PubMed Health⌕ Search

Biomedical subjects

A Tsubahara

Publications and source records attributed to A Tsubahara.

8 recordsLinked to original sources
PubMed1995

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.

Adult↗
PubMed1994

Waveform analysis of compound nerve action potentials: a computer simulation.

A compound nerve action potential (CNAP) recorded from surface of the skin is composed of single nerve fiber action potentials propagating at various conduction velocities (CVs). Based on this assumption, we constructed two CNAPs simulating those at the digit elicited by stimulation of the median nerve at the wrist (CNAP-Wr) and the elbow (CNAP-El). Distribution of the nerve fiber CVs used for the simulation was estimated from actual recordings of 12 healthy subjects. Mean ratio of the CNAP amplitude (CNAP-Wr/CNAP-El) was 2.2, and that of the duration was 0.76. First, to analyze how CV distributions affect CNAP waveforms artificially in our computer program, we altered mean CV or standard deviation (SD) of the estimated distribution, and reconstructed CNAPs. Results indicated that as the mean CV was made slower, the ratio of the CNAP amplitude increased and that of the duration decreased. Similar changes of the ratios were also shown when the SD of the CV distribution was increased without changing the mean CV. Secondly, to make constructed CNAPs more similar to actual recordings, we added artificial noise to the constructed waves and had 11 electromyographers read onset and peak latencies. The average of maximum CVs calculated from the onset latencies of CNAPs-Wr was 62m/sec, and that from the latency difference between CNAPs-Wr and -El was 70m/sec. Both CVs were slower than the genuine maximum (77m/sec) given to the simulation program. The mean CV calculated from latency difference of the major positive peaks of the CNAPs was 62m/sec being close to the mode (62m/sec) or mean (60m/sec) value of the given distribution.

Action Potentials↗
PubMed1991

Two types of abnormal somatosensory evoked potentials in chronic cerebellar ataxias.

To investigate subclinical sensory impairment in spinocerebellar degenerations, median nerve somatosensory evoked potentials (SEPs) were examined in 16 patients with chronic cerebellar ataxia who were originally diagnosed by clinical neurologists as having olivopontocerebellar atrophy (OPCA). Two types of abnormal SEP patterns were found in six patients. Two patients had the SEP pattern of peripheral neuropathy, which was also detected by peripheral sensory nerve conduction studies. Four patients had abnormal SEPs seen in patients with the lesions in the central nervous system (dorsal column, medial lemniscus). Magnetic resonance imaging (MRI) showed multiple sclerosis (MS). It is possible that clinically diagnosed OPCA sometimes includes a similar form of Friedreich's ataxia with subclinical sensory fiber neuropathy detected by SEPs and peripheral sensory conduction studies. In cases of lesions in the central nervous system demonstrated by both SEPs and MRI, there must be a follow-up in order to make a final diagnosis. In those cases, an alternative diagnosis of MS must be considered when the temporal profile of symptoms and signs characteristic of MS is observed.

Adult↗
PubMed1991

Fibrillation potentials do not originate in type 1 muscle fibers?

Electrophysiological and muscle histochemical studies of denervated muscle were performed simultaneously in order to determine the relationship between fibrillation potentials and muscle fiber type. Fibrillation potentials recorded in the soleus muscle 2 weeks after resection of the sciatic nerve revealed a lower firing rate than in the extensor digitorum longus (EDL) muscle of the same rats. The majority of muscle fibers stained for adenosine triphosphatase (ATPase) activity after preincubation at pH 9.4, 4.6, and 4.3 in the soleus muscle were type 1 fibers, while most of those in the EDL were of type 2. Moreover, one of the rats, which demonstrated no fibrillation potentials in the soleus muscle, was found to have no type 2A or 2B fibers histochemically, in the same soleus muscle. These findings suggest that fibrillation potentials may not originate in type 1 fibers.

Action Potentials↗
PubMedDate not supplied

Objective parameters in magnetic resonance imaging (MRI) for neuromuscular diagnosis: preliminary findings.

T1 relaxation time (T1 time), T2 relaxation time (T2 time), and proton (rho) density in the thigh muscles of 20 normal healthy volunteers and three patients with muscle atrophy in the lower extremity were measured in order to select the useful MRI parameters for neuromuscular diagnosis. Since the standard deviation (SD) of both T1 and T2 times in each muscle was found to be within a relatively small range, these values were expected to be useful MRI parameters for neuromuscular diagnosis. On the contrary, rho density was not a valid parameter for diagnosis, as it was demonstrated to have large SDs in the muscles. The differences of these parameters in the three patients also supported the fact that MRI was useful for discriminating between the various types of muscular abnormalities based on relaxation times. The longer T1 and T2 times in women suggested that the content of water in skeletal muscle was higher in women than in men. Moreover, the T1 time in the dominant limbs was found to be shorter than in the non-dominant limbs for rectus femoris only in both men and women, while there were no differences in T2 time in these muscles.

Adult↗
PubMedDate not supplied

Extent of pyramidal tract wallerian degeneration in the brain stem on MRI and degree of motor impairment after supratentorial stroke.

The relationship between Wallerian degeneration in the brain stem and degree of motor impairment is discussed. Using MRI we studied 172 supratentorial stroke patients, whose motor impairment was graded according to Brunnstrom stage. Wallerian degeneration was represented by a T2 high-intensity area in the brain stem, and its cross-sectional extent was measured at the cerebral peduncle level. Wallerian degeneration was detected in 99 patients (57.6%). The area of T2 high intensity was significantly correlated with Brunnstrom stage. Multiple regression analysis showed that the upper extremity stage contributed most to the visualization of Wallerian degeneration. This is partly because the pyramidal tract participates in fine and precise movement. The extent of the area of Wallerian degeneration is found to be helpful in making a prognosis with respect to motor impairment in the upper extremity.

Adult↗
PubMedDate not supplied

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

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.

Adipose Tissue↗