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Biomedical subjects

Y Mitamura

Publications and source records attributed to Y Mitamura.

At least 37 records · Page 2Linked to original sources
PubMed1998

[Corneal endothelial cell damage associated with pars plana vitrectomy].

We performed a prospective study of corneal endothelial damage associated with pars plana vitrectomy in 51 eyes of 46 patients. The corneal endothelium was examined with a specular microscope preoperatively and three months postoperatively. The mean endothelial cell loss for 51 eyes was 11.54%. The 51 eyes were divided into three groups, and the mean cell loss was 25.85% in the pars plana lensectomy (including anterior capsule removal) combined group, 7.53% in the phacoemulsification combined group, and 1.91% in the phakic group. The corneal epithelium removal did not affected the cell loss. The cell loss for the phacoemulsification combined group did not differ significantly from that for the control group (6 eyes received only phacoemulsification). In the pars plana lensectomy combined group the cell loss was related significantly with gas tamponade duration. This study suggests that we must note the endothelial cell damage in vitrectomy-pars plana lensectomy combined with gas tamponade.

Adolescent↗
PubMed1998

[Surgical outcomes of vitrectomy for retinal detachment due to macular hole with proliferative vitreoretinopathy].

We retrospectively studied surgical outcomes in 13 patients (13 eyes) who underwent vitrectomy for proliferative vitreoretinopathy (PVR) due to macular hole. While the success rate of the initial surgery was only 46% (6 eyes), retinal reattachment was ultimately obtained in 92% (12 eyes) with additional surgery. Reattachment rate in the initial was poor in eyes with posterior staphyloma. It was better in eyes treated with macular buckling and/or scleral encircling, and in eyes without iatrogenic retinal tears. These results indicate that appropriate treatment for the macular hole as well as extensive removal of vitreous gel and vitreoretinal traction are necessary in order to obtain the successful results in vitrectomy for PVR due to macular hole.

Aged↗
PubMed1996

A ferrofluidic seal specially designed for rotary blood pumps.

One of the key technologies required for rotary blood pumps is sealing of the motor shaft. A ferrofluidic seal was developed for an axial flow pump. The seal body was composed of a plastic magnet and two pole pieces. This seal was formed by injecting ferrofluid into the gap between the pole pieces and the motor shaft. To contain the ferrofluid in the seal and to minimize the possibility of ferrofluid making contact with blood, a shield with a small cavity was provided on the pole piece. Sealing pressure of the seal was measured. The sealing pressure was maintained at more than 23.3 kPa (175 mm Hg) for a motor speed up to 11,000 rpm. The specially designed ferrofluidic seal for sealing out liquids is useful for axial flow blood pumps.

Blood Flow Velocity↗
PubMed1994

Blood compatibility of sputter-deposited alumina films.

The surface modification of metals by the application of blood compatible ceramics is one approach to developing durable and blood-compatible materials. The blood compatibility of sputter-deposited alumina films was investigated in vitro. The alumina films were prepared by reactive sputtering and conventional sputtering. Diffractometer studies of the alumina films indicate that the sputter-deposited alumina films have amorphous structures. Electron spectroscopy chemical analysis studies of the alumina films indicate that the sputter-deposited alumina films are nonstoichiometric (O/A1 ratio of 1.15-1.66). We examined the platelet reaction to the alumina films and the intrinsic coagulation factor XII activation by the alumina films. Medical grade segmented polyurethane was also tested. The alumina films experienced an adhesion of about 50% fewer platelets than the segmented polyurethane. Also, fewer platelet morphologic changes were observed on the alumina films than on the segmented polyurethane. Factor XII activation was less on the alumina films than on the segmented polyurethane. Surface modification by the sputter-deposited alumina films is promising for developing blood-compatible and durable materials.

Aluminum Oxide↗
PubMed1994

Fracture toughness of single crystal alumina in air and a simulated body environment.

The critical intensity factor KIC of a single crystal alumina (1100)-plane in air and in a simulated body environment was measured. Based on these measurements, the estimated durability of a single crystal alumina disk in a ceramic heart valve was determined. Standard single-edge notched beam specimens were prepared. The specimens were classified into three groups: a) stored in air (n = 10), b) immersed in Ringer's solution for 2 months (n = 11), and c) immersed in Ringer's solution for 4 months (n = 6). KIC was 2.345 +/- 0.072 MPam1/2 for specimens stored in air, 2.141 +/- 0.147 in Ringer's solution for 2 months, and 2.005 +/- 0.153 in Ringer's solution for 4 months. The KIC decreased for specimens stored in Ringer's solution (P < .01), but it did not differ significantly between 2 and 4 months. The decrease of KIC is the stress corrosion effect of Ringer's solution at the crack tip, and is not associated with an overall deterioration of strength. The stress intensity factor for possible cracks (length: 0.4 mm) in the single crystal alumina was calculated. Maximum stress was assumed 2.668 MPa (= 40 x 500 mm Hg). The stress intensity factor calculated was far less than the KIC. The single crystal alumina disk can endure a static pressure of 500 mm Hg.

Air↗
PubMed1994

Development of a compact, highly efficient, totally implantable motor-driven assist pump system.

We have developed a compact, highly efficient, totally implantable assist pump system, which consists of a motor-driven assist pump and a transcutaneous energy and optical information transmission system. The motor-driven assist pump consists of a.d.c. brushless motor and a specially designed miniature ball screw. A magnetic coupling mechanism between the blood pump and an actuator provides active blood filling via mild suction force. The controller consists of a PID follow-up controller using an 8-bit one-chip microcomputer. The volume of the pump is 350 ml, and its controller is 210 ml. Pump outflow of 5.8 L/min was obtained against a mean after-load of 100 mm Hg. The pump showed a high efficiency rate and good durability. An efficiency rate of 19-21% (pump output/motor input) was obtained during 87 days of continuous pumping. No mechanical trouble occurred for an accumulated period of 6 months.

Alloys↗
PubMed1992

The valvo-pump, an axial blood pump implanted at the heart valve position: concept and initial results.

The valvo-pump, an axial nonpulsatile blood pump implanted at the heart valve position, has been developed. The valvo-pump consists of an impeller and a motor, which are encased in a housing. An impeller with 5 vanes (22.0 mm in diameter) is used. The impeller is connected to a samarium-cobalt-rare earth magnet direct current (DC) brushless motor measuring 21.3 mm in diameter and 18.5 mm in length. Sealing is achieved by means of a ferrofluidic seal. A pump flow of 10.5 L/min was obtained at a pump differential pressure of 3.3 kPa (25 mm Hg), and a flow of 4.9 L/min was obtained at 7.0 kPa (53 mm Hg). Sealing was kept perfect against a pressure of 29.3 kPa (220 mm Hg) at 9,000 rpm.

Equipment Design↗
PubMed1992

A ferrofluidic actuator for an implantable artificial heart.

The feasibility of using a ferrofluidic actuator for an artificial heart was studied. A ferrofluidic actuator directly drives magnetic fluids simply by applying a magnetic field to the ferrofluids and does not require a bearing. Magnetic fluid in a U-shaped glass cylinder was placed in an air gap of a solenoid. When a magnetic flux of 0.32 T was applied to the interface of the ferrofluid and air, the ferrofluid was displaced and a pressure of 7.58 kPa (57 mm Hg) was obtained. An array of three poles of solenoids was mounted near the U-shaped glass cylinder. The solenoids were sequentially activated and deactivated. A pressure of 9.98 kPa (75 mm Hg)/-1.33 kPa (-10 mm Hg) was obtained. Calculations indicate that a magnetic flux of 0.49 T is enough to obtain a pressure of 13.3 kPa (100 mm Hg). A ferrofluidic actuator is promising for use with an implantable artificial heart.

Electric Power Supplies↗
PubMed1991

Investigation of parameter estimator and adaptive controller for assist pump by computer simulation.

The multi-output adaptive controller of a left ventricular assist device (LVAD) was studied by computer simulation. The controller regulated two outputs--mean aortic pressure (mAoP) and mean atrial pressure (mLAP)--by regulating vacuum pressure (input). The autoregressive models were used to describe the circulatory system. The parameters of the models were estimated by the recursive least squares method. Based on the autoregressive models, the vacuum pressure minimizing a performance index was searched. The index used was the weighted summation of the square errors. Responses of the adaptive controller were simulated when the contractility of the left ventricle was decreased at various rates and the peripheral resistance was changed. Both the mAoP and mLAP were controlled to their predicted values in the steady state. The steady-state errors of the mAoP were less than a few mm Hg, and those of the mLAP were lower than 1 mm Hg. Consequently, the estimated parameters can be regarded as true parameters, and the adaptive controller has the potential to control more than two outputs. The multioutput adaptive controller studied is useful in controlling the LVAD according to the change in circulatory condition.

Aorta, Thoracic↗
PubMed1990

Development of an implantable motor-driven assist pump system.

A motor-driven artificial pump and its transcutaneous energy transmission (TET) system have been developed. The artificial pump consists of a high-speed dc brushless motor driving a ball screw and magnetic coupling mechanism between the blood pump and ball screw. The ball screw transfers high-speed rotary motion into low-speed rectilinear motion by a single component. Magnetic coupling enables active blood filling without applying an excess negative pressure to the pump. The transcutaneous transformer is formed from a pair of concave/convex ferrite cores. This design minimizes lateral motion of the external core. Information on motor voltage is transmitted through the skin by infrared pulses. The motor voltage is regulated by controlling the duty ratio of the square pulse supplied to the primary coil. Pump flow of 5.6 l/min was obtained with a mean outlet pressure of 100 mmHg at a drive rate of 100 bpm under preload of 15 mmHg. The performance of synchronous pumping has been very satisfactory. Continuous pumping was maintained by the backup battery in the case of interruption of TET. 24 W were transmitted by TET system with 78 percent of efficiency. Temperature rise of the internal core was 0.2 C. The developed system is promising as an implantable assist pump system.

Animals↗
PubMed1990

Catheter-type defibrillation electrode using glassy carbon: results of electrode implantation.

The implantable defibrillator, developed by Dr Michel Mirowski, is a remarkable electric therapeutic device which has been in clinical use since 1980 in the treatment of life-threatening arrhythmia. However, as the present life span of this device is only 3 years, research is being carried on to extend the lifetime with improved stimulation methods, circuits and electrodes. In particular, the electrode system which is inserted into the right ventricle has more than 50 times the electrode area of a pacing electrode and is prone to degradation. What is needed is biocompatibility and electrical stability, similar to that of cardiac pacemaker electrodes, which can be used for more than 10 years. For this purpose, we focused on a conductive ceramic as a new material for the defibrillation electrode instead of the previously-used metal. We selected glassy carbon as our electrode material and tested the surface condition through acute and chronic animal experiments. No clots formed around the electrodes after a 3-month implantation, nor were there surface disorders after the defibrillation stimulations. We concluded that glassy carbon is a promising material for future defibrillation electrodes.

Animals↗
PubMed1989

Role of physical properties of resistance vessel wall in regulating peripheral blood flow--II. Structural and mechanical behavior.

In order to examine the structural and mechanical properties of the vessel wall resistance when subjected to autoregulatory flow control, a mechanical model for the vascular wall was derived from a mathematical model. The mechanical model was an analogue model which connected in series the Maxwell model (elastic modulus: K3) with the parallel elements of Hill's model (elastic modules: K2) and Hooke's elastic model (elastic modulus: K1); it was also mathematically equivalent to the Spring model (see part I). The structural and mechanical properties of the resistance vessel wall were characterized by the three elastic moduli (K1, alpha K2 and K3) [mmHg]. The parameter alpha was a modification factor of the elastic modulus K2 given by the myogenic mechanism. After a numerical analysis of the experimental data given by the mechanical model, we confirmed that the arterial pressure range for autoregulatory flow controls shifted to the upper region with an increase of the elastic modulus K1 and the flow regulation was reduced.

Animals↗
PubMed1989

Development of a ceramic heart valve.

A durable and thromboresistant ceramic heart valve comprised of a single crystal alumina disk and titanium nitride (TiN) valve ring has been developed. Blood compatibility was examined by scanning electron microscopy (SEM) examinations of the valves implanted in sheep for 35 (#1), 26 (#2), 20 (#3), 23 (#4), and 26 (#5) days. The single crystal alumina and TiN surfaces were free of platelet aggregation or fibrin networks, except for some depositions of fibrin and platelets on the outflow TiN ring in #3, and isolated red cells on the outflow TiN ring in #5. Durability testing under high pressure (1750 mmHg = 233 KPa) pulsatile conditions showed that the safety factor of the ceramic valve was more than seven times greater than anticipated. The ceramic valve is promising as an artificial heart valve.

Animals↗
PubMed1989

Effects of venous pressure elevation on myogenic vasoconstrictive responses to static and dynamic arterial pressures.

In order to establish the nature of the stretch-evoked dynamic properties of vascular smooth muscle in arterioles, we have examined the static and dynamic effects of both arterial pulse pressure and elevated venous pressure on the resistance vessels (arteries and arterioles) in an intestinal mesenteric preparation derived from dogs. The dynamic myogenic response to stretch stimuli was directly related to both the frequency of arterial pulse pressure (1-20 c/min) and the level of venous pressure (0-45 mmHg). Under elevated venous pressure (20 mmHg), the mean arterial flow decreased with an increase in the frequency of arterial pulse pressure. The arteriolar vascular tone (namely, vascular resistance) was seen to be enhanced. We found that elevated venous pressure promotes active constriction (9-53%) of arteriolar smooth muscle (myogenic mechanism). The elevation of venous pressure also caused a rhythmic constriction (vasomotion) in the site of both vein and artery, which was completely abolished by an alpha-blocker (phentolamine). The results suggest that during venous pressure elevation a very pronounced myogenic constriction in terminal arterioles is caused by either a local neural reflex or a propagated myogenic response in the arteriolar network.

Animals↗
PubMed1989

The effect of left ventricular assist device (LVAD) on cardiac reserve in dogs.

The effect of LVAD on the preservation of cardiac reserve against ischemic damage was studied using Sarnoff's ventricular function curve. An LVAD was implanted between the canine left atrium and the aorta. Left ventricular function was measured by changing the height of the reservoir connected to the left atrium. The left ventricular function curve (LVFC) was drawn by plotting left ventricular stroke work (LVSW) against left atrial pressure (LAP). The coronary artery was occluded under a pump-on (ON group) or pump-off (OFF group). After reperfusion, measurements were repeated and changes in the LVFC caused by ischemia were compared in both groups. The gradient of the LVFC was significantly reduced by ischemia (107 +/- 15 ml/beat----80 +/- 14, n = 13) but not in the ON group. LVSW under normal preload did not significantly change in either group. This suggests that the LVAD preserved cardiac reserve against ischemic damage.

Animals↗
PubMed1988

Myocardial oxygen tension during left ventricular bypass.

The effect of an assist pump on the heart was evaluated on the basis that myocardial gas tensions reflect the balance between oxygen supply and consumption in local regions of the myocardium. A left ventricular assist device (LVAD) was implanted in dogs between the left ventricle (LV group), or the left atrium (LA group) and the aorta. The assist pump was driven in a counterpulsation mode. A silicone catheter for mass spectrometry was inserted into the myocardium to monitor continuously myocardial oxygen and carbon dioxide tensions (PmO2, PmCO2). Coronary sinus blood flow (CSBF) was measured by completing an extracorporeal flow loop between the coronary sinus and the jugular vein. During LVAD counterpulsation, the LV pressure was reduced and diastolic arterial pressure (i.e. coronary perfusion pressure) was increased. Total LV bypass was obtained in the LV group, and partial LV bypass in the LA group. In the LV group, PmO2 was 18.3 +/- 1.9 mmHg with pump-off and increased to 26.4 +/- 3.0 during LV bypass (N = 10, p less than 0.005). PmCO2 was 45.3 +/- 1.8 mmHg with pump-off and decreased to 40.2 +/- 1.5 during bypass (N = 10; p less than 0.005). CSBF significantly decreased during LV bypass from a control value of 24.1 +/- 2.74 ml/min/100g to 16.3 +/- 1.69 in LV group (N = 10; p less than 0.001). It was 43.4 +/- 8.0 ml/min/100g in the pump-off and 31.9 +/- 7.2 during LV bypass in the LA group (N = 7; p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗