Biomedical subjects

M Trippel

Publications and source records attributed to M Trippel.

At least 19 recordsLinked to original sources

PubMed1996

Computer assisted brain surgery for small lesions in the central sensorimotor region.

The capacity of a new optical navigation device is demonstrated by six microsurgical procedures for small subcortical lesions within the central sensorimotor strip. This small series is aimed at less invasive resection in this functionally critical region, independently of primary diagnosis and outcome. Guided by high resolution CT imaging data five brain tumours and one cavernous angioma was selectively located and most sparingly removed without additional sensorimotor deficit. In two cases improvement of a pre-operative paresis was observed immediately after surgery. Thanks to light-weight freehand pointing instruments and a ranging accuracy of +/- 1 mm, damage to functionally important brain areas and vessels was avoided by using uncommonly oblique, e.g., transsulcal ways of access which would hardly have been possible even with guidance by conventional stereotaxy. The demanding systematic cortical stimulation of the precentral gyrus applied in three cases was only sensitive in infiltrating tumours-e.g., low grade astrocytomas-where for want of adjuvant therapy it was essential to proceed to the extreme limits of resection. In general, precise anatomical localisation by computer aided surgery (CAS) is sufficient in small central lesions which guarantees minimally invasive surgery. The potential of this new, soon commercially available optical navigation system in (neuro) surgery, quality control and teaching is discussed.

Adult↗

PubMed1995

Modulation of sural nerve somatosensory evoked potentials during stance and different phases of the step-cycle.

In order to investigate the modulation of somatosensory processing during stance and locomotion, sural nerve somatosensory evoked potentials were recorded during both stance and different phases of the step-cycle. Characteristic sequences of negative-positive waves were elicited, consisting of an early component, N40, presumably of subcortical origin, followed by a P50-N80-P220 complex of cortical origin. The N40 and N40-P50 components had similar amplitudes in both gait and stance. However, the P50-N80 component was attenuated whereas the N80-P220 complex became biphasic during gait. Within the step-cycle, amplitudes of the cortical components P50-N80 and N80-P110 were larger prior to footfall and smaller at the beginning of the support phase. The results demonstrate that locomotion produces a modulatory effect on somatosensory input at a cortical level. Within the step-cycle, excitability of the somatosensory cortex is increased during the middle and late swing phases and decreased during the support phase. Such modulation may contribute to an improved detection of foot contact at touchdown.

Adult↗

PubMed1995

Optically-navigable operating microscope for image-guided surgery.

In computer-assisted surgery (CAS), optical digitizing is state-of-the-art. Unfortunately standard navigation instruments, e.g. small, LED-equipped pointers are frequently shadowed by the operating microscope when the camera-array is ceiling- or rack-mounted. Thus, for microsurgery, a navigation module consisting of a reference panel mounted onto the housing of the microscope and an object distance measuring unit attached in front of the objective lens was developed. By means of this navigation module the microscope can be located in space with an accuracy of +/- 1-2 mm. Focusing errors due to the high depth of view of modern microscopes and individual refraction anomalies are eliminated by laser distance measurement. This device has been clinically tested since September 1994 and a typical case is reported.

Humans↗

PubMed1994

Task-dependent modulation of short- and long-latency electromyographic responses in upper limb muscles.

Records were made of electromyographic (EMG) responses of both upper limb muscles and the corresponding elbow joint movements following sinusoidal (0.3 Hz) isometric displacement of the elbow joint itself. Two motor conditions were tested. Firstly, the subjects had to control elbow position and secondly control joint torque. Randomly timed, flexing or extending ramp impulses were induced at different displacement velocities and amplitudes. Following long duration displacements (> 100 msec) the recorded EMG responses could clearly be separated into 3 different components (M1-M3). The M1 component was of constant duration but M3 corresponded to the duration of the ramp displacement. It is proposed that the M1 component is "coded" by the acceleration signal and the M3 component by the velocity signal. Only the shape of the M2 component was dependent upon the actual motor condition. With the subjects controlling the elbow joint angle the M2 components in the arm flexor and extensor EMG responses exhibited a peak whose rate of rise was dependent on displacement velocity. However, when elbow torque was controlled by the subjects the M2 component exhibited a plateau whose amplitude was dependent on displacement velocity. The amplitude of the M2 component was significantly larger during position-control than during torque-control. We propose that the difference in the behaviour of the EMG responses may be achieved by the appropriate central regulation of gamma-motoneurone activity or, alternatively, by selective modulation of different receptor inputs between the two tasks.

Adult↗

PubMed1993

Increased amplitude of cutaneous reflexes during human running as compared to standing.

The amplitude of H-reflexes is decreased during walking as compared to standing and a further reduction is seen during running as compared to walking. Does a similar reduction occur for reflexes elicited by cutaneous stimulation? To answer this question, the electromyographic (EMG) responses in biceps femoris (BF) and tibialis anterior (TA) to a 20 ms train of 5 electrical pulses, were recorded. This stimulus was applied to the sural nerve at the ankle, either at 16 different phases of the step cycle in human volunteers running on a treadmill at 8 km/h or at different isometric contraction levels of TA and BF in the same subjects during standing, imitating the postures of different phases of the step cycle. The mean latency of the main responses in BF of all subjects was 76 ms. Similar responses (P2), with a latency of 79 ms were seen in TA in 6 of the 10 subjects. For a constant strength of stimulation (2 times perception threshold) during isometric contractions at different levels in early stance imitation, the mean reflex ratio's (reflex/background) of BF and TA responses were 1.07 and 0.53, respectively, while the ratio's for these 2 muscles during running were 1.78 and 1.1. The higher reflex ratio's in running were primarily due to the large facilitatory responses, which were present during most of the step cycle but rarely during voluntary contractions in the subjects during standing. At the end of the swing phase, however, the responses in BF and TA were predominantly suppressive, as were most of the responses to stimulation applied to the standing subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1993

Human stance on a sinusoidally translating platform: balance control by feedforward and feedback mechanisms.

With subjects standing on a treadmill moving sinusoidally backward and forward, recordings of electromyographic (EMG) leg and trunk muscle activity, head and joint movements and platform torque were made with the subjects' eyes open or closed. The sinusoidal frequency was changed, stepwise and randomly, between 0.5, 0.3 and 0.25 Hz. The amplitude of the deflection was constant at +/- 12 cm. During an adapted sinus cycle, the maximum leg muscle EMG activity was recorded in the tibialis anterior around the posterior turning point and in the gastrocnemius around the anterior turning point in the treadmill cycle. This activity was associated with a forward inclination of the body around the posterior point and a straightening of the body at the anterior point. Both the degree of body inclination and the corresponding EMG activity were dependent upon the sinusoidal frequency. The programmed adjustment of the body inclination was such that the result of inertial and gravitational forces acting on the body coincided with the axis of the body at the posterior turning point. At the anterior point, the adjustment was achieved mainly by strong activation of the leg extensors. The latencies of the compensatory muscle responses to a change in treadmill frequency were significantly shorter at the posterior point for the gastrocnemius than for the tibialis anterior, and at the anterior point for the tibialis anterior than for the gastrocnemius. No correlated changes were seen in the corresponding head and joint movements. The difference in latency can best be attributed to the different body postures during the sinusoid. Early activation of the gastrocnemius is required due to the forward-directed impulse to the inclined body at the posterior point, and of the tibialis anterior muscle due to the backward-directed impulse to the erect body at the anterior point. It is suggested that afferent input from extensor load receptors provides information about the position of the body's centre of gravity relative to the support surface and determines the generation of the EMG responses. Adaptation of both the EMG and biomechanical patterns to a new sinusoidal frequency of the treadmill occurred within four cycles after the change. Biomechanically, this was reflected as a change in the body posture. Vision did not significantly affect these changes. In conclusion, standing on a sinusoidally moving platform, the nervous system acts to control the position of the body's centre of gravity relative to the feet. Body posture is adjusted in such a way that the forces acting on the body during the treadmill movements become minimised.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1993

Stretch-induced electromyographic activity and torque in spastic elbow muscles. Differential modulation of reflex activity in passive and active motor tasks.

Stretch-evoked electromyographic (EMG) activity and torque signals have been studied in elbow joint muscles of both sides of patients with spastic hemiparesis and healthy subjects. In order to reveal differences in the generation of muscle tone between clinical assessment and functional movement, stretches of different velocities and amplitudes were applied during passive and quasi-functional active motor tasks. In spastic patients the strength and duration of the EMG responses following stretching of flexor and extensor muscles during both passive and active tasks were dependent on the stretch velocity and duration, respectively. This effect was seen on both the spastic and unaffected side. Under passive conditions EMG activity after stretching was negligible in the limb muscles of healthy subjects, of small amplitude in unaffected limbs of the patients, but was strong in affected muscles. Under active conditions, the amplitude of the early (M1) component of the EMG signal was larger, while the later components (M2 and M3) were smaller. These differences were due more to a change in reflex gain than to a change in reflex threshold when the stretch velocity signal was the basis for calculation. It is suggested that in spastic paresis, modulation of stretch-induced EMG activity in the spastic limb becomes restricted to a smaller range with a poor ability to switch off under passive conditions. Furthermore, the reflex EMG activity suffers a reduced facilitation under active conditions. In comparison with unaffected limbs the stretch-evoked torque on the affected side was increased under passive conditions (due to the extra EMG activity) and decreased under active conditions (due to a reduced EMG activity). An increased torque to EMG ratio was found in spastic flexor and extensor muscles during active tasks. This is thought to be due to changes in mechanical muscle fibre properties suffered as a consequence of defective muscle activation following cerebral lesions. The consequences for clinical assessment of muscle tone and therapy of spastic movement disorder are discussed.

Adult↗

PubMed1992

Phase-dependent reversal of reflexly induced movements during human gait.

To investigate whether phase-dependent reversals in reflex responses on electromyography (EMG) are accompanied by movement reversals, a series of human volunteers were studied for their behavioural responses to sural nerve stimulation during running or walking on a treadmill. Low-intensity stimulation (less than 2.5 x perception threshold, T) of the sural nerve yielded facilitatory responses in the tibialis anterior muscle (TA), correlated with an induced ankle dorsiflexion (mean maximum 4 degrees) in early swing. The same stimuli yielded primarily TA suppression and weak ankle plantar flexion (mean maximum 1 degree) at end swing. The correlated induced knee angle changes did not precede the ankle changes, and they were relatively small. Mean maximum flexion in early swing was 6.2 degrees, while mean maximum extension was 3.7 degrees. High-intensity stimulation of the sural nerve (greater than 2.5 x T) always gave rise to suppression of the ongoing activity. This resulted in a second type of movement reversal. During late stance and early swing the responses in TA were suppressive (i.e. below background activity) and related to ankle plantar flexion. In contrast, the responses during early and middle stance consisted of suppression in extensor activity (gastrocnemius medialis and soleus) and ankle dorsiflexion. The data are discussed in terms of a new hypothesis, which states that the responses to electrical stimulation of cutaneous nerves during locomotion do not correspond directly to corrections for stumbling following mechanical perturbations during the step cycle. Instead, the data invite a reinterpretation in terms of the opening and closing of reflex pathways, presumably by a central pattern generator for locomotion.

Adult↗

PubMed1992

Regulation of bipedal stance: dependency on "load" receptors.

According to recent observations, influence of body load has to be taken into account for the neuronal control of upright stance in addition to the systems known to be involved in this regulation (e.g. afferent input from vestibular canals, visual and muscle stretch receptors). The modulation of compensatory leg muscle electromyographic (EMG) responses observed during horizontal body posture indicates the existence of a receptor system which responds to loading of the body against the supporting platform. This receptor should be located within the extensor muscles because a compensatory EMG response and a loading effect on this response was only present following translational, but not rotational impulses. As the EMG responses were identical to those obtained during upright stance, it is argued that these load receptors activate postural reflexes. According to recent observations in the spinal cat, this afferent input probably arises from Golgi tendon organs and represents a newly discovered function of these receptors in the regulation of stance and gait.

Biomechanical Phenomena↗

PubMed1992

Developmental aspects of stance regulation, compensation and adaptation.

Recordings of electromyographic (EMG) leg muscle activity, head and joint movements and platform torque were taken in healthy subjects within three age groups (approximately 6, 10 and greater than 22 years) standing upright upon a sinusoidally moving treadmill. The sinusoidal frequency was randomly changed between 0.5, 0.33 and 0.25 Hz, while the amplitude of the deflection was constant (+/- 12 cm). During an adapted sinus, forward inclination of the body at the posterior turning point was associated with a slowly increasing tibialis anterior and decreasing gastrocnemius activity, while straightening of the body at the anterior turning point was associated with a sharply increasing gastrocnemius and decreasing tibialis anterior activity. The angle of forward inclination was greatest in the groups of children and was dependent upon both the sinus frequency and the child's height. The presumed programmed adjustment of the body inclination was such that the net effect of both inertial and gravitational forces acting on the body coincided approximately with the axis of the body at the posterior turning point. Changes of sinusoidal frequency were followed by compensatory responses, the amplitude of which depended upon the velocity of the body's displacement and the height of the subjects. In all three subject groups the response latencies were significantly shorter at the posterior turning point for the gastrocnemius response to a change from 0.5 to 0.25 Hz (105 ms for children and 119 ms for adults) than for the tibialis anterior response to a change from 0.25 to 0.5 Hz for which the values were 162 and 169 ms, respectively. This difference could be attributed to the forward inclination of the body at the posterior turning point which requires an earlier onset of compensatory extensor activity in order to maintain equilibrium. Adaptation to a new sinusoidal frequency occurred within 4 cycles following a change in sinus frequency. The phase shifts between treadmill position and the biomechanical and EMG signals that occurred during the adaptational process suggest that the position of the body's centre of gravity is the variable controlled by the programmed leg muscle activation. In young children the phase shifts during adaptation were absent, which may contribute to their greater instability. It is concluded that posture is continually adjusted in such a way that the resulting torque acting on the body during the treadmill movement becomes minimized. For this regulation load receptors in addition to the classical afferent impulses from visual, vestibular and muscle stretch receptors could play a major role.

Acclimatization↗

PubMed1992

Visually induced destabilization of human stance: neuronal control of leg muscles.

With subjects standing on a treadmill both the treadmill and an optical flow pattern were moved sinusoidally (0.25 Hz) and the effect of delaying the presentation of the image with respect to treadmill movement was analysed. Around the posterior turning point of treadmill movement a modulation of the tibialis anterior EMG was observed, the onset, duration and amplitude of which were dependent upon the phase-shift between the movements of the legs and the image. At times around the anterior turning point a corresponding modulation, but only of EMG amplitude, occurred in the extensor muscles. Little adaptational changes in EMG activity were seen during successive cycles. Consequently during a specific sensitive phase of the sinus tibialis anterior EMG, responses are evoked in which strength depended on the velocity of the optical flow pattern. The modulation of the extensor activity is necessary for a 'resetting' of the neutral body position.

Adaptation, Physiological↗

PubMed1992

Influence of subjects' height on the stabilization of posture.

In order to investigate the influence of subjects' height in stabilization of body sway, postural EMG reactions were analysed following perturbation of posture during stance on a force measuring platform. Perturbing momenta of different strengths were unexpectedly applied at the back (level of the center of gravity) after being matched to the body weight of each subject. EMG activity of the antagonistic leg muscles and head, hip and ankle joint movements were recorded. There was a close correlation between displacement amplitude at the ankle joint and height of the subject, with the largest displacements in small subjects. The consequence of this relationship was that 1) The compensatory reactions consisted of larger gastrocnemius responses and a stronger coactivation of the tibialis anterior; 2) Momenta of increasing strength resulted in a larger increment of both ankle joint displacement and gastrocnemius EMG responses in small compared to larger subjects. In analogy to tip-toeing movements, it is concluded that the coactivation pattern is typical for stance conditions with a restricted area of support in order to reduce body sway. On the basis of latency measurements it is suggested that the response pattern is induced by proprioceptive information from the impact site of the momentum.

Adolescent↗

PubMed1991

Compensation of human stance perturbations: selection of the appropriate electromyographic pattern.

Perturbations of stance evoke purposive EMG patterns which are directed to hold the body's centre of gravity over the feet. Dorsiflexing rotation of the feet is followed by a monosynaptic stretch reflex response in the gastrocnemius muscle, succeeded by a late compensatory tibialis anterior activation. Backward translation of the feet elicits only a compensatory polysynaptic EMG response in the gastrocnemius muscle, while an early gastrocnemius response is absent. The amplitude modulation of the gastrocnemius H-reflex has been investigated during the early part of the two modes of perturbation. Only during translational perturbation a progressive decrease in gastrocnemius H-reflex amplitude started within 5 ms after onset of displacement. The degree of the reduction in amplitude in the former perturbation was dependent on the displacement velocity. Only the contact forces (torques) differed between the two modes of perturbations within the first 10 ms after onset of perturbations. It is suggested that signals from pressure receptors within the body are responsible for the early change in H-reflex amplitude during translational perturbations and it is concluded that the simplest spinal reflex is under very rapid and powerful moment-to-moment control by changes in peripheral feedback. In view of a strong reciprocal modulation of monosynaptic and polysynaptic reflex responses, the later purposive EMG responses may be determined by early changes in presynaptic inhibition of group I afferents.

Adult↗

PubMed1991

Reflex activity and muscle tone during elbow movements in patients with spastic paresis.

Reflex behavior and tension development in upper limb muscles were analyzed and comparisons made between the unaffected and spastic sides of patients with spastic hemiparesis. During sinusoidal (0.3-Hz) isometric or isotonic elbow tracking, with a control either of joint position or of torque, randomly timed displacements were induced (at one of three velocities) stretching either the activated flexor or the extensor muscles. On the spastic side, exaggerated short-latency reflexes were apparent, but in contrast, the amplitude of long-latency electromyography (EMG) responses was reduced. The latter responses were differentially modulated on the unaffected side, predominantly by the acceleration signal during control of position and more by the velocity signal during control of torque, while the mode of muscle contraction (isometric or isotonic) had little influence on this behavior. This difference in reflex modulation was lost on the spastic side. The functional consequence of this reduced EMG modulation could be difficulty in performing finely controlled arm movements. The ratio of torque to EMG activity during displacements was higher for both background and reflex-induced EMG on the spastic limb than on the unaffected side. This effect was more pronounced for the flexor than for the extensor muscles. Consequently, the development of spastic muscle hypertonia cannot be attributed to an increase in EMG activity. It is suggested that secondary to a supraspinal lesion, mechanical muscle properties change in such a way that the activated spastic muscle develops more tension when it is stretched.

Adolescent↗

PubMed1991

Selective activation of human soleus or gastrocnemius in reflex responses during walking and running.

Phase-dependent reflex modulation was studied by recording the electromyographic (EMG) responses in soleus (SOL) and gastrocnemius medialis (GM) to a 20 ms train of 5 electrical pulses, applied to the sural or tibial nerve at the ankle, in 14 volunteers walking or running on a treadmill. Although both the spontaneous activity and the reflex responses were usually similar for both muscles, instances were identified in which separate control was evident. During walking (4 km/h), activity in SOL started earlier in the stance phase than GM activity. Correspondingly, the amplitude of the reflex responses was larger in SOL than in GM in early stance, both ipsi- and contralateral to the side of stimulation. In some cases, the same stimulus could elicit contralaterally a suppression of GM in synchrony with a facilitation of SOL. These crossed extensor reflexes had a low threshold (1.2 x T) and a latency ranging from 72 to 105 ms. During running (8 km/h or more), responses were seen selectively in GM instead, without concomitant responses in SOL. Such responses had a latency ranging from 82 to 158 ms and they appeared during the first extension phase, at the end of the swing phase. In addition, selective GM responses, with latencies above 200 ms, were seen near the transition from stance to swing during running. These instances of separate reflex control of SOL and GM were correlated with step cycle periods during which the motoneurones of either one of these muscles received more spontaneous activation than the other. Nevertheless, it is argued that premotoneuronal gating must also be involved since the increased amplitude of the crossed SOL responses (in early stance) and of GM responses (at end swing) was not strictly linked to an elevated amount of spontaneous activity during these parts of the step cycle as compared to other parts.

Adolescent↗

PubMed1990

Amplitude modulation of the human quadriceps tendon jerk reflex during gait.

Amplitude modulation of the quadriceps tendon jerk reflex was investigated during the step cycle in normal human subjects. Reflex amplitude was compared with that obtained during a control stance condition, with "equivalent" levels of EMG activity and limb position. During gait there was a progressive decrease in the reflex amplitude early in the stance phase, i.e. during yielding of the knee, and it remained reduced throughout the step cycle. This pattern of changes in reflex amplitude correlated with neither the quadriceps EMG activity nor with the knee joint movements. The behavior of the tendon reflex was similar to that described for the modulation of the quadriceps H-reflex during the early stages of the stance phase of gait. In the latter study it was argued that changes in presynaptic inhibition of quadriceps la terminals could account for the amplitude modulation. We conclude that there is no dramatic change in the gamma drive to quadriceps muscle spindles: tendon reflexes are modulated during the step cycle in much the same way as H-reflexes, in spite of the peripheral and central differences between them. Similar behavior has been described for the soleus H-reflex and Achilles tendon reflex during gait although the modulation of these reflexes followed a different pattern than that seen in the quadriceps.

Achilles Tendon↗

PubMed1990

Gating and reversal of reflexes in ankle muscles during human walking.

Phase-dependent reflex modulation was studied by recording the electromyographic (EMG) responses in ankle flexors (Tibialis Anterior, TA) and extensors (Gastrocnemius Medialis, GM and Soleus, SOL) to a 20 ms train of electrical pulses, applied to the tibial or sural nerve at the ankle, in human volunteers walking on a treadmill at 4 km/h. For low intensity stimuli (i.e. 1.6 times perception threshold), given during the swing phase, the most common response was a suppression of the TA activity with a latency of 67 to 118 ms. With high intensity of stimulation (i.e. 2.8 x T), a facilitatory response appeared in TA with a latency of 74 ms. This latter response was largest during the middle of the swing phase, when it was correlated with exaggerated ankle dorsiflexion. The TA reflex amplitude was not a simple function of the level of spontaneous ongoing activity. During stance, TA responses were small or absent and accompanied by a suppression of the GM activity with a latency ranging from 62 to 101 ms. A few subjects showed an early facilitatory, instead of a suppressive, GM response (88 to 136 ms latency). They showed a phase-dependent reflex reversal from a dominant TA response during swing to a facilitatory GM response with an equivalent latency during stance. The GM facilitation occurred exclusively during the early stance phase and habituated more than the TA responses. It is concluded that phase-dependent gating of reflexes occurs in ankle muscles of man, but only when vigorous extensor reflexes are present. More commonly, a phase-dependent modulation is seen, both of facilitatory and suppressive responses.

Adolescent↗

PubMed1989

Human postural reflexes and gravity--an under water simulation.

This study represents the first attempt to investigate the influence of gravity on postural adjustments. Subjects were displaced while standing under water on a movable platform, while the buoyancy of the body was adjusted by using a variety of lead vests. Under water, an approximately linear relationship was found between body weight and impulse directed electromyographic response amplitudes in the leg and thigh muscles. Loading of the subjects out of water resulted in a saturation of the response amplitude. The biomechanical signals recorded during the displacements indicated that neither vestibulospinal nor muscle proprioceptive reflex mechanisms can account for the effect observed under water. It is suggested that the EMG responses are mediated by reflexes which are activated by pressure receptors within the body in order to hold the centre of gravity over the feet.

Adult↗