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Biomedical subjects

V Dietz

Publications and source records attributed to V Dietz.

At least 19 recordsLinked to original sources
PubMed1999

Changes of tibia bone properties after spinal cord injury: effects of early intervention.

OBJECTIVE: To evaluate the effectiveness of an early intervention program for attenuating bone mineral density loss after acute spinal cord injury (SCI) and to estimate the usefulness of a multimodality approach in diagnosing osteoporosis in SCI. DESIGN: A single-case, experimental, multiple-baseline design. SETTING: An SCI center in a university hospital. METHODS: Early loading intervention with weight-bearing by standing and treadmill walking. PATIENTS: Nineteen patients with acute SCI. OUTCOME MEASURES: (1) Bone density by peripheral computed tomography and (2) flexural wave propagation velocity with a biomechanical testing method. RESULTS: Analysis of the bone density data revealed a marked decrease of trabecular bone in the nonintervention subjects, whereas early mobilized subjects showed no or insignificant loss of trabecular bone. A significant change was observed in 3 of 10 subjects for maximal and minimal area moment of inertia. Measurements in 19 subjects 5 weeks postinjury revealed a significant correlation between the calculated bending stiffness of the tibia and the maximal and minimal area moment of inertia, respectively. CONCLUSION: A controlled, single-case, experimental design can contribute to an efficient tracing of the natural history of bone mineral density and can provide relevant information concerning the efficacy of early loading intervention in SCI. The combination of bone density and structural analysis could, in the long term, provide improved fracture risk prediction in patients with SCI and a refined understanding of the bone remodeling processes during initial immobilization after injury.

Adult↗
PubMed1999

Electrophysiological recordings in patients with spinal cord injury: significance for predicting outcome.

The clinical assessment of the level, extent and severity of spinal cord injury (SCI) can be supplemented by electrophysiological recordings. These techniques also provide an early diagnosis of neurological deficits in patients with acute SCI and are of prognostic value even in uncooperative patients. Electrophysiological recordings (motor evoked potentials (MEP) and somato-sensory evoked potentials (SSEP)) are of similar significance in predicting functional outcome of ambulatory capacity, hand- and bladder function as the clinical examination according to the ASIA standards. EMG, neurographic and reflex recordings of acute SCI patients within spinal shock are even more sensitive in assessing an associated damage of the peripheral motor pathways (ie of motoneurones and nerve roots) than the clinical examination and allow the possibility of predicting the development of muscle tone or muscle atrophy. The evaluation of impairment of the autonomic nervous system after SCI by clinical examination is restricted. In contrast, recordings of the sympathetic skin response (SSR) can provide information about the extent and level of lesions of the spinal sympathetic nervous system which are related to autonomic dysfunction. Therefore, electrophysiological recordings supplementary to the clinical examination are helpful for planning and selecting the appropriate therapeutical approaches within the rehabilitation programme. Furthermore, they allow the prediction of functional outcome and the objective assessment of recovery of specific parts of the spinal and peripheral fibre tracts.

Electromyography↗
PubMed1999

Impaired modulation of quadriceps tendon jerk reflex during spastic gait: differences between spinal and cerebral lesions.

In healthy subjects, functionally appropriate modulation of short latency leg muscle reflexes occurs during gait. This modulation has been ascribed, in part, to changes in presynaptic inhibition of Ia afferents. The changes in modulation of quadriceps tendon jerk reflexes during gait of healthy subjects were compared with those of hemi- or paraparetic spastic patients. The spasticity was due to unilateral cerebral infarction or traumatic spinal cord injury, respectively. The modulation of the quadriceps femoris tendon jerk reflex at 16 phases of the step cycle was studied. The reflex responses obtained during treadmill walking were compared with control values obtained during gait-mimicking standing postures with corresponding levels of voluntary muscle contraction and knee angles. In healthy subjects the size of the reflexes was profoundly modulated and was generally depressed throughout the step cycle. In patients with spinal lesion the reflex depression during gait was almost removed and was associated with weak or no modulation during the step cycle. In patients with cerebral lesion there was less depression of the reflex size associated with a reduced reflex modulation on the affected side compared with healthy subjects. On the 'unaffected' side of these patients reflex modulation was similar to that of healthy subjects, but the reflex size during gait was not significantly different from standing control values. These observations suggest that the mechanisms responsible for the depression of reflex size and the modulation normally seen during gait in healthy subjects are impaired to different extents in spasticity of spinal or cerebral origin, possibly due to the unilateral preservation of fibre tracts in hemiparesis.

Adolescent↗
PubMed1999

CO2 reactivity of the cerebral hemoglobin concentration in healthy term newborns measured by near infrared spectrophotometry.

CO2 reactivity of cerebral hemoglobin concentration was studied in 16 healthy term neonates on days 1 and 4 after birth using the near infrared spectrophotometry (NIRS) technique. The aim was to establish data on the physiological range of CO2 reactivity in healthy newborns and to investigate the influence of postnatal age on it. The CO2 reactivity measured by NIRS is expressed as the change of the total cerebral hemoglobin concentration (tHbR) per change of CO2 tension in micromol/l/kPa. We evaluated CO2 reactivity during increases and decreases of transcutaneous CO2 partial pressure and found in our methodological setting the data of the increases more reliable. In all infants but 1 we found a tHbR on day 1 with a mean value of 8.19 micromol/l/kPa (-1.39 to 18.87), in all infants on day 4 with a mean value of 9.54 micromol/l/kPa (2.76-25. 88). There is a trend to higher values between day 1 and day 4 (difference = 2.25 micromol/l/kPa; p = 0.08). The noninvasive NIRS technique enabled us to test the cerebrovascular CO2 reactivity of the tHbR for the first time in healthy term newborns. Data on its physiologic range and variability are presented and compared to findings from ventilated infants and other age groups. As the CO2 reactivity might be an indicator for infants at risk of cerebral damage, it is necessary to have data on the physiological range of this parameter.

Brain↗
PubMed1999

Regional differences of cerebral hemoglobin concentration in preterm infants measured by near infrared spectrophotometry.

Near infrared spectrophotometry has been used to measure total cerebral hemoglobin concentration (micromol/l) as a major indicator of the oxygen transport capacity in neonates. The aim of this study was to find out how the position of the probe influences the quality of the measurement and the actual cerebral hemoglobin concentration-values. We studied 10 healthy preterm infants with a mean gestational age of 31.5 weeks and a birthweight of 1513 g. The data were collected by a two channel near infrared spectrophotometry system using a geometrical principle to measure absolute cerebral hemoglobin concentration. The incoming signal of the light emitting diode as a value allows a prediction of the quality of the measurement: a high value refers to a high signal/noise ratio. Starting from the centre of the forehead (0%) for each measurement the probe was moved by 2.5% of the headcircumference to the left respectively right side of the head up to 20%. The cerebral hemoglobin concentration-values increased from 87 respectively 93 micromol/l up to 164 respectively 173 micromol/l on the right respectively left side, while the light emitting diode signal-values decreased from 21 respectively 21 down to 10 respectively 11, the more laterally the probe was moved. There were two plateaus of these variables in the frontal (0-5%) respectively lateral (15-20%) region. A further investigation on a solid phantom for premature heads showed that hair has either no or a contrary effect on the cerebral hemoglobin concentration-values than expected. The extracerebral tissue (soft tissue, skull, cerebrospinal fluid layer) is discussed to have a significant influence on the light attenuation in adult heads. Still there is no evidence for a significant effect on prematures, because this overlying tissue is much thinner and more translucent than the one in adults. Absolute cerebral hemoglobin concentration measured by near infrared spectrophotometry is substantially influenced by the position of the probe at the infant's head. Considering our results we recommend placing the probe at 2.5% of the headcircumference away from the centre of the forehead for the measurement of cerebral hemoglobin concentration in premature infants.

Brain↗
PubMed1998

Task dependence of muscle synchronization in human hand muscles.

We put forward the hypothesis that synchronous muscle activation would be less frequent with increasingly more complex grip tasks. Six subjects performed a visuo-motor step-tracking task using the precision and the power grip. During the experiment transcranial magnetic stimuli were applied. Electromyographic activity was recorded from the hand muscles active in both tasks. Muscle synchronization was found to be enhanced during the power grip as compared to the precision grip. Magnetic stimulation had a stronger effect during the precision grip than during the power grip. Our findings are in favour of a variable organization of muscle activation in hand muscles during various tasks and support the stronger contribution of the corticomotoneuronal system in the precision than the power grip.

Brain↗
PubMed1998

Cortical facilitation of cutaneous reflexes in leg muscles during human gait.

During human gait, cortical convergence on sural nerve reflex pathways was investigated by means of transcranial magnetic stimulation (TMS) of the cortex in five phases of the step cycle during human walking on a treadmill. Muscular responses to paired electrical and magnetic stimulation were compared with the linear summation of the individual stimuli. For both the tibialis anterior (TA) and biceps femoris (BF) muscles, the averaged data of four subjects showed a significant facilitation mainly in the swing phase of the step cycle. It is suggested that facilitation of corticospinal input onto cutaneous reflex pathways is enhanced specifically in these periods of the step cycle.

Adult↗
PubMed1998

Influence of body load on the gait pattern in Parkinson's disease.

The influence of body unloading (to 75, 50, and 25% body weight) on lower leg muscle activation during treadmill walking was investigated in patients with Parkinson's disease, age-matched and young healthy subjects. The aim of the study was to test the hypothesis that patients suffer from impaired extensor load receptor function. Although lower leg flexor muscle electromyographic (EMG) activity was relatively independent of body load, lower leg extensor EMG activity was markedly load sensitive. The EMG amplitude of the latter decreased with body unloading during stepping in all three groups of subjects. The load sensitivity progressively increased from patients to age-matched to young healthy subjects. In addition, the absolute level of leg extensor EMG amplitude during the stance phase of stepping became progressively larger from patients to age-matched subjects to young healthy subjects. It is suggested that decreased sensitivity of extensor load reflex mechanisms contributes to impaired gait in elderly subjects and is more pronounced in parkinsonian patients.

Aged↗
PubMed1998

Comparison of absolute cerebral haemoglobin concentration in neonates measured directly and by the oxygen swing method both based on near infrared spectrophotometry.

The total cerebral haemoglobin concentration (tHb in mumol/l) as a major indicator of the oxygen transport capacity is investigated in neonates. Two methods to determine tHb by near infrared spectrophotometry (NIRS) have evolved so far: The first method requires a slow oxygenation change with reference to arterial oxygen saturation (tHbo-method). The second method is based on a geometrical principle and a two channel NIRS instrument (tHbg-method). The aim of this study was to compare both methods quantitatively. 15 clinically stable preterm infants needing supplemental oxygen were included in this study. For each method the measurements of three infants were excluded due to unsatisfactory measurement quality. The remaining 9 neonates had a mean gestational age of 29 (range 25.1 to 31.4) weeks, birthweight of 1272 (740 to 1690) g and a postnatal age of 2.6 (0.5 to 5) days. In each infant 6 tHbo measurements were carried out. During each tHbo measurement the mean of the continuously available tHbg (Cerebral Redox Monitor 2020, Johnson & Johnson Medical) was calculated. The mean of all successful tHbo and corresponding tHbg was determined for each infant. The mean tHbg was 151 mumol/l (range 62 to 223 mumol/l) and the mean tHbo was 59 mumol/l (27 to 113 mumol/l). The regression line between the two methods was tHbg = 1.34 x tHbo + 72 mumol/l. The r was 83.6%. The correlation suggests, that both methods can be applied to measure tHb. However, it has to be taken into account that the tHbg-method returns significantly higher values than the tHbo-method.

Birth Weight↗
PubMed1998

Adaptational effects during human split-belt walking: influence of afferent input.

The modification of the normal locomotor pattern of humans was investigated using a split-belt locomotion protocol (treadmill belt speeds of 4.5 km/h and 1.5 km/h for the right and left legs, respectively) and also by changing afferent input from the legs (30% reduction or increase in body weight by suspending subjects in a parachute harness or by wearing a lead-filled vest). After a control-speed training period (10 min) of symmetrical walking (3 km/h each leg) and a period (10 min) of split-belt walking, the adjustment back to the control speed resulted in a mean speed difference between the right leg and the left leg of 0.85 km/h. Adjustment of belt speed on either side was performed by the hands using a potentiometer. For comparison, also speed adjustment by the feet via feedback derived from changes in the treadmill drive current was studied. No significant difference was obtained when both modes of adjustment were compared. Body unloading or loading during the training period resulted in an improved adjustment of treadmill belt speed. This suggests that load receptor information plays a major role in the programming of a new walking pattern.

Adaptation, Physiological↗
PubMed1998

Functional outcome following spinal cord injury: significance of motor-evoked potentials and ASIA scores.

OBJECTIVE: Prediction of outcome of ambulatory capacity and hand function in tetraplegic patients with spinal cord injury (SCI) using neurologic examination, according to the protocol of the American Spinal Injury Association (ASIA) and motor-evoked potentials (MEP). DESIGN: Correlation study on a prospective cohort. SETTING: SCI center, university hospital. PATIENTS: Thirty-six patients with acute and 34 with chronic SCI. OUTCOME MEASURES: (1) ASIA motor and sensory scores, (2) MEP recordings of upper and lower limb muscles, and (3) outcome of ambulatory capacity and hand function. RESULTS: In acute and chronic SCI, both the initial ASIA scores and the MEP recordings were significantly related (p < .0001) to the outcome of ambulatory capacity and hand function. In tetraplegic patients, the MEP of the abductor digiti minimi muscle (Spearman correlation coefficient, .75; p < .0001) and the ASIA motor score for the upper limbs (Spearman correlation coefficient, .83; p < .0001) were most related to the outcome of hand function. Ambulatory capacity could be predicted by the ASIA motor score of the lower limbs (Spearman correlation coefficient, .78; p < .0001) and by MEP recordings of the leg muscles (Spearman correlation coefficient, .77; p < .0001). In patients with acute SCI, for the period 6 months posttrauma, the ASIA motor score increased significantly (ANOVA, p < .05), whereas the ASIA sensory scores and MEP recordings were unchanged (ANOVA, p > 0.1). CONCLUSION: Both ASIA scores and MEP recordings are similarly related to the outcome of ambulatory capacity and hand function in patients with SCI. MEP recordings are of additional value to the clinical examination in uncooperative or incomprehensive patients. The combination of clinical examination and MEP recordings allows differentiation between the recovery of motor function (hand function, ambulatory capacity) and that of impulse transmission of descending motor tracts.

Activities of Daily Living↗
PubMed1998

Evidence for a load receptor contribution to the control of posture and locomotion.

A basic aspect of the neuronal control of bipedal stance and gait represents the antigravity function of leg extensors. Proprioceptive reflexes involved in the maintenance of body equilibrium depend on the presence of contact forces opposing gravity. Extensor load receptors are thought to signal changes of the projection of the body's centre of mass with respect to the feet. 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. In humans, evidence for a significant contribution of the load receptor to leg muscle activation has come from immersion experiments. Compensatory leg muscle activation depends on the actual body weight. Furthermore, recent experiments in paraplegic patients showed that the beneficial effects of a locomotor training critically depends on the initial degree of body unloading and reloading during the course of the training period.

Animals↗
PubMed1998

The effects of unilateral pyramidal tract section on hindlimb motor performance in the rat.

Most investigations on selective lesions of the pyramidal tract in rodents have focused on the functional impairment of the forelimbs. This study describes the effects of a unilateral transection of the pyramidal tract rostral to the decussation on hindlimb function. Using kinematic locomotion analysis, the narrow beam test, open field locomotion ranking, analysis of footprints and air righting, we found severe impairments including hypermetria, trunk instability, lateral shifts in weight support, toe dragging, and hindlimb exo-rotation. Most impairments recovered rapidly within the first week after operation. Slight hypermetria persisted after 4 weeks. The rather mild long term deficits after unilateral pyramidotomy may stress the need for extremely sensitive behavioural tasks to enable the detection. We conclude that the possibility to correlate regenerative changes following selective pyramidal tract lesions with hindlimb function is thus limited.

Animals↗
PubMed1998

Locomotor capacity and recovery of spinal cord function in paraplegic patients: a clinical and electrophysiological evaluation.

Recent studies have shown that a locomotor pattern can be induced and trained into paraplegic patients under conditions of body unloading using a moving treadmill. The present study investigated the behaviour of the locomotor pattern and also the relationship of its development to the spontaneous recovery of spinal cord function assessed by clinical and electrophysiological (tibial nerve somatosensory evoked potentials and motor evoked potentials) examinations. The earliest time that spinal locomotor activity could be induced was when signs of spinal shock had disappeared. This activity was distinct from spinal stretch reflex activity. In complete and incomplete paraplegic patients an increase of gastrocnemius electromyographic activity occurred during the stance phase of a step cycle with daily locomotor training over the whole training period of 12 weeks. This was coincident with a significant decrease in body unloading. In contrast to this, neither clinical nor electrophysiological examination scores improved after the onset of training in both patient groups. Only in incomplete paraplegic patients was there an insignificant increase in sensory and motor scores obtained in the neurological examination during the time period before onset of training. An improvement of locomotor function by training was also seen in patients with paraplegia due to a cauda lesion. Therefore, in patients with a spinal cord lesion training effects on muscles and tendons are present in addition to those on the spinal locomotor centres. The findings of this study may be relevant for future clinical treatment of paraplegic patients.

Adolescent↗
PubMed1998

Stumbling reactions in man: influence of corticospinal input.

The aim of this study was to evaluate the degree of contribution of supraspinal input to the generation of the compensatory leg muscle activation following stance perturbation. Therefore, evoked motor response (EMR) input-output relations of two different motor tasks were compared at 3 distinct periods: (1) the basic period of muscular activity during standing, i.e. when no additional cortical or spinal activity due to the different tasks is to be expected, (2) the pre-movement period with low background activity, when different spinal and cortical inputs to the motoneuronal pool can be assumed and (3) the period of plateau EMG activity of compensatory and voluntary motor task. Transcranial magnetic stimulation (TMS) just below the motor threshold was applied randomly at 19 different time-intervals before and during the onset of stance perturbation and for comparison during an equivalent voluntary foot-dorsiflexion task. Recordings of electromyographic (EMG) activity from the tibialis anterior (TA) and corresponding ankle-joint movements were made from both legs. Forward-directed displacements were induced by randomly-timed ramp impulses of constant acceleration upon a moveable platform. For comparison, leg muscle EMG was recorded during isometric foot dorsiflexion during stance while leaning back against a support. The stance perturbations were followed by a compensatory response (CR) in the TA with a mean onset time of 81 ms. During the basic period of muscular activity and the period of plateau EMG activity there was no significant difference of the input-output relation between stance perturbation and the voluntary motor task. However, in the voluntary task compared with the CR, there was significantly greater input-output relation (facilitation) of the EMR in the TA following TMS, which may be related to an increased cortical influence. In contrast to this result of the CR following stance perturbation, a facilitation of the EMR was described for hand muscles under corresponding conditions of automatic compensation for muscle stretch, suggesting a transcortical reflex loop. This difference in the results from upper and lower extremity muscles favors the assumption of a predominantly spinal generation of the TA-CR following stance perturbation.

Adult↗
PubMed1998

Locomotor pattern in paraplegic patients: training effects and recovery of spinal cord function.

Recent studies have shown that a locomotor pattern can be induced and utilized by paraplegic patients under conditions of body unloading using a moving treadmill. The present study investigated the behaviour of the locomotor pattern and also the relationship of its development to the spontaneous recovery of spinal cord function assessed by clinical and electrophysiological (tibial nerve somatosensory evoked potentials and motor evoked potentials) examinations. The earliest time that spinal locomotor activity could be induced was when signs of spinal shock had disappeared. This activity was distinct from spinal stretch reflex activity. In complete paraplegic patients the locomotor pattern improved spontaneously without training. This was coincident with both an increase of gastrocnemius electromyographic activity during the stance phase of gait and a decrease of body unloading. These effects reached a plateau after about 5 weeks. In complete and incomplete paraplegic patients a near linear increase of gastrocnemius electromyographic activity occurred during the stance phase of a step cycle with daily locomotor training over the whole training period of 12 weeks. This was also coincident with a significant decrease of body unloading. In contrast to this, neither clinical nor electrophysiological examination scores improved after the onset of training in both patient groups. Only in incomplete paraplegic patients was there recovery, albeit statistically insignificant, of spinal cord function according to the sensory and motor scores obtained in the neurological examination during the time period before onset of training. An improvement of locomotor function by training was also seen in patients with paraplegia due to a cauda lesion. Such training effects on muscles and tendons could be separated from those on the spinal locomotor centres. The findings of this study may be relevant for the future clinical treatment of paraplegic patients.

Adolescent↗