. The present study investigated whether sensory feedback also plays an important role during walking in 20 healthy human subjects, by arresting or unloading the ankle extensors 6 deg for 210 ms in the stance phase of gait. 2. During the stance phase of walking, unloading of the ankle extensors significantly (P < 0.05) reduced the soleus activity by 50 % in early and mid-stance at an average onset latency of 64 ms. 3. The onset and amplitude of the decrease in soleus activity produced by the unloading were unchanged when the common peroneal nerve, which innervates the ankle dorsiflexors, was reversibly blocked by local injection of lidocaine (n = 3). This demonstrated that the effect could not be caused by a peripherally mediated reciprocal inhibition from afferents in the antagonist nerves. 4. The onset and amplitude of the decrease in soleus activity produced by the unloading were also unchanged when ischaemia was induced in the leg by inflating a cuff placed around the thigh. At the same time, the group Ia-mediated short latency stretch reflex was completely abolished. This demonstrated that group Ia afferents were probably not responsible for the decrease of soleus activity produced by the unloading. 5. The findings demonstrate that afferent feedback from ankle extensors is of significant importance for the activation of these muscles in the stance phase of human walking. Group II and/or group Ib afferents are suggested to constitute an important part of this sensory feedback.

Adult↗

PubMed2000

Peripheral and central effect of baclofen on ankle joint stiffness in multiple sclerosis.

The effect of baclofen on the soleus stretch reflex and peripheral muscle function was tested in 10 multiple sclerosis (MS) patients with spasticity in the lower extremities. Peroral baclofen (15-60 mg daily) induced a decrease in the twitch torque of the soleus muscle elicited by supramaximal nerve stimulation. The torque was 15.1 +/- 5.5 Nm with baclofen and 17.1 +/- 5.0 Nm without baclofen (P = 0.03). The slope of the background torque/EMG relation was also changed from 1.53 Nm/microV with baclofen to 1.13 NM/microV without it (P = 0.03), and the soleus stretch reflex threshold decreased from 11.4 degrees /s (3.1-62.8) to 6.2 degrees /s (3.1-25.1) without baclofen medication (P = 0.03) in the relaxed muscle. Furthermore, baclofen induced an approximately 20% decrease in the total stiffness at the ankle joint at all contraction levels due to a decrease in the short-latency stretch reflex. From a clinical point of view, the peripheral action of baclofen may be unfortunate. Spasticity is often accompanied by weakness, which may be the major cause of any disability. Consequently, reduction in spasticity by the central effect of baclofen may be counteracted by its influence on muscle properties. In addition, treatment of spasticity by baclofen may unmask weakness.

Adult↗

PubMed2000

Cerebral activation during bicycle movements in man.

The cerebral activation during bicycle movements was investigated by oxygen-15-labelled H2O positron emission tomography (PET) in seven healthy human subjects. Compared to rest active bicycling significantly activated sites bilaterally in the primary sensory cortex, primary motor cortex (M1) and supplementary motor cortex (SMA) as well as the anterior part of cerebellum. Comparing passive bicycling movements with rest, an almost equal activation was observed. Subtracting passive from active bicycle movements, significant activation was only observed in the leg area of the primary motor cortex and the precuneus, but not in the primary sensory cortex (S1). The M1 activation was positively correlated (alpha=0.75-0.85, t=6.4, P<10(-5)) with the rate of the active bicycle movements. Imagination of bicycle movements compared to rest activated bilaterally sites in the SMA. It is suggested that the higher motor centres, including the primary and supplementary motor cortices as well as the cerebellum, take an active part in the generation and control of rhythmic motor tasks such as bicycling.

Adult↗

PubMed2000

Kinematic and kinetic analysis of the walking pattern in hemiplegic patients with foot-drop using a peroneal nerve stimulator.

OBJECTIVE: To analyze the walking pattern in hemiplegic patients using a peroneal nerve stimulator to locate possible harmful mechanical effects on the musculo-skeletal system. DESIGN: Eight hemiplegic patients participated in the study. All patients had used a peroneal nerve stimulator regularly for more than two years and were able to perform unassisted walking. BACKGROUND: Peroneal nerve stimulators are widely applied for correction of foot-drop in hemiplegic patients. The stimulators do not induce normal dorsi-flexion, but a rather exaggerated dorsi-flexion and eventually eversion which might be harmful. METHODS: Three-dimensional kinematic and kinetic analyses of the walking patterns at self-selected speeds were performed with the patients walking without the stimulator and with the stimulator turned on. RESULTS: The walking speed increased on average from 0.77 (S.D., 0.83) to 0.84 (S.D., 0.11) (7.6%, P=0. 005) when the stimulator was used, however no uniform changes in the walking pattern and joint loads were observed. The total work (generation+absorption) produced by the affected leg (both with and without the peroneal nerve stimulator) was significantly lower (P=0. 005) than that of the contralateral leg. Deviations from normal power profiles were observed both on the affected and the contralateral side, and the walking efficiency was 57% lower compared to normal subjects. The estimated peak bone-on-bone forces corresponded to about 50% of what previously has been observed during normal walking at self-selected speed. CONCLUSIONS: The use of the peroneal nerve stimulator do not introduce any excessive and potential harmful mechanical loads. RELEVANCE: Applied correctly, the peroneal nerve stimulator can be used as an aid for foot-drop correction in hemiplegic patients without causing excessive wear on the joints in the lower extremity.

Analysis of Variance↗

PubMed2000

Evidence for transcortical reflex pathways in the lower limb of man.

The existence of transcortical reflex pathways in the control of distal arm and hand muscles in man is now widely accepted. Much more controversy exists regarding a possible contribution of such reflexes to the control of leg muscles. It is often assumed that transcortical reflex pathways play no, or only a minor, role in the control of leg muscles. Transcortical reflex pathways according to this view are reserved for the control of the distal upper limb and are seen in close relation to the evolution of the primate hand. Here we review data, which provide evidence that transcortical reflexes do exist for lower limb muscles and may play a significant role in the control of at least some of these muscles. This evidence is based on animal research, recent experiments combining transcranial magnetic stimulation with peripheral electrical and mechanical stimulation in healthy subjects and neurological patients. We propose that afferent activity from muscle and skin may play a role in the regulation of bipedal gait through transcortical pathways.

Animals↗

PubMed2000

Inhibition of the triceps surae stretch reflex by stimulation of the deep peroneal nerve in persons with spastic stroke.

OBJECTIVE: To reduce the triceps surae stretch reflex by electrical stimulation of the deep peroneal nerve. DESIGN: Intervention study. SETTING: Research institution. PARTICIPANTS: Sample of convenience of 10 spastic stroke individuals. INTERVENTION: After the deep peroneal nerve was stimulated between 0.9 and 4 times tibialis anterior motor threshold, the triceps surae was stretched to elicit a reflex. MAIN OUTCOME MEASURE: The triceps surae stretch reflex was quantified by the amplitude of the reflex electromyography (EMG) in soleus and medial gastrocnemius muscles and mean ankle moment. Paired t test and the Wilcoxon signed rank test (p < .05) were used to evaluate the effect of conditioning stimulation. RESULTS: The soleus stretch reflex EMG was reduced significantly (p < .001) by stimulating the deep peroneal nerve to 25%+/-6% (standard error) of the unconditioned value (relaxed triceps surae). The optimal interval between stimulation and stretch was 141+/-15 msec. The velocity threshold increased significantly (p = .006) from a median value of 8 degrees per second to 33 degrees per second and the area under the stretch velocity/stretch reflex relation decreased significantly (p < .001) (soleus EMG). CONCLUSIONS: The stretch reflex of relaxed triceps surae in persons with spastic stroke can be extensively reduced by stimulating the deep peroneal nerve at several times motor threshold of the tibialis anterior.

Aged↗

PubMed2000

Nerve cuff recordings of muscle afferent activity from tibial and peroneal nerves in rabbit during passive ankle motion.

Activity from muscle afferents regarding ankle kinesthesia was recorded using cuff electrodes in a rabbit preparation in which tactile input from the foot was eliminated. The purpose was to determine if such activity can provide information useful in controlling functional electrical stimulation (FES) systems that restore mobility in spinal injured man. The rabbit's ankle was passively flexed and extended while the activity of the tibial and peroneal nerves was recorded. Responses to trapezoidal stimulus profiles were investigated for excursions from 10 degrees to 60 degrees using velocities from 5 degrees/s to 30 degrees/s and different initial ankle positions. The recorded signals mainly reflect activity from primary and secondary muscle afferents. Dorsiflexion stretched the ankle extensors and produced velocity dependent activity in the tibial nerve, and this diminished to a tonic level during the stimulus plateau. The peroneal nerve was silent during dorsiflexion, but was activated by stretch of the peroneal muscles during ankle extension. The responses of the two nerves behaved in a reciprocal manner, but exhibited considerable hysteresis, since motion that relaxed the stretch to the driving muscle produced an immediate cessation of the prior stretch induced activity. A noted difference between the tibial and peroneal nerve responses is that the range of joint position change that activated the flexor afferents was greater then for the extensor afferents. Ankle rotation at higher velocities increased the dynamic stretch evoked responses during the stimulus ramp but showed no effect on the tonic activity during the stimulus plateau. Prestretching the muscles by altering the initial position increased the response to the ramp movement, however, for the peroneal nerve, when the prestretch brought the flexor muscles near to their maximal lengths, the response to additional stretch provided by the ramp movement was diminished. The results indicate that the whole nerve recorded muscle afferent activity may be useful for control of FES assisted standing, because it can indicate the direction of rotation of the passively moved ankle joint, along with coarse information regarding the rate of movement and static joint position.

Afferent Pathways↗

PubMed2000

Baclofen increases the soleus stretch reflex threshold in the early swing phase during walking in spastic multiple sclerosis patients.

The effect of baclofen on walking performance was examined in nine spastic multiple sclerosis patients. In addition, nine healthy subjects were tested as controls. The modulation of the short latency soleus stretch reflex was closer to normal with baclofen compared to the recordings without baclofen, the modulation index being 74% (range: 60 - 100) with baclofen and 62% (range: 20 - 100) without baclofen, P=0.03. In healthy subjects the modulation index was 100% (range: 52 - 100). In the early swing phase the threshold of the soleus stretch reflex was significantly higher during baclofen medication being 139 deg/s (range: 63 - 302) compared with 93 deg/s (range: 37 - 187) without baclofen, P=0.004. The relation between the stretch velocity (input) and the amplitude of the stretch reflex (output) in early swing phase was unchanged being 0. 27 microVs/deg (range: 0.1 - 1.51) in patients with baclofen and 0. 24 microVs/deg (range: 0.08 - 0.79) without baclofen, P=0.25. Baclofen induced no change in input - output properties of the stretch reflex during walking compared with findings in a sitting position at matched EMG activity. There was a significant correlation between clinical spasticity score and stretch reflex threshold in the early swing phase (rho=-0.61, P=0.04) and between clinical spasticity score and the slope of the best linear fit in the early swing phase (rho=0.72, P=0.009).

Adult↗