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Biomedical subjects

N Kuwayama

Publications and source records attributed to N Kuwayama.

At least 37 records · Page 2Linked to original sources
PubMed1995

The characteristics of laser-Doppler flowmetry for the measurement of regional cerebral blood flow.

The fundamental characteristics of laser-Doppler flowmetry (LDF), especially the depth of cerebral blood flow (CBF) measurement, have not been widely studied in the brain tissue; however, LDF has been widely used in recent clinical and experimental studies. We investigated the depth of CBF measurement and other characteristics related to the use of LDF in the brain. In an animal experimental study, the distribution of laser light and the depth of CBF measurement of LDF were measured by using modified LDF probes. CBF in various conditions was also measured by the LDF and hydrogen clearance method. Laser light of low output lost directivity and was dispersed into a hemispherical form in the brain tissue. The depth of CBF measurement was approximately 100 to 400 microns, depending on the intensity of the emitted laser light, and was affected by changes of CBF. In the physiological condition, the close correlation between the values of CBF by the LDF and hydrogen clearance method was obtained. After cardiac arrest, the CBF value of LDF did not immediately show a 0 value. LDF has several special characteristics, and the sample volume was very small. It is important to pay attention to the several special characteristics of LDF.

Animals↗
PubMed1994

Dural arteriovenous fistulae involving the transverse-sigmoid sinus and foramen magnum.

The authors present a rare case of dural arteriovenous fistulae (AVFs) involving both the transverse-sigmoid sinus and the foramen magnum, which was treated successfully with multi-staged endovascular procedures. The transverse-sigmoid sinus, which was thrombosed proximally and distally, was occluded by transarterial embolization followed by intraoperative embolization of the sinus using platinum coils. The dural AVF involving the foramen magnum was occluded via a transvenous approach.

Arteriovenous Fistula↗
PubMed1994

Treatment of traumatic facial arteriovenous fistula with embolization and surgical excision--a case report.

A 57-year-old male presented with a traumatic arteriovenous fistula on his face. The fistula was first treated with transarterial embolization and subsequently resection. His course was complicated by several recurrences of his fistula prior to definitive surgical treatment. The treatment of facial arteriovenous fistula and its complications are discussed in this article.

Arteries↗
PubMed1994

Estimation of triggering work of breathing. The dependence on lung mechanics and bias flow during pressure support ventilation.

Work of breathing necessary to trigger a ventilator (WOBtr) was calculated during pressure support ventilation (PSV), and the effect of bias flow on WOBtr was evaluated. A spring-loaded bellows type lung model with two bellows placed in series was used to simulate spontaneous breathing. A Venturi mechanism of jet flow generated subatmospheric pressure inside the diaphragm bellows simulated inspiratory effort. The lung compliance (CL) was set at 0.3 L/cm H2O or 0.05 L/cm H2O. The airway resistance (Raw) was set at 5, 20, or 50 cm H2O/L/s. Pressure support levels were increased from 0 to 45 cm H2O. Sensitivity was set at 2 cm H2O. No bias flow was used at first. The WOBtr was calculated using a pressure-volume (P-V) loop derived from the diaphragm bellows movement during the triggering period. We determined WOBtr and its dependence on the various pressure support (PS) levels, CL and Raw. To evaluate the effects of bias flow on WOBtr and triggering delay, a ventilator was put in the PSV mode, with various bias flow rates (from 0 to 20 L/min) at a sensitivity of 2 cm H2O. We found that when no bias flow was used, WOBtr increased with an increase in both Raw and end-expiratory lung bellows pressure which was considered as auto-PEEP. With bias flow, both triggering delay and WOBtr increased. An increase in bias flow at a given PS level resulted in both decreased pressure support time and tidal volume (VT). It is concluded that the bias flow system is not desirable for use during PSV.

Airway Resistance↗
PubMed1994

Multiple cerebral vascular malformations and spontaneous regression--case report.

A female infant manifested a rare case of spontaneous regression of a vascular malformation in the occipital lobe after removal of another arteriovenous malformation in the frontal lobe. She was born with multiple nevi on the face, body, and upper and lower extremities. She demonstrated developmental retardation at 8 months of age. Computed tomography at 11 months of age demonstrated ventricular enlargement and a mass in the subdural portion of the left anterior fossa. Magnetic resonance images demonstrated signal void signs in the left frontal lobe, which suggested vascular malformation. Cerebral angiograms disclosed two vascular malformations. The malformation in the frontal lobe was totally removed. Cerebral angiograms 25 days after the operation failed to demonstrate either vascular malformation previously observed. Hemodynamic change following the removal of the arteriovenous malformation may have contributed to the occlusion of the remaining malformation.

Cerebral Angiography↗
PubMed1994

Radiation exposure in endovascular surgery of the head and neck.

PURPOSE: To evaluate the radiation risk to the operator and the patient during endovascular surgery of the head and neck. METHODS: The dose was measured using thermoluminescence dosimeters attached at the body surface of the operator and the patient during 15 endovascular surgeries (3 for arteriovenous malformation, 8 for dural arteriovenous fistulas, and 4 for other disorders of the head and neck). The dose was measured at seven sites on the operator and at five sites on the patient. RESULTS: The mean number of digital subtraction angiography studies and fluoroscopy time were 21 +/- 10 and 73 +/- 24 minutes, respectively. The equivalent dose range at each site in the operator was 0.12 to 0.88 mSv (glabella), 0.06 to 1.1 and 0 to 0.09 mSv (neck, outside and inside the protector, respectively), 0 to 0.20 mSv (left should, inside the protector), 0.09 to 1.99 mSv (left arm), 0.05 to 3.55 mSv (left hand), and 0 to 0.49 mSv (pubis, inside the protector). Those in the patients were 3.1 to 136 mSv (glabella), 13 to 5441 mSv (right temporal area), 4 to 186 mSv (left temporal area), 0.1 to 51 mSv (neck), and 0 to 0.62 mSv (pubis). CONCLUSIONS: The total doses at the operator's eyes and left hand during the course of a year may exceed the dose limits recommended by the International Commission on Radiological Protection. Operators should wear not only body protectors, but also thyroid protectors and lead glass spectacles. The equivalent dose at the right temporal area of the patient may exceed the deterministic dose for transient erythema or alopecia of the skin even in one endovascular procedure.

Adolescent↗
PubMed1993

Effect of adding diamond particles on the fracture toughness of apatite ceramics.

Composite ceramics dispersed through diamond particles with hydroxyapatite as a matrix were prepared by firing at 1250 degrees C under reduced pressure or normal atmosphere. The fracture toughness and physical properties of sintered composite ceramics were examined to determine methods of strengthening hydroxyapatite ceramics. The diamond crystal in composite ceramics was transformed to graphite by firing and the fracture toughness of hydroxyapatite ceramics increased with diamond addition. At 10 wt% diamond, the maximum value for fracture toughness was obtained, and the further addition of diamond particles over 10 wt% caused fracture toughness to decrease. Such increases in fracture toughness were considered the result of microcracking which occurred during the transformation from diamond to graphite.

Dental Porcelain↗
PubMed1992

Influence of the acute stress on agonist-stimulated phosphoinositide hydrolysis in the rat cerebral cortex.

1. The present study was carried out in order to elucidate the influence of the acute stress on alpha 1-adrenergic, serotonin-2 (5-HT2) and muscarinic cholinergic (M-Ach) receptors-mediated phosphoinositide (PI) hydrolysis in rat cerebral cortex slices. 2. In rat cerebral cortex slices, noradrenaline (NA), serotonin (5-HT) and carbachol stimulated [3H]inositol-monophosphate (IP1) accumulation in a concentration-dependent manner. 3. The forced swimming test (FST) for 15 min induced a significant reduction of 5-HT-stimulated [3H]IP1 accumulation, but this stress situation did not produce a significant alteration of NA- and carbachol-stimulated [3H]IP1 accumulation. 4. The FST for 15 min did not affect the density and affinity of alpha 1-adrenergic, 5-HT2 and M-Ach receptors. 5. In a mild acute stress situation, the intracellular signal transduction mediated by 5-HT was promptly inhibited as compared to the signal transduction mediated by NA or carbachol. This inhibition may be induced by an acute uncoupling of 5-HT2 receptor-mediated intracellular signal transduction.

Adrenergic alpha-Agonists↗
PubMed1992

Influence of tempering method on residual stress in dental porcelain.

The porcelain component of a porcelain-fused-to-metal restoration is strengthened by residual (tempering) stresses which are induced by cooling procedures followed in dental laboratories. The thermophysical properties of materials and cooling rate are the main factors which determine the residual stress. In this paper, the temperatures in the midplane of body-porcelain disks were measured from a heat-soak temperature (1000 degrees C) to room temperature during two different cooling procedures: slow cooling in air and forced-air cooling. Experimental results approximated exponential cooling wherein the cooling rates could be represented by a linear equation of temperature. Residual stresses, as affected by the tempering method and thickness of a porcelain disk, were calculated by computer simulation for regions away from the edges. The following temperature-dependent factors were incorporated into the simulation: elastic modulus, viscosity, and coefficient of thermal expansion. The cooling rate dependencies of the glass transition temperature and the temperature distribution during cooling were also included. The cooling rates used in this simulation were derived from the tempering data. The agreement between development of transient and residual stresses--calculated by computer simulation for various cooling methods, and the tendency toward failures of porcelain disks subjected to the tempering processes--was examined. Simulated residual stresses were also in good agreement with those measured by the indentation fracture method of Marshall and Lawn (1977) and Anusavice et al. (1989).

Computer Simulation↗
PubMed1992

Giant meningioma fed by the anterior choroidal artery: successful removal following embolization--case report.

A 53-year-old female was admitted with apathy, left sensory and motor disturbance, left homonymous hemianopsia, and dressing apraxia. Computed tomography and magnetic resonance imaging showed a huge mass markedly enhanced in and around the right trigone. Cerebral angiography revealed rich vascularity of the tumor mainly fed by the right anterior choroidal artery. The feeding vessel was embolized with microfibrillar collagen after superselective catheterization. Seven days later, the tumor was totally removed with low blood loss. The histological diagnosis was fibroblastic meningioma. She was discharged without neurological deficit, except for left homonymous hemianopsia.

Arteries↗
PubMed1992

Etiological evaluation of dural arteriovenous malformations of the lateral and sigmoid sinuses based on histopathological examinations.

Controversy persists concerning the pathogenesis of dural arteriovenous malformations (AVM's) and whether they are congenital or acquired. Furthermore, it remains undetermined whether the lesion is located in the sinus itself or within the sinus wall. In order to elucidate the pathogenesis of dural AVM's of the lateral and sigmoid sinuses, histopathological profiles of this disease were studied in serial sections of completely resected lesions from three patients. The essential lesion was histologically confirmed to be a dural arteriovenous fistula within the wall of the venous sinuses. The etiology process of this disease and its progression were evaluated.

Adult↗
PubMed1991

Modified thermal diffusion flow probe for the continuous monitoring of cortical blood flow.

A small thermal diffusion flow probe has been developed to monitor the dynamic changes in cerebral blood flow in small animals. Constantan wire was used as a heat source to make a miniature probe. The pair of thermocouples used to detect the heat gradient between two gold plates was elongated to avoid heat conduction between them, and this improvement allowed us to make quantitative measurements. After several basic experiments, local cerebral blood flow was measured simultaneously, using both the modified thermal probe and the hydrogen clearance method in four rabbits. A close relationship was obtained between the local cerebral blood flow values measured by hydrogen clearance (F, ml/100g/min) and the reciprocal of the thermocouple voltage (1/V;1/mV). The regression line was F = 29111(1/V - 1/226), (r = 0.92, P less than 0.001). We suggest that the modified thermal probe is a reliable and quantitative means of measuring flow. In addition, another probe modified for clinical use was evaluated. Continuous monitoring of local cerebral blood flow in postoperative patients was performed, and some illustrative cases are described.

Aged↗
PubMed1991

Differences in critical cerebral blood flow with age in swine.

Normal cerebral blood flow (CBF), critical CBF at a flat reading of the electroencephalogram (EEG), and reversibility of the flat EEG after reperfusion were investigated in a total of 59 pigs, including seven newborns (1 to 3 days of age), 38 juveniles (1 month old), and 14 adults (7 months old). The CBF was determined by the hydrogen clearance method; the EEG was recorded continuously and a power spectrum analysis was performed. Cerebral ischemia was produced by occlusion of both common carotid arteries and induction of hypotension (approximately 50 mm Hg). The flat EEG reversibility was investigated for 3 hours after reperfusion. As parameters of brain development, the neuronal density and the time at which the S-100 protein appeared in the brain were examined. Normal CBF was highest in neonatal pigs and decreased with age. The critical CBF at a flat EEG was lowest in newborn pigs and was elevated with development of the brain. Tolerance against cerebral ischemia was greatest in newborn pigs.

Aging↗
PubMed1990

Viscosity of dental porcelains in glass transition range.

Changes in the viscosity of dental porcelain as a function of temperature are the controlling factor determining incompatible stresses in porcelain-fused-to-metal restorations. A new method was used to estimate viscosity using a viscoelastic analytical model that considers the relation between the heating rate and deformation temperature (Td) of dental porcelain with stress applied during heating. The activation energy of viscous flow and the viscous constant in the Arrhenius equation were calculated for six kinds of commercial body and opaque porcelains. The effect of the heating rate on the instantaneous coefficient of thermal expansion was also measured. Tg onset was graphically determined using data on thermal deformation and agreed well with the strain point as defined by viscosity. The data gathered in this study was also compared to the experimental results of previous works by others.

Dental Porcelain↗
PubMed1990

Temperature dependence of thermal expansion coefficient for palladium-based binary alloy.

Temperature dependencies of thermal expansion coefficients for the alloys of Pd-Ag, Pd-Cu and Pd-Co binary systems were measured at temperatures up to 900 degrees C, with heating and cooling rates of 5 degrees C/min. The coefficient of thermal expansion of alloys with no transformation in the temperature range of interest in porcelain firing was well approximated by a linear equation of temperature. The constants in the equation were shown as a function of the weight for the added element. Thermal expansion of the palladium-based alloy with no transformation was well estimated at any temperature range and at any composition by using the constants represented here. The coefficients of thermal expansion before and after order-disorder transformation and magnetic transformation were measured in Pd-Cu and Pd-Co alloys, respectively. The results suggest that transient and residual stresses in porcelain-fused-to-metal restorations can be effectively controlled by making use of transformation of the alloy.

Cobalt↗
PubMed1990

Effects of preparation conditions in aqueous solution on properties of hydroxyapatites.

Hydroxyapatite powders (HAP: Ca10(PO4)6(OH)2) were prepared from calcium nitrate and di-ammonium hydrogen phosphate at various temperatures in aqueous solution in the absence and presence of carbon dioxide. In the absence of carbon dioxide, the crystallinities as well as the calcium to phosphate ratio (Ca/P ratio) of HAP powders increased with an increase in the preparation temperature. Calcium ion deficiency caused low Ca/P ratios of HAP powders. Such HAP powders decomposed thermally to beta-tricalcium phosphate (beta-TCP: Ca3(PO4)2) at 800 degrees C in 3 hours whereas HAP powders with sufficient calcium were stable at 1200 degrees C for 3 hours. In the presence of carbon dioxide as well the crystallinities of HAP powders increased with an increase in the preparation temperature, but carbonate-bearing HAPs were obtained instead of pure HAP. In addition, calcium carbonate was obtained along with carbonate-bearing HAP prepared below 60 degrees C.

Calcium↗
PubMed1990

[Finite element analysis on physiological mobility of individual teeth].

The initial movement of the tooth was investigated by the finite element method. The mechanical properties of the periodontal membrane were estimated from the results of the simulation. The analysis was made by using an 8 point isoparametric finite element method. The upper central incisor with an axial directional load was simulated. The concept of the apparent elastic modulus was introduced to the stress-strain relation of the soft tissue, that is, soft tissue such as the periodontal membrane and the gingiva was considered to have stress dependent elastic moduli. At the first stage of the simulation, the stress and strain distributions in the paradentium were calculated by the conventional method. From the next stage, the apparent elastic moduli for the soft tissue were introduced to the calculation, that is, the elastic moduli for the soft tissue were computed from the calculated equivalent stresses of the previous stage. The calculations were repeated until the displacement values converged. The initial displacement of the tooth was not proportional to the applied load but showed a non-linear relationship. The relationship between load and displacement was approxiated by the n-th power equation. These results were in agreement with the clinical experimental results. The periodontal membrane is built up of different elastic moduli. The elastic moduli were low at the alveolar edge and the root apex. The equivalent stresses of the periodontal membrane were marked low in the alveolar edge and the root apex. In conclusion, the concept of the apparent elastic modulus is useful to investigate the initial movement of the tooth and estimate the mechanical properties of the periodontal membrane.

Computer Simulation↗