A Wolter imager on the Z machine to diagnose warm x-ray sources.

A new Wolter x-ray imager has been developed for the Z machine to study the emission of warm (>15 keV) x-ray sources. A Wolter optic has been adapted from observational astronomy and medical imaging, which uses curved x-ray mirrors to form a 2D image of a source with 5 × 5 × 5 mm3 field-of-view and measured 60-300-µm resolution on-axis. The mirrors consist of a multilayer that create a narrow bandpass around the Mo Kα lines at 17.5 keV. We provide an overview of the instrument design and measured imaging performance. In addition, we present the first data from the instrument of a Mo wire array z-pinch on the Z machine, demonstrating improvements in spatial resolution and a 350-4100× increase in the signal over previous pinhole imaging techniques.

Intrarater reliability of manual passive movement velocity in the clinical evaluation of knee extensor muscle tone.

OBJECTIVE: To quantify the relationship between therapist-applied velocity of passive movement during a manual muscle test of muscle tone and the level of muscle tone represented by the relaxation index of the pendulum test. DESIGN: Comparison of therapist-applied passive limb movement velocity during a manual muscle test with the same subject's level of muscle tone measured by the pendulum test. Three different therapists tested each subject. The relation between the velocity scores and pendulum test scores both intratherapist and intertherapist were assessed statistically by means of analysis of variance and correlation coefficients. SETTING: A university-affiliated tertiary care outpatient and inpatient spinal cord injury rehabilitation center. PARTICIPANTS: Twenty-two volunteer subjects with spinal cord injuries. MAIN OUTCOME MEASURES: Passive knee angular displacement data were collected during both manual knee muscle testing and pendulum tests by using an electrogoniometer. RESULTS: The therapists produced significantly different movement velocities during the manual muscle tests (p < .05). A significant correlation (p < .001) was found between pendulum test scores and passive velocities, indicating that in higher levels of muscle tone, the greater stretch reflex present provided greater resistance against the therapist force and subsequently decreased the velocity of the passive stretching. CONCLUSIONS: Measurement of average velocity during passive stretching by itself can be used to evaluate muscle tone.

Spinal posture during stooped walking under vertical space constraints.

STUDY DESIGN: Simultaneous spine kinematic variables in sewage workers were quantified using a two-dimensional video-based gait analysis system. OBJECTIVES: To identify patterns of spinal posture in a population of sewage workers pushing waste matter through tunnels while walking stooped under various height constraints. SUMMARY OF BACKGROUND DATA: Working with stooped postures is one of several occupational risk factors that have been associated with spinal disorders. However, the specific changes in spinal posture during stooped walking under various height constraints have not been documented. METHODS: A video-based gait analysis system was used to measure spinal posture in 22 sewage workers. Angles of the cervical, thoracic, and lumbar spine in the sagittal plane were assessed during walking with five levels of height constraint, from upright walking to stooped walking under a headroom restriction of 105 cm. Correlations among gait parameters, demographic data, and clinical results were determined. Linear regression analysis was performed to examine which variables have the largest impact on the posture resulting from a given vertical height constraint when age and body height are held constant. RESULTS: Mean angular values changed significantly with increasing headroom restrictions, with increases in cervical and thoracic extension as well as lumbar flexion. The cervical and thoracic angles were best correlated with height constraint, followed by lumbar angle and stride length. The inverse relation between cervical and thoracic angle during upright walking increased with increasing vertical space constraints, whereas the relation between the thoracic and lumbar angles decreased. Subjects with decreased abdominal muscle strength adopted a significantly more kyphotic thoracic posture when walking under headroom constraints than subjects with normal abdominal muscle strength. CONCLUSIONS: Combined walking and pushing under vertical space constraints was associated not only with the expected increased flexion of the lumbar spine, but also with greater extension (i.e., reduced kyphosis) of the thoracic spine.

Relationship between craniomandibular disorders and poor posture.

The purpose of this research was to show that a relationship between craniomandibular disorders (CMD) and postural abnormalities has been repeatedly postulated, but still remains unproven. This study was intended to test this hypothesis. Twenty-five CMD patients (mean age 28.2 years) were compared with 25 gender and age matched controls (mean age 28.3 years) in a controlled, investigator-blinded trial. Twelve postural and ten muscle function parameters were examined. Measurements were separated into three subgroups, consisting of those variables associated with the cervical region, the trunk in the frontal plane, and the trunk in the sagittal plane. Within these subgroups, there was significantly more dysfunction in the patients, compared to control subjects (Mann-Whitney U test p < 0.001, p < 0.05, p < 0.01). Postural and muscle function abnormalities appeared to be more common in the CMD group. Since there is evidence of the mutual influence of posture and the craniomandibular system, control of body posture in CMD patients is recommended, especially if they do not respond to splint therapy. Whether poor posture is the reason or the result of CMD cannot be distinguished by the data presented here.

EMG fatigue patterns accompanying isometric fatiguing knee-extensions are different in mono- and bi-articular muscles.

OBJECTIVES AND METHODS: Isometric, fatiguing knee-extensions at 30%, 50% and 70% maximum voluntary contraction (MVC) were performed by 18 healthy human subjects. Surface electromyographic (SEMG) activity was recorded from the mono-articular vastus medialis (VM) and vastus lateralis (VL) muscles, and the bi-articular rectus femoris muscle (RF). To make the bi-articular muscle work under (1) constant and (2) similar working conditions as the two mono-articulars do, the hip was fixed in a flexed position. The root mean square (RMS) SEMG recorded during fatigue was standardized to the respective values of MVC. The mean coefficients of regression of the RMS and median frequency (MF) changes were then analyzed by multivariate analysis of variance. RESULTS: The load effect upon the muscle fatigue changes, as measured by increase in RMS EMG, differed between the bi-articular muscle and the two mono-articulars, in that the parameter dropped with maximum load for the bi-articular, whilst it remained stable or even increased for the mono-articulars. This might suggest that the mono- and bi-articular muscles have different roles in fatigue tasks where the bi-articulars function purely as mono-articulars. By contrast, such a clear dichotomy between the bi-articular RF and the two mono-articulars, VM and VL, was lacking for the fatigue parameter of MF. CONCLUSIONS: As these findings were confined to the changes in RMS EMG, different neuronal coding mechanisms for the mono- and bi-articular muscles in the central nervous system may be inferred.

Calculation of multi-segment rigid body joint dynamics using MATLAB.

A computational model of the human upper limb was developed utilizing a matrix calculation software package (MATLAB) and a public domain suite of subroutines [Robotics Toolbox (1)]. An easily configurable model of a rigid body, serially linked manipulator was established, avoiding the need for complex numerical equations to be formulated. A generalized model of the upper limb was used to study throwing action of individual subjects by incorporating body segment parameters and kinematic data. Estimates of joint moments were calculated for multiple time instances. This technique can be utilized and adapted for modelling any arbitrary serially linked manipulator system. Inverse and forward kinematics and kinetics can be calculated, enabling biomechanical simulations to be undertaken.

Control of functional electrical stimulation with extended physiological proprioception.

The use of functional electrical stimulation (FES) of muscle for paraplegic locomotion, or grasp augmentation in tetraplegia, is limited by the variability in muscle response to stimulation as a result of several external and internal factors. Previous approaches to this problem have used position-servo controllers, which have been shown to function satisfactorily in the laboratory. However, such systems will fail should obstacles be encountered or should the stimulation hardware develop a fault. To prevent such potentially dangerous failures some form of sensory feedback is required. This paper describes the first application of a technique known as extended physiological proprioception (EPP) to the control of FES to compensate for muscle response variability and provide proprioceptive feedback via the appropriate sensory pathways. In the experimental system described, a paraplegic subject controlled the extension of his paralysed knee by shoulder protraction. A Bowden cable linked the two joints, and a dynamometer in this cable was used to derive the control signal for a computer-controlled stimulator which delivered surface stimulation to the quadriceps muscle group. Modelling and parameter identification were performed by analysis of the step response, and the controller was designed from consideration of the root locus. The advantages of the system, in terms of improved proprioceptive feedback and reduced limb-positioning error were assessed in a test of joint positioning accuracy with vision occluded. The EPP system showed improvements over both open and closed-loop position-servo controllers.

Rhyme, rime, and the onset of reading.

There is recent evidence that children naturally divide syllables into the opening consonant or consonant cluster (the onset) and the rest of the syllable (the rime). This suggests an explanation for the fact that preschool children are sensitive to rhyme, but often find tasks in which they have to isolate single phonemes extremely difficult. Words which rhyme share a common rime and thus can be categorized on that speech unit. Single phonemes on the other hand may only be part of one of these speech units. This analysis leads to some clear predictions. Young children, even children not yet able to read, should manage to categorize words on the basis of a single phoneme when the phoneme coincides with the word's onset ("cat," "cup") but not when it is only part of the rime ("cat," "pit"). They should find it easier to work out that two monosyllabic words have a common vowel which is not shared by another word when all three words end with the same consonant ("lip," "hop," "tip") but the odd word has a different rime than when the three words all start with the same consonant ("cap," "can," "cot") and thus all share the same onset. The hypothesis also suggests that children should be aware of single phonemes when these coincide with the onset before they learn to read. We tested these predictions in two studies of children aged 5, 6, and 7 years. The results clearly support these predictions.

Influence of walking speed on gait parameters.

Modern three-dimensional gait analysis systems give information on joint angles and moments in the sagittal and coronal planes, for which normal ranges may not be readily available in the literature. Since patients with joint disease tend to walk slowly and with a short stride, it is essential that normal ranges for gait parameters should be defined with reference to speed of walking. This we have done using a population of 10 normal male subjects aged from 18 to 63 years, walking at speeds which range from very slow to very fast. The ranges of knee angle and moment are given, together with the changes in these parameters with walking speed. Peak knee flexion moment is strongly related to walking speed, whereas coronal plane knee angle is virtually independent of it. The stride length is probably the best basis for deciding the normal range for a particular measurement.