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T Musha

Publications and source records attributed to T Musha.

At least 55 records · Page 3Linked to original sources
PubMed1990

Do optimal dipoles obtained by the dipole tracing method always suggest true source locations?

Scalp potentials generated by a concentrated electric source in the brain are very similar to potentials generated by an electric dipole at the source position. In this sense a concentrated source in the brain is modelled as an electric dipole. When the source is diffuse such a dipole which best approximates the scalp potential is called an optimal dipole. Its position is calculated by the Dipole Tracing Method based on a realistic head model with homogeneous electric conductivity. There are 2 major difficulties inherent in this method: (1) The low electric conductivity of the skull causes systematic shifts of the optimal dipole positions from the true positions of concentrated sources; (2) the optimal dipoles cannot specify diffuse source positions. The first difficulty is overcome by using the numerical correction obtained by comparing the known dipole positions generated within a human head with their optimal ones. The second difficulty is removed to a certain extent by comparing the optimal dipole positions obtained with the 1-dipole and 2-dipole models together with their dipolarity. We have obtained criteria for the validity of the dipole approximation and source concentration.

Brain↗
PubMed1990

Computer simulation of supraventricular tachycardia with the Wolff-Parkinson-White syndrome using three-dimensional heart models.

Supraventricular tachycardias with the Wolff-Parkinson-White (WPW) syndrome have been successfully simulated using a newly developed simulation system. The heart model, including atria and ventricles, was constructed of about 50,000 discrete elements (model cells) in three dimensions with 1.5-mm spatial resolution. The model cells covered all of the types of cells in the actual heart, including the normal myocardium, special conduction system and abnormal cells, such as the bundle of Kent (accessory pathway) and ectopic pacemaker (premature beat). Different model cells were specified by their electrophysiologic parameters, such as action potential, refractory period, and conduction velocity. The WPW syndrome was simulated by setting an accessory pathway between the right atrium and ventricle. Based on this model a premature atrial beat was introduced, which initialized the tachycardia. By adjusting the parameters, three types of reciprocal supraventricular tachycardia were simulated with the reentry circuits (1) formed anterogradely by the A-V node and retrogradely by the accessory pathway, (2) formed anterogradely by the accessory pathway and retrogradely by the A-V node, and (3) confined within the A-V node. Time relations for initializing and maintaining the tachycardias were evaluated. The simulated ECGs were in good agreement with the clinical findings.

Computer Simulation↗
PubMed1990

Reduction of the number of electrodes in the measurement of body surface potential distribution.

The number of electrodes required to reproduce a body surface potential map (BSPM) can be reduced by making use of the correlations among potentials measured at different sites on the body surface, as pointed out by Lux et al. in 1978. In the present paper, we have introduced two distinct methods which can be used to improve the accuracy of the potential estimation. In the first method, the BSPMs are divided into several classes according to the direction of the vectorcardiogram, while the temporal as well as the spatial correlations are taken into account in the second method. They are called the 'partition method' and the 'spatiotemporal correlation method', respectively. By means of the partition method using 40 electrodes, the estimation error becomes 75% of that estimated with the Lux method, which is equivalent to the Lux method with 47 electrodes. In other words, the partition method saves seven electrodes. When the electrodes are restricted on the chest, our methods are more effective. In particular, the partition method saves no less than 20 electrodes.

Electrocardiography↗
PubMed1989

An interpretation of 1/f fluctuations in neuronal spike trains during dream sleep.

The mesencephalic reticular formation (MRF) neurons are regarded as contributing to the activation of the cerebral cortex. We have investigated the statistical characteristics of the single neuronal activity in the MRF of cat during two activated states: paradoxical sleep (PS) and state in which the animal is watching birds (BW). 1/f-like spectra are observed for both PS and BW states, being more pronounced for PS state. For the interpretation of these findings, we have applied the clustering Poisson process, which not only gives rise to a 1/f spectrum but also suggests a generation mechanism. The MRF neuronal activities in PS and BW are closely fitted by the clustering Poisson process, both in terms of power spectral density and counting statistics. These results strongly suggest that the activities of MRF neurons in PS and BW can be interpreted as the superpositions of randomly occurring clusters which consist of various number of impulses.

Animals↗
PubMed1989

Effects of cavities on EEG dipole localization and their relations with surface electrode positions.

Effects of cavities in the human head on EEG dipole localization have been investigated by computer simulation. The human head is represented by a homogeneous spherical conductor including an eccentric spherical cavity which approximates effects of actual cavities inside the head. The homogeneous sphere model is used for assessing the effects caused by neglecting the cavity in the volume conductor model in the inverse dipole fitting procedure. Four electrode configurations have been examined to investigate their relation to the EEG inverse dipole solution. After examination of 2520 dipoles in the brain, the effects of cavities in the human head are found to be negligible when the dipole is located in the cortex or in the subcortex. When the dipole is located in the brain stem, the EEG inverse dipole solution is strongly affected by the cavity and is sensitive to the electrode configuration on the scalp. The EEG inverse dipole solution in the deep brain is sensitive to inhomogeneity in the lower part of the head when a single positive or negative potential pole is observed by the electrodes on the scalp, and at the same time is sensitive to the extent of the scalp covered by the electrodes. In conclusion, the electrodes should cover as much of the upper scalp as possible for deep source localization.

Algorithms↗
PubMed1989

Clinical application of electrocardiographic computer model.

A three-dimensional computer model was developed to stimulate the ventricular depolarization and repolarization in a clinical setting. The ventricle is composed of approximately 50,000 units arranged in a cubic close-packed structure and the specialized conduction system is distributed so as to obtain the excitation sequence resembling normal ventricular depolarization. The normal distribution of action potential waveforms with the longest duration on the endocardium and the shortest on the epicardium is used in the model. The heart model is mounted in a homogeneous torso model, and the body surface potential distribution generated by the electric dipoles is calculated using the boundary element method. The QRST waveforms corresponding to the normal and some abnormal heart conditions, such as bundle branch block, myocardial infarction, apical hypertrophic cardiomyopathy, and Wolff-Parkinson-White syndrome, is obtained by assuming the abnormal area with altered electrical properties. Thus the three-dimensional computer model may provide further insight into the genesis of the clinical electrocardiogram.

Bundle-Branch Block↗
PubMed1989

Effects of opioid agonists on sympathetic and parasympathetic transmission to the dog heart.

Effects of leu- and met-enkephalin, pentazocine and morphine on negative or positive chronotropic response to vagal nerve stimulation or cardiac sympathetic nerve stimulation were examined in anesthetized dogs in order to determine whether opioid receptors modulate vagal and sympathetic transmission. Leu- and met-enkephalin (10-100 micrograms/kg i.v.) and pentazocine (100-1000 micrograms/kg i.v.) inhibited bradycardic response to vagal nerve stimulation (1-4 Hz) in a dose-dependent manner. Morphine (300 and 1000 micrograms/kg i.v.) did not affect vagal bradycardia. The inhibitory effect of leu-enkephalin (30 micrograms/kg) and pentazocine (300 micrograms/kg) was effectively antagonized by naloxone (1000 micrograms/kg i.v.). Bradycardic response to intracoronary injection of methacholine (0.1, 0.3 and 1 microgram) into the right coronary artery was unaffected by leu-enkephalin (30 micrograms/kg). On the other hand, leu-enkephalin and pentazocine did not modify tachycardic response to sympathetic nerve stimulation (1-8 Hz). Morphine attenuated sympathetic tachycardia only slightly. These results suggest that presynaptic opioid receptors, probably delta type, are present in the vagus nerves, and that the activation of opioid receptors inhibit vagal transmission to the dog heart. In contrast, the presence of opioid receptors in the cardiac sympathetic nerves is not evident.

Animals↗
PubMed1989

Inhibition of vagal transmission by cardiac sympathetic nerve stimulation in the dog: possible involvement of opioid receptor.

The inhibitory effect of cardiac sympathetic nerve stimulation (SNS) on bradycardic response to vagal nerve stimulation was examined in anesthetized dogs pretreated with atenolol or propranolol to prevent tachycardia caused by SNS or norepinephrine infusion. The amplitudes of vagal bradycardia (0.5, 1, 2, and 4 Hz) during 10 and 30 Hz of SNS were significantly smaller than those during the resting state. The inhibitory effect of 10 Hz of SNS was neither affected by prazosin (10, 30 and 100 micrograms/kg i.v.) nor by yohimbine (10, 30 and 100 micrograms/kg i.v.). The SNS-induced inhibition of vagal bradycardia was inhibited by naloxone (0.3 and 1 mg/kg i.v.) or by naltrexone (0.3 and 1 mg/kg i.v.). Vagal bradycardia was unaffected by intracoronary infusion of norepinephrine (3 micrograms/min) into the right coronary artery, whereas it was effectively inhibited by leu-enkephalin (10, 30 and 100 micrograms/kg i.v.). Bradycardia induced by intracoronary injection of methacholine (0.3, 1 and 3 micrograms) was unaffected by SNS. These results suggest that a presynaptic alpha adrenoceptor mechanism is not involved in the SNS-induced inhibition of vagal bradycardia in the dog, and suggest further that an opioid receptor mechanism may be responsible for the inhibition.

Blood Pressure↗
PubMed1989

[Relationship between coagulation-fibrinolysis kinetics and the severity and predictability of toxemia of pregnancy].

Various attempts have been made in recent years to identify the cause and pathophysiology of toxemia of pregnancy from the standpoint of changes in blood coagulation and fibrinolysis. It is believed that in toxemia of pregnancy, the fibrinolytic process changes as coagulation is augmented. However, definite conclusions about this sequence of events have not yet been reached. This study was designed to analyze the severity of toxemia of pregnancy and to examine the possibility of anticipating its onset from the standpoint of coagulation-fibrinolysis kinetics. The patient population comprised 116 women divided into 4 groups: I) A control group of 10 normal, nonpregnant women; II) Fifty-four normal pregnant women who were followed up from early pregnancy until delivery; III) Twenty-four women who were followed up from early pregnancy until delivery and developed toxemia of pregnancy; and IV) Twenty-eight women with severe toxemia of pregnancy of the pure type who were referred to our institution at the onset of the disease and were treated as inpatients. Intergroup comparison yielded the following results. 1. In group II (normal pregnancy), a significant increase was observed, first in fibrinopeptide B beta and then in fibrinopeptide A, as the pregnancy progressed. This suggested the acceleration of coagulation and fibrinolysis due to pregnancy. 2. In group III (6 of 24 cases developed severe toxemia of pregnancy), AT-III increased, while protein C and hematocrit levels increased relative to those on the normal pregnancy group during the 2nd trimester. Thus, changes in coagulation functions occurred before the onset of toxemia of pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)

Antithrombin III↗
PubMed1988

Dipole-tracing of 'awareness' attenuating the cortical components of somatosensory evoked potentials.

Using the dipole-tracing method, the source generators of N18, P22 and P40 of the somatosensory evoked potential (SEP) were estimated as the equivalent dipole. After voluntary action of the thumb flexion, no changes were observed in N18 or P40, but the amplitude of P22 was suppressed. The after-effects of intention accompanied by a voluntary action or the subject's awareness that electrical stimulation will be given after the voluntary action were treated as 'awareness'. By subtracting the pure SEP from SEP during 'awareness', it was found that the equivalent dipole of 'awareness' of P22 was located at the same region of pure P22, but the vector was of opposite orientation. 'Awareness' attenuated the perceptive potential of SEP like P22 generated in the cortex.

Awareness↗
PubMed1987

Dipole-tracing method applied to human brain potentials.

A new computer-aided method was developed to estimate the location of an electric source generator (e.g. a current dipole) in the human brain. Brain activity such as somatosensory evoked potentials was recorded with 21 surface electrodes over the scalp. To solve the inverse problem, it was assumed that only one dipole is elicited at a given time, and that the head is embedded in an infinite and homogeneous conductor. The exact geometry of the human head was measured from 17 slices of CT-images of a real head to arrange a human head model. A dipole with a given moment and location is assumed in the head model. Potential distribution elicited by the dipole is compared with potential distribution which was the actual recorded one. The optimal dipole location was calculated, using the simplex method. Hence, the optimal dipole moment was obtained. The accuracy of estimation as an equivalent dipole was expressed in terms of dipolarity.

Brain↗
PubMed1987

Computer simulation of the Wolff-Parkinson-White syndrome utilizing a human heart model.

The relationship between the location of an accessory pathway and body surface ECG waveforms was investigated by computer simulation of the WPW syndrome using a human heart model. The 3-dimensional heart model is composed of 50,000 units so as to represent the details of ventricular excitation. Ten typical accessory pathways near the A-V groove were examined, which correspond to Gallagher's classification of the WPW syndrome based on their surgical experience. Twelve-lead ECG waveforms were calculated for these 10 cases and were compared with the clinical observations of Gallagher et al. The polarities of the delta waves at 40 msec after the onset of the QRS were listed. The agreement of our model with the clinical data obtained by Gallagher et al is 87%. Details of changes in the ECG waveforms were also examined by changing ther terminal location of the accessory pathway along the radial and longitudinal directions in the ventricles, and it was found that the ECG waveforms of the limb leads are more sensitive to this difference in the preexcited location than those of the chest leads. The simulated epicardial isochronic patterns also agree with the measurements.

Computer Simulation↗