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Biomedical subjects

Y Niimi

Publications and source records attributed to Y Niimi.

At least 73 records · Page 4Linked to original sources
PubMed1999

[Cerebral ischemia in patients with orthostatic syncope--the significance of orthostatic hypotension and large vessel disease in the cervical and intracranial region].

We performed 90 degrees head-up tilting test for 10 minutes in 100 patients (66 men and 34 women) aged 50 years or more suffering from transient orthostatic syncope and measured their systolic blood pressure. Orthostatic hypotension (OH) was found in 51 patients, predominantly in men (38 cases). OH was complicated by large vessel disease (LV) as shown by MR angiography or carotid artery ultrasonography in 19 cases (37.3%). Progressive cerebral ischemia was found more frequently in patients with both OH and LV than in those with OH alone. Within the patients with OH alone, the drop in orthostatic blood pressure was greater in cases where progressive cerebral ischemia was present. In patients with both OH and LV, the minimum orthostatic systolic blood pressure was lower in those with progressive cerebral ischemia. These facts show that the marked drop in orthostatic blood pressure may be related to cerebral ischemic lesions and that the combination of OH and LV may develop cerebral ischemia in older patients with transient orthostatic syncope.

Aged↗
PubMed1999

Comparison [correction of Compariso] of sympathetic nerve response to head-up tilt in summer [correction of sumer] and winter.

The seasonal adaptation of humans is accomplished metabolically by increased or decreased body heat production and by cardiovascular adjustments which result in decreased or increased heat loss from the body. The sympathetic nervous system plays an important role in thermoregulation and in blood pressure regulation. Muscle sympathetic nerve activity (MSNA) has an essential role in blood pressure regulation in humans. However, it has not yet been clarified how the MSNA changes during seasonal adaptation or how these changes may contribute to long-term thermoregulation in relation to blood pressure regulation. The purpose of the present study was to elucidate if seasonal variations exist in responses of the sympathetic nervous system in humans for gravity-dependent blood pressure regulation.

Acclimatization↗
PubMed1999

Effects of aging on leg vein filling and venous compliance during low levels of lower body negative pressure in humans.

To evaluate the fluid shift and leg venous compliance during orthostatic stress with advancing age, 12 aged and 5 young healthy males were subjected to graded lower body negative pressures (LBNP) of -5, -10, and -15 mmHg. Cardiovascular variables were monitored continuously, and leg venous compliance was determined by venous occlusion plethysmography. Neither heart rate nor mean arterial pressure changed significantly in any subject during LBNP. A progressive decrease in the thoracic fluid volume index and a gradual increase in the leg fluid volume index, indicating a fluid shift towards the lower body were observed significantly in the young group (p<0.05), while these changes were not significant in the aged group. A linear reduction in peripheral venous pressure could be seen during graded LBNP in all subjects, but the reduction rate was smaller in the aged group. Baseline leg venous compliance was reduced in the elderly (p<0.05). During LBNP, venous compliance decreased in all subjects, but the decrease was significantly smaller in the aged group (p<0.05). It is suggested that the smaller fluid shift and smaller decreased leg venous compliance in aged people during gravitational stress were mainly due to the vascular and ventricular stiffness induced by an age-related reduction in visco-elasticity of the peripheral venous and ventricular walls.

Adult↗
PubMed1999

Endovascular treatment of spinal vascular malformations.

Endovascular treatment is considered as the first choice of treatment for most cases of spinal vascular malformations. Clinical presentation, natural history, and origin of symptoms are briefly described on spinal cord arteriovenous malformations, spinal dural arteriovenous fistulas, epidural fistulas, and paraspinal fistulas. Pretherapeutic evaluation, materials and technique for embolization, post-therapeutic management, results, and follow-up are discussed for each disease.

Arteriovenous Malformations↗
PubMed1998

Tissue distribution of pathological lesions and Hu antigen expression in paraneoplastic sensory neuronopathy.

We investigated the distribution of lesions and Hu antigen expression in two autopsied cases of anti-Hu antibody-positive paraneoplastic sensory neuronopathy (carcinomatous subacute sensory neuropathy). Pathological changes in both patients were limited to the primary sensory neurons, some of the sympathetic ganglia and hippocampal regions. The lesions showed a multifocal distribution that differed among the spinal segmental levels and in the individual dorsal root ganglia as well as in the nerve fascicles. Western blot analysis of the patients' serum revealed that Hu antigens were extensively and widely expressed throughout the central nervous system, sensory and sympathetic ganglia and cancer cells, but not in the non-neural visceral tissues. Reverse transcriptase-polymerase chain reaction also showed that the Hu D, Hu C, Hel-N1 and Hel-N2 mRNAs were extensively and widely expressed through the neural tissues and cancer cells, but not in the visceral tissues. Thus, the distribution of antigen expression was very different from that of the lesions. Taken together with the distribution of lesions and Hu antigen expression, it is suggested that factors other than anti-Hu antibodies are also involved in the pathogenesis of this neuronopathy.

Adenocarcinoma↗
PubMed1998

Immunolocalization of matrix metalloproteinases in rabbit carotid arteries after balloon denudation.

Extracellular matrix-degrading enzymes may play a key role in vascular remodeling after arterial wall injury. We investigated the immunolocalization of matrix metalloproteinases (MMPs) in rabbit carotid arteries after balloon denudation. Positive immunostaining for MMP-1, -2, -3, and -9 appeared through the neointima 1 week after balloon denudation. The localization of immunopositive smooth muscle cells (SMCs) for MMP- 1, -3, and -9, particularly for MMP-9, was almost similar to that of replicative SMCs and became confined to the luminal surface layer of the neointima at later time periods. However, MMP-2-positive SMCs appeared also in the basal layer of the neointima at 2 weeks, increased at 4 weeks, and then totally occupied the neointima at 6 weeks. The MMP-2-positive SMCs in the basal layer of the neointima at 4 and 6 weeks were negative for proliferation-associated antigens and were surrounded by extracellular matrix proteins. Our results suggest that all MMPs act in coordination to promote replication and migration of SMCs in the earlier phases of neointimal formation and that MMP-2 independently contributes to the later stages by facilitating the migration but not replication of SMCs from the media to the intima.

Animals↗
PubMed1998

The safety system for the rotary blood pump, combination of the valve and LVAD pulsatile mode: in vitro test.

The significant amount of regurgitation produced by a stopped rotary blood pump is one of the major considerations for its use as an implantable left ventricular assist device (LVAD), especially if the pump accidentally stops. The installation of a valve is an option for the solution of this potential problem. However, this option may lead to thrombogenic problems, particularly if the valve motion is restricted. This in vitro study analyzes the valve performance and assesses the credibility of a rotary blood pump valve. A pulsatile pump was used as the natural heart and a centrifugal pump as the LVAD. The valve was positioned into the LVAD outflow. In the low speed range (<1,000 rpm in this test condition), normal valve motion was maintained. Also, the valve model provided a higher mean bypass flow than the model without a valve due to reduced regurgitation. However, the valve motion was drastically restricted when in the high speed range (>1,600 rpm in this condition). The pulsatile mode was applied to the LVAD by periodically changing the impeller speed (40 bpm); subsequently, a constant valve motion could be provided. A possibility exists that this pulsatile mode application could eliminate thrombosis formation around the valve. A conclusion was made that the combination of a valve and an LVAD in a pulsatile mode is considered to be a unique safety system for a rotary blood pump.

Blood Pressure↗
PubMed1998

Evaluation of platelet adhesion and activation on materials for an implantable centrifugal blood pump.

A totally implantable centrifugal artificial heart has been developed in which a pivot bearing supported centrifugal pump is used as a blood pump. The following have been adopted as blood contacting materials in our pump: titanium alloy (Ti-6A1-4V) for the housing and impeller, alumina ceramic (Al2O3) for the male pivots, and ultrahigh molecular weight polyethylene (PE) for the female pivots. Greater antithrombogenicity is required for an implantable blood pump. To examine the thrombogenicity of these materials, we evaluated in vitro platelet adhesion and activation, which may play key roles in thrombogenesis on foreign surfaces. Ti-6A1-4V, Al2O3, and PE were compared with polycarbonate (PC), silicone carbide (SiC), and pure titanium (pTi). Platelet adhesion was assessed using monoclonal antibody (CD61) directed against glycoprotein IIIa. Platelet activation was evaluated by measuring P-selectin (GMP-140) released from irreversibly activated platelets. Each material with a surface area of 16.6 cm2 was incubated with 2.5 ml of plasma or 2.5 ml of heparinized fresh whole blood for 3 h at 37 degrees C. The optical density (OD) at a wavelength of 450 nm for CD61 was 0.93+/-0.35 in PC, 0.34+/-0.13 in PE, 0.27+/-0.13 in pTi, 0.26+/-0.01 in Al2O3, 0.21+/-0.04 in SiC, and 0.12+/-0.12 in Ti-6A1-4V. The GMP-140 levels of the tested materials were not significantly different from the control value (45.9+/-7.2 ng/ml). These results indicate that Al2O3, PE, and Ti-6A1-4V, which are incorporated into our implantable centrifugal pump, have satisfactory antithrombogenic properties in terms of platelet adhesion. However, platelet activation by any material was not observed under the static condition in this study.

Alloys↗
PubMed1997

Effect of heat stress on muscle sympathetic nerve activity in humans.

To elucidate the effect of heat stress on the sympathetic nervous system, we evaluated changes in muscle sympathetic nerve activity (MSNA), plasma arginine vasopressin (AVP), tympanic temperature, skin blood flow, cardiac output, mean blood pressure, and heart rate in 9 subjects in response to acute heat stress induced by raising the ambient temperature from 29 to 34 degrees C and then to 40 degrees C. With the heat exposure, MSNA was significantly increased with a significant increase in tympanic temperature. Skin blood flow and heart rate were also significantly increased, while mean blood pressure tended to decline and cardiac output tended to increase. The combination of the increased MSNA and skin blood flow may have caused the redistribution of the circulatory blood volume from the muscles to the skin, facilitating convection heat loss. The increases in MSNA counteracted the lowered blood pressure during heat exposure. Thus, the increased MSNA may play an important role both in thermoregulation and in the maintenance of blood pressure against heat stress.

Adult↗
PubMed1997

Smooth muscle cell proliferation, elastin formation, and tropoelastin transcripts during the development of intimal thickening in rabbit carotid arteries after endothelial denudation.

Extracellular matrix formation and smooth muscle cell proliferation are two major factors contributing to the development of intimal thickening after arterial injury. We investigated the elastin formation, tropoelastin transcripts, and proliferation of smooth muscle cells during the development of intimal thickening in rabbit carotid arteries after balloon endothelial denudation. Tropoelastin transcripts, identified by in situ hybridization using a digoxigenin-labeled probe, and elastin staining in the thickened intima were minimal 1 week after endothelial denudation when smooth muscle cell proliferation appeared throughout the thickened intima. A strong signal for tropoelastin transcripts was seen in the basal layer of the thickened intima 2 weeks after endothelial denudation, and then in the surface layer of the thickened intima 4 weeks after endothelial denudation. Immunohistochemistry for proliferating cell nuclear antigen and Ki-67, both markers for proliferating cell nuclei, showed that tropoelastin transcripts and elastin formation increased when smooth muscle cells enter quiescence after the end of the proliferative phase in the intima. Our findings strongly suggest that elastin synthesis and smooth muscle cell proliferation are tightly regulated during the repair of arterial wall injury.

Animals↗
PubMed1997

Expression of p53 protein and p53 gene transcripts in rabbit carotid arteries after balloon denudation.

Smooth muscle cell (SMC) proliferation may be positively or negatively regulated by various factors after arterial wall injury. We investigated the hypothesis that the p53 protein may play a role in regulating SMC proliferation. We examined p53 protein expression and p53 gene transcript distribution in rabbit carotid arteries over a period of 6 weeks after balloon denudation in relation to SMC proliferation. The number of p53-positive SMCs in the neointima reached a maximum 2 weeks after balloon denudation when proliferating SMCs, decreased and were confined to the luminal surface of the intima. The p53-positive SMCs in the neointima almost paralleled the distribution of proliferating cell nuclear antigen (PCNA)-positive SMCs but not that of Ki-67-positive cells. Double immunofluorescence showed the simultaneous nuclear localization of both p53 protein and PCNA in intimal SMCs. Strong signals for p53 gene transcripts, identified by in situ hybridization, were observed in SMCs showing positive immunostaining for p53 protein. Our results indicate that p53 protein and p53 gene transcript levels increase, are closely linked to the proliferation of SMCs in the thickened intima, and play a key role in the regulation of cell proliferation during the repair process after arterial wall injury.

Animals↗
PubMed1997

Echocardiographic evaluation of global left ventricular function during high thoracic epidural anesthesia.

OBJECTIVES: To assess the effects of high thoracic epidural anesthesia on left ventricular (LV) diastolic filling and systolic function in patients without heart disease. DESIGN: Prospective study. SETTING: University hospital. PARTICIPANTS: 24 ASA physical status I and II patients scheduled for elective noncardiac surgery. INTERVENTIONS: Patients received high thoracic (HTE; n = 12) or low thoracic (LTE; n = 12) epidural anesthesia. MEASUREMENT AND MAIN RESULTS: Left ventricular diastolic filling was noninvasively determined by precordial echocardiography using a pulsed Doppler technique and with a newly developed acoustic quantification (AQ) method that automatically detects endocardial borders and measures cavity area. All measurements were performed in awake premedicated patients. In the HTE group, the extent of sensory blockade of T1-T5, at the least, was induced with 2% lidocaine 5 ml. During HTE, systolic blood pressure (119 +/- 16 vs. 108 +/- 14 mmHg, p < 0.01), heart rate (73 +/- 9.8 vs. 63 +/- 6.8 beats/min, p < 0.01), cardiac output (CO; 4.5 +/- 1.1 vs. 3.8 +/- 1.2 L/min, p < 0.05), and fractional area change (50 +/- 11 vs. 37 +/- 11%, p < 0.01) decreased significantly, whereas end diastolic area (9.4 +/- 1.4 vs. 10.3 +/- 1.1 cm2, p < 0.01) and end systolic area (4.8 +/- 1.3 vs. 6.0 +/- 1.1 cm2, p < 0.05) showed a significant increase. As a result, stroke volume was kept constant (63 +/- 14 vs. 60 +/- 19 ml). Pulsed Doppler derived indices such as peak velocity during the early filling (E) and the atrial contraction (A) phases, peak early to atrial velocity ratio (E/A), and acceleration time remained unchanged. AQ derived peak dA/dt during the early diastolic (D1) and the atrial contraction phases (D2) and D1/D2 also remained unchanged. In contrast, in the LTE group, no significant differences were noted in all systolic and diastolic indices obtained by pulsed Doppler and AQ method. CONCLUSIONS: High thoracic epidural anesthesia causes a decrease in CO without changing LV ejection and diastolic filling performance in healthy subjects.

Adult↗
PubMed1997

Parenchymal damage in the territory of the anterior choroidal artery following supraophthalmic intracarotid administration of CDDP for treatment of malignant gliomas.

We treated ten patients with malignant glioma by intracarotid chemotherapy with cis-diamminedichloroplatinum (CDDP) and/or 3-(4-amino-2-methyl-5-pyrimidinyl)methyl-1-(2-chloroethyl)-3-nitrosourea (ACNU). Three of the patients who underwent supraophthalmic intracarotid infusion of CDDP developed a low-density area in the basal ganglia on CT scan or an enhancing lesion in the hypothalamic region on MRI, with or without neurologic symptoms. No patient had such complications with supraophthalmic infusions of ACNU, or with cervical intracarotid infusion of CDDP or selective infusion of CDDP via the anterior or middle cerebral arteries. Supraophthalmic intracarotid administration of CDDP may augment drug delivery to tumors and prevent visual complications, but is accompanied by considerable risk of parenchymal damage in the territory of the anterior choroidal artery. Possible mechanisms for such complications are discussed.

Adult↗
PubMed1997

Embolization of spinal dural arteriovenous fistulae: results and follow-up.

OBJECTIVE: To evaluate the efficacy of embolization for spinal dural arteriovenous fistulae (SDAVF). METHODS: We reviewed 49 cases of SDAVF treated by embolization. An acrylic material was used in all except two cases. Variable stiffness microcatheters were used in 38 cases. RESULTS: "Adequate" initial treatment was performed in 39 cases (80%). After the introduction of variable stiffness microcatheters, the initial success rate of embolization increased to 87% (33 of 38 cases). Eight patients underwent subsequent embolization for recurrence after "adequate" embolization. Causes of recurrence were collateralization in five cases, development of new fistulae in one, and unknown in two. Two additional patients developed subsequent aggravation of the symptoms, probably caused by progressive venous thrombosis, that responded to heparinization. Ten cases were initially "inadequately" embolized. Five of the 10 cases were treated before the introduction of variable stiffness microcatheters. Each of three of the remaining five cases had a common trunk from which the feeder and a spinal cord artery arose. CONCLUSION: Embolization with an acrylic material should be the first choice of treatment for SDAVF, unless a spinal cord artery shares the same pedicle as the feeder of SDAVF. Subsequent aggravation of the symptoms after embolization can occur by various mechanisms. Therefore, periodic and long-term follow-up examinations are important.

Aged↗
PubMed1997

Effects of ultrathin silicone coating of porous membrane on gas transfer and hemolytic performance.

To assess the effect of an ultrathin (0.2 microm) silicone-coated microporous membrane oxygenator on gas transfer and hemolytic performance, a silicone-coated capillary membrane oxygenator (Mera HP Excelung-prime, HPO-20H-C, Senko Medical Instrument Mfg. Co., Ltd., Tokyo, Japan) was compared with a noncoated polypropylene microporous membrane oxygenator of the same model and manufacturer using an in vitro test circuit. The 2 oxygenators showed little difference in the oxygen (O2) transfer rate over a wide range of blood flow rates (1 L/min to 8 L/min). The carbon dioxide (CO2) transfer rate was almost the same in both devices at low blood flow rates, but the silicone-coated oxygenator showed a decrease of more than 20% in the CO2 transfer rate at higher blood flow rates. This loss in performance could be partly attenuated by increasing the gas/blood flow ratio from 0.5 or 1.0 to 2.0. In the hemolysis study, the silicone-coated membrane oxygenator showed a smaller increase in plasma free hemoglobin than the noncoated oxygenator. The pressure drop across both oxygenators was the same. These results suggest that the ultrathin silicone-coated porous membrane oxygenator may be a useful tool for long-term extracorporeal lung support while maintaining a sufficient gas transfer rate and causing less blood component damage.

Adult↗
PubMed1997

Effects of pulsatile flow on gas transfer of membrane oxygenator: MENOX EL-4000 and Gyro C1-E3 pulsatile mode.

It is acknowledged that pulsatile flow enhances the gas exchange performance of membrane oxygenators. However, the data for currently developed oxygenators are limited. In this study, the effect of pulsatile flow was assessed utilizing the MENOX EL-4000 oxygenator. The in vitro test was performed following the Association for the Advancement of Medical Instrumentation (AAMI) standards. Pulsatile flow was produced by the Gyro C1-E3 centrifugal pump with periodical changing of the impeller speed. In Study 1, the following 3 groups were created and examined: nonpulsatile flow, pulsatile flow of 40 bpm, and pulsatile flow of 60 bpm. The blood flow rate was maintained at 3 L/min, and the V/Q ratio was 1. In Study 2, four groups were examined, nonpulsatile flow with V/Q = 1, nonpulsatile with V/Q = 2, pulsatile with V/Q = 1, and pulsatile with V/Q = 2. The blood flow rate was maintained at 4 L/min, and the pulse frequency was set at 40 bpm. In study 1, although O2 transfer was not enhanced, CO2 transfer was significantly improved (40-50%) by pulsatile flow, regardless of pulse frequency. Study 2 demonstrated that pulsatile flow resulted in improved CO2 transfer as did higher ventilation (V/Q = 2). Furthermore, even after applying higher ventilation, the pulsatile mode enhanced CO2 transfer more than the nonpulsatile mode. It was considered that the pulsatile mode induced an active secondary flow and enhanced mixing effects, and consequently CO2 transfer was improved. In conclusion, the pulsatile flow significantly enhanced the CO2 transfer of the MENOX oxygenator. It is indicated that applying the pulsatile mode is a unique and effective method to improve the gas exchange performance for a current membrane oxygenator.

Analysis of Variance↗