R. H. J. M. Gooskens

Mechanisms underlying accuracy in fast goal-directed arm movements in man.

This study investigated how accuracy is attained in fast goal-directed arm movements. Subjects were instructed to make arm extension movements over three different distances in random order, with and without visual feedback. Target width was varied proportionally with distance. Movement time was kept as short as possible, but there were well-defined limits with respect to accuracy. There appeared to be a large relative variability (variation coefficient [VC]) in the initial acceleration. The VC in the distance the hand moved during the acceleration phase was much smaller. This reduction was accompanied by a strong negative correlation between the initial acceleration and the duration of the acceleration phase. Further, the VC in the total distance moved was less than the VC in the distance moved during acceleration. This result indicates asymmetry between the acceleration and the deceleration phase. This is confirmed by the negative correlation between the distance the hand moved during acceleration and the distance it moved during deceleration. Withdrawal of visual feedback had a significant effect on movement accuracy. No differences were found in the parameters of the acceleration phase in the two feedback conditions, however. our results point to the existence of a powerful variability compensating mechanism within the acceleration phase. This mechanism seems to be independent of visual feedback; this suggests that efferent information (efference copies) and/or proprioceptive information is/are responsible for the timing of agonist and antagonist activation. The asymmetry between the acceleration and deceleration phase contributes to a reduction in the relative variability in the total distance moved. The fact that the withdrawal of visual feedback affected movement variability only during the deceleration phase indicates that visual information is used in the adjustment of antagonist activity.

Visuomotor performance of normal and clumsy children. I: Fast goal-directed arm-movements with and without visual feedback.

The mechanisms underlying accuracy in fast goal‐directed arm‐movements were investigated in normal and clumsy children in two age‐groups, six to seven and 10 to 11 years. Clumsy children in both age‐groups had a longer movement time than normal children; this difference increased slightly when there was visual feedback. For both normal and clumsy children, the relative variability of the total distance moved was smaller than that of the distance moved during acceleration, indicating a variability reduction mechanism in the course of a movement. In the six‐ to seven‐year‐old group, the relative variability of the distance moved during acceleration and of the total distance was larger for clumsy than for normal children; this did not reach significance in the 10‐ to 11‐year‐old group. It is suggested that motor difficulties are linked to inaccuracy in open‐loop control processes and to less efficient use of visual feedback.

VISUOMOTOR PERFORMANCE OF NORMAL AND CLUMSY CHILDREN. II: ARM-TRACKING WITH AND WITHOUT VISUAL FEEDBACK

Tracking performance was investigated in normal and clumsy children in two age‐groups, six to seven and 10 to 11 years. Target signals moving unpredictably along a straight line had to be tracked, both with and without visual feedback. Performance was described in three ways: (1) performance in the low‐frequency range (LF); (2) the delay between target signal and tracking movement (DL); and (3) a measure of tracking quality or over‐all similarity in the shape of target signal and tracking movement (Q). Clumsy children in both age‐groups had a lower tracking quality (Q) and longer delay (DL) than the normal children. Disturbances in the regulation of attention seemed to affect tracking performance, particularly of the six‐ to seven‐year‐old clumsy children. There was no significant difference between normal and clumsy children in the effect of visual feedback on tracking performance. This suggests that clumsiness is not linked to disturbance of integration of visual feedback information and motor processes.

Value of transcranial Doppler indices in predicting raised ICP in infantile hydrocephalus

Cerebral hemodynamic changes in infants with progressive hydrocephalus have been studied with the transcranial Doppler (TCD) technique. Several authors have referred to the correlation between the hemodynamic changes and increased intracranial pressure (ICP). Despite conflicting conclusions on the value of pulsatility index (PI) measurements for monitoring infantile hydrocephalus, these pulsatility indices are the most commonly used for this purpose. Although clinical signs of raised ICP are highly variable and unreliable in infants, assumptions have been made in most of the studies about the presence of elevated ICP on the basis of the patients clinical state. Few studies have reported on actual ICP values, however, and a direct relationship between ICP and TCD changes has never been adequately demonstrated. In the present study, this relationship was investigated in long-term simultaneous TCD/ICP measurements, in an attempt to develop a noninvasive method of monitoring the effect of ICP on intracranial hemodynamics. Two groups of data sets were established. Group I consisted of pre- and postoperative (shunt implantation) TCD/ICP measurements. Group II were long-term simultaneous TCD/ICP recordings showing significant ICP variations. In most of the postoperative measurements there was a decrease in the average PI and RI values. The correlation between PI or RI and ICP in the long-term simultaneous recordings, however, was generally poor. The risk of obtaining false positive or false negative PI or RI values in short-term measurements was also demonstrated. It can be concluded from our results, besides the wide range of reference values for the Doppler indices and extracranial influences upon them, that the present Doppler indices are inadequate for monitoring the complex intracranial dynamic responses in patients with raised ICP.

Longitudinal diffusion-weighted imaging in infants with hydrocephalus: decrease in tissue water diffusion after cerebrospinal fluid diversion.

OBJECTnProgressive hydrocephalus may lead to edema of the periventricular white matter and to damage of the brain parenchyma because of compression, stretching, and ischemia. The aim of the present study was to investigate whether cerebral edema can be quantified using diffusion-weighted imaging in infants with hydrocephalus and whether CSF diversion could decrease cerebral edema.nnnMETHODSnDiffusion-weighted MR imaging was performed in 24 infants with progressive hydrocephalus before and after CSF diversion. Parametric images of the trace apparent diffusion coefficients (ADCs) were obtained. The ADCs of 5 different cortical and subcortical regions of interest were calculated pre- and postoperatively in each patient. The ADC values were compared with age-related normal values. Mean arterial blood pressure and anterior fontanel pressure were measured immediately after each MR imaging study.nnnRESULTSnAfter CSF diversion, the mean ADC decreased from a preoperative value of 1209 +/- 116 x 10(-6) mm(2)/second to a postoperative value of 928 +/- 64 x 10(-6) mm(2)/second (p < 0.005). Differences between pre- and postoperative ADC values were most prominent in the periventricular white matter, supporting the existence of preoperative periventricular edema. Compared with age-related normal values, the preoperative ADC values were higher and the postoperative ADC values were lower, although within normal range. The decrease in ADC after CSF drainage was more rapid than the more gradual physiological decrease that is related to age. The preoperative ICP was elevated in all patients. After CSF diversion the ICP decreased significantly to within the normal range. A linear correlation between ADC values and ICP was found (correlation coefficient 0.496, p < 0.001). In all patients the mean arterial blood pressure was within physiological limits both pre- and postoperatively.nnnCONCLUSIONSnThis study shows a rapid and more extensive decrease in ADC values after CSF diversion than is to be expected from physiological ADC decrease solely due to increasing patient age. The preoperative ADC increase can be explained by interstitial edema caused by transependymal CSF leakage or by vasogenic edema caused by capillary compression and stretching of the brain parenchyma. This study population of infants with (early recognized) hydrocephalus did not suffer from cytotoxic edema. These findings may help to detect patients at risk for cerebral damage by differentiating between progressive and compensated hydrocephalus.

Intramedullary rodding in type III osteogenesis imperfecta. Effects on neuromotor development in 10 children.

We studied retrospectively gross motor development and the impact of intramedullary rodding in 10 children with type III osteogenesis imperfecta (OI). There was a pronounced delay in motor development and the order in achieving gross motor milestones differed from the normal developmental sequence. Static milestones developed at an earlier stage than dynamic milestones. Intramedullary rodding of the lower extremities prior to the age of 3.5 years enhanced neuromotor development, especially regarding the milestones supported standing, rolling from prone to supine and crawling with abdomen on the floor. The different sequence in achieving gross motor milestones should have implications for future rehabilitation programs and for orthopedic surgery.

Spinal fusion in children with spina bifida: influence on ambulation level and functional abilities.

The aim of this study was to determine the influence of spinal fusion on ambulation and functional abilities in children with spina bifida for whom early mobilization was stimulated. Ten children (three males and seven females) with myelomeningocele were prospectively followed. Their mean age at operation was 9.3xa0years (standard deviation (SD): 2.4). Spinal curvature was measured according to Cobb. Pelvic obliquity and trunk decompensation were measured as well. The ambulation level was scored according to Hoffer, and functional abilities, as well as the amount of caregiver assistance, were documented using the Pediatric Evaluation of Disability Inventory. All patients were assessed before surgery and three times after surgery, with a total follow-up duration of 18xa0months after surgery. After spinal fusion, magnitude of primary curvature decreased significantly (p=0.002). Pelvic obliquity and trunk decompensation did not change. In spite of less immobilization as compared with other reported experiences, ambulation became difficult in three out of four patients who had been able to ambulate prior to surgery. Functional abilities and amount of caregiver assistance concerning self-care (especially regarding dressing upper and lower body, and self-catheterization) and mobility (especially regarding transfers) showed a nonsignificant trend to deterioration within the first 6xa0months after surgery, but recovered afterwards. From pre-surgery to 18xa0months after surgery, functional skills on self-care showed borderline improvement (p=0.07), whereas mobility did not (p=0.2). Mean scores on caregiver assistance improved significantly on self-care (p=0.03), and borderline on mobility (p=0.06), meaning that less caregiver assistance was needed compared with pre-surgery. The complication rate was high (80%). In conclusion, within the first 6xa0months after spinal fusion, more caregiver assistance is needed in self-care and mobility. It takes about 12xa0months to recover to pre-surgery level, while small improvement is seen afterwards. After spinal fusion, ambulation often becomes difficult, especially in exercise walkers. These findings are important for health-care professionals, in order to inform and prepare the patients and their parents properly for a planned spinal fusion.The aim of this study was to determine the influence of spinal fusion on ambulation and functional abilities in children with spina bifida for whom early mobilization was stimulated. Ten children (three males and seven females) with myelomeningocele were prospectively followed. Their mean age at operation was 9.3xa0years (standard deviation (SD): 2.4). Spinal curvature was measured according to Cobb. Pelvic obliquity and trunk decompensation were measured as well. The ambulation level was scored according to Hoffer, and functional abilities, as well as the amount of caregiver assistance, were documented using the Pediatric Evaluation of Disability Inventory. All patients were assessed before surgery and three times after surgery, with a total follow-up duration of 18xa0months after surgery. After spinal fusion, magnitude of primary curvature decreased significantly (p=0.002). Pelvic obliquity and trunk decompensation did not change. In spite of less immobilization as compared with other reported experiences, ambulation became difficult in three out of four patients who had been able to ambulate prior to surgery. Functional abilities and amount of caregiver assistance concerning self-care (especially regarding dressing upper and lower body, and self-catheterization) and mobility (especially regarding transfers) showed a nonsignificant trend to deterioration within the first 6xa0months after surgery, but recovered afterwards. From pre-surgery to 18xa0months after surgery, functional skills on self-care showed borderline improvement (p=0.07), whereas mobility did not (p=0.2). Mean scores on caregiver assistance improved significantly on self-care (p=0.03), and borderline on mobility (p=0.06), meaning that less caregiver assistance was needed compared with pre-surgery. The complication rate was high (80%). In conclusion, within the first 6xa0months after spinal fusion, more caregiver assistance is needed in self-care and mobility. It takes about 12xa0months to recover to pre-surgery level, while small improvement is seen afterwards. After spinal fusion, ambulation often becomes difficult, especially in exercise walkers. These findings are important for health-care professionals, in order to inform and prepare the patients and their parents properly for a planned spinal fusion.

Monitoring intracranial dynamics by transcranial Doppler—a new Doppler index: Trans systolic time

Since the introduction of transcranial Doppler sonography (TCD) several investigators have described the relationship between raised intracranial pressure (ICP) and Doppler waveform. This waveform has been expressed by several indices, such as the pulsatility index (PI) and the resistance index (RI). These indices are used to demonstrate the presence of raised ICP. In childhood hydrocephalus this information can be used to indicate the need for shunt implantation. However, PI and RI do prove to have certain disadvantages as both are strongly influenced by the heart rate. Moreover, both indices have a broad range of reference values, especially in children. Therefore, they are not very reliable for detecting insidious changes in the ICP. These drawbacks are due to the fact that these indices are composed of blood flow velocity measurements and do not embody the slope of the TCD waveform itself. An ideal TCD waveform analysis should be performed concerning the time-related changes of the velocities. We present a hydrodynamic model, with its electrical analogue, which shows the effects of raised ICP on the intracranial hemodynamic system. Based on these physical findings we define a new Doppler index, the Trans Systolic Time, reflecting specific changes in the TCD waveform induced by changes in the mean ICP. The applicability of this index, compared with PI and RI, is illustrated by consecutive simultaneous TCD and AFP measurements in three children with hydrocephalus.

Noninvasive detection of the distinction between progressive and compensated hydrocephalus in infants: is it possible?

OBJECTnClinical signs and symptoms of hydrocephalus can be clear and specific, but also subtle, nonspecific, or even absent. It may be difficult to decide whether shunt placement is indicated, especially in infants. Therefore, there is a need for the development of better noninvasive detection methods to distinguish between compensated and (slowly) progressive hydrocephalus. Early interference can reverse the cerebral damage, whereas the detection of a nonpathological state in infants with compensated hydrocephalus avoids the complications of unnecessary shunt procedures. Using MR imaging, the authors investigated cerebral blood flow (CBF) and apparent diffusion coefficients (ADCs) measured in infants with clinically compensated hydrocephalus.nnnMETHODSnThe diagnosis of compensated hydrocephalus was made on the basis of clinical criteria, consisting of no signs or symptoms of increased intracranial pressure (ICP), measurement of a normal ICP, and standard MR imaging showing enlarged ventricles. Flow measurements through both internal carotid arteries and the basilar artery were considered to represent the total CBF. In addition, ADC values were assessed in 5 different regions of interest in the brain parenchyma using diffusion weighted imaging. Brain volumetric measurement was performed to express CBF in ml/100 cm(3) brain/min, thus compensating for physiological CBF growth over time. Mean arterial blood pressure was manually measured to exclude this factor as a cause of a possible change in CBF. Intracranial pressure measurement was performed noninvasively using the Rotterdam Teletransducer.nnnRESULTSnEighteen infants with clinically compensated hydrocephalus were included. The mean CBF was 53.5 ml/100 cm(3) of brain/min. The individual CBF values were graphically compared with age-related normal CBF values and fell in the normal range. Mean ADC value was 890.0 x10(-6) mm(2)/sec. Apparent diffusion coefficient values per region of interest were graphically compared with normal ADC values per region of interest and fell within the normal range.nnnCONCLUSIONSnIn infants with hydrocephalus, normal CBF and low ADC values, as measured using MR imaging, are associated with compensated hydrocephalus and may support a conservative approach with respect to the decision on whether to place a shunt.

Arm-tracking performance with and without visual feedback in children and adults: developmental changes.

Tracking performance was investigated in children (aged 6-7 and 10-11) and in adult subjects. Target signals, moving unpredictably along a straight line, were tracked with the preferred arm, alternately with and without visual feedback. Qualitative observations indicate that tracking is based on continuous adjustments of the ongoing response to the continuously changing target position. No step-and-hold strategy could be detected in any of the three age groups. Tracking performance was described with four simple parameters, derived from linear systems analysis: (a) the delay between target signal and tracking movement (DL); (b) performance at the low-frequency range (LF), (c) performance at the high-frequency range (HF); and (d) a measure of tracking quality or overall similarity in the shape of target signal and tracking movement (Q). There was a considerable improvement in tracking performance with age, even after the age of 10-11, which was mainly demonstrated by a decrease in DL and increases in HF and Q. Tracking performance decreased only to a small extent when visual feedback was withdrawn. Age-related differences in the contribution of visual feedback to tracking performance could not be demonstrated.