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Biomedical subjects

C Ohkubo

Publications and source records attributed to C Ohkubo.

At least 19 recordsLinked to original sources
PubMed2001

Modulatory effects of static magnetic fields on blood pressure in rabbits.

Acute effects of locally applied static magnetic fields (SMF) on pharmacologically altered blood pressure (BP) in a central artery of the ear lobe of a conscious rabbit were evaluated. Hypotensive and vasodilator actions were induced by a Ca(2+) channel blocker, nicardipine (NIC). Hypertensive and vasoconstrictive actions were induced by a nitric oxide synthase (NOS) inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME). The hemodynamic changes in the artery exposed to SMF were measured continuously and analyzed by penetrating microphotoelectric plethysmography (MPPG). Concurrently, BP changes in a central artery contralateral to that of the exposed ear lobe were monitored. SMF intensity was 1 mT and the duration of exposure was 30 min. A total of 180 experimental trials were carried out in 34 healthy adult male rabbits weighing 2.6-3.8 kg. Six experimental procedures were chosen at random: (1) sham exposure without pharmacological treatment; (2) SMF exposure alone; (3) decreased BP induced by a single intravenous (iv) bolus injection of NIC (100 microM/kg) without SMF exposure; (4) decreased BP induced by injection of NIC with SMF exposure; (5) increased BP induced by a constant iv infusion of L-NAME (10 mM/kg/h) without SMF exposure; (6) increased BP induced by infusion of L-NAME with SMF exposure. The results demonstrated that SMF significantly reduced the vasodilatation with enhanced vasomotion and antagonized the reduction of BP via NIC-blocked Ca(2+) channels in vascular smooth muscle cells. In addition, SMF significantly attenuated the vasoconstriction and suppressed the elevation of BP via NOS inhibition in vascular endothelial cells and/or central nervous system neurons. These results suggest that these modulatory effects of SMF on BP might, in part, involve a feedback control system for alteration in NOS activity in conjunction with modulation of Ca(2+) dynamics.

Animals↗
PubMed2001

Acute effects of whole-body exposure to static magnetic fields and 50-Hz electromagnetic fields on muscle microcirculation in anesthetized mice.

Acute microhemodynamic effects of static and alternating magnetic fields at a threshold level were investigated on modulating the muscle capillary mirocirculation in pentobarbital-anesthetized mice. The skin in a tibialis anterior was circularly removed with 1.5 mm diameter for intravital-microscopic recording of the capillary blood velocity in the tibialis anterior muscle. Fluorescein isothiocyanate (FITC)-labeled dextran (MW 150 kDa) was used for an in vivo fluorescent plasma marker of the muscle capillaries. Following a bolus injection of FITC-dextran solution into the caudal vein, the peak blood velocity in the muscle capillaries was measured prior to, during, and following exposure to static magnetic fields (SMF) or 50-Hz electromagnetic fields (EMF) using a fluorescence epi-illumination system. The whole body of experimental animals, placed on the observing stage of a fluorescence microscope, was exposed to SMF (0.3, 1 and 10 mT) or 50-Hz EMF (0.3 and 1 mT) for 10 min using a specially devised electromagnet. For sham exposure, the electromagnet was not energized. During exposure and post-exposure to SMF of 10 mT, the peak blood velocity significantly increased as compared to sham exposure. After the withdrawal of SMF and 50-Hz EMF of 1 mT, significant similar effects on the blood velocity were present or enhanced. These findings suggest that field intensity of 1 mT might be considered as a threshold level for enhancing muscle microcirculation under pentobarbital-induced hypnosis.

Animals↗
PubMed2001

Comparative study of maxillary complete dentures constructed of metal base and metal structure framework.

A removable denture designed using a three-dimensional cast metal framework (hereafter referred to as the 'structurally designed' denture) could extend denture longevity because it is unbreakable and easy to adjust. The aim of the present clinical study was to compare two types of maxillary removable dentures: conventional dentures and structurally designed denture. One edentulous and five partially dentate patients were fitted with two maxillary dentures made from the same impression and same occlusal relationship. About 20 days after delivery of the denture, masticatory analysis was conducted chewing phase (open, closed, and occluded); coefficients of variation and average variation were calculated. Denture vibration during tapping was then measured using an accelerometer. The patients were also interviewed about comfort, ease of chewing, speech, stability, aesthetics and preference for regular use. For both masticatory movements and denture vibration, there were no significant differences (P>0.1) between the conventional denture and the structural design denture. In evaluating the dentures according to each criteria, the significant superiority of one denture over the other could not be determined. However, all patients subjectively preferred the structurally designed dentures for regular use. According to these findings, structurally designed dentures do not appear to have any particular physiological problems as compared with the conventional dentures.

Acceleration↗
PubMed2000

Shear bond strengths of polymethyl methacrylate to cast titanium and cobalt-chromium frameworks using five metal primers.

STATEMENT OF PROBLEM: Poor chemical bonding of a denture base resin to cast titanium frameworks often introduces adhesive failure and increases microleakage. PURPOSE: This study examined the shear bond strengths of a denture base resin to cast pure titanium, Ti-6Al-4V, and a cobalt-chromium alloy using various adhesive primers. MATERIAL AND METHODS: Disks (6.0 mm diameter, 2.5 mm thick) were cast of the 3 alloys. The disk surfaces were grit-blasted with 50 microm alumina and treated with 5 different metal primers (Metal Primer II ¿MP]; Cesead Opaque primer ¿OP]; Meta Base ¿MB]; experimental primer ¿EP]; Siloc bonding system ¿SI]). A denture base resin (Palapress Vario) was then applied on the disks with hole-punched sticky tape (bonding area of 5.0 mm) and a Teflon (PTFE, New Age Industries Inc, Willow Grove, Pa.) ring (6.0 mm diameter x 2.0 mm thick). Specimens without primer were also prepared as controls. All specimens were immersed in 37 degrees C water and thermocycled up to 2,000 cycles. Shear bond strength values were determined at a crosshead speed of 0.5 mm/min. Data were statistically analyzed using 3-way ANOVA, followed by 1-way ANOVA and the Scheffé multiple range test. RESULTS: Primers significantly (P <.05) improved shear bond strengths of denture base resin to all metals, among which no significant differences were found. Specimens primed with OP, MP, and EP showed higher bond strengths than did those primed with MB. After thermocycling, the bond strengths of MB and SI decreased substantially; MB showed the least durability (22.8% to 35.5% decrease) among the primers. CONCLUSION: The application of 5 primers significantly improved the shear bond strengths of a denture base resin to cast CP titanium, Ti-6Al-4V, and Co-Cr alloy. OP and MP primers exhibited greater bond strength and durability than did MB and SI.

Analysis of Variance↗
PubMed2000

Cutting efficiency of air-turbine burs on cast titanium and dental casting alloys.

OBJECTIVE: The purpose of this study was to investigate the cutting efficiency of air-turbine burs on cast free-machining titanium alloy (DT2F) and to compare the results with those for cast commercially pure (CP) Ti, Ti-6Al-4V alloy, and dental casting alloys. METHODS: The cast metal (DT2F, CP Ti, Ti-6Al-4V, Type IV gold alloy and Co-Cr alloy) specimens were cut with air-turbine burs (carbide burs and diamond points) at air pressures of 138 or 207 kPa and a cutting force of 0.784 N. The cutting efficiency of each bur was evaluated as volume loss calculated from the weight loss cut for 5 s and the density of each metal. The bulk microhardness was measured to correlate the machinability and the hardness of each metal. RESULTS: The amounts of DT2F cut with the carbide burs were significantly (p < 0.05) greater than for the other titanium specimens at either 138 or 207 kPa. The diamond points exhibited similar machining efficiency among all metals except for Type IV gold alloy. The increase in the volume loss of Co-Cr alloy (Vitallium) cut with the diamond points showed a negative value (-29%) with an increase in air pressure from 138 to 207 kPa. There was a negative correlation between the amounts of metal removed (volume loss) and the hardness (r2 = 0.689) when the carbide burs were used. SIGNIFICANCE: The results of this study indicated that a free-machining titanium alloy (DT2F) exhibited better machinability compared to CP Ti and Ti-6Al-4V alloy when using carbide fissure burs. When machining cast CP Ti and its alloys, carbide fissure burs possessed a greater machining efficiency than the diamond points and are recommended for titanium dental prostheses.

Alloys↗
PubMed2000

The machinability of cast titanium and Ti-6Al-4V.

This study investigated the machinability (ease of metal removal) of commercially pure (CP) titanium and Ti-6Al-4V alloy. Both CP Ti and Ti-6Al-4V were cast into magnesia molds. Two types of specimens (with alpha-case and without alpha-case) were made for CP Ti and Ti-6Al-4V. Machinability (n = 5) was evaluated as volume loss (mm3) by cutting/grinding the 3.0 mm surface using fissure burs and silicon carbide (SiC) under two machining conditions: (1) two machining forces (100 or 300 gf) at two rotational speeds (15000 or 30000 rpm) for 1 min, and (2) constant machining force of 100 gf and rotational speed of 15000 rpm for 1, 2, 5, 10, and 30 min. As controls, conventionally cast Co-Cr and Type IV gold alloys were evaluated in the same manner as the titanium. When fissure burs were used, there was a significant difference in the machinability between CP titanium with alpha-case and without alpha-case. On the other hand, there was no appreciable difference in the amount of metal removed for each tested metal when using the SiC points.

Alloys↗
PubMed2000

Neutral zone approach for denture fabrication for a partial glossectomy patient: a clinical report.

According to the neutral zone concept, an appropriate denture form can be molded into a physiologic tooth arrangement by using a narrow rim bar occlusion, tissue conditioner, and a direct relining technique for both intaglio and cameo surfaces by using VLC reline resin. Denture stability can be obtained with this "border molding" technique, not only for edentulous patients but also for those with oral deformities.

Aged↗
PubMed1999

Biphasic effects of static magnetic fields on cutaneous microcirculation in rabbits.

The biphasic effects of locally applied static magnetic fields (SMF) on the cutaneous microcirculation within a rabbit ear chamber (REC) were evaluated under conscious conditions. The microcirculatory vasomotion within a REC was measured continuously and analyzed multilaterally by microphotoelectric plethysmography, a real-time image analyzer and an image shearing monitor. SMF intensities at the REC were controlled at 1 mT and the duration of exposure was 10 min. Seventy-eight experimental trials were carried out on 22 healthy adult rabbits weighing 2.6-3.5 kg. Five experimental groups were chosen at random: 1) no pharmacological treatment or SMF exposure, 2) increased vascular tone induced by noradrenaline infusion without SMF exposure, 3) increased vascular tone induced by noradrenaline infusion with SMF exposure, 4) decreased vascular tone induced by acetylcholine infusion without SMF exposure, 5) decreased vascular tone induced by acetylcholine infusion with SMF exposure. The results demonstrated that SMF significantly enhanced vasodilatation, with increased vasomotion under noradrenaline-induced high vascular tone as well as vasoconstriction with reduced vasomotion under acetylcholine-induced low vascular tone. This suggests, therefore, that SMF can modulate vascular tone due to biphasic modification of vasomotion in the cutaneous tissue.

Acetylcholine↗
PubMed1999

Effect of weight change of mandibular complete dentures on chewing and stability: A pilot study.

STATEMENT OF PROBLEM: Little is known as to whether denture weight contributes to the retention and stability of mandibular complete denture. PURPOSE: This study compared the jaw movements and denture retention, stability, and comfort of heavy and light weight mandibular complete dentures. MATERIAL AND METHODS: Mandibular complete dentures of 12 subjects were duplicated using an autopolymerized polymethyl methacrylate (PMMA) resin. The heavy weight denture was set with weights (20 or 60 g) and the lightweight denture was packed with wax instead of weights. Masticatory movements (3 times each) and denture stability (5 times each) were measured. The subjects expressed their denture preference for comfort and chewing. Results were analyzed using ANOVA and Wilcoxon tests at significance level of alpha=.10. RESULTS: Masticatory movements and denture retention were not significantly (P >.10) affected by increasing the weight. Five subjects preferred the heavy denture and 4 subjects preferred light denture for comfort; 3 subjects had no preference. CONCLUSION: The weight of a well-fitting mandibular complete denture did not affect jaw movements, denture stability, or patient preference.

Acrylic Resins↗
PubMed1999

The influence of frequent and excessive intake of glucose on microvascular aging in healthy mice.

OBJECTIVE: The purpose of this study was to verify the following working hypothesis. Even in healthy individuals with normoglycemic adaptability, microvascular aging caused by the accumulation of advanced glycosylation end products (AGEs) in vascular walls would occur, when the blood glucose level is maintained intermittently high due to frequent and excessive sugar intake for a prolonged period. METHODS: Male BALB/c mice were divided into four groups: the S group raised with glucose-enriched feed and the C group with ordinary feed, as well as the SG group with the glucose-enriched feed and special drinking water supplemented with 0.25% aminoguanidine (AG), and the CG group with ordinary feed and this special drinking water. After 6 months, a mouse dorsal skinfold chamber was mounted on the skin of the back for the intravital-microscopic observations of microvasculature. RESULTS: Blood glucose levels were within normal ranges in all four animal groups, indicating their saccharometabolism to be normal. An autofluorescent AGE-positive ratio in the S group was 71.4%, and that in the C group was 33.3%. Mean caliber of arterial microvessels was smallest in the S group. The SG and CG group showed the caliber larger than the groups without AG. Vascular lesion indices were significantly larger in the S group than those of the groups with AG. The indices were particularly small in the SG group. A decrease of amplitudes in thicker vessels and an increase of vasomotor frequencies in thinner ones were demonstrated in the S group. The features of vasomotion differed in the groups with and without AG. CONCLUSIONS: Microvascular aging was clearly noticed in the S group. It has been concluded that vasomotor inhibition was generated in addition to hypertrophy and fragility in arterial microvessels of the group. It is further concluded that AG protects blood vessels from hypertrophy and fragility, but it downregulates vasomotion.

Aging↗
PubMed1997

Comparative strengths of metal framework structures for removable partial dentures.

STATEMENT OF PROBLEM: The framework of removable partial dentures often breaks where the metal retention for the resin denture base attaches to the clasp and major connector. PURPOSE: To study these failure factors, various types of three-dimensional simulated denture frameworks were designed to measure their ultimate strengths and stiffnesses under static load. This study also sought to determine which could be recommended for long-term clinical service. MATERIAL AND METHODS: Three groups of three-dimensional frameworks (double, T-shaped, and trussed structure) were designed, and two groups of classic framework designs (uniform and nonuniform skeleton) were used with an acrylic resin block as a control (n = 5 per group). Fatigue strength, stiffness and amount of strain, and free-end displacement under dynamic loads were measured for each framework. The fatigue strength was determined with a constant-loading fatigue test by counting the number of loading cycles required to induce catastrophic failure. RESULTS: With 20 kgf of load, four T-shaped samples and three trussed structure samples failed at 30,000 to 60,000 loading cycles. No samples of double structure group failed until 100,000 loading cycles. CONCLUSIONS: Three-dimensional frameworks, especially the double structure, have significant differences in fatigue strength and can provide long-term clinical service.

Chromium Alloys↗
PubMed1995

Selectin- and integrin-mediated T-lymphocyte rolling and arrest on TNF-alpha-activated endothelium: augmentation by erythrocytes.

The adhesive and hemodynamic forces that lead to lymphocyte rolling and arrest on activated endothelium and the biophysical role of various adhesion molecules and blood elements in this process are poorly understood. By quantifying their behaviour both in vivo and in vitro, we show here that erythrocytes facilitate selectin- and integrin-mediated rolling and binding of T-lymphocytes on tumor necrosis factor alpha-activated endothelium. The relative contribution of selectins and integrins to this process can be distinguished by using a simple mathematical expression of lymphocyte capture within the range of physiological shear stress. The need for selectin participation in lymphocyte capture increases with shear stress (> 1 dyn/cm2), and both beta 1 and beta 2 integrins act in synergy to produce adhesive drag on captured cells. These findings are potentially useful in developing strategies for intervening with T-cells in a variety of normal and pathological responses as well as for the delivery of genetically modified T-cells to their targets in vivo.

Animals↗
PubMed1995

Physiological reaction and manual performance during work in cold storages.

Subjects were 10 workers (Group R) working in two cold storages (air temperature was between -20 degrees C and -23.2 degrees C), and eight workers (Group C) working in a general storehouse (air temperature was between 12 degrees C and 15.2 degrees C). They were all male workers operating forklift-trucks. Average (SE) age for Group R was 41.4(1.3) years and for Group C was 47.3(1.6) years. Hand tremor, handgrip strength, pinch strength, counting task, flicker value, peak flow rate and blood pressure were measured five times (before work, at 10 a.m., before lunch, at 3 p.m. and after work) per day. Blood samples were collected before lunch. Free fatty acid (FFA) of Group R was significantly higher than that of Group C. There were no significant differences in handgrip strength, pinch strength, counting task, flicker value and peak flow rate between Group R and Group C. However, changes in hand tremor and diastolic blood pressure for Group R were significantly greater than those for Group C. Only for Group R, there was a significant relationship between FFA and the hand tremor values measured the second time. Work loads of Group R would be increased by not only the extreme coldness but also large temperature difference between the inside and the outside of the cold storages. The actual forklift work in these cold storages did not cause a distinct reduction in manual performance, but caused an increase in stress which would be expressed as an increase in catecholamine excretion.

Adaptation, Physiological↗
PubMed1992

[A successfully treated case of thoracic meningocele with von Recklinghausen's disease].

Intrathoracic meningocele is an uncommon disease. Only 95 cases in the foreign literature and 13 cases in Japanese literature have been reported since Phol Meningocele occurs most frequently in the sacral and lumbar spinal regions. In this present paper, an 18-year-old female with intrathoracic meningocele associated with neurofibromatosis is described. The patient was admitted to our Surgical Clinic with a complaint of constrictive pain in the upper chest. The meningocele was diagnosed preoperatively and resected surgically by left thoracotomy. The patient has been followed up to for six years without any evidences of local recurrence. However, she recently complains of headache and weakened eyesight because of pituitary tumor, the operative indication of which is now discussed.

Adolescent↗
PubMed1992

Modulation of hepatic and pulmonary drug-metabolizing enzyme activities of rabbits by dietary cholesterol.

Modulation of the activities of drug-metabolizing enzymes by dietary cholesterol was studied in rabbits. In male rabbits fed a 1.5% cholesterol-diet, an elevated levels of serum cholesterols and triglycerides were observed from the early phase of cholesterol-feeding. At 12 weeks after the onset of cholesterol feeding, a marked increase was observed in the wet weights of livers but not of lungs, while total contents of lipids and cholesterols were elevated in both tissues in cholesterol-fed animals. The content of collagen was increased significantly in livers, but not in lungs and the phase I drug-metabolizing enzyme activities were significantly reduced in livers but remained unchanged in lungs by cholesterol feeding. On the other hand, the phase II drug-metabolizing enzyme activities varied depending on the enzymes in both tissues. The results demonstrate that dietary cholesterol induces different effects on rabbit liver and lung and that the modulation of the hepatic enzymes by dietary cholesterol in rabbits differs from that in rats, mice and guinea pigs in which the activity of the enzymes are elevated by dietary cholesterol.

Animals↗
PubMed1991

Interleukin 2 induced leukocyte adhesion to the normal and tumor microvascular endothelium in vivo and its inhibition by dextran sulfate: implications for vascular leak syndrome.

The maximum dose of interleukin 2 (IL-2) alone or with adoptively transferred lymphocytes is limited by the vascular leak syndrome, resulting from an increase in vascular permeability. Using intravital microscopy to quantify cell interaction in vivo and the Miles assay to assess changes in vascular permeability, we have shown that IL-2 increases both leukocyte-endothelial cell adhesion and vascular permeability in the cutaneous tissue of rabbits. Both of these processes can be reversed to a large extent using dextran sulfate (Mr approximately 500,000; 10 mg/kg body weight), a nonspecific blocker of leukocyte-endothelial adhesion. These results suggest that increased leukocyte (probably lymphocyte) adhesion to the postcapillary microvasculature contributes significantly to the IL-2 induced increase in permeability. Therefore, as more specific inhibitors of leukocyte-endothelial adhesion become available, improved strategies could be developed to control or prevent IL-2 toxicity.

Animals↗