Modulation of spinal reflex by assisted locomotion in humans with chronic complete spinal cord injury.

OBJECTIVE: In healthy subjects, spinal reflexes (SR) evoked by non-noxious tibial nerve stimulation consist of an early (60-120ms latency) and an occasional late-appearing (120-450ms latency) component in the ipsilateral tibialis anterior. In chronic (>1year) complete spinal cord injured (cSCI) subjects early components are small or lacking while late components are dominant. Here we report on the modulation of SR by assisted locomotion in healthy and chronic motor cSCI subjects. METHODS: SR was evoked by tibial nerve stimulation at the terminal stance phase during assisted locomotion and was compared to SR recorded during upright stance. RESULTS: In chronic cSCI subjects only a late SR component was consistently present during upright stance. However during assisted locomotion, an early SR component appeared, while amplitude of the late SR component became small. In contrast, in healthy subjects the early SR component dominated in all conditions, but a small late component appeared during assisted locomotion. CONCLUSION: A more balanced activity of early and late SR components occurred in both subject groups if an appropriate proprioceptive input was provided. SIGNIFICANCE: Early and late SR components are assumed to reflect the activity of separate neuronal circuits, which are associated with the locomotor circuitry possibly by shaping the pattern.

Changes in spinal reflex and locomotor activity after a complete spinal cord injury: a common mechanism?

Locomotor activity and spinal reflexes (SRs) show common features in different mammals, including humans. Here we report the time-course of the development of locomotor activity and SRs after a complete spinal cord injury in humans. SRs evoked by tibial nerve stimulation were studied, as was the leg muscle electromyography activity evoked by mechanically assisted locomotion (Lokomat) in biceps femoris, rectus femoris, tibialis anterior and gastrocenmius medialis. Around 8 weeks after the injury, an early SR component (latency 60-120 ms) appeared, as in healthy subjects, and a well-organized leg muscle activity was present during assisted locomotion. At around 6 months after injury an additional, late reflex component (latency 120-450 ms) appeared, which remained even 15 years after the spinal cord injury. In contrast, the early component had markedly decreased at 18 months after injury. These changes in SR were associated with a loss of electromyography activity and a successively stronger electromyography exhaustion (i.e. decline of electromyography amplitude), when comparing the level of electromyography activity at 2 and 10 min, respectively, during assisted locomotion. These changes in electromyography activity affected mainly the biceps femoris, gastrocenmius medialis and tibialis anterior but less so the rectus femoris. When the amplitude relationship of the early to late SR component was calculated, there was a temporal relationship between the decrease of the early component and an increase of the late component and the degree of exhaustion of locomotor activity. In chronic, severely affected but sensori-motor incomplete spinal cord injury subjects a late SR component, associated with an electromyography exhaustion, was present in subjects who did not regularly perform stepping movements. Our data are consistent with the proposal of a common mechanism underlying the changes in SR activity and locomotor activity after spinal cord injury. These findings should be taken into consideration in the development of novel rehabilitation schemes and programs to facilitate regeneration-inducing therapies in spinal cord injury subjects.

A pencil beam model for photon dose calculation.

A method for photon dose calculation in radio therapy planning using pencil beam energy deposition kernels is presented. It is designed to meet the requirements of an algorithm for 3-D treatment planning that is general enough to handle irregularly shaped radiation fields incident on a heterogeneous patient. It is point oriented and thus faster than a full 3-D convolution algorithm and uses the same physical data base to characterize a clinical beam as a full 3-D convolution algorithm. It is shown that photon therapy beams can be characterized with great accuracy from a combination of precalculated Monte Carlo energy deposition kernels and dose distributions measured in a water phantom. The data are used to derive analytical pencil beam kernels that are approximately partitionated into the dose from (i) primary released electrons and positrons, (ii) scattered, bremsstrahlung, and annihilation photons, (iii) contaminating photons, and (iv) charged particles from the collimator head. A semianalytical integration method, based on triangulation of the field, is developed for dose calculation using the analytical kernels. Dose is calculated in units normalized to the incident energy fluence which facilitates output factor calculation. For application in heterogeneous media, a scatter correction factor is derived using monodirectional convolution along the ray path. In homogeneous media results are compared with measurements and in heterogeneous media with Monte Carlo calculations and the Batho method.

[Recurrent idiopathic arteriovenous malformation of the back of the hand]. / Rezidivierende idiopathische arterio-venöse Missbildung am Handrücken.

This is a case report of a 36-year-old male, operated twice (1974 and 1989) due to an idiopathic arteriovenous malformation on the dorsum of the hand. This rare and often recurrent vascular affection of the hand, its diagnosis and surgical management are reviewed and discussed.