Biomedical subjects

Michiaki Imamura

Publications and source records attributed to Michiaki Imamura.

14 recordsLinked to original sources

PubMed2006

Endothelin receptors, localized in sympathetic nerve terminals of the heart, modulate norepinephrine release and reperfusion arrhythmias.

Endothelin (ET)-1 is an endogenous vasoconstrictor which modulates norepinephrine (NE) release in myocardial ischemia reperfusion. Recent studies have demonstrated the pro- or anti-arrhythmic effects in reperfusion. The present studies were undertaken to test the hypothesis that ET receptors located in sympathetic nerve terminals modulate NE release associated with reperfusion arrhythmias (ventricular fibrillation; VF). Immunohistochemical studies showed that both ETA and ETB receptors exist in the sympathetic nerve varicosities, which were stained positive for tyrosine hydroxylase (TH) in the left ventricular wall in guinea pigs. Isolated guinea pig hearts were subjected to 20 min of normothermic global ischemia followed by 30 min reperfusion. Exogenously applied ET-1 (0.1 and 1 nM) dose-dependently increased NE release and the duration of VF, but these responses were significantly suppressed with the Na(+)/H(+) exchanger inhibitor, 5-(N-ethyl-N-isopropyl)-amiloride (10 microM). The ETA receptor antagonist (BQ123, 1 microM) and nonselective ET receptor antagonist (PD142893, 1 microM) significantly attenuated NE release and VF, whereas the ETB receptor antagonist (BQ788,300 nM) markedly elevated NE release but did not affect VF. These studies provide the first evidence that both ETA and ETB receptors, located in the sympathetic nerve varicosities, modulate NE release, at least in part, in association with reperfusion arrhythmias.

Animals↗

PubMed2006

Cardiopulmonary bypass influences the plasma levels of calcitonin gene-related peptides in dogs: effects of hemofiltration and hemodilution.

Calcitonin gene-related peptides (CGRP), which are potent vasodilators, are elevated during cardiopulmonary bypass (CPB) in humans. We evaluated the plasma levels of CGRP in dogs during CPB with hemofiltration with and without hemodilution. Female beagles were divided into control (n=5) and hemodilution (n=5) groups. The CPB with hemofiltration was performed with or without hemodilution. For the measurement of CGRP, blood samples were collected pre-CPB, during CPB, and post-CPB. The concentrations of CGRP in the hemofiltration solution were measured. Although the CPB elevated the plasma CGRP levels in both groups, its elevation was significant in the hemodilution group when compared to the pre-CPB levels. CGRP levels returned to normal post-CPB. Significant differences were found between the two groups in the CGRP amount in hemofiltration. The results show that hemofiltration should be used during CPB to decrease the plasma levels of CGRP.

Animals↗

PubMed2006

Cardiopulmonary bypass for adults with congenital heart disease: pitfalls for perfusionists.

The fixed incidence of congenital heart defects and improved survival have resulted in increasing numbers of adults with congenital heart disease (CHD) who have undergone complex repairs and/or palliations. Eventually, there will be more adults with CHD than children. They will require cardiac surgical interventions associated with progression of their CHD or for age-related disease, such as coronary revascularization. During bypass, anatomical shunts may exist within or without the heart. Left-to-right shunts can result in dramatically lower systemic blood flow than pump flow due to 'steal', while pulmonary edema ensues due to excessive pulmonary flow. Right-to-left shunts carry risks of massive air embolism and double or triple venous cannulation may be necessary. Cannulation of composite reconstructed aortas may be difficult, risking dissection or aortic obstruction, and double arterial cannulation may be indicated. Aberrant coronary arterial and venous anatomy may .preclude adequate myocardial preservation with common techniques and can be complicated by aortic insufficiency. Valves and conduits may exhibit failure. Conventional monitoring, such as central venous oximetry, may be misleading. Monitoring, such as serial lactate measurement, near-infrared spectroscopy and transcranial Doppler blood velocity, offer advantages for such patients. The perfusionist needs to be aware of such conditions as much congenital aberrancy may present unexpectedly during cardiac surgery.

Adult↗

PubMed2005

Sympathetic denervation and reinnervation after the maze procedure.

UNLABELLED: We evaluated serial changes in cardiac sympathetic nerve distribution using 123I-metaiodobenzylguanidine (123I-MIBG) after the Maze procedure. The Maze procedure, in which multiple incisions are made in the atrium, has been concomitantly performed with mitral valve (MV) surgery in an attempt to eliminate atrial fibrillation (AF). Although attenuation of the sinoatrial node response to exercise and a reduction of left ventricular function (left ventricular ejection fraction [LVEF]) in early stages after the Maze procedure have been suggested, factors leading to these changes have not been clarified. METHODS: Thirteen patients with MV disease were enrolled in this study. Six of them had undergone MV surgery and the Maze procedure (Maze+), and 7 had undergone MV surgery without the Maze procedure (Maze-). All patients underwent cardiac 123I-MIBG imaging preoperatively and 10 d and 1 y after surgery to assess 123I-MIBG uptake (heart-to-mediastinum count ratio of early planar images [H/M]) and the washout rate (WR). Radionuclide ventriculography was also performed to calculate LVEF 3 d after each 123I-MIBG imaging. RESULTS: The LVEF of the Maze+ group significantly decreased 10 d after surgery (44.2 +/- 4.8; mean +/- SD) compared with that before surgery (60.3 +/- 6.9; P < 0.05) and significantly increased at 1 y (65.2 +/- 2.9) compared with that at 10 d (P < 0.05). In the Maze- group, there was no significant change 10 d (53.0 +/- 12.3) and 1 y (58.6 +/- 4.8) after surgery compared with that before surgery (60.4 +/- 4.6) (P = not significant, each). In the Maze+ group, the H/M (1.51 +/- 0.18) was significantly lower at 10 d after than that at the preoperative stage (1.90 +/- 0.25; P < 0.05) but significantly recovered at 1 y (2.23 +/- 0.18; P < 0.05) with a similar transient increase in the WR (36.7% +/- 6.1% at preoperative stage; 46.9% +/- 3.4% at 10 d; 39.9% +/- 6.5% at 1 y; P < 0.05, each). On the other hand, the Maze- group did not show a significant change in the H/M (1.94 +/- 0.32, 2.06 +/- 0.18, and 2.13 +/- 0.17, respectively; P = not significant, each) but did exhibit a significant decrease in the WR (40.4% +/- 5.1%, 37.0% +/- 5.1%, and 32.9% +/- 2.5%, respectively; P < 0.05, each). Changes in the H/M of both groups significantly correlated with the change in LVEF (r = 0.82; P < 0.05), and the WR showed a significant inverse correlation with changes in the LVEF (r = -0.81; P < 0.05). CONCLUSION: Cardiac sympathetic nerves were denervated at early stage and reinnervated at late stage after the Maze procedure. Such adrenergic nerve changes may be correlated, at least in part, with changes in left ventricular function after this procedure.

3-Iodobenzylguanidine↗

PubMed2005

Experimental studies on artificial blood usage for hemodilution during cardiopulmonary bypass.

BACKGROUND: Although hemodilution is usually utilized during cardiopulmonary bypass (CPB), hemodilution can cause adverse effects such as hypotension and hypoxia. The purpose of this study was to evaluate a novel perfluoro-octyl bromide (PFOB) emulsion, one of perfluorochemicals (PFCs) emulsions, administered during hemodilution CPB. METHODS: Fifteen dogs were subjected to CPB for 2 hours under mild hypothermia. Animals were divided into three groups; control group, hemodilution group and PFOB group. During the experiment, hemodynamics, complete blood count and blood chemistry were monitored. In addition, serum complement titer (CH50), bradykinin and histamine concentrations were also measured. RESULTS: Heart rate (HR) was markedly elevated in the hemodilution groups (p<0.05). Mean arterial pressure (MAP) did not change in the three groups. White blood cell (WBC) and platelet (PLT) count did not significantly differ among the three groups. Plasma lactate concentration was markedly elevated only in hemodilution group during late phase of CPB (p<0.05). In the hemodilution group, CH50, bradykinin and histamine, were markedly elevated during the CPB and just after CPB (p<0.05). CONCLUSIONS: The present study demonstrated possible benefits of the new PFC emulsion during cardiac surgery by counteracting the adverse effects of hemodilution during CPB.

Analysis of Variance↗

PubMed2005

Big help for small hearts.

The ACH Heart Center is a comprehensive, full-service resource for infants and children with congenital and acquired heart disease. UAMS physicians and nurses and ACH nurses and staff are here to care for these children both directly and by providing support to pediatricians and primary care physicians within Arkansas and the surrounding states.

Arkansas↗

PubMed2004

Venovenous extracorporeal membrane oxygenation for cyanotic congenital heart disease.

BACKGROUND: Severe, refractory hypoxemia complicating uncorrected cyanotic congenital heart disease is a potentially lethal condition, even when urgent surgical intervention is undertaken. When a viral pneumonia initiates hypoxemia, the likelihood of a satisfactory outcome is further reduced. We examined our policy of venovenous extracorporeal membrane oxygenation support through the hypoxic event and performing delayed surgery, if required, to separate from extracorporeal membrane oxygenation. METHODS: A single institution, retrospective review of an Institutional Review Board approved database was undertaken. Over a 6-year period, 18 instances were identified for 17 patients who became acutely hypoxemic from either inadequate pulmonary blood flow (8 instances) or a viral pneumonia (10 instances) complicating their cyanotic heart disease. Demographics, duration of venovenous extracorporeal membrane oxygenation and outcomes are reported. RESULTS: The length of venovenous extracorporeal membrane oxygenation ranged from 13.5 to 362.5 hours (mean 130 +/- 121 hours). During 10 supports, operations were performed to facilitate weaning from support. In 7 patients, extracorporeal support was weaned during this surgery. Follow-up was obtained in all patients over a period ranging from 4 months to 7 years (mean 39.0 +/- 23.0 months). There were two late deaths due to sepsis 1.4 and 2.5 months after extracorporeal support. CONCLUSIONS: Venovenous extracorporeal membrane oxygenation allows time for the recovery of acute hypoxic insult and resolution of some viral pneumonia processes. Palliative surgical procedures may be safely undertaken during extracorporeal support. Viral pneumonia is a risk for prolonged support. Venovenous extracorporeal membrane oxygenation is useful in these high-risk patients.

Child, Preschool↗

PubMed2004

Magnetic resonance flow analysis of classic and extracardiac Fontan procedures: the seesaw sign.

BACKGROUND: Energy inefficiencies lead to Fontan procedure failures. Our purpose was to quantify energy inefficiencies of various Fontan procedures using flow analysis. MATERIALS AND METHODS: The study included 12 patients with Fontan operations; 7 with classic trans-atrial flow and five extra-cardiac Fontans. Flow analysis was used to determine the systolic and diastolic flow in the superior vena cava and inferior venous circulations (IVC, right atrium or conduit). Retrograde flow fractions were calculated. Inferior venous flow analysis was obtained in 12 patients and superior vena cava in 9 patients. RESULTS: A seesaw pattern (augmented inferior venous flow during diastole and augmented superior vena cava flow in systole) was present in five of seven patients with trans-atrial Fontan procedures, but no patient with an extra-cardiac Fontan procedure. Significant retrograde flow occurred in the superior vena cava in three children with trans-atrial Fontan procedures (retrograde flow fractions of 15-22%). Inferior venous flow occurred predominantly during diastole in five of seven children with trans-atrial Fontan procedures. Retrograde flow occurred in all seven children with the retrograde flow fractions ranging from 9 to 37% (mean 25%). Extracardiac Fontan flow was characterized by continuous balanced flow during systole and diastole. The association of the seesaw pattern with trans-atrial Fontan procedures was statistically significant (p = 0.028). CONCLUSIONS: Classic trans-atrial Fontan procedures are characterized by energy inefficiency creating a seesaw flow pattern of forward and reverse flow. Extra-cardiac Fontan procedures are more energy efficient. Magnetic resonance imaging is useful in detecting flow inefficiencies in patients palliated by the Fontan procedure.

Adolescent↗

PubMed2002

The extracardiac Fontan procedure without cardiopulmonary bypass: technique and intermediate-term results.

BACKGROUND: The extracardiac Fontan procedure (ECF) usually requires cardiopulmonary bypass (CPB). In this report, the results and techniques of this procedure without CPB at a single institution are presented. METHODS: Between August 1992 and December 2001, ECF without CPB was achieved in 24 of 44 patients undergoing an ECF. Mean age at surgery was 5.9 +/- 2.9 years, and mean weight was 20.7 +/- 12.6 kg. Diagnoses were tricuspid atresia in 9 patients, single-ventricle with pulmonary outflow tract obstruction in 7, pulmonary atresia/intact septum in 5, and other complex single-ventricle physiology in 3. Initial palliation was by arterial to pulmonary artery shunt in 21 and pulmonary artery banding in 1. A bidirectional cavopulmonary connection was created in 23 patients. A temporary inferior vena caval-to-atrial shunt was used to complete the procedure without CPB. Median graft size was 16 mm (range 14 to 20 mm). RESULTS: There was no early mortality, and 68% of patients were discharged without complications. Complications included persistent cyanosis in 4 patients, persistent pleural effusions in 2 (one chylous), and phrenic nerve injury in 1. Median postoperative hospital stay was 16 days (range 10 to 50) days. At a mean follow-up of 44 +/- 28 months, there was no conduit obstruction. One patient died 11 months postoperatively, and 1 patient received a heart transplant 26 months post-ECF. CONCLUSIONS: At intermediate term follow-up, the ECF without CPB appears to be safe and technically reproducible in selected cases. Ongoing follow-up of these patients is necessary to document the theoretical advantages of avoiding CPB.

Child, Preschool↗

PubMed2002

Giant pseudoaneurysm of the right ventricular outflow tract after repair of truncus arteriosus: evaluation by MR imaging and surgical approach.

One year after surgical repair of the truncus arteriosus, a 1-year 8-month-old boy was found to have a pseudoaneurysm of the right ventricular outflow tract (RVOT). Cine-magnetic resonance imaging (MRI) showed a narrow communication between the RVOT and aneurysm. MRI was useful to evaluate the anatomical and spatial relations between the pseudoaneurysm and the surrounding structures, therefore an appropriate approach was chosen. Thus, a median sternotomy approach was carried out and ordinary central cannulation was feasible to establish a cardiopulmonary bypass. The defect was successfully repaired with reconstruction using a monocuspid outflow patch. MRI provided useful information for deciding the surgical approach.

Aneurysm, False↗

PubMed2002

Carrier-mediated norepinephrine release and reperfusion arrhythmias induced by protracted ischemia in isolated perfused guinea pig hearts: effect of presynaptic modulation by alpha(2)-adrenoceptor in mild hypothermic ischemia.

Yohimbine, an alpha(2)-adrenoceptor antagonist, has been reported to protect hypoxic myocardium and inhibit carrier-mediated norepinephrine (NE) release and reperfusion arrhythmias (ventricular fibrillation; VF) in normothermic ischemia. In heart surgery, mild hypothermic (tepid) cardioplegia has been reported to reduce metabolic demand and permit immediate recovery of cardiac function. Therefore, we determined the effect of yohimbine on NE release and reperfusion arrhythmias in isolated perfused guinea pig hearts of tepid temperature (32 degrees C) ischemia model. Stepwise increase of global ischemia period (20, 40, and 60 min) induced a progressive increase of NE release and duration of VF. Neuronal uptake 1 inhibitor desipramine (100 nM) and Na(+)-H(+) exchanger inhibitor 5-N-ethyl-N-isopropyl-amiloride (10 microM) decreased NE and VF in 60-min hypothermic ischemia. This indicated that NE release induced by protracted tepid ischemia was due to carrier-mediated release. Yohimbine (1 microM) markedly reduced NE release and VF (p < 0.01 versus control) and 5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine [UK 14,304 (UK); 10 microM], an alpha(2)-adrenoceptor agonist, increased NE release and VF (p < 0.01 versus control). Yohimbine (1 microM) prevented the potentiated effect of UK (10 microM) in hypothermia (p < 0.01 versus UK). Our findings indicate that presynaptic reduction of carrier-mediated NE release seems to be one of the most important factors controlling reperfusion arrhythmias, and alpha(2)-adrenoceptor blockade by yohimbine (1 microM) in tepid ischemia may contribute to effective myocardial protection in terms of NE release and reperfusion arrhythmia.

Adrenergic alpha-2 Receptor Antagonists↗

PubMedDate not supplied

Simplified technique for patch augmentation and chorda reconstruction of left atrioventricular valve in complete atrioventricular septal defect.

Management of the left AV valve is the most crucial component of the repair of complete atrioventricular septal defect (cAVSD). A scarcity or deficiency of leaflet tissue may compromise satisfactory repair in a small number of patients with cAVSD, especially in patients with a normal karyotype. We describe the case of a 44-day-old baby who had cAVSD with severe left atrioventricular valve regurgitation due to dysplastic bridging leaflets. The repair was successfully performed by augmenting leaflet tissue and reconstructing the chorda using single patch. This technique could be one of the options in the repair of valves in order to avoid valve replacement in a small infant, although material of patch and reoperation need to be considered.

Cardiac Catheterization↗

PubMedDate not supplied

Cardioprotective effect of perfluorochemical emulsion for cardiac preservation after six-hour cold storage.

Perfluoro-octyl bromide (PFOB) emulsion is capable of transferring oxygen to tissues even at 4 degrees C, suggesting an application in myocardial preservation. We evaluated the cardioprotective effect of PFOB emulsion added to the storage solution. Guinea pig hearts were isolated (n = 24) and perfused with Krebs-Henseleit solution (KHS) and then cooled and perfused with St. Thomas Hospital II solution (STS). The hearts were stored in three different solutions: STS (STS group), oxygenated (O2) STS (O2 STS group), and O2 STS with PFOB emulsion (30%) (O2 STS + PFOB group) for 6 hours at 4 degrees C. After storage, rewarming was performed, followed by reperfusion with KHS. Left ventricular developed pressure of O2 STS + PFOB group was significantly higher than that of the other groups during reperfusion (p < 0.01). There was no difference among the three groups in O2 extraction and cardiac efficiency; however, cardiac oxygen consumption in the O2 STS + PFOB group significantly improved during reperfusion. In the O2 STS + PFOB group, creatinine kinase, lactate dehydrogenase, and myocardial water content were significantly decreased (p < 0.01). This study suggests that PFOB emulsion is beneficial for the cardioprotection of donor hearts, allowing a prolonged cardiac storage time.

Animals↗

PubMedDate not supplied

The first successful DeBakey VAD child implantation as a bridge to transplant.

A 14-year-old boy with repaired transposition of the great arteries and ventricular septal defect presented with atrial flutter and severe congestive heart failure. Despite successful cardioversion and optimal medical therapy, the patient deteriorated and was supported with extracorporeal membrane oxygenation (ECMO). Two days after initiating ECMO support, we implanted the DeBakey VAD Child ventricular assist device (MicroMed Technology, Inc., Houston, TX) under the Humanitarian Device Exemption program. Later, he was able to pursue normal daily activities including physical rehabilitation and ambulation in the hospital. After 56 days, he underwent a successful cardiac transplantation. After 3 months, he had good cardiac function and no evidence of rejection. The DeBakey VAD Child device is a valuable option for cardiac support as a bridge to transplantation.

Adolescent↗