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Biomedical subjects

K Mizuguchi

Publications and source records attributed to K Mizuguchi.

At least 91 records · Page 5Linked to original sources
PubMed1994

Flow visualization in the Baylor total artificial heart.

To analyze the flow patterns of the left and right blood chambers of the total artificial heart (TAH), flow visualization studies were performed. Two setup levels were used for the flow visualization studies. For estimating the global flow patterns, the pumps were illuminated using incandescent light, and the patterns were recorded by either videotape or photography. To evaluate sectional flow patterns, a laser light was applied, and the pump could be scanned segmentally. The flow patterns were recorded by a high-speed camera. A signal was also used that synchronized the timing of the camera shutter to the pusher-plate movement signal. In the left pump chamber, major stagnations were observed in the middle area of the inflow site. To solve this problem, a modification was made that changed the inflow direction appropriately. After evaluation of the inflow port direction, a proper flow pattern was obtained, which was validated by a global flow visualization study. Furthermore, both pump chambers indicated excellent flow patterns as obtained by a segmental flow visualization study method utilizing a laser light. The Baylor TAH demonstrated excellent flow patterns in flow visualization studies, with antithrombogenicity expected. These flow visualization studies are very useful not only for validations of global flow patterns but also for validations of local areas of stagnation in various blood pumps.

Equipment Design↗
PubMed1994

Totally implantable total artificial heart and ventricular assist device with multipurpose miniature electromechanical energy system.

A multipurpose miniature electromechanical energy system has been developed to yield a compact, efficient, durable, and biocompatible total artificial heart (TAH) and ventricular assist device (VAD). Associated controller-driver electronics were recently miniaturized and converted into hybrid circuits. The hybrid controller consists of a microprocessor and controller, motor driver, Hall sensor, and commutation circuit hybrids. The sizing study demonstrated that all these components can be incorporated in the pumping unit of the TAH and VAD, particularly in the centerpiece of the TAH and the motor housing of the VAD. Both TAH and VAD pumping units will start when their power line is connected to either the internal power pack or the external battery unit. As a redundant driving and diagnostic port, an emergency port was newly added and will be placed in subcutaneous location. In case of system failure, the skin will be cut down, and an external motor drive or a pneumatic driver will be connected to this port to run the TAH. This will minimize the circulatory arrest time. Overall efficiency of the TAH without the transcutaneous energy transmission system was 14-18% to deliver pump outputs of 4-9 L/min against the right and left afterload pressures of 25 and 100 mm Hg. The internal power requirement ranged from 6 to 13 W. The rechargeable batteries such as NiCd or NiMH with 1 AH capacity can run the TAH for 30-45 min. The external power requirement, when TETS efficiency of 75% was assumed, ranged from 8 to 18 W. The accelerated endurance test in the 42 degrees C saline bath demonstrated stable performance over 4 months. Long-term endurance and chronic animal studies will continue toward a system with 5 years durability by the year 2000.

Animals↗
PubMed1994

Flow pattern analysis of the Baylor total artificial heart.

To obtain an optimal design of the left blood chamber of the total artificial heart (TAH), flow visualization studies were performed. Information on velocities in critical areas of the left chamber was gathered using sectional pulsed laser light. The flow patterns on the entire pumping duration were photographed frame by frame. The inflow port, the opposite of the inflow and outflow of the pump (bottom area), and the diaphragm/housing junction were the focal areas. The pump conditions, such as chamber pressure, preload and afterload pressure, pumping rate and roller screw, and displacement were recorded. Major stagnations and a low washout effect were observed in the bottom region. The closing of the inflow valve was irregular. In order to solve this problem, the inflow valve angle was changed 20 degrees. A comparison study showed a better valve closing characteristic, and no stagnation areas were observed with this new valve angle. Various velocity profiles confirmed the results. The valve closing characteristics is described in relationship to back flow.

Blood Flow Velocity↗
PubMed1994

Does hematocrit affect in vitro hemolysis test results? Preliminary study with Baylor/NASA prototype axial flow pump.

The effect of hematocrit (Ht) on in vitro hemolysis test results (i.e., index of hemolysis) was evaluated using a Baylor/NASA prototype axial flow pump. Red blood cell suspensions of six different Ht (5, 10, 15, 20, 30, 40%; n = 30) were prepared and used for this evaluation. The pump was operated for 60 min under 5 L/min flow conditions, and blood samples were taken every 10 min to measure plasma free hemoglobin levels. The normalized index of hemolysis (NIH) was calculated using the regression line slope between time and plasma free hemoglobin level, and relationships between NIH and Ht or hemoglobin (Hb) were checked. NIH and Ht had a statistically significant (p < 0.0001) correlation with a coefficient of fit of 0.976, and NIH and Hb had a statistically significant (p < 0.0001) correlation with a coefficient of fit of 0.976. To reduce the effect of Ht, NIH/Ht was proposed and compared with a modified index of hemolysis (MIH), which was normalized by the Hb level of blood. NIH/Ht and MIH had a poor correlation with Ht (coefficient of fit, 0.608) and Hb (coefficient of fit, 0.577), respectively. When blood that has a wide range of Ht or Hb values is used for in vitro hemolysis tests, NIH/Ht is suggested for use as an index of hemolysis to evaluate the hemolysis characteristics of rotary blood pumps because MIH has no dimension and it requires Hb values. In contrast, NIH/Ht has a dimension of g/100 L, which is quite understandable, and it does not require measurement of Hb levels of blood; it is therefore cost-effective.

Animals↗
PubMed1993

Ethyl all-cis-5,8,11,14,17-icosapentaenoate modifies the biochemical properties of rat very low-density lipoprotein.

The biochemical properties of serum very low-density lipoprotein (VLDL) were investigated in rats given highly purified all-cis-5,8,11,14,17-icosapentaenoate (EPA), an ethyl-ester derivative (EPA-E). The elution time (gel filtration) of VLDL from EPA-E-treated serum was increased significantly compared with that of the control. EPA-E-treated VLDL isolated by ultracentrifugation exhibited a marked decrease in triglyceride content with a relative increase in cholesterol. In treated VLDL, a significant increase in the ratio of apo E/apo C was observed. There was a remarkable increase in the content of EPA in all the fractions of phospholipids, cholesteryl esters and triglycerides after EPA-E treatment, resulting in n-3 polyunsaturated fatty acid-rich VLDL. EPA-E also reduced the incorporation of [14C]oleate into triglycerides in hepatic microsomes and the rate of hepatic triglyceride secretion. Moreover, lipoprotein lipase activity in heparin-injected plasma was increased in rats given EPA-E without there being an effect on hepatic triglyceride lipase activity. These findings indicate that EPA-E exerts an inhibitory effect on hepatic triglyceride synthesis/secretion and a stimulatory effect on triglyceride degradation, resulting in a reduction in particle size and an increase in the ratio of apo E/apo C. Triglyceride-poor and EPA-rich VLDL may rapidly be converted into the density of intermediate low-density lipoprotein and low-density lipoprotein and/or may be absorbed into the liver rapidly.

Animals↗
PubMed1993

Mechanism of the lipid-lowering effect of ethyl all-cis-5,8,11,14,17-icosapentaenoate.

The effect of highly purified ethyl all-cis-5,8,11,14,17-icosapentaenoate (EPA-E) on cholesterol metabolism in rats was examined to clarify the mechanism of its hypolipidemic action. Pretreatment with EPA-E reduced the increase in plasma radioactivity after oral administration of [14C]cholesterol. The conversion of [14C]3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) to [14C]mevalonic acid was significantly inhibited in liver microsomes obtained from rats treated with EPA-E. There was an increase in free cholesterol and a marked rise in the eicosapentaenoic acid (EPA) content of phospholipids in these microsomes. EPA-E restored the suppression of biliary secretion induced by feeding a casein-rich diet to bile duct-cannulated rats. Furthermore, when serum lipoprotein (d < 1.210) from rats given EPA-E was i.v. injected into normal rats, a more rapid elimination of cholesterol was observed as compared to that in rats injected with lipoprotein from EPA-E-untreated rats. This rapid clearance was found in the lipoprotein fractions of d < 1.006 and 1.006 < d < 1.063. These findings suggest that EPA-E has an inhibitory effect on intestinal cholesterol absorption and hepatic cholesterol biosynthesis, and an enhancing effect on hepatic biliary secretion. EPA-E would also seem to cause modification of serum lipoproteins, whereby their clearance from the serum is increased.

Administration, Oral↗
PubMed1993

Exercise coronary flow reserve of bilateral internal thoracic artery bypass grafts.

We attempted to quantify the exercise coronary flow reserve in 20 patients with bilateral internal thoracic artery grafts to the left coronary arteries (group I) who had complete revascularization. The coronary sinus blood flow was measured by the continuous thermodilution method both at rest and during exercise (50 W for 8 to 9 minutes) approximately 1 month after the operation. These results were compared with 30 patients treated with an internal thoracic artery and saphenous vein grafts to the left coronary arteries (group II) and 9 patients with saphenous vein grafts alone to the left coronary arteries (group III). There were no differences among the three groups in age, sex, number of vessels involved, heart rate, double products, left ventricular (LV) end-diastolic pressure, LV ejection fraction, LV end-diastolic volume, or LV mass at the time of study. None of the 59 patients in the study had abnormally enlarged LV end-diastolic volume or increased LV mass. The postoperative coronary sinus blood flow per 100 grams of LV mass at rest was similar among the three groups (73.0 +/- 28.4 mL/min per 100 g LV mass in group I, 73.4 +/- 31.1 mL/min per 100 g LV mass in group II, and 75.9 +/- 28.5 mL/min per 100 g LV mass in group III [not significant]) and significantly (p < 0.01) increased by exercise, although the differences between groups during exercise were not significant (158.9 +/- 45.9, 153.5 +/- 72.1, and 148.3 +/- 60.0 mL/min per 100 g LV mass, respectively [not significant]).(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Pressure↗
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

In vitro performance of the Baylor/NASA axial flow pump.

A cooperative effort between Baylor College of Medicine and NASA/Johnson Space Center is under way to develop an implantable axial flow left ventricular assist device (LVAD). The pump is intended as an assist device for either pulmonary or systemic circulatory support for more than 3 months' duration. Currently, in vitro studies are under way to reduce the hemolysis generated by the axial flow pump. A system utilizing a testing matrix has been developed to analyze the effects of different pump parameters on hemolysis. The following parameters are being investigated: impeller blade tip geometry, impeller/flow tube clearance, impeller/stator clearance, number of impeller blades, number of stator blades, and length of the impeller. To date, an index of hemolysis of 0.038 g/100 L has been achieved. The test matrix is not complete, and further improvements are expected.

Animals↗
PubMed1993

Development of the Baylor-Nikkiso centrifugal pump with a purging system for circulatory support.

The Baylor-Nikkiso centrifugal pump is a magnetically coupled system with a V-ring seal separating the pump and the actuator chamber. To prevent thrombus formation behind the impeller and to extend the life of the pump to 2 weeks of continuous operation, we incorporated a purging chamber behind the V-ring seal. An external pump connected to this purging chamber infused fluid at a constant rate to wash the shaft-seal area. To evaluate the effectiveness of the purging system, we have carried out biventricular bypass experiments using calves. The purging system was successful in reducing the level of thrombus formation after 2 weeks of operation. The results of these studies confirmed that the Baylor-Nikkiso centrifugal pump with this purging system is suitable for at least 2 weeks of continuous operation as a circulatory support system.

Animals↗
PubMed1993

A fluid dynamic analysis of a rotary blood pump for design improvement.

The proper design of a left ventricular assist device (LVAD) requires an understanding of the pump's fluid dynamic and biocompatible properties. A hydraulically efficient system minimizes the power required for pumping. Biocompatibility refers to the ability to pump blood with minimal hemolysis and thrombus formation. Typically, shear stresses below a threshold level will not damage blood significantly. A fluid dynamic analysis of a prototype centrifugal pump designed for use as an LVAD was performed to establish flow characteristics. A flow visualization technique using Amberlite particles suspended in a glycerin/water blood analogue was used. The system was illuminated with a 1 mm planar beam strobed helium-neon laser, and the results were recorded photographically. An analysis of photographs revealed laminar and turbulent flows with vortices within an illuminated plane in both the inlet and outlet port areas. From these data, velocity and shear stress profiles were generated that showed possible areas of improvement. It was concluded that the outlet port design could be improved by changing its angle and the continuity of its expansion. The inlet port could also be improved by smoothing the transition area between the inlet tube and the pump body to allow for gradual acceleration of the entering fluid.

Blood Flow Velocity↗
PubMed1993

Two-layer membrane model for iontophoretic drug transport through excised rat skin.

Iontophoretic and passive transport of an ionized drug (sulfisoxazole) across excised rat skin was studied using a two-chamber cell with four electrodes under successive experimental conditions: without electrical current (stage-I) and with electrical current (stage-II). Two iontophoretic/diffusion models, i.e. a one-layer membrane model and a two-layer membrane model, in which a difference in the electrical potential gradient was taken into account between the stratum corneum and epidermis/dermis layer, were constructed to describe the non-steady-state drug permeation process during ionotrophoresis. The observed iontophoretic lag-time was two times greater than the calculated value based on the one-layer membrane model. According to the two-layer membrane model, the calculated ionotophoretic lag-time agreed with the observed value. It was revealed by model adaptation to the observed data that the stratum corneum fraction of the electro-chemical potential difference across the whole skin caused by the iontophoresis was around 90%. This result was consistent with the observation that the direct current resistance of whole skin was seven times greater than that of stripped skin.

Animals↗
PubMed1993

Hypothermic ventricular fibrillation with pulsatile coronary perfusion during repair of ventricular septal perforation following infarction.

Emergency or urgent surgery for ventricular septal perforation (VSP) following acute myocardial infarction still carries a high operative mortality rate. Hypothermic fibrillatory arrest studies without aortic cross-clamping and using continuous pulsatile coronary flow were performed to improve this result. Of 19 patients suffering from VSP, 12 underwent hypothermic (mean(s.d.) blood temperature 23.5(1.7) degrees C) ventricular fibrillation with concomitant pulsatile systemic and continuous coronary perfusion (group 1), and seven underwent deep hypothermic cardioplegic ischaemic arrest with systemic pulsatile perfusion alone (group 2). The two groups were comparable in terms of age, sex, location of infarction, number of coronary arteries involved, interval between infarction and surgery, and preoperative maximum enzyme levels and haemodynamics. Pulsatile flow with a mean(s.d.) pulse pressure of 48(13) mmHg was produced by an intra-aortic balloon pumping device in both groups. Operative exposure in the two groups was comparable. In group 1, mean(s.d.) cardiac output in the early postoperative period (within 3 h of procedure) was significantly higher than in group 2 (4.2(0.9) versus 2.6(0.7)lmin-1m-2, P < 0.01). The 30-day operative mortality rate was significantly lower in group 1 (8% (80% confidence interval 1-29%)) than in group 2 (57% (80% confidence interval 28-83%)) (P < 0.05). On the basis of these results, hypothermic fibrillatory arrest with continuous pulsatile coronary perfusion can be recommended for myocardial protection during surgery for VSP associated with severe heart failure or cardiogenic shock.

Aged↗
PubMed1992

Internal thoracic artery grafting for congenital coronary malformations.

We report 2 patients with congenital coronary anomalies (atresia of left main coronary artery and anomalous origin of the left coronary artery from the pulmonary artery) successfully treated with single or double internal thoracic artery grafting. Because the internal thoracic artery has a potential for circumferential as well as longitudinal development, and because of the uncertainty of ultimate vein graft function, we believe that the internal thoracic artery is the best graft material for the treatment of congenital coronary malformations requiring bypass operation in children, adolescents, or even in adults.

Child↗
PubMed1992

Hypolipidemic effect of ethyl all-cis-5,8,11,14,17-eicosapentaenoate (EPA-E) in rats.

We examined the effect of ethyl all-cis-5,8,11,14,17-eicosapentaenoate (EPA-E) with high purity on circulating lipids in rats under several experimental conditions. In normolipidemic rats, EPA-E decreased the lipids in a dose-dependent manner. Clofibrate (100 mg/kg/day) was more potent in lowering the lipids than EPA-E (1000 mg/kg/day). In high cholesterol diet-fed rats, EPA-E (300 mg/kg/day) decreased the total cholesterol. However, clofibrate (300 mg/kg/day) had little effect on the total cholesterol. In hypertriglycemic rats induced by corn oil, EPA-E (300 mg/kg/day) or clofibrate (100 mg/kg/day) reduced the rise of triglycerides. EPA-E (300 mg/kg/day), clinofibrate (100 mg/kg/day) or clofibrate (300 mg/kg/day) caused a significant reduction in the lipids induced by the injection of Triton WR-1339. Furthermore, EPA-E (300 mg/kg/day) or clinofibrate (100 mg/kg/day) decreased the elevation of lipids produced by feeding the rats a casein-rich diet. These results show that EPA-E possesses potent inhibitory activity on experimental hyperlipidemia induced either exogenously or endogenously.

Animals↗
PubMed1992

Adrenal myelolipoma associated with congenital adrenal 21-hydroxylase deficiency.

The occurrence of adrenal myelolipomas is reported in an untreated patient with congenital adrenal 21-hydroxylase deficiency. Laparotomy demonstrated the presence of two lesions, a large tumor which arose from an ectopic adrenal cortex and a smaller tumor in the left adrenal gland. Six cases of adrenal myelolipomas and congenital adrenal hyperplasia have been reported in the literature. All patients were associated with excessive ACTH secretion for a long period of time. The relative frequency of this association, coupled with the observation by Selye and Stone (Am J Pathol 26:211, 1950) that anterior pituitary extracts cause myelolipomatous changes in rats, may indicate a possible role for ACTH in the development of myelolipomas.

Adrenal Gland Neoplasms↗