Yasutomo Okajima

THE RELATIONSHIPS BETWEEN TRUNK FUNCTION AND THE FINDINGS OF TRANSCRANIAL MAGNETIC STIMULATION AMONG PATIENTS WITH STROKE

In this study, we investigated the relationship between the motor evoked potentials obtained from trunk muscles and the clinical function of trunk muscle. Twenty patients with unilateral hemispheric stroke and 11 healthy adults were examined. The responses of the bilateral external oblique muscles and the erector spinae muscles to the magnetic stimulation of multiple sites over both cortical hemispheres were recorded. Trunk muscle performance was assessed using the Trunk Control Test and Stroke Impairment Assessment Set. In the stroke group, stimulation of the affected hemisphere resulted in a motor evoked potential in only one patient, while the other 19 stroke patients produced no response to stimulation of the affected hemisphere. Stimulation of the unaffected hemisphere evoked bilateral responses in 19 patients. Further, stimulation of the unaffected hemisphere in the stroke group produced larger motor evoked potentials in the ipsilateral muscles than the motor evoked potentials recorded in the ipsilateral muscles of the control group. The clinical assessment scores of trunk function (i.e. Trunk Control Test and trunk items of Stroke Impairment Assessment Set) were correlated with the amplitudes of the motor evoked potentials of the ipsilateral external oblique muscle that were evoked by stimulation of the unaffected hemisphere. Our results suggest that the recovery of trunk function after stroke is associated with an increase in ipsilateral motor evoked potentials in the external oblique muscle upon stimulation of the unaffected hemisphere, suggesting a role for compensatory activation of uncrossed pathways in recovery of trunk function.

Current status of rehabilitation medicine in Asia: A report from New Millennium Asian Symposium on Rehabilitation Medicine

With the aim of promoting rehabilitation medicine in Asian countries, where the number of persons with disability occupies a significant proportion in the world, New Millennium Asian Symposium on Rehabilitation Medicine was held in February 2001 in Tokyo, under the sponsorship of the Japanese Association of Rehabilitation Medicine. Twenty-three guest speakers from 14 Asian countries and regions participated in the 2-day meeting. With a structured questionnaire that was sent to the participants beforehand, demographic data related to rehabilitation practice and information on training and certification in rehabilitation medicine in the participating countries were collected, and presented at the meeting. Based on these data, the current status of rehabilitation medicine in Asia was summarized. The symposium marked an important step forward for the promotion of rehabilitation medicine in Asia.

Interactions of somatosensory evoked potentials: simultaneous stimulation of two nerves

To analyse the mechanism by which sensory inputs are integrated, interactions of somatosensory evoked potentials (SEPs) in response to simultaneous stimulation of two nerves were examined in 12 healthy subjects. Right, left and bilateral median nerves were stimulated in random order so that a precise comparison could be made among the SEPs. The arithmetical sum of the independent right and left median nerve SEPs was almost equal within 40 msec of stimulus onset to that evoked by the simultaneous stimulation of bilateral median nerves. However, a difference emerged after 40 msec. The greatest difference was recorded after 100 msec. Sensory information from right and left median nerves may interact in the late phase of sensory processing. Left median, left ulnar, and both nerves together were stimulated. The sum of the SEPs of left median and ulnar nerves was not equal to that evoked by the simultaneous stimulation of the two nerves even at early latencies. Differences between them were first recorded at 14-18 msec and became greater after 30-40 msec. It is suggested that the neural interactions between impulses in the median and ulnar nerves begin below the thalamic level.

Age-related changes of water and fat content in muscles estimated by magnetic resonance (MR) imagine

The pixel values in fat/water suppression magnetic resonance (MR) images were measured for the thigh muscles of 18 healthy volunteers to investigate age-related changes in muscle water and fat content. Prior to the human studies the reproducibility of the data was confirmed using phantoms. The standard deviations (SDs) of the pixel values for one of the phantoms examined five times were found to be within a relatively narrow range. Both the pixel values in the fat suppression images (PV1) and the pixel values in the water suppression images (PV2) of all muscles tended to be higher in the oldest group. The results indicate that the water and fat content of skeletal muscles is higher in aged persons. Moreover, the PV1 in the non-dominant limbs was found to be increased in the extensor muscles of the knee joints, while the PV2 in the non-dominant limbs did not show a significant difference, except for the rectus femoris.

Estimation of the conduction velocity distribution of human sensory nerve fibers.

A new method for estimating the distribution of conduction velocities (DCV) of peripheral nerve fibers has been developed. It also enables estimation of single nerve fiber action potential (SFAP), which agrees with the physiological knowledge. Two compound nerve action potentials (CAPs) elicited by electrical stimulation of a nerve bundle were recorded at different conduction distances. The distances between the stimulation and recording electrodes were measured on the skin surface along the nerve bundle. Starting with an arbitrary SFAP, the first estimated DCV was calculated from a CAP by the regularized non-negative least squares method. The next SFAP was then calculated by deconvolution of the other CAP and the estimated DCV. A lowpass filter with an appropriate cutoff frequency was used to obtain better conversion. The process was iterated until the CAP error defined as /CAP(calculated)-CAP/(2) was small enough. The conduction distances contained errors in measurement, especially in the distal segment, that distorted the estimated results. The Fibonacci search, therefore, was adopted to optimize the distance according to the CAP error. The accuracy of this method was demonstrated by a simulation study performed with two CAPs calculated from an arbitrary bimodal DCV and a biphasic SFAP to which a Gaussian white noise was added. The reliability of this method was checked in normal subjects by recording a pair of CAPs elicited by stimulation of the median nerve at the wrist and the elbow.

A new method of estimating the distribution of muscle fiber conduction velocities

A computer-assisted method of estimating the distribution of muscle fiber conduction velocities is described. An electrode array composed of 2 stimulating and 4 recording electrodes is used to record surface muscle action potentials (MAPs) in response to direct muscle stimulation. The velocity distribution and the single muscle fiber action potential (SFAP) are calculated from the recorded MAPs by an iterative method of estimation. The estimation is based on the assumption that the spatial orientation of each muscle fiber viewed from the recording electrodes is the same along the muscle fibers and a MAP is recorded as a linear summation of all SFAPs. The accuracy of this estimation is demonstrated using simulated MAPs. The method is also tested on MAPs containing simulated amplifier noise, stimulus artifact, and errors in distance between electrodes. Finally we applied this method to MAP recordings of the biceps brachii in 23 healthy subjects. The velocity distribution was successfully estimated in 20 cases. The average of the estimated distributions was smaller than that described by previous workers. The reasons for the difference are discussed.

Relationship between nerve and muscle fiber conduction velocities of the same motor unit in man.

To test the hypothesis that the nerve fiber conduction velocity of a motor unit is correlated with the muscle fiber conduction velocity of the unit, the collision technique was used to discriminate the motor unit action potentials elicited by stimulation of a group of nerve fibers with known conduction velocity. Muscle fiber conduction velocity was determined from the propagating action potentials of the unit recorded by a surface electrode array. A weak but significantly positive correlation was found between nerve and muscle fiber conduction velocities in the thenar muscle of human subjects. The results indicate that the size principle that governs the relation between nerve and muscle fiber size is a fairly weak principle with occasional exceptions.

Accelerometric evaluation of ataxic gait: therapeutic uses of weighting and elastic bandage.

Two-dimensional (fore-aft and vertical) acceleration of locomotion was measured in 10 normal subjects and 13 patients with idiopathic olivopontocerebellar atrophy who were ataxic but able to walk without any assistance. Accelerometers were tightly placed on the third lumbar vertebra. Asymmetry and unsmoothness indices of locomotion defined from the line spectra of the accelerometric data were computed. Reproducibility of the indices was checked in the normal subjects and patients. The index values were significantly correlated with visual rating of gait unsteadiness in the patients. The indices for vertical components were significantly increased when subjects walked slowly. Effects of weights and bandages on gait were analysed by the fore-aft components of the indices. They were attached to both lower extremities. Weighting or bandaging did not change, or even increased the index values in most of the normal subjects. The indices were also unchanged in the patients. However, some of the patients showed significant improvement with weights or bandages. Mechanisms of therapeutic effects of weighting and elastic bandages on ataxia are discussed.

Recovery functions of somatosensory vertex potentials in man: interaction of evoked responses from right and left fingers

Somatosensory vertex potentials (SVPs) were examined in 12 healthy subjects in response to painful electrical stimulation of the finger. SVPs consisted of N1, P1, and N2. The average latencies of the 3 peaks were 150, 225, and 350 msec, respectively. The latency and amplitude of each potential were reproducible for each subject. Recovery functions of the SVPs were analyzed in 10 subjects. A pair of stimuli were delivered to the right or left finger with interstimulus intervals (ISIs) of 50, 100, 150, 200, 350, 500 and 650 msec. SVPs partially recovered with the shortest ISI (50 msec). Full recovery could not be obtained even with the longest ISI (650 msec). Differences in recoveries within 650 msec of ISI were not observed between right and left stimulations. To examine the interaction between SVPs evoked by right and left finger stimulation, recovery functions from prior contralateral finger stimulation were analyzed with the same ISIs. SVP recoveries for right after left or left after right patterns of stimulus delivery were nearly the same as those for ipsilateral ones. It is suggested that SVPs are generated at nearly the same site in the sensory pathway regardless of the side stimulated.

The size index as a motor unit identifier in electromyography examined by numerical calculation

A computer simulation was performed to investigate the size index as a motor unit identifier in electromyography. The size index calculated from the amplitude and area of the simulated motor unit action potential (MUP) was plotted against the distance between the needle electrode and current source to show how the index changes as a function of the distance. The index of the MUP also was plotted against the number of muscle fibers belonging to a single motor unit, the size of the motor unit territory, and the diameter of the muscle fibers in order to establish the major determinants of the index. The index was relatively constant for the distance less than 2 mm between the needle electrode and closest edge of the current source. It changed logarithmically with the number of muscle fibers and with the diameter of the fibers.