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Biomedical subjects

V Dietz

Publications and source records attributed to V Dietz.

At least 145 records · Page 8Linked to original sources
PubMed1995

Epidemiology and clinical characteristics of acute flaccid paralysis associated with non-polio enterovirus isolation: the experience in the Americas.

The Pan American Health Organization adopted as a goal the interruption of transmission of wild poliovirus from the americas by 1990. Collection and processing of stool specimens from patients with acute flaccid paralysis (AFP) to identify wild poliovirus is critical for monitoring the success of the eradication programme. In the study described, cases of AFP in children less than 15 years of age reported in the Americas from 1989 to 1991 were evaluated to investigate the epidemiology of AFP associated with the isolation of non-polio enterovirus (NPEV), to characterize their clinical presentation, and to compare their clinical characteristics with those of AFP cases associated with the isolation of wild poliovirus (confirmed as poliomyelitis). The results show that the notification pattern for AFP associated with NPEV isolates is similar to that for all AFP cases. While AFP associated with NPEV isolates generally differs clinically from confirmed poliomyelitis, 2-21% of cases met one of three case definitions for poliomyelitis. Following the eradication of poliomyelitis, countries can therefore anticipate the continued reporting of cases of AFP that clinically mimic poliomyelitis but which are associated with NPEV. The study also confirms that NPEV circulation is common and that most isolates were from cases that did not resemble poliomyelitis. It is therefore questionable whether characterization of NPEV isolates is essential for global eradication of poliomyelitis and consequently whether allocation of resources for that purpose can be justified.

Acute Disease↗
PubMed1994

Locomotor activity in spinal man.

We studied whether spinal locomotor centres of patients with paraplegia can be activated by external stimuli. In patients with complete paraplegia, coordinated stepping movements were induced by weight support and standing on a moving treadmill. The pattern of leg muscle electromyographic (EMG) activity was similar to that seen in healthy subjects although EMG amplitude was smaller. With daily training the amplitude of gastrocnemius EMG activity increased during weight-bearing phase of stepping and the degree of inappropriate tibialis anterior activity decreased. Patients with incomplete paraplegia profited from the training programme in that their walking on a stationary surface improved even when unsupported. Our results may suggest new ways to improve mobility of patients with paraplegia.

Adult↗
PubMed1994

Low vaccination levels of US preschool and school-age children. Retrospective assessments of vaccination coverage, 1991-1992.

OBJECTIVE: To obtain estimates on (1) the percentage of children who were up-to-date on the recommended childhood vaccination series, (2) the percentage of children who were age-appropriately immunized, and (3) coverage levels by individual vaccines. DESIGN: Vaccination levels were estimated by conducting retrospective immunization coverage surveys of the school health records of children entering kindergarten or first grade in the 1990-1991 or 1991-1992 school year. A multistage cluster survey design was used. SETTING: Survey sites were selected from among the 60 largest urban areas in the United States. One small city and one rural area were selected for comparison. RESULTS: By their second birthday, 11% to 58% (median, 44%) of the children were fully vaccinated. Stricter measurement criteria lowered coverage levels further. Completed series levels at school entry were 71% to 96% (median, 87%). CONCLUSIONS: Vaccination levels at the second birthday were far below the goal for the year 2000. All health providers need to administer vaccines according to the recommended schedule.

Child↗
PubMed1994

Vestibular and somatosensory contributions to responses to head and body displacements in stance.

The relative contribution of vestibular and somatosensory information to triggering postural responses to external body displacements may depend on the task and on the availability of sensory information in each system. To separate the contribution of vestibular and neck mechanisms to the stabilization of upright stance from that of lower body somatosensory mechanisms, responses to displacements of the head alone were compared with responses to displacements of the head and body, in both healthy subjects and in patients with profound bilateral vestibular loss. Head displacements were induced by translating two 1-kg weights suspended on either side of the head at the level of the mastoid bone, and body displacements were induced translating the support surface. Head displacements resulted in maximum forward and backward head accelerations similar to those resulting from body displacements, but were not accompanied by significant center of body mass, ankle, knee, or hip motions. We tested the effect of disrupting somatosensory information from the legs on postural responses to head or body displacements by sway-referencing the support surface. The subjects' eyes were closed during all testing to eliminate the effects of vision. Results showed that head displacements alone can trigger medium latency (48-84 ms) responses in the same leg and trunk muscles as body displacements. Nevertheless, it is unlikely that vestibular signals alone normally trigger directionally specific postural responses to support surface translations in standing humans because: (1) initial head accelerations resulting from body and head displacements were in opposite directions, but were associated with activation of the same leg and trunk postural muscles; (2) muscle responses to displacements of the head alone were only one third of the amplitude of responses to body displacements with equivalent maximum head accelerations; and (3) patients with profound bilateral vestibular loss showed patterns and latencies of leg and trunk muscle responses to body displacements similar to those of healthy subjects. Altering somatosensory information, by sway-referencing the support surface, increased the amplitude of ankle muscle activation to head displacements and reduced the amplitude of ankle muscle activation to body displacements, suggesting context-specific reweighting of vestibular and somatosensory inputs for posture. In contrast to responses to body displacements, responses to direct head displacements appear to depend upon a vestibulospinal trigger, since trunk and leg muscle responses to head displacements were absent in patients who had lost vestibular function as adults.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1994

Human neuronal interlimb coordination during split-belt locomotion.

Human interlimb coordination and the adaptations in leg muscle activity were studied during walking on a treadmill with split belts. Four different belt speeds (0.5, 1.0, 1.5, 2.0 m/s) were offered in all possible combinations for the left and right leg. Subjects adapted automatically to a difference in belt speed within 10-20 stride cycles. This adaptation was achieved by a reorganization of the stride cycle with a relative shortening of the duration of the support and lengthening of the swing phase of the "fast" leg and, vice versa, in support and swing duration on the "slow" leg. The electromyogram EMG patterns were characterized by two basic observations: (1) onset and timing of EMG activity were influenced by biomechanical constraints. A shortening of the support phase on the faster side was related to an earlier onset and increase in gastrocnemius activity, while a coactivation pattern in the antagonistic leg muscles was predominant during a prolonged support phase on the slower side. (2) A differential modulation of the antagonistic leg muscles took place. An increase in ipsilateral belt speed in combination with a constant contralateral belt speed was associated with an almost linear increase in ipsilateral gastrocnemius and contralateral tibialis anterior EMG activity, while the contralateral gastrocnemius and ipsilateral tibialis anterior EMG activity were little affected. It is concluded that a modifiable timing within the stride cycle takes place with a coupling between ipsilateral support and contralateral swing phase. The neuronal control of this coupling is obviously based on ipsilateral modulation of leg extensor EMG by proprioceptive feedback and an appropriate central (e.g. spinal) modulation of contralateral tibialis anterior EMG activity.

Adult↗
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↗
PubMed1994

Analyses of 94 consecutive spinal cord injury patients using ASIA definition and modified Frankel score classification.

Serial neurological examinations were analysed on 94 consecutive spinal cord injury (SCI) patients admitted for rehabilitation to the Swiss Paraplegic Center at the Clinic Balgrist Zurich, Switzerland between 1987 and 1992. Patients' data were examined adopting ASIA and modified Frankel definitions in order to compare the two classifications in terms of consistency and prognostic value. The modified Frankel definition was subdivided into five categories (A, B, C, D and E). On admission (discharge) 43 (37) patients were classified as Frankel A, 23 (11) patients in group B, 26 (42) patients in group C, 2 (2) patients as Frankel D and 0 (2) patients in group E. A qualitative analysis of the results on the base of a maximal score of 100 points (A = 0, B = 25, C = 50, D = 75 and E = 100 points) suggested a mean score improvement from 21.5 (+/- 22.5) to 29.0 (+/- 26.3) or 7.5 (+/- 7.1), regarding all 94 patients during follow up (admission/discharge). The median improvement was one modified Frankel grade (A/B to B/C). No detailed assessments were yielded concerning motor and sensory functions. Using ASIA definition, a continuous numerical score of motor and sensory function was observed. Recovery during follow up was determined by detailed motor and sensory function. For all 94 patients (quadriplegics and tetraplegics), the average motor recovery according to the ASIA definition was 9.4 (+/- 9.6). The mean ASIA motor score improved from 52.2 (+/- 17.3) on admission to 61.6 (+/- 17.9) on discharge.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

A quantitative assessment of presynaptic inhibition of Ia afferents in spastics. Differences in hemiplegics and paraplegics.

Soleus H-reflex facilitation evoked by a supramaximal conditioning stimulation to the femoral nerve was investigated in 28 healthy control subjects and 35 spastic patients of whom 17 were paraplegics with bilateral spinal cord lesion and 18 were hemiplegics with unilateral cerebral lesion. Heteronymous facilitation from quadriceps to soleus was measured 0.4 ms after onset, while the monosynaptic Ia excitation is still uncontaminated by any non-monosynaptic effect and can be used to assess ongoing presynaptic inhibition on Ia terminals to soleus motor neurons. In paralegics, this heteronymous Ia facilitation was significantly larger than in control subjects (all individual results in these patients being above the mean observed in controls). This must reflect a decrease in presynaptic inhibition of Ia terminals in the paraplegics explored here. There was no correlation between this decreased presynaptic inhibition of Ia terminals and the degree of spasticity measured by Ashworth's scale. Surprisingly, the amount of heteronymous Ia facilitation in hemiplegics was the same as in normal subjects. This indicates that presynaptic inhibition of Ia terminals is unchanged in these patients and disagrees with the usual interpretation of reduced vibratory inhibition of the soleus H-reflex in hemiplegics. It is argued that this disagreement is due to the fact that vibratory inhibition of the reflex also depends on post-activation depression following repetitive synaptic transmission.

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

Gating of reflexes in ankle muscles during human stance and gait.

Holding the body's centre of gravity steady represents the crucial variable for the stabilization of posture in upright stance in man. Results from two experimental approaches suggest that force-dependent receptors are required, in addition to the well-known systems involved in sway stabilization, for equilibrium control. One approach concerns bilateral leg muscle activation during stance. Unilateral or bilateral leg displacements were induced while subjects stood on a treadmill with split belts. A unilateral displacement induced a bilateral EMG response. During bilateral displacements the EMG activity was linearly summed or subtracted, depending on whether the legs were displaced in the same or opposite directions. Both legs acted in a cooperative manner: each limb affected the strength of muscle activation and the time-space behaviour of the other. This interlimb coordination is suggested to be mediated by spinal interneuronal circuits, which are themselves under supraspinal (e.g., cerebellar) control. The other approach concerns the modulation of postural reflexes under stimulated "microgravity" ir. water immersion. An approximately linear relationship was found between contact forces and impulse-directed EMG response amplitudes in the leg muscles. Out of water loading of the subjects resulted in no further increase of the response amplitude. It was concluded that the function of proprioceptive reflexes involved in the stabilization of posture depends on the presence of contact forces opposing gravity. Extensor load receptors are thought to signal changes of the projection of body's centre of mass with respect to the feet. The interaction of the afferent input from these receptors with the other systems involved in postural control is not yet fully understood.

Ankle↗
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↗
PubMed1993

Patients with spastic hemiplegia at different recovery stages: evidence of reciprocal modulation of early/late reflex responses.

Reflex electromyographic (EMG) muscle responses were recorded from abductor pollicis brevis (APB) and tibialis anterior (TA) muscles of fifty patients with spastic hemiplegia. Responses in the muscles were evoked during voluntary muscle contraction (about 20% of maximum voluntary effort) by submaximal but suprathreshold electrical stimulation of the median (at the wrist) and common peroneal (at the neck of the fibula) nerves respectively. Three EMG peaks (R1, R2 and R3) could be recorded after the direct muscle response (M). There was only a slight difference in R1-R2 latency interval of about 5 ms between upper and lower limbs on the unaffected side of the patients making it unlikely that this late response of the lower limb involves a long loop pathway, although this possibility cannot be discounted for the later, R3, response. Reflex behaviour was analysed for three clinical identifiable recovery stages of voluntary movements in the spastic limbs (synergistic, isolated and useful movements). The major finding was that an increase in the amplitude of the early response "R1" was associated with a decreased amplitude and delayed latency of the late response "R2" on the spastic side. The amplitude of R1 in the three different recovery stages decreased significantly, whereas the amplitude of R2 increased significantly with improvement of the functional stage of the limb. A significant negative linear correlation was found between R1 and R2 amplitude changes in upper as well as lower limbs. A refractoriness of the motor neuron pool as a possible explanation for the decreased R2 amplitude could be discounted. These findings together with recent work on reflex development in children support the hypothesis of reciprocal modulation of early and late reflex signals by supraspinal motor centers.

Adult↗
PubMed1993

Impaired activation pattern in antagonistic elbow muscles of patients with spastic hemiparesis: contribution to movement disorder.

Surface electromyographic "EMG" activity in biceps brachii (agonist muscle) and triceps brachii (antagonist muscle) as well as the discharge behaviour of motor units "MUs" (needle recording) in biceps brachii muscle were recorded during slow (0.33 Hz) and fast (0.66 Hz) voluntary elbow flexion movements (auditory matching task) in fifty patients with spastic hemiplegia. In the spastic limbs, a long lasting, small amplitude tonic co-contraction of antagonist muscles was seen during slow flexions (SF) in 29 cases. This effect was strongest during the fast elbow flexion movements (FF). In 33 patients a triphasic pattern of muscle activation was observed on the unaffected side but not on the spastic side. The amplitude of the agonist surface EMG was significantly reduced and the amplitudes of the MU potentials recruited during maximal effort were generally smaller on the spastic side compared to the unaffected side. The agonist-antagonist activation pattern was analysed with respect to three clinically identifiable functional recovery stages of voluntary movements in the spastic limbs, namely synergistic, isolated and useful movements. The MU amplitudes and the amplitude of the surface EMG activity in the agonist muscle recorded during FF movements became significantly larger whereas the amplitude of the antagonist tonic activity became smaller with increasing functional recovery of the limb. It is concluded that impaired recruitment of type II motor units in the agonist muscles and the inability to selectively activate the agonist muscle contribute to the deficit in motor performance in spastic paresis.

Adult↗
PubMed1993

Reflex behavior and programming in Parkinson's disease.

Several aspects of characteristically impaired postural adjustments indicate a defective central programming of the respective EMG patterns in PD. This may be due to deficits in the supraspinal control of spinal interneuronal circuits. This impairment obviously contributes to the difficulty of these patients in performing two motor acts simultaneously. In addition, parkinsonian patients exhibit a reduced sensitivity of polysynaptic reflexes in the leg extensor muscles which correlates with their postural instability. The activity of monosynaptic reflexes is negligible, as in healthy subjects. The impairment of proprioceptive reflex function may be partially compensated for by changes of intrinsic muscle stiffness. Discrepancies in the literature about the behavior of the polysynaptic EMG responses in parkinsonian patients may in part arise from the fact that it depends on both the particular muscle under study and the actual motor task investigated.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗