Biomedical subjects

Ryohei Yozu

Publications and source records attributed to Ryohei Yozu.

27 records · Page 2Linked to original sources

PubMed2003

Neuroprotective effects of N-methyl-D-aspartate receptor antagonist on aspartate induced neurotoxicity in the spinal cord in vivo.

OBJECTIVE: Much evidence has been gathered to show that neurotoxicity of excitatory amino acids is mainly activated through an N-methyl-D-aspartate (NMDA) receptor cascade. We evaluated the protective effects of NMDA receptor antagonists, MK-801 and CGS19755 on spinal cord neurons using the NMDA receptor mediated neurotoxicity model in vivo. METHODS: New Zealand white rabbits underwent an infrarenal aortic isolation. Group A animals (n = 7) received segmental aspartate (50 mM) infusion for 10 minutes. Group B animals (n = 6) were pretreated with MK-801 (6mg/kg), a noncompetitive NMDA receptor antagonist, that was administrated intravenously for 3 hours beginning 1 hour before the segmental infusion of aspartate (50 mM) of 10 minutes. Group C animals (n = 6) received pretreatment with CGS19755 (30mg/kg), a competitive NMDA receptor antagonist, that was administrated in the same fashion as group B, followed by the segmental infusion of aspartate (50 mM). Neurologic status was scored at 12, 24, and 48 hours after operation using the Tarlov score. All the animals were sacrificed for histologic assessment at 48 hours. RESULTS: Group A animals exhibited paraplegia or paraparesis with marked neuronal necrosis. Group B and C animals showed significantly better neurologic function compared with group A (p = 0.0013, A vs. B) (p = 0.0011, A vs. C). Pathohistological change was not observed in group B and C animals. CONCLUSIONS: NMDA receptor antagonists can have protective effects on spinal cord neurons against aspartate induced neurotoxicity. This model may be useful in assaying protective agents in the spinal cord against neuronal injury mediated by NMDA receptors in vivo.

Animals↗

PubMed2003

Cardioscopic guidance of linear lesion creation for radiofrequency ablation.

BACKGROUND: The broad use of catheter ablation of atrial fibrillation is limited by the difficulty inherent in creating transmural linear lesions under fluoroscopy. Therefore, we evaluated cardioscopy as a more accurate method of guiding the catheter for the placement of linear lesions. METHODS: Nineteen swine underwent endocardial ablation to create linear conduction block lesions in the right atrium under cardioscopy (group I, n = 13) or fluoroscopy (group II, n = 6). In both groups, the linear lesion was created between the superior and inferior vena cava, perpendicular to hexapolar electrodes placed on the epicardial surface. Each swine received two pairs of epicardial hexapolar electrodes: one pair to measure the conduction delay time across the ablated line and another pair for pacing. The time spent to complete the ablation, number of trials and effective ablations, ratio of effective ablations to trials, length of the lesion, conduction delay under pacing, and postmortem pathology were compared between the two groups. RESULTS: Statistically significant differences were found for the time required for ablation, ratio of effective ablation to total number of trials, and conduction delay. Histologic analysis revealed more homogenous, continuous lesions in group I. CONCLUSIONS: Cardioscopy facilitated the placement of a conduction block line more efficiently than ablation performed under fluoroscopy. Landmarks of tissue relevant to ablation are readily visualized by cardioscopy. Moreover, cardioscopy can be useful for the development of a guiding catheter for the ablation of atrial fibrillation.

Animals↗

PubMed2003

Liberal use of tricuspid valve detachment for transatrial ventricular septal defect closure.

BACKGROUND: Although temporary tricuspid valve detachment is useful for improved visualization of ventricular septal defect through right atriotomy, liberal use of this adjunct is not widely supported, mainly because of concerns about iatrogenic complications such as heart blocks and tricuspid valve dysfunction. The objective of this study was to determine whether liberal use of this adjunct can improve operative outcome. METHODS: Between January 1997 and March 2002, trans-atrial closure of isolated ventricular septal defect (conoventricular or canal type) was performed in 87 consecutive patients. Tricuspid valve detachment was used in 4 out of 44 patients (prudent-use group) and 19 out of 43 patients (liberal-use group) in the first and second half of this period, respectively (p = 0.0002). Patient demographics and use of other surgical and cardiopulmonary bypass techniques remained virtually unchanged during this period. RESULTS: In the prudent-use group, there was one operative death with prolonged bypass time and one residual defect that required reoperation; neither of these patients underwent tricuspid valve detachment. All other patients (both groups) were free from mortality and clinically significant complications, including heart block, tricuspid regurgitation, and residual defect. The liberal-use group had shorter cardiopulmonary bypass time than the prudent-use group (59 +/- 14 vs 67 +/- 22 minutes, p = 0.037). CONCLUSIONS: Tricuspid valve detachment should be used liberally for moderate- or even low-difficulty exposure of ventricular septal defect, regardless of patient background, because it is a safe and effective adjunct that can improve speed, programmability, reproducibility, and reliability.

Adolescent↗

PubMed2003

Apico-pulmonary artery conduit repair of congenitally corrected transposition of the great arteries with ventricular septal defect and pulmonary outflow tract obstruction: a 10-year follow-up.

BACKGROUND: In conventional repair of the congenitally corrected transpositions of the great arteries associated with ventricular septal defect and pulmonary outflow tract obstruction, the placement of the left ventricle-pulmonary artery conduit is at risk owing to probable compression by the sternum, heart block, or injury to the mitral anterior papillary muscle. Apical placement of the left ventriculotomy for the inflow conduit rather than in the midportion or base placement may avoid these complications, although this results in a long and winding extracardiac conduit that may be short-lived because of the proliferation of pseudointima. METHODS: Between 1985 and 1990, a nonvalved Dacron woven-fabric graft conduit was placed between the left ventricular apex and pulmonary artery in 5 patients (mean age, 6.2 +/- 1.7 years) who were then followed for at least 10 years. RESULTS: No iatrogenic heart blocks or mitral regurgitation developed. All patients were complaint-free during the follow-up period, although 1 patient who was clinically well died suddenly in the 10th follow-up year. Cardiac catheterization in the 10th follow-up year indicated a pressure gradient of 21 +/- 6 mm Hg across the conduit, and angiography revealed that the conduit diameter was 91% +/- 6% of the original conduit diameter. CONCLUSIONS: The reportedly poor early and late outcomes that occur after a conventional repair of congenitally corrected transpositions of the great arteries associated with ventricular septal defect and pulmonary outflow tract obstruction, which places an extracardiac conduit between the left ventricle and the pulmonary artery, may be partially neutralized by relocating the inflow position to the apex.

Abnormalities, Multiple↗

PubMed2003

Mortality and morbidity after total arch replacement using a branched arch graft with selective antegrade cerebral perfusion.

BACKGROUND: The early outcome after aortic arch surgery has improved. However, some operative survivors have died as a result of postoperative problems soon after discharge. This study determines the factors affecting mortality within 1 year of total arch replacement. METHODS: Between July 1993 and November 2001, 103 patients (mean age 65 +/- 11 years, 26 women, 35 dissections) underwent total arch replacement through a median sternotomy using a branched arch graft with selective cerebral perfusion. Eighteen operations including 14 acute dissections were performed on an emergency basis. Concomitant procedures were root replacement in 5 patients, mitral valve replacement in 1, coronary artery bypass in 14, and open endovascular stent-graft in 9. The average time (minutes) for bypass, aortic cross-clamp, selective cerebral perfusion, and distal arrest were respectively 273 +/- 79, 163 +/- 54, 145 +/- 36, and 69 +/- 22. RESULTS: Mechanical heart support was necessary in 3 patients. Stroke occurred in 9 patients, transient neurologic dysfunction in 7, and paraplegia/paraparesis in 4. The only independent determinant for postoperative stroke was a history of stroke (odds ratio 16.3, 95% confidence interval: 2.8 to 93.8). Thirty-one patients required ventilator support for more than 5 days. Hemodialysis was needed in 5 patients. Sternal infection or mediastinitis occurred in 6 patients. The in-hospital mortality was 12% (12 of 103). The actuarial survival rate at 1 year was 83%, and was 67% at 5 years. For the 1-year mortality independent determinants were emergency surgery (odds ratio 5.3, 95% confidence interval: 1.6 to 17.9) and age 75 years or older (odds ratio 4.0, 95% confidence interval: 1.1 to 13.9). CONCLUSIONS: Total arch replacement using a branched arch graft with selective antegrade cerebral perfusion has a favorable 1-year mortality rate except for patients undergoing emergency surgery and for elderly patients.

Adult↗

PubMed2003

Effects of atrial fibrillation on coronary artery bypass graft flow.

OBJECTIVES: No detailed studies exist of coronary artery bypass graft flow during atrial fibrillation. We examined the effects on bypass graft flow of atrial fibrillation following coronary artery bypass grafting. METHODS: Immediately after surgical revisualization, atrial fibrillation was induced in 18 patients by high frequency atrial pacing. Hemodynamic variables were measured in sinus rhythm and atrial fibrillation. The graft flow in pedicled left internal thoracic artery grafts and in saphenous vein grafts was also measured using transit-time flowmetry. RESULTS: Left internal thoracic artery graft flow had a greater diastolic component than saphenous vein graft flow, as shown by the percent diastolic time-flow integral (86 +/- 10% in the left thoracic artery and 62 +/- 12% in the saphenous vein, P < 0.0001). The induced atrial fibrillation caused significant deterioration in hemodynamics: heart rate and central venous pressure increased, and mean arterial pressure and cardiac index decreased (all P < 0.0025). In left internal thoracic artery grafts (n = 18) and also in saphenous vein grafts (n = 20), graft flow decreased significantly with atrial fibrillation (44.3 +/- 26.2 to 26.2 +/- 20.7 ml/min in the left internal thoracic artery, P = 0.0003; 39.7 +/- 15.6 to 33.3 +/- 14.3 ml/min in the saphenous vein, P = 0.001). The reduction in graft flow due to atrial fibrillation was much larger in left internal thoracic artery grafts than in saphenous vein grafts (P = 0.0008). CONCLUSIONS: Direct measurement of coronary artery bypass graft flow shows that atrial fibrillation after surgery significantly reduces graft flow. The effect is much larger in left internal thoracic artery grafts with their strong diastolic component than in saphenous vein grafts.

Aged↗

PubMed2003

An estimation method of hemolysis within an axial flow blood pump by computational fluid dynamics analysis.

Evaluation of hemolysis within a blood pump on a computer is useful for developing rotary blood pumps. The flow fields in the axial flow blood pump were analyzed using computational fluid dynamics (CFD). A blood damage index was calculated based on the changes in shear stress with time along 937 streamlines. Hemolysis of the pumps was measured using bovine blood. A good correlation between the computed and measured hemolysis results was observed. CFD analysis is useful for estimating hemolysis of rotary blood pumps on a computer.

Animals↗

PubMed2003

Computational fluid dynamics analysis of an intra-cardiac axial flow pump.

A low rate of hemolysis is an important factor for the development of a rotary blood pump. It is, however, difficult to identify the areas where hemolysis occurs. Computational fluid dynamics (CFD) analysis enables the engineer to predict hemolysis on a computer. In this study, fluid dynamics throughout intracardiac axial flow pumps with different designs were analyzed three-dimensionally using CFD software. The computed pressure-flow characteristics of the pump were in good agreement with the measurements. The Reynolds shear stress was computed along particle trace lines. Hemolysis was estimated on the basis of shear stress (tau) and its exposure time (Deltat): dHb/Hb = 3.62 x 10(-7)(tau)(i)(2.416) x Delta(t)(i)(0.785). Particle damage increased with time along the particle trace lines. Hemolysis of each of the pumps was measured in vitro. The computed hemolysis values were in good agreement with the experimental results. CFD is a useful tool for developing a rotary blood pump.

Computational Biology↗

PubMed2002

Minimally invasive cardiac surgery by the port-access method.

Recently, minimally invasive surgery has come to be an important theory in cardiac surgery, the goal of which is shortening of hospital stay, earlier recovery of employment, and cosmetics. In this paper, we will describe our experience with port-access cardiac surgery conducted under the support of our new technology. This study assesses the quality of cardiac surgery performed by the port-access method. The author developed a direct endoaortic clamp balloon (Yozu balloon). This balloon is a triple-lumen balloon catheter of 3.6 mm in outer diameter and 40 cm in full length. The balloon is inserted directly into the ascending aorta. Injection of cardioplegic solution and aortic vent can be conducted. Also, we introduce a modified Cosgrove flex clamp to apply in small-incision surgery, aiming at a less invasive procedure. The modified point is that the original, united Cosgrove flex clamp can be divided into the handle part equipped with a ratchet, and the bellows part equipped with a clamp jaw. By this modification, it became possible to apply the Cosgrove flex clamp transthoracically; that is, it became possible to conduct aortic clamping safely and securely through this small port of 8 mm in diameter. Port-access cardiac surgery is one of the developing and promising methods of cardiac operation. In view of future technological progress, we can expect the gradual but wide popularization of this method.

Cardiac Surgical Procedures↗