• Journal of Biomedical Engineering Research
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• v.17 no.3
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• pp.387-394
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• 1996

This paper presents a Neural Network Identification(NNI) method for modeling of highly complicated nonlinear and time varing human system with a pneumatically driven mock circulatory system of Left Ventricular Assist Device(LVAD). This system consists of electronic circuits and pneumatic driving circuits. The initiation of systole and the pumping duration can be determined by the computer program. The line pressure from a pressure transducer inserted in the pneumatic line was recorded System modeling is completed using the adaptively trained backpropagation learning algorithms with input variables, heart rate(HR), systole-diastole rate(SDR), which can vary state of system. Output parameters are preload, afterload which indicate the systemic dynamic characteristics. Consequently, the neural network shows good approximation of nonlinearity, and characteristics of left Ventricular Assist Device. Our results show that the neural network leads to a significant improvement in the modeling of highly nonlinear Left Ventricular Assist Device.

• Journal of Biomedical Engineering Research
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• v.15 no.1
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• pp.19-26
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• 1994

Sulfonated poly (ethyleneoxide)-grafted polyurethane (PU-PEO-$SO_3$) prepared by bulk modification was coated on a blood sac for electrohydraulic left ventricular assist device (ELVAD) implanted in dogs and its in vivo blood compatibility on shear stress was studied as compared with untreated Po. The effect of the wall shear stress on the protein adsorption unlike platelet adhesion is dependent on the surface characteristics of the material, although less proteins seem to be adsorbed in the region of the high shear stress. The thickness of total proteins adsorbed on PU-PEO-SOJ (400 ${\AA}$) by trans¬mission electron microscopy(TEM) was considerably lower than that of untreated PU(l,000~1,600 ${\AA}$), but PU-PEO-$SO_3$ showed high albumin adsorption, low fibrinogen and IgG adsorption, and low platelet adhesion as compared with untreated PU, suggesting that PU-PEO-$SO_3$ is more in vivo blood compatible. Therefore, it appears that such a blood compatible PU-PEO-$SO_3$ is useful for blood contacting biomaterials including artificial organs.

• Journal of Chest Surgery
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• v.29 no.11
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• pp.1218-1222
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• 1996

The reported incidence of postcardiotomy cardiogenic shock not responding to conventional therapy is still 0.1 to 0.8%. For this group of patients, more aggressive form of circulatory support must be employed. Centrifugal pumps are a ventricular assist device most commonly used on this purpose, due to low cost and easy availability. Currently, however, clinical experience of centrifugal pumps as a ventricular assist device is rarely reported in Korea. From January 1992 to January 1996, 2986 patients underwent cardiac operations on cardiopulmonary bypass at Seoul National University Hospital. Refractory postcardiotomy cardiac failure requring ventricular support with a Biomedicus centrifugal pump developed in ten of these patients. There were eight men and two women, ranged in age from nine years to 77 years with a mean of 50$\pm$20 years. The primary surgical procedures consisted of isolated coronary revascularization in four patients, combined coronary revascularization and aortic valve replacement in two, aortic dissection repair in two, pulmonary embolectomy in one, and heart transplantation in one. Of the ten patients, five had left ventricular assistance, one had right ventricular assistance, and four had biventricular assistance. Duration of ventricular assistance ranged from 24 to 175 hours, with a mean of 76$\pm$51 hours. Seven patients were weaned from ventricular assistance, and four of them discharged. The causes of death for nonsurvivors were progressive cardiac failure in two patients and multiorgan failure, intractable ventricular fibrillation, irreversible brain injury, and mechanical problem, respectively, in the other four. Survival was not predicted by time on cardiopulmonary bypass, aortic cross-clamp time, or duration of ventricular support. Major complications included bleeding(7), renal failure(6), infection(3) and neurologic complication(2). These results indicate that a centrifugal pump can provide reasonably satisfactory short-term circulatory support.

• Proceedings of the KOSOMBE Conference
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• v.1994 no.05
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• pp.146-147
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• 1994

• Journal of Chest Surgery
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• v.38 no.8 s.253
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• pp.523-528
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• 2005

Background: Investigation of the change of ventricular function and mitral regurgitation after surgical repair of patient with anomalous origin of left coronary artery from the pulmonary artery (ALCAPA) is key issue for the better surgical outcome. Material and Method: From April 1986 to July 2002, 12 patients presented with ALCAPA. The median age at repair was 4 months. Surgical methods included left coronary artery transfer to the aorta (10), Takeuchi procedure (1), saphenous vein free graft bypass (1). Mitral valve was repaired in 1. Result: There were 2 hospital death $(16.7\%)$. The mean follow-up period was $7.1\pm4.1$ years (range, 7 months to 13 years). Four patients required postoperative circulatory assist for $2.2\pm1.1$ days and one needed left ventricular assist device (LVAD) for 1day. Postoperative echocardiography demonstrated significant improvements in mean fractional shortening $(33.4\pm9.1\%\;vs\;17.7\pm9.6\%,\;n=10,\;p<0.05);$ left ventricular end diastolic dimension $(33.4\pm7.3\;mm\;vs\;44.8\pm7.0\;mm,\;n=10,\;p<0.05)$ and systolic dimension $(22.2\pm7.5\;mm\;vs\;33.4\pm7.9\;mm,\;n=10,\;p<0.05)$. Severities of mitral regurgitation decreased in all survivors at 1st and 4th year follow-up echocardiography. There were 2 reoperation due to residual MR and right ventricular outflow obstruction (Takeuchi case). Conclusion: Anatomic repair of anomalous left coronary artery from the pulmonary artery offered an excellent surgical results, especially in terms of the recovery of left ventricle function and mitral regurgitation. However, preoperative indications for mitral procedure is to be evaluated.

• Journal of Chest Surgery
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• v.30 no.3
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• pp.275-281
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• 1997

The radial artery as a graft for myocardial revascularization was introduced by Carpentier in the early 1970s. Mid-term results were unfortunately discoura ing, and the clinical experience with this graft was interrupted. At the end of the 1980s, these authors reproposed the same arterial conduit with more satisfying results, because of improved technique and pharmacological management of the graft. Between October 1994 and July 1995, 36 patients underwent myocardial revascularization with a radial artery graft in Seiong General Hospital. Left internal mammary artery was concomitantly used as a pedicled Vift in 34 patients. Fifteen patients (42%) had a complete arterial waft revascularization. A total of 12) distal anastomoses were performed (average 3.4 per patient), including 36 left internal mammary artery wafts (two sequential in 2 patients), and 23 saphenous vein grafts. The remaining 64 distal anastomoses were perFormed with radial artery grafts (mean 1.8 per patient). The radial arteries were anastomosed to the circumflex (n=38), diagonal (n= 18), right coronary(n=G), and left anterior descending coronary artery(n=2). The percent ge of radial artery graft anastomoses (64) to the total anastomoses(123) was 52%. The radial artery was used as a single graft in 10 patients, as a sequential graft in 25 patients, and two grafts in 1 patient. Twenty patients underwent associated procedures coronary endarterectomy (14), coronary artery patch angioplasty (4), mitral valve repair (1), and repair of ventricular septal rupture (1). One patient died of low cardiac output syndrome and the others had no perioperative myocardial infarction. There are no ischemic and functional complications in the arm or hand aftcr removal of the radial artery. Only 1 patient required reexploration of the am, for the hematoma evacuation, and 2 patients complained transient thumb dysesthesia of the side of the havested arm. This dysesthesia improved within one month. Postoperative angiovaphic controls were obtained in 11 patients(31%) postoperative 79 to 210 days (mean 126 days). The patency rate were as follows : left internal mammary artery (100%), saphcnous vein (100%), and radial artery(95%). We concluded that the radial artery is useful alternative graft, but long term clinical and angiographic studies are required to derterminc whether wider application is warranted.

• Proceedings of the KOSOMBE Conference
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• v.1996 no.05
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• pp.207-212
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• 1996

We developed pneumatic blood pump and its driving system as a pediatric ventricular assist device. The blood pump is diaphragm type system and its blood contacting area is coated with Bio-Span. The driving unit Is consists of dual pumps, valves for the reliable blood pumping and its controller uses 80C196(Intel) as a main processor. The acute animal experiment was performed with dogs and its body weight is about 20 kg. The maximum cardiac output is about 2.1 l/min and the pressure and flow curves showed reliable operation as assist device.

• Journal of Chest Surgery
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• v.30 no.2
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• pp.158-163
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• 1997

From July 1994 to August 1995, 32 patients underwent coronary artery bypass surgery. There were 14 men and 18 women. The mean age was 59 years (range from 37 to 81 years). Preoperatively 26 patients had unstable angina pectoris and 6 patients had stable angina pectoris. Nine patients had previous myocardial infarction hi tory. Five patients had preoperative left ventricular ejection fraction of 40% or less, The involved risk factors were as follows ; smoking 19 cases, hypertension 16 cases, hypercholesterolemia 14 cases, diabetes mellitus 6 cases, and obesity 3 cases.21 patients had three-vessel disease, 7 patients had two-vessel disease, 2 patients had one-vessel disease and 2 patients had left main coronary artery disease. We performed 103 distal bypasses out of 32 cases, and the mean number of grafts per patients is 3.22. We used arterial grafts (left internal mammary artery,)1, radial artery; 2) in 32% of total grafts. Postoperative complications were low cardiac output, perioperative myocardial infarction, respiratory failure and atrial fibrillation, etc. Early mortality was 6.25% (2/32). The causes of deaths were low cardiac output (1), and perioperative myocardial infarction(1).

• Journal of Biomedical Engineering Research
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• v.18 no.4
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• pp.429-438
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• 1997

Mechanical valve is one of the most widely used implantable artificial organs of which the reliability is so important that its failure means the death of patient. Therefore early noninvasive detection is essentially required, though mechanical valve failure with thrombosis is the most common. The objective of this paper is to detect the thrombosis formation by spectral analysis and neural network. Using microphone and amplifier, we measured the sound from the mechanical valve which is attached to the pneumatic ventricular assist device. The sound was sampled by A/D converter(DaqBook 100) and the periodogram is the main algorithm for obtaining spectrum. We made the thrombosis models using pellethane and silicon and they are thrombosis model on the valvular disk, around the sewing ring and fibrous tissue growth across the orifice of valve. The performance of the measurment system was tested firstly using 1 KHz sinusoidal wave. The measurement system detected well 1KHz spectrum as expected. The spectrum of normal and 5 kinds of thrombotic valve were obtained and primary and secondary peak appeared in each spectrum waveform. We find that the secondary peak changes according to the thrombosis model. So to distinguish the secondary peak of normal and thrombotic valve quantatively, 3 layer back propagation neural network, which contains 7, 000 input node, 20 hidden layer and 1 output was employed The trained neural network can distinguish normal and valve with more than 90% probability. As a conclusion, the noninvasive monitoring of implanted mechanical valve is possible by analysing the acoustical spectrum using neural network algorithm and this method will be applied to the performance evaluation of other implantable artificial organs.

• Proceedings of the KOSOMBE Conference
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• v.1996 no.05
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• pp.84-87
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• 1996

We have been developed electrohydraulic left ventricular assist device and done various in vivo evaluation on the device. Through the in vivo experiment conducted from Jan. 23, 1996 to Feb. 8, we could have experience of long-term evaluation fur the first time. The sheep used in this experiment had survived for 16 days. We used new actuator with reduced size and linear motion guide replacing oil box and ball bearings. Also, we used improved blood chamber with reduced size, reduced weight facilitating fixing the chamber to animal's body, and polymer sac having improved folding pattern. Against suction problem, we used absolute pressure limiter only. Motor current for driving this new actuator was not much higher than older one. Effective stroke volume was about 48 cc. Thrombosis was found around top area and peripheral boundary of the sac and valves. There was no sign of damage from suction problem in the atrium observed at autopsy. Main cause of death was presumed to be progressive formation of thrombosis in the cannulae. In this paper, the results of this experiment are documented.