Biomedical subjects

B G Min

Publications and source records attributed to B G Min.

At least 37 records · Page 2Linked to original sources

PubMed1999

Static state hemodynamic variables estimation model for the moving-actuator type total artificial heart. Part. I--cardiac output estimation.

Cardiac output estimation is a very important study for the artificial heart. In this paper, we developed a cardiac output estimation model for the moving-actuator type total artificial heart (MA-TAH) that was developed at Seoul National University Hospital. The proposed model is simple and provides beat-by-beat mean cardiac output estimation. Moreover, it uses non-invasively acquired signals. Model parameters were adjusted with in vitro data by least mean square (LMS) algorithm. Results showed that the proposed scheme gives a mean estimation error of about 0.1 (l/min) for the given data. This ensures the suitability of the proposed model.

Cardiac Output↗

PubMed1999

Static state hemodynamic variables estimation model for the moving-actuator type total artificial heart. Part II - Aortic pressure estimation.

Aortic pressure (AoP) estimation is a very important study for the artificial heart. In this paper, we developed a AoP estimation model for the moving-actuator type total artificial heart (MH-TAH) that was being developed at Seoul National University Hospital. The proposed model is simple and provides beat-by-beat mean AoP estimation. Moreover, it uses non-invasively acquired signals. Model parameters were adjusted with in vitro data by least mean square (LMS) algorithm. Results showed that the proposed scheme gives a mean estimation error of about 8 (mmHg). This ensures the suitability of the proposed model. The proposed approach can also be applied to the model setup of pulmonary arterial pressure (PAP) estimation by using the symmetric characteristics between AoP and PAP.

Algorithms↗

PubMed1999

Design of the solar cell system for recharging the external battery of the totally-implantable artificial heart.

The solar cell as the advanced alternative energy resource was found to be acceptable for increasing battery running time of the totally-implantable artificial heart. A sample of the wireless charging system with solar cell base gives a maximum battery running time around 9 hours and some physical and psychological freedom to the patient. This improvement will assist the application of the implantable artificial heart for a longer period of time and with added convenience to the recipient.

Electric Power Supplies↗

PubMed1998

Implantable control, telemetry, and solar energy system in the moving actuator type total artificial heart.

The moving actuator type total artificial heart (TAH) developed in the Seoul National University has numerous design improvements based upon the digital signal processor (DSP). These improvements include the implantability of all electronics, an automatic control algorithm, and extension of the battery run-time in connection with an amorphous silicon solar system (SS). The implantable electronics consist of the motor drive, main processor, intelligent Li ion battery management (LIBM) based upon the DSP, telemetry system, and transcutaneous energy transmission (TET) system. Major changes in the implantable electronics include decreasing the temperature rise by over 21 degrees C on the motor drive, volume reduction (40 x 55 x 33 mm, 7 cell assembly) of the battery pack using a Li ion (3.6 V/cell, 900 mA.h), and improvement of the battery run-time (over 40 min) while providing the cardiac output (CO) of 5 L/min at 100 mm Hg afterload when the external battery for testing is connected with the SS (2.5 W, 192.192, 1 kg) for the external battery recharge or the partial TAH drive. The phase locked loop (PLL) based telemetry system was implemented to improve stability and the error correction DSP algorithm programmed to achieve high accuracy. A field focused light emitting diode (LED) was used to obtain low light scattering along the propagation path, similar to the optical property of the laser and miniature sized, mounted on the pancake type TET coils. The TET operating resonance frequency was self tuned in a range of 360 to 410 kHz to provide enough power even at high afterloads. An automatic cardiac output regulation algorithm was developed based on interventricular pressure analysis and carried out in several animal experiments successfully. All electronics have been evaluated in vitro and in vivo and prepared for implantation of the TAH. Substantial progress has been made in designing a completely implantable TAH at the preclinical stage.

Algorithms↗

PubMed1997

Moving actuator type total artificial heart with reverse position of the aortic and pulmonary conduits.

Adequate intrathoracic anatomical compatibility is one of the most important considerations in designing a fully implantable total artificial heart (TAH). We have recently developed an innovative concept of reverse positioning of the aortic and pulmonary conduits to facilitate anatomical compatibility of the moving actuator type TAH. The pulmonary conduit of this TAH is designed to be located posterior to the aortic conduit, which results in a substantial reduction in the anteroposterior diameter of this heart, as well as the virtual elimination of the compression of the low pressure pulmonary conduit. In ovine orthotopic implantation experiments with this model of the TAH, we consecutively achieved 3 day survival in 1 sheep and 2 day survival in another. To the best of our knowledge, these were the first significant short-term survival cases in the orthotopic implantation of electric TAHs in sheep.

Animals↗

PubMed1997

Do sheep really have problems with cardiopulmonary bypass for total artificial heart implantation?

Although the use of sheep in total artificial heart (TAH) implantation has many advantages, they are known to show a significant morbidity rate on cardiopulmonary bypass (CPB); this has been considered to be a major limiting factor in using them for TAH experiments. We conducted a series of ovine CPB experiments to evaluate the sheep's pathophysiological response to CPB. CPB-related hemolysis, bleeding, and lung dysfunction were analyzed in 5 sheep, which had undergone CPB, used at our hospital for TAH implantation. Four of the 5 sheep survived the experimental procedures, and 3 of them survived on a long-term basis. Unacceptable degrees of hemolysis related to CPB were not observed. Postoperative bleeding was not remarkable, and coagulation test results did not show significant abnormal findings. Acute lung injuries of a mild to moderate degree were found mainly at the microscopic level, but rarely had clinical significance. In conclusion, this experiment suggests that sheep can be used for the animal model for TAH implantation with acceptable risk on CPB circuits and techniques are used.

3,4-Methylenedioxyamphetamine↗

PubMed1996

Plasma protein adsorption to sulfonated poly(ethylene oxide)-grafted polyurethane surface.

Adsorption of proteins (fibrinogen, albumin, and gamma globulin) from plasma onto surface-modified PUs (PU-PEO, PU-SO3, and PU-PEO-SO3) was evaluated. Adsorbed fibrinogen at steady state decreased in the order PU-SO3 > PU > PU-PEO-SO3 > PU-PEO, suggesting that sulfonate groups have specific high affinity to fibrinogen. The intermediate fibrinogen adsorption on PU-PEO-SO3 can be explained by the compensatory effect between the low protein binding affinity of the PEO chain and the high fibrinogen binding affinity of the sulfonate group. In addition, PU-PEO-SO3 showed a very fast fibrinogen adsorption due to the high accessibility of the sulfonate group to fibrinogen by the poly(ethylene oxide) (PEO) spacer. The kinetic profiles of their surfaces showed that as the adsorption time increases, fibrinogen initially adsorbed was decreased and a plateau reached, demonstrating that all the surfaces exhibited the Vroman effect (the fibrinogen displacement phenomenon). PU-PEO showed the least fibrinogen and albumin adsorption among PUs, confirming the known nonadhesive property of PEO chains. It is very interesting that PU-PEO-SO3 exhibited the highest adsorption of albumin and the lowest adsorption of IgG. Therefore, it may be concluded that such adsorption behaviors of proteins to PU-PEO-SO3 contribute to improved blood compatibility.

Adsorption↗

PubMed1996

Total artificial heart using neural and fuzzy controller.

The aortic pressure (AoP) and pulmonary artery pressure (PAP) are important factors for the long-term survival of the patient receiving an implant of a total artificial heart (TAH). A new afterload regulation method using neural controllers has been developed for a moving actuator type TAH. Without any transducer, the proposed neural controller, based on the predetermined peak level of the motor current, regulates AoP by adjusting the actuator velocity. At the same time, a fuzzy controller based on expert knowledge prevents the PAP from being abnormally high. The proposed controller not only regulates the pump output on the maintenance of the normal AoP and PAP, but it also successfully controls the suction in the right heart. In vitro tests show that the proposed neural and fuzzy controllers effectively regulate AoP and PAP as well as prevent atrial suction.

Blood Pressure↗

PubMed1996

A new automatic cardiac output control algorithm for moving actuator total artificial heart by motor current waveform analysis.

A new automatic cardiac output control algorithm for an implantable electromechanical total artificial heart (TAH) was developed based on the analysis of motor current waveform without using any transducer. The basic control requirements of an artificial heart can be described in terms of three features: preload sensitivity, afterload insensitivity, and balanced ventricular output. In previous studies, transducers were used to acquire information on the hemodynamic states for automatic cardiac output control. However, such a control system has reliability problems with the sensors. We proposed a novel sensorless automatic cardiac output control algorithm (ACOCA) providing adequate cardiac output to the time-varying physiological demand without causing right atrial collapse, which is one of the critical problems in an active filling device. In vitro tests were performed on a mock circulatory system to assess the performance of the developed algorithm and the results show that the new algorithm satisfied the basic control requirements of the cardiac output response.

Algorithms↗

PubMed1996

A new polymer valve for mechanical circulatory support systems.

A new low-cost artificial heart valve with easily modified dimensions according to its application was developed using segmented polyurethane (SPU). It consists of a convex frame and a concave membrane which floats in the center of the frame while working. The hydrodynamic performance of the polymer valve was compared with that of the Björk-Shiley mechanical valve using a mock circulatory testing system. The hydrodynamic performance of this valve was superior to the Björk-Shiley mechanical valve. The valve was applied to a ventricular assist device (VAD) developed in our institute. In vivo performances of these systems were tested using mongrel dogs. During the experiments, there were no complications related to malfunction of the valve. At postmortem examinations, no thrombus formation was found on the valve surface, and no embolus was detected in the kidneys. We believe this valve could prove a very useful alternative for valves of mechanical circulatory support systems (MCSS) such as VAD and TAH.

Animals↗

PubMed1995

Heparin-like anticoagulant activity of sulphonated poly(ethylene oxide) and sulphonated poly(ethylene oxide)-grafted polyurethane.

Sulphonated poly(ethylene oxide) (PEO-SO3) and PEO-SO3-grafted polyurethane (PU-PEO-SO3) were prepared by bulk modification and their anticoagulant and heparin-like activities were investigated. Anticoagulant activity measured by activated partial thromboplastin time of PU-PEO-SO3 displayed 2%, whereas that of PEO-SO3 itself reached 14% as compared to free heparin. In addition, the anticoagulant effects of these sulphonated polymers were not due to factor Xa inhibition but mainly thrombin inhibition. From the clotting time measurements using reptilase instead of thrombin and antithrombin III (AT III), PEO-SO3 and PU-PEO-SO3 indicated heparin-like activity which represents both prolonged thrombin time (TT) and normal reptilase time and increased TT in the presence of AT III. Thrombin was also neutralized by sulphonated polymers to a great extent. Therefore, the anticoagulant and heparin-like activities of PEO-SO3 and PU-PEO-SO3 seem to contribute to their improved blood compatibility.

Anticoagulants↗

PubMed1995

Adhered platelet morphology in diabetes mellitus.

We compared the morphology of platelets obtained from diabetic patients in various stages of retinopathy and nephropathy with those of control patients. The platelets were collected on to polyethylene films, processed and observed under scanning electron microscopy. Different platelet morphologies were observed within the diabetic group, correlating with the severity of complications, whereas platelets appeared normal in the control group. After more extensive follow-up and comparative studies, these preliminary observations could provide another diagnostic tool for detecting and evaluating severe complications associated with diabetes.

Case-Control Studies↗

PubMed1994

Improved visualization of stimulated nodules by adaptive enhancement of digital chest radiography.

RATIONALE AND OBJECTIVES: Although digital radiography of the chest has a wide dynamic range, difficulties still remain in visualizing the acquired images faithfully on gray-scale displays (cathode-ray tube [CRT] displays), which have a much lower level of luminance than film view boxes. We propose an adaptive-enhancement algorithm for digital chest radiography that provides faithful visualization of the chest on the CRT. METHODS: We investigated the contrast sensitivity of a CRT monitor and developed an image processing algorithm that compresses the dynamic range and enhances image contrast selectively in the mediastinal area and that transforms the gray scale to visualize the image by use of the full effective dynamic range of the CRT. We performed a receiver-operating characteristic (ROC) study by using simulated nodules to evaluate the clinical value of the proposed algorithm. RESULTS: The processed images provided improved visualization of both mediastinal and lung regions. The area under the ROC curve for retrocardiac or subdiaphragmatic nodule detection increased significantly (from 0.69 to 0.79; P < 0.05). The area under the ROC curve for lung nodule detection also increased (from 0.64 to 0.75; P < 0.1), although not to the level of statistical significance. CONCLUSION: The proposed algorithm allows improved visualization of nodules on digital chest radiographs with the CRT display.

Algorithms↗

PubMed1993

In vivo biostability and calcification-resistance of surface-modified PU-PEO-SO3.

To examine the biostability and calcification-resistance of polyurethanes (PUs), the surface of PU was grafted with hydrophobic perfluorodecanoic acid (PFDA) (PU-PFDA), hydrophilic polyethyleneoxide (PEO) (PU-PEO1000), and further negatively charged sulfonate groups (PU-PEO1000-SO3). An in vivo animal test was conducted by subcutaneous implantation in rats during 2, 4 and 6 months. A scanning electron microscope study demonstrated that the degree of surface cracking on explanted PUs was increased in the following order: PU-PFDA > PU > PU-PEO1000 > PU-PEO1000-SO3. In the results of energy dispersive x-ray analysis and inductively coupled plasma atomic emission spectrometry, the deposition of calcium was found abundantly, but that of phosphorus was hardly in existence in all implanted PUs, suggesting that this calcium compound is not a hydroxyapatite. The calcium contents, regardless of implantation time, were also increased in the same order (PU-PFDA > PU > PU-PEO1000 > PU-PEO1000-SO3). After 6 months implantation, no severe tissue reactions were observed and calcification almost occurred on polymer surfaces in all implants. Such superior biostability and anticalcification of PU-PEO1000-SO3 might be attributed to synergistic effects of its excellent surface smoothness, sulfonate acid (SO3-) groups, nonadhesive and mobile PEO, and the high hydrophilicity and enhanced blood compatibility. Therefore, PU-PEO1000-SO3 is promising as biostable and calcification-resistant biomaterial.

Animals↗

PubMed1993

Adsorption behavior of fibrinogen to sulfonated polyethyleneoxide-grafted polyurethane surfaces.

Fibrinogen adsorptions to surface modified polyurethanes (PU, PU-PEO, and PU-PEO-SO3) were studied from plasma in vitro. PU and PU-PEO surfaces demonstrated that initial adsorption increases with increasing plasma concentration in kinetic profiles and adsorption time in adsorption profiles as a function of plasma concentration, but after the plateau is reached, its adsorption amount decreases as plasma concentration (0.2-2.0%) and adsorption time (1-120 min) increase, respectively. In contrast, PU-PEO-SO3 showed that initial adsorption is almost same regardless of plasma concentration and adsorption time, which is due to the high affinity of surface sulfonate group to fibrinogen. All the surfaces indicated the Vroman effect at about 0.6% plasma concentration; however, the displacement was relatively low. Adsorbed amount of fibrinogen at steady state decreased in the order: PU > PU-PEO-SO3 > PU-PEO, regardless of adsorption time and plasma concentration. The adsorption behavior of PU-PEO-SO3 is attributed to both effect of low binding affinity of PEO chain and high affinity of pendant sulfonate group toward fibrinogen.

Adsorption↗

PubMed1993

Preparation and surface properties of PEO-sulfonate grafted polyurethanes for enhanced blood compatibility.

In order to improve the thromboresistance of the commercial polyurethane(PU), its surface modification was accomplished by three new different methods and their surface characteristics were investigated using ATR-FTIR, ESCA, SEM, and dynamic contact angle measurements. Sulfonations using propane sultone were performed directly onto PU or onto hydrophobic dodecanediol (DDO) grafted PU or onto hydrophilic poly(ethyleneoxide) (PEO) grafted PU. ESCA data coincided well with ATR-IR results, as more 0 at. % for PEO grafted PUs and the presence of S for the sulfonated PUs were revealed. At SEM observation the surfaces of PU-DDO and PU-PEO were relatively smooth, whereas all the sulfonated PU surfaces showed excellent smoothness and homogeneity. The hydrophilicity of the surfaces was considerably increased after PEO grafting or sulfonation. In addition, all the sulfonated PU surfaces, particularly PU-PEO-SO3, which has further hydrophilicity, exhibited complete wetting behavior due to the negatively charged SO3 groups.

Alkanesulfonates↗

PubMed1992

Surface characteristics and blood compatibility of polyurethanes grafted by perfluoroalkyl chains.

Polyurethane (PU) surface was chemically modified by grafting of perfluorodecanoic acid (PFDA) to produce a highly hydrophobic surface to compare the blood compatability with hydrophilic poly(ethylene oxide) (PEO) grafted PUs. The advancing contact angle of modified PU-PFDA was increased up to 115 deg, while that of untreated PU was 86 deg. The PFDA grafted PU exhibited less adhesion and shape change of platelets than untreated PU, and the activated partial thromboplastin time (APTT) of PU-PFDA was considerably extended. The ex vivo occlusion time of untreated PU was only 50 min, but that of PFDA grafted PU was extended to 130 min, indicating that this hydrophobic surface is significantly blood compatible. It is interesting to find that the enhanced blood compatibility of very hydrophobic PU-PFDA was equivalent to hydrophilic PU-PEO.

Biocompatible Materials↗

PubMed1991

Negative cilia concept for thromboresistance: synergistic effect of PEO and sulfonate groups grafted onto polyurethanes.

In order to investigate the interaction between various sulfonated polyurethanes (PUs) and blood, a commercial PU surface was chemically modified by poly(ethylene oxide) (PEO), dodecanediol(DDO), and propane sultone to give hydrophilic, hydrophobic, and negative sulfonated surfaces, respectively. The blood compatibility of modified PUs was evaluated by an in vitro platelet adhesion test, activated partial thromboplastin time (APTT), and prothrombin time (PT) measurements as well as an ex vivo rabbit A-A shunt method. In the platelet adhesion test, the hydrophilic PEO grafted PUs showed less platelet adhesion than untreated PU and hydrophobic DDO grafted PU. Sulfonated PU-PEO exhibited a lower degree of adhesion and shape change of platelet. The APTT and PT, especially APTT, of the sulfonated PUs were extended, whereas those of PU-PEO and PU-DDO did not show any significant change compared with untreated PU. Meanwhile, in the ex vivo experiment, hydrophilic PEO grafted PUs showed longer occlusion times than untreated PU or hydrophobic DDO grafted PU. In addition, the incorporation of SO3 groups at the end of PU-DDO and PU-PEO, particularly PU-PEO-SO3, exhibited an enormous prolongation in occlusion time, indicating a synergistic effect of the hydrophilic PEO and the negative SO3 groups on thromboresistance. These occlusion times corresponded well to in vitro evaluation results: the less adhesion and shape change of platelet and the longer APTT and PT, the more extended the ex vivo occlusion time.

Animals↗