Search PubMed⌕ Search

Biomedical subjects

I Sakuma

Publications and source records attributed to I Sakuma.

At least 109 records · Page 6Linked to original sources
PubMed1993

A seal-less centrifugal pump (Baylor Gyro Pump) for application to long-term circulatory support.

We are developing a new centrifugal pump, the Baylor Gyro Centrifugal Pump (Gyro Pump), which can function for more than 2 weeks. The concept of the Gyro Pump is that a one-piece rotor-impeller with embedded permanent magnets, driven directly by a brushless direct current motor stator placed outside, rotates like a "gyroscope," and the rotor-impeller is supported by one pivot bearing at the bottom in accordance with the gyroscopic principle. This concept enables us to eliminate a driving shaft and a seal between the driving shaft and the blood chamber, which results in extending the life of the centrifugal pump. The blood passes through the space between the motor stator and the rotor to the impeller portion. In this preliminary phase, two pivot bearings were applied to support the rotor-impeller at the top and the bottom inside the blood chamber. Both pivot bearings showed less blood trauma and less thrombogenicity in in vitro and in vivo studies. The Gyro Pump is a promising second-generation centrifugal pump for long-term circulatory support in the near future.

Animals↗
PubMed1993

Left and right pump output control in one-piece electromechanical total artificial heart.

Left master alternate (LMA) ejection control based on the left pump fill method was implemented for a one-piece electromechanical total artificial heart (TAH). The TAH consists of left and right pusher-plate-type blood pumps sandwiching a compact electromechanical actuator comprising a direct current (DC) brushless motor and a planetary roller screw. The motor rotation is controlled on the basis of the roller-screw position as detected by a Hall effect sensor and a commutation pulse counting method. Since the pusher-plate shaft and roller screw are decoupled during filling, both pumps fill passively with the right and left atrial pressure. To obtain response to the right atrial pressure change in the LMA mode, the left fill trigger level as detected by a Hall effect position sensor is adjusted to operate the pump at a higher rate and to drive the right pump at 85-90% of the full stroke level. The in vitro evaluation demonstrated that this method can respond to right atrial pressure changes provided that the right pump is operated at less than the full stroke level. When the preload is high and the right pump goes into full stroke operation, the left eject level can be decreased to run the pump at a higher rate and to transfer more blood from the right to the left. In the in vivo evaluation, which lasted 1 week in a 95 kg calf, the left and right atrial pressures were kept within physiological ranges.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Development of an all-in-one percutaneous cardiopulmonary support system.

This paper deals with development of an all-in-one percutaneous cardiopulmonary support (PCPS) system. In recent years, PCPS has been used for the treatment of acute myocardial infarction. A prototype of a compact all-in-one PCPS system was developed. The system contains a centrifugal pump and an extra-capillary flow-type membrane lung in one body. The system has a priming volume of 250 ml, which allows for PCPS with no additional blood. The in vitro tests and an ex vivo test were conducted. The system produces 1.6-5 L/min of flow in the experiments. The O2 transfer rate was 310 ml/min, and the CO2 transfer rate was 300 ml/min at a blood flow rate of 5 L/min. This device is compact, requires less priming volume than a standard system, and is easy-to-handle in the experiments. The system is considered applicable to percutaneous cardiopulmonary support.

Animals↗
PubMed1993

Baylor Gyro Pump: a completely seal-less centrifugal pump aiming for long-term circulatory support.

A seal-less centrifugal pump aiming for long-term circulatory support has been developed. In this model, shaft seals that cause thrombus formation and blood leakage were eliminated. A brushless direct current motor was incorporated as a driving unit, and pivot bearings were used to support the impeller. With reference to its motor-driven system, this pump was named the M-Gyro Pump. The first model (M1) yielded an index of hemolysis of 0.005 g/100 L using bovine blood and demonstrated satisfactory performance as a right heart assist for 2 days (4 L/min, 60 mm Hg, 1,800 rpm). The second model (M2) has been developed for left heart assist by employing a stronger motor. The pump capacity was improved to 6 L/min against 240 mm Hg at 1,800 rpm, but significant heat generation was observed. By optimization of motor efficiency, the M2 model can be improved to meet the requirements of a pump for left heart assist.

Animals↗
PubMed1993

Close correlation between cytoplasmic Ca++ levels and release of an endothelium-derived relaxing factor from cultured endothelial cells.

We studied whether there is a quantitative relationship between free cytosolic Ca++ levels and the release of an endothelium-derived relaxing factor (EDRF) from cultured fetal bovine aortic endothelial cells (EC). EC pretreated with indomethacin were stimulated by the agonists adenosine triphosphate (ATP), bradykinin (BKN), acetylcholine (ACh) and calcium ionophore (A23187) in various concentrations (10(-8)-10(-5) M), and the amount of EDRF released was determined on the basis of endothelium-free rabbit aortic ring relaxation and cultured smooth muscle cell cGMP content. Changes in intracellular Ca++ concentration ([Ca++]i) in response to the same stimuli were determined by photometric fluorescence microscopy using the fluorescent calcium indicator Fura-2. EC stimulation by ATP and A23187 induced dose-dependent increases in both [Ca++]i and the amount of EDRF released. BKN increased both [Ca++]i and EDRF release upon initial exposure (10(-8)M), but there were no further changes at higher concentrations. ACh induced no significant changes in either [Ca++]i or EDRF release. There was a close quantitative correlation between agonist-induced changes in [Ca++]i and the amount of EDRF released (relaxation response in aortic rings and cGMP levels.) (p < 0.001) Removal of extracellular Ca++ eliminated continuous elevation in both [Ca++]i and the amount of EDRF induced by ATP (10(-5)M), BKN (10(-8)M) and A23187 (10(-6)M). These findings suggest that intracellular Ca++ levels are directly linked to the amount of EDRF released, and that extracellular Ca++ is essential for EDRF release because its influx is involved in the continuous elevation of [Ca++]i.

Acetylcholine↗
PubMed1993

[Effect of enalapril on left ventricular hypertrophy and left ventricular function in patients with hypertension].

The aim of this study was to study the effect of enalapril (E) on left ventricular (LV) mass, LV function and blood renin-angiotensin (RA) in patients with hypertension. Sixteen hypertensives were included in this study (WHO I 8, WHO II 8, 49.5 +/- 10.5 yrs). They were examined for blood pressure and heart rate. Chest X-ray film, echocardiography (echo), X-ray computed tomography (CT) and RA before and after about 6 months of E administration were studied. The LV mass was calculated by CT. The LV function was measured by echo. RAS was unchanged during this study. LV mass was significantly reduced after E (121.4 +/- 25.6 vs 104.6 +/- 13.7 g/cm2). The LV systolic function was unchanged after E, but LV diastolic function improved. It was shown that the long-term administration of E improves LV hypertrophy and LV diastolic function without any change of RAS.

Adult↗
PubMed1993

[Effects of intravenous injection of ioversol, a nonionic contrast medium, on circulating blood volume: comparison among different combinations of its dose and volume injected].

Effects on circulating blood volume (CBV) of the intravenous injection of a nonionic contrast medium, ioversol, with various doses were assessed in order to find a way of injection with less effects on systemic circulation. Ioversol was injected as a bolus to 20 mongrel dogs at doses of A: 3.75 ml/kg (n = 8) or B: 2 ml/kg (n = 6) of a solution containing 320 mg iodine per ml, or C: 2 ml/kg (n = 6) of a 240 mgI/ml solution. Colloid oncotic pressure (COP) of the bloods drawn before and 1, 2, 3, 5 min after the injection of ioversol was measured by a needle type osmometer, and changes in CBV were calculated using the COP values. Upon injection of ioversol CBV increased rapidly and then gradually returned to the preinjection levels. The change in CBV induced by ioversol was significantly less than those reportedly induced by an ionic contrant medium, iothalamate, and a nonionic medium, iopamidol, and comparable to that by another nonionic medium, iohexol. The degree of increase in CBV and the blood concentration of ioversol were related to the amount, but not the volume, of ioversol injected. Thus, ioversol proved to be one of the low osmotic nonionic contrast media with less effects on CBV. Furthermore, it is suggested that the amount, rather than volume, of contrast medium should be taken into consideration when the angiography of the patients with reduced cardiac function, children or aged patients is performed in whom the contrast medium-induced CBV expansion needs to be as less as possible.

Animals↗
PubMed1993

Flow-induced calcium transients and release of endothelium-derived relaxing factor in cultured vascular endothelial cells.

Cytoplasmic Ca2+ response to flow and its relation to the release of endothelium-derived relaxing factor (EDRF) by endothelial cells were studied in vitro. Intracellular Ca2+ concentration ([Ca2+]i) and EDRF were measured using Fura-2 and photometric fluorescence microscopy, and a bioassay method using a rabbit aortic ring, respectively. Cultured endothelial cells were exposed to flow in Hanks' balanced salt solution containing various concentrations of ATP in a specially designed apparatus. At ATP levels over 100 nM, the application of flow to cells led to an apparent increase in [Ca2+]i and when flow stopped [Ca2+]i returned to the resting level. When the flow rate was increased stepwise, [Ca2+]i increased flow-rate dependently at around 500 nM ATP. At a constant flow rate, endothelial cells were then exposed to the perfusate, the ATP concentration of which was increased stepwise, and the simultaneous changes in [Ca2+]i and release of EDRF were measured. Both [Ca2+]i and EDRF increased as ATP concentrations increased, and there was a proportional relationship between the two. The range of the ATP-induced increase in [Ca2+]i was similar to that of the flow-rate dependent changes observed at 500 nM ATP. These results suggest that vascular endothelial cells have a mechanism by which changes in flow rate or shear stress are recognized at an appropriate concentration of extracellular ATP and the information is converted into changes in [Ca2+]i. Moreover, the flow-induced changes in [Ca2+]i may be involved in the regulation of EDRF release by endothelial cells.

Adenosine Triphosphate↗
PubMed1992

Hepatic venous hemoglobin oxygen saturation predicts liver dysfunction after hepatectomy.

A fiberoptic flow-directed catheter inserted into the hepatic vein continuously measures hepatic venous oxygen hemoglobin saturation (ShvO2). This study determined whether intraoperatively measured ShvO2 could predict postoperative serum activities of aminotransferases and patient outcome in 83 patients undergoing hepatectomy. The duration of intraoperative ShvO2 less than or equal to 10, 20, 30, 40, and 50% was calculated in each case. Significant increases in postoperative serum aminotransferases were associated with more than 1, 11, 31, 51, and 181 min of duration of ShvO2 less than or equal to 10, 20, 30, 40, and 50%, respectively. The incidence of postoperative liver failure significantly increased when the duration of ShvO2 less than or equal to 20, 30, and 40% exceeded 11, 31, and 51 min, respectively. The mortality from liver failure was significantly higher when the duration of ShvO2 less than or equal to 30 and 40% exceeded 31 and 51 min, respectively. Therefore, intraoperative monitoring of ShvO2 may predict not only the increase in postoperative serum aminotransferases but also patient outcome in terms of postoperative liver failure after hepatectomy.

Adult↗
PubMed1992

Development of totally implantable electromechanical artificial heart systems: Baylor ventricular assist system.

An implantable electromechanical ventricular assist system (VAS) intended for permanent use has been developed. It consists of a conically shaped pumping chamber, a polyolefin (Hexsyn) rubber diaphragm attached to a conically shaped pusher-plate, and a compact roller-screw actuator. Design stroke volume is 63 ml. The device weighs 620 g, and has a total volume of 348 ml. The pump can provide 8 L/min flow against 120 mm Hg afterload with a preload of 10 mm Hg. The inner surfaces are biolized by dry gelatin coating, with inflow and outflow ports accommodating tissue valves. Three subacute in vivo validation studies have been conducted in calves up to two weeks. The entire system functioned satisfactorily in both the fill/empty and the fixed-rate modes. There was no thromboembolic complication without anticoagulation. The pump showed reasonable anatomical fit inside the left thorax. This VAS is compact, efficient, quiet, and easy to control.

Animals↗
PubMed1992

A compact centrifugal pump for cardiopulmonary bypass.

A majority of the cardiopulmonary bypass (CPB) systems still utilize bulky roller pumps. A direct-drive small centrifugal pump intended for second-generation CPB pump has been developed. The pump has a 50 mm diameter impeller and provides a 6 L/min flow at 3,000 rpm against 300 mm Hg. A flexible drive shaft allows us to separate the pump head from the console resulting in easier manipulation. An in vitro study showed that the pump generated less hemolysis (index of hemolysis = 0.0011, comparable to the value for Bio-medicus BP-80). To improve blood flow around the shaft-seal region and to reduce thrombus formation around the shaft, six holes were drilled through the impeller. In biventricular bypass experiments using calves, our pump demonstrated excellent antithrombogenicity and durability for 48 h. And the compact and atraumatic centrifugal pump system showed excellent performance and easy manipulation under actual CPB conditions in animal.

Animals↗
PubMed1992

Development of an atraumatic small centrifugal pump for second-generation cardiopulmonary bypass.

A small and light direct-drive centrifugal pump has been developed for cardiopulmonary bypass. In the development process, blood compatibility studies including a hemolysis study, an in vitro fluid dynamic performance study, and in vivo durability and feasibility studies were performed. The centrifugal pump with a 50 mm diameter impeller resulted in almost the same index of hemolysis value as did a Bio-Medicus centrifugal pump. Heat dissipation from the motor was prevented by using a flexible drive cable. Forty-eight-hour sealing durability around the driving axis was accomplished by using a fluoro-rubber V-ring that connected to the hard chrome-plated stainless steel. In vitro and in vivo performances of the pump were satisfactory. Thrombus formation behind the impeller was prevented by using a holed impeller that generated blood flow from the back to the surface of the impeller. Elimination of air during priming procedures was also easier with this modification. This centrifugal pump has one-quarter of the priming volume, size, and weight of magnetically coupled centrifugal pump systems.

Animals↗
PubMed1992

New nonradioactive microspheres and more sensitive X-ray fluorescence to measure regional blood flow.

We developed new nonradioactive microspheres and used more sensitive X-ray fluorescence spectrometers than used previously to measure regional blood flow in the heart and other organs. We demonstrated the chemical stability of eight kinds of heavy element-loaded microspheres and validated their use for regional blood flow measurement by comparing duplicate flows measured with radioactive and/or nonradioactive microspheres in both acute and chronic dog experiments. The wavelength-dispersive spectrometer (Philips PW 1480) has a higher sensitivity than the previously described X-ray fluorescent system and reduced the number of microspheres required for accurate measurement. The fine energy resolution of this system makes it possible to increase the numbers of different kinds of microspheres to be quantitated, but at present only eight kinds are available. We also used a synchrotron radiation-excited energy dispersive spectrometer. The monochromatic synchrotron radiation allowed us to obtain much higher signal-to-background ratios of X-ray fluorescence spectra than with the wavelength-dispersive system (50 dB more for Zr-loaded microspheres) and will enable analysis of fluorescent activity in smaller regions (< 20 mg) than the radioactive method does.

Animals↗
PubMed1992

NG-methyl-L-arginine, an inhibitor of L-arginine-derived nitric oxide synthesis, stimulates renal sympathetic nerve activity in vivo. A role for nitric oxide in the central regulation of sympathetic tone?

Continuous production of endothelium-derived nitric oxide (NO) in peripheral vessels has been shown to modulate vascular resistance and blood pressure. NO is also formed in the brain upon activation of glutamate receptors, which are thought to mediate central autonomic reflexes. In the present study we assessed whether NO plays a role in central autonomic regulation. For this, we have investigated the effects of NG-methyl-L-arginine (NMA), a selective inhibitor of NO synthesis from L-arginine, on sympathetic renal nerve activity (RNA), blood pressure, and heart rate in the anesthetized rat. NMA elicited a dose-dependent sustained increase in blood pressure (approximately 20 and 30 mm Hg, 5 minutes after 10 and 50 mumol/kg i.v., respectively). Heart rate and RNA decreased transiently (15 beats per minute and 40%, respectively); RNA subsequently increased (100%) while blood pressure remained elevated. Baroreceptor deafferentation markedly altered these responses to NMA; the transient decreases in heart rate and RNA were abolished, whereas the increases in RNA and blood pressure were significantly potentiated. After spinal C-1-C-2 transection, there was no increase in RNA, and blood pressure increased to a smaller extent. L-Arginine blocked the NMA-induced increases in blood pressure and RNA. Thus, in addition to modulating vascular resistance by a peripheral action, NO may also play a role in the central regulation of sympathetic tone.

Animals↗
PubMed1992

Potential clinical applications of the oxygen carrying solutions.

Two major areas of research of the oxygen carrying solutions are 1) utilization of hemoglobin and 2) perfluorochemicals. Even though they are not perfect red blood cell substitutes, the "oxygen carrying solutions" have many potential clinical applications because they will reach tissues more easily than normal human red cells and can deliver oxygen directly to tissues. In this paper, important examples of such usages are suggested. Additional clinical and non-clinical applications of the oxygen carrying solutions may be added in the near future.

Artificial Organs↗
PubMed1992

A central nervous system action of nitric oxide in blood pressure regulation.

We had reported that the systemic administration of N omega-methyl-L-arginine (L-NMA), a specific inhibitor of nitric oxide (NO) synthesis from L-arginine (ARG), raises arterial blood pressure (BP) while paradoxically enhancing central sympathetic outflow. Cervical spinal cord transection abolishes the increase in sympathetic outflow and attenuates the pressor effect of L-NMA. Thus, in addition to lowering BP by direct vasorelaxation, NO may also act in the central nervous system to reduce vascular sympathetic tone. To test this hypothesis we have injected L-NMA directly into the central nervous system in anesthetized rats. Intracisternally (i.c.), L-NMA elicited a small pressor response accompanied by a marked increase in sympathetic renal nerve activity (RNA). In contrast, the inactive stereoisomer N omega-methyl-D-arginine had neither pressor nor neural effects. The increases in RNA and BP elicited by i.c. L-NMA were abolished by spinal cord transection at C1 to C2 and by the i.v. administration of ARG. When administered i.c., ARG also abolished the increase in RNA elicited by i.v. L-NMA and significantly attenuated the pressor response. Thus, our findings indicate that L-NMA acts centrally by an ARG-reversible mechanism in the anesthetized rat to stimulate sympathetic nerve activity. Inasmuch as centrally synthesized NO has been postulated to play a second messenger and/or neurotransmitter role, our findings suggest that one such function would be the central regulation of sympathetic outflow and hence, BP.

Animals↗
PubMed1992

[A family of Marchesani syndrome with mitral valve prolapse and anuloaortic ectasia].

Marchesani syndrome consists of short statue, small spherical lens, glaucoma and brachydactyly, which are manifestations of hyperplastic connective tissue disease in systemic organs of mesodermal origin (Marchesani 1939). Among nearly 200 cases of Marchesani syndrome reported in the ophthalmology field, none has shown cardiac manifestations which typically characterize Marfan syndrome caused by hypoplastic connective tissue disorders. We experienced 2 cases which met the diagnosis of Marchesani syndrome and yet showed annuloaortic ectasia and mitral valve prolapse. A 30-year-old man and a 26-year-old woman who are siblings suffered from manifested brachydactyly, spherophakia, glaucoma and cardiac involvements. Their parents are in consanguinity. These unprecedented cases with mixed manifestations provide the evidence of possible gene-crossing between these 2 dystrophic mesodermal disorders.

Adult↗