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Biomedical subjects

A Ishizawa

Publications and source records attributed to A Ishizawa.

At least 19 recordsLinked to original sources
PubMed2005

Suppression of Hall-term effects by gyroviscous cancellation in steady collisionless magnetic reconnection.

The formation of an ion-dissipation region, in which motions of electrons and ions decouple and fast magnetic reconnection occurs, is demonstrated during a steady state of two-dimensional collisionless driven reconnection by means of full-particle simulations. The Hall-term effect is suppressed due to the gyroviscous cancellation at scales between the ion-skin depth and ion-meandering-orbit scale, and thus ions are tied to the magnetic field. The ion frozen-in constraint is strongly broken by nongyrotropic pressure tensor effects due to ion-meandering motion, and thus the ion-dissipation region is formed at scales below the ion-meandering-orbit scale. A similar process is observed in the formation of an electron-dissipation region. These two dissipation regions are clearly observed in an out-of-plane current density profile.

Journal Article↗
PubMed2004

Shell model for rotating turbulence.

A modified shell model for rotating turbulence is proposed. The effect of rotation is introduced by a randomized linear term. Randomization is shown to be important in correctly modeling the rotation effect. Numerical simulation shows that the exponent of the energy spectrum in the inertial range changes from -5/3 to -2 as rotation rate increases. The mechanism behind this change is explained by weak turbulence theory and supported by numerical results.

Journal Article↗
PubMed2002

Measurements of blue shifts due to collisionless absorption in harmonic generation from subpicosecond laser-produced plasmas.

Harmonic generation from solid surface plasmas is studied using a subpicosecond Nd:glass laser system. For a 45 degrees angle of incidence, the speculars up to the fifth harmonics are blue shifted when the laser intensity exceeds 2 x 10(16) W cm(-2). The second harmonic is blueshifted by approximately 16 A, and the fifth harmonic is blue shifted by approximately 51 A for p polarization at the intensity of 1 x 10(17) W cm(-2). We observed the blue shift of the fifth harmonics and found that the magnitude of blue shift is higher compared with that for the second harmonics. The blue shift is interpreted as a collisionless absorption due to the anomalous skin effect. It is also found that the divergence of harmonics preserves a smaller divergence when using a shorter pulse length for the driving laser.

Journal Article↗
PubMed2001

Direct closure of ostium primum defect in the repair of atrioventricular septal defect.

BACKGROUND: Patch closure is generally performed for atrial septation of an atrioventricular septal defect. We recently developed a new surgical technique for repairing atrioventricular septal defects that avoids the use of any patch material for closing the atrial septal defect. We report our experience with this procedure. METHODS: Seven patients (complete type: 5, partial type: 2) underwent this new operation. The diameters of the atrial septal defects were measured by transesophageal echocardiography. The preoperative electrocardiograms were compared with those taken after the operations. RESULTS: Diameters of the atrial defects ranged from 3 to 10 mm. Electrocardiograms before and after the operations did not change. No significant atrioventricular valve regurgitation and no residual shunts were detected by postoperative echocardiography. CONCLUSIONS: This method simplifies the repair of atrioventricular septal defects. In the short-term results, no arrhythmia and no valve regurgitation was seen.

Blood Vessel Prosthesis Implantation↗
PubMed2001

Non-surgical closure of atrial septal defect.

BACKGROUND: Recently many devices for the transcatheter closure of atrial septal defect (ASD) were developed in the world. Several ASD closing devices, such as Clamshell device, buttoned device, ASD occluder system (ASDOS), Angel Wings, are not fully acceptable from a practical point of view. We reported the clinical trials of transcatheter closure of ASD for Clamshell double umbrella device and Amplatzer septal occluder (ASO) in Japan. METHODS: Clamshell devices were implanted in 11 patients. Clinical trials for ASO device were carried out in 34 patients in Japan. We reported the results of 17 patients in National Children's Hospital. RESULTS: Clamshell devices were implanted in all of the patients successfully. Minimal residual shunt was present in four patients (36%), 1 year after the procedure by Doppler color flow imaging. Nine of 11 umbrellas demonstrated fracture of the stainless steel arm. Arm fracture occurred between 1 week and 12 months after implantation. The implantations of ASO device were successful in all of the 17 patients. Sixteen out of 17 (94.1%) had complete closure in the average observation period of 5.5 months. Complications were minimal and transient. CONCLUSIONS: With respect to complete closure rate, easy manipulation, and complication rate, ASO is the best transcatheter ASD closure device among all the devices at the present time.

Adolescent↗
PubMed2001

Quantitative analysis of hypertrophy in cardiac chambers in cyanotic tetralogy of Fallot.

Although early total corrective repair for cyanotic tetralogy of Fallot is now safely performed at many institutions, long-term complications after surgical repair have been demonstrated. Therefore, the optimal procedure and timing for surgical treatment remain controxersial. In the present study, we conducted a quantitative analysis of the hypertrophy of all four chambers of 87 autopsied hearts of cyanotic tetralogy of Fallot and 71 normal control hearts utilizing the myocardial mass index, and evaluated the progression of lesions with advancing age. In cyanotic tetralogy of Fallot, hypertrophy of the right ventricle progresses immediately after birth, with that of the right atrium developing soon after. The left side of the heart is normal or slightly atrophied which could be corrected by sufficient palliative intervention or total corrective repair. The growth curves of both ventricles were parallel to those of normal hearts for the period studied. Pulmonary atresia, palliative operation, and total corrective repair have been shown to have some influence on the morphological characteristics of hearts of cyanotic tetralogy of Fallot.

Child, Preschool↗
PubMed2001

[Middle fossa arachnoid cyst presenting an interesting clinical course: a case report].

The mechanism of the disappearance of arachnoid cysts is not fully understood. We report a case of arachnoid cyst which disappeared after head injury. A 28-year-old male was found to have an arachnoid cyst in the left middle fossa following head injury. We followed him up, because he had no symptoms. Two weeks later, he suffered from severe headache. CT image showed a dilatation of the subdural space, and his symptom deteriorated. We performed subdural-perifocal shunt, but one month after, he developed a subdural hematoma. The subdural hematoma was irrigated through a burr hole. His symptom disappeared post operatively. Two months later, CT image showed the disappearance of subdural hematoma and the arachnoid cyst. This case suggested one of the mechanisms involved in the disappearance of arachnoid cyst after head injury.

Adult↗
PubMed2001

Variations observed during a 1999 dissection course--their sum and analysis.

A systematic study of anomalies in all body areas of 12 male and 12 female cadavers was attempted from data obtained during a 1999 dissection course. A total of 229 anomalies (132 in males, 97 in females) were observed, and they were comprised of 142 varieties. Classified by system, there were 71 (45 varieties) muscular, 118 (71) vascular, 29 (18) neural, 10 (7) visceral and 1 bone anomaly; by region, there were 50 in the head and trunk, 56 in the upper limbs, and 52 in the lower limbs. The other 71 anomalies were vascular ones confined to the viscera (61) and visceral (10). A maximum of 26 anomalies, including 10 muscular, 14 vascular and 2 neural anomalies, were ascertained to exist coincidentally in a single male. Among vascular anomalies, the visceral ones (61) were dominant. In all structures, 75% of the varieties of anomalies were single occurrences. In the text, the multiple occurrence of anomalies in an individual and their relationships are discussed.

Aged↗
PubMed2000

Heart transplantation in children in foreign countries with reference to medical, transportation, and financial issues.

Heart transplantation is increasingly becoming accepted worldwide as therapy for end-stage heart failure not only in adult patients but also in pediatric practice. The new law in Japan for organ transplantation from brain-dead patients was established on 16 October 1998, but there is no definite law or protocol for brain death in children under the age of 6 years and children less than 15 years of age cannot become donors. These facts make organ transplantation from the cadavers of neonates, infants and young children almost impossible in Japan, even though there are children who need heart or heart-lung transplantation. The present authors have to date transferred 8 patients to the USA or Germany for heart transplantation: 4 successfully underwent heart transplantation, but 4 died during the waiting period overseas. There are many things to consider; not only the medical problems involved in transportation, but also the financial issues when transferring patients to other countries. This report details the experience with the 8 cases that were transferred overseas for heart transplantation, and highlights the problems that need to be considered.

Child↗
PubMed2000

Influence of age (body size) on the Fontan circulation--analysis by a theoretical model.

Among the original selection criteria for the Fontan operation, the recommended age at the time of surgery has been 4 years or older, but recent clinical data have indicated the feasibility of this procedure in younger patients. Because age may influence the properties of the systemic vascular bed, changes in systemic vascular resistance (Rs) and systemic vascular compliance (Cs) associated with physical development were quantified in 86 pediatric patients without known abnormalities of the systemic circulation, and the effects of age (body size) on Fontan circulation were then analyzed using an analytical model of the cardiovascular system. As the body surface area (BSA) of the patient decreased, Cs also decreased significantly (r=0.81, p<0.001). Based upon this relationship between BSA and Cs, the analytical model showed that the impedance (ventricular afterload) of the Fontan circulation significantly increased as Cs decreased with the decrease in BSA. Moreover, the increase in impedance in response to changes in heart rate or Rs was inversely proportional to the BSA. However, these findings were significant only when the BSA was below 0.3 m2. Small BSA, or a lower age, has minimal effects on the Fontan circulation until it comes close to the infant value, and thus the Fontan procedure may be feasible much earlier than formerly recommended when the hemodynamics are otherwise acceptable.

Age Factors↗
PubMed1999

Correlation of anatomic and hemodynamic features with aortic valve leaflet deformity in doubly committed subarterial ventricular septal defect.

The records of 153 patients with doubly committed subarterial ventricular septal defect (DCVSD) who underwent intracardiac repair were analyzed to evaluate factors responsible for aortic valve leaflet deformity. The patients were divided into two groups according to their echocardiographic and angiographic features as well as anatomic findings at operation: DCVSD without (17/153, 11.1%) and with arterial valve offsetting (136/153, 88.9%). Aortic regurgitation (AR) was much more prevalent in the patients with (50.0%) than in those without leaflet deformity (2.2%, P < 0.01). Arterial valve offsetting is one of the major contributing factors to the development of leaflet deformity, accounting for 5.9% in the patients without offsetting and 46.3% in those with offsetting (P < 0.01). Among the patients with arterial valve offsetting, the pulmonary-to-systemic pressure ratio was significantly higher (P < 0.01) in the patients without (0.76 +/- 0.14) than in those with leaflet deformity (0.36 +/- 0.12), suggesting that pulmonary hypertension might prevent the aortic valve leaflet from prolapsing in DCVSD. In addition, increased severity of aortic valve leaflet deformity and subsequent AR were observed with increasing age. These results suggest that aging and the presence of arterial valve offsetting as well as the absence of pulmonary hypertension might be factors responsible for aortic valve leaflet deformity and subsequent AR in DCVSD. The anatomic and hemodynamic features in DCVSD have a great impact on the development of aortic valve leaflet deformity and subsequent AR.

Adolescent↗
PubMed1999

Long-term results of the fenestrated Fontan operation. Progress of patients with patent fenestrations.

The fenestrated Fontan operation was introduced as a modification of the "completed" Fontan operation for patients with high risk factors, and low operative mortality has frequently been reported. However, use of the umbrella device is now restricted, and this procedure should be performed without subsequent closure. In this paper, we review our clinical experience with this procedure and discuss ongoing problems. Sixteen patients (4 tricuspid atresia and 12 other cardiac anomalies including 5 cases of univentricular heart) underwent the fenestrated Fontan operation (7 atriopulmonary and 9 total cavopulmonary connection). All of them have some risk factors for a completed Fontan operation. There were three early deaths of the 16. Two experienced an anticipated thromboembolic accident, one of which involved the pulmonary aspect while the other involved the arterial aspect. Patients who survived the operation have progressed well and have a clinical status of New York Heart Association class I, with the exception of one late death due to congestive heart failure. There have been no thromboembolic accidents in this group during the late follow-up period. Spontaneous closures of the fenestrations were noted in two patients. The late mean Qp/Qs value in patients with patent fenestrations was 0.80 +/- 0.1, SaO2 was 88.8 +/- 5.6%, and right atrial pressure was 9.7 +/- 3.8 mmHg. No major problems have been encountered in patients with a patent fenestration over extended periods. A modified Fontan operation to fit a permanently open fenestration may be considered as a final surgical option for certain high-risk patients.

Adolescent↗
PubMed1998

Hemolysis complicating coil occlusion of patent ductus arteriosus.

We report on 5 patients who developed hemolysis (the Hemolysis group) following coil occlusion for PDA, and compare their data to 66 cases which were not complicated by hemolysis despite residual leak (the No Hemolysis group). A significant leak with a heart murmur was more frequent in the Hemolysis group than in the No Hemolysis group. The ratio of the sum of the loop diameter of coils to the minimal diameter of the ductus (C/D) in those who developed persistent hemolysis that needed a second intervention (2.2+/-0.4) was significantly smaller than in the No Hemolysis group (3.1+/-1.1). Persistent hemolysis can occur if a significant residual shunt remains after implantation of coils with small C/D. As this complication may be avoided by complete closure or, if not complete, a minimal leak, we should be careful to make residual leaks as small as possible by the use of multiple coils.

Anemia, Hemolytic↗
PubMed1998

Transcatheter occlusion of patent ductus arteriosus with a new detachable coil system (DuctOcclud): a multicenter clinical trial.

A multicenter clinical trial of DuctOcclud, a new detachable coil for transcatheter occlusion of patent ductus arteriosus (PDA), was conducted. DuctOcclud was used in 35 patients (12 male and 23 female) for transcatheter occlusion of PDA between January, 1996, and April, 1997. The age of the patients ranged from 0.5 to 27.2 years (median 7.6 years) and weight from 6.3 to 70.0 kg (median 23.0 kg). The smallest diameter of PDA was 2.0+/-0.7 mm (range 1.0-3.3 mm). Pulmonary-systemic flow ratio (Qp/Qs) was 1.3+/-0.3 (range 1.0-2.2). The coils were successfully implanted in 32 (91%) patients. Of 31 patients who were followed 6 months after the procedure, 26 (84%) had no residual shunt and 5 (16%) had trivial residual shunt. One patient had infective endocarditis 1 month after the procedure but recovered completely. There were no incidences of coil embolization, hemolysis, late coil migration, or pulmonary artery stenosis. We conclude that DuctOcclud is a safe and effective device of transcatheter occlusion of PDA.

Adolescent↗
PubMed1997

Balloon angioplasty for aortic coarctation--report of a questionnaire survey by the Japanese Pediatric Interventional Cardiology Committee.

The aim of this study was to analyze the results of a questionnaire survey regarding acute and late effects of balloon angioplasty for aortic coarctation in Japan. Considerable controversy still exists regarding the effectiveness and safety of balloon angioplasty in native coarctation. Moreover, little information about this mode of treatment is available from Japan. A questionnaire was sent to 55 Japanese institutions with pediatric cardiology units. A total of 208 patients from 35 institutions were reported and analyzed for indications for balloon angioplasty, acute and late results, and complications. Balloon angioplasty was performed in 56 patients with native coarctation (group I) and in 152 patients with postoperative recoarctation (group II). In group I, the pressure gradient across the coarcted site decreased significantly from 34 +/- 19 to 16 +/- 21 mmHg (p < 0.001), and the diameter of the coarcted site increased significantly from 3.7 +/- 1.7 to 6.0 +/- 2.5 mm (p < 0.001). In group II the pressure gradient significantly decreased from 41 +/- 20 to 15 +/- 15 mmHg (p < 0.001) and the diameter of the coarcted site significantly increased from 4.2 +/- 2.2 to 6.8 +/- 3.1 mm (p < 0.001). The restenosis rate was significantly higher in group I (19/41, 46%) than in group II (25/139, 18%) (p = 0.0006). Redilation was successfully performed in 27 of 29 of the patients with restenosis. Major complications included femoral pulse loss, transient bradycardia, and arrhythmia. No patient died of a cardiac event related to the procedure. The significant risk factors for late restenosis included type of coarctation, age under 4 months, balloon size used, pressure gradient and coarctation diameter before the procedure. Balloon angioplasty is a suitable treatment for aortic coarctation in both native coarctation and postoperative recoarctation. Restenosis was significant after initial balloon angioplasty in native coarctation but redilation was effective in most cases. The most significant risk group for restenosis is young children with native coarctation.

Adolescent↗