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Biomedical subjects

K Imoto

Publications and source records attributed to K Imoto.

At least 109 records · Page 6Linked to original sources
PubMed1993

Coronary arterial tree remodeling in right ventricular hypertrophy.

We investigated coronary vascular adaptations occurring in right ventricular hypertrophy (RVH). Six pigs had RVH induced by pulmonary artery stenosis for 5 wk. Three pigs served as controls. At autopsy we made silicone elastomer casts of the right coronary arteries (RCA) and collected morphometric data. We organized the segments and their diameters and lengths into a framework of a modified Strahler's ordering scheme in which the order number of an offspring is increased only if its diameter is greater than the diameters of its parents by a specific amount. The segments of the same order arranged in series are combined into elements. In RVH the total number of orders of vessels was larger than the control by 1; the total number of elements in each order increased greatly, whereas the diameters and lengths of each order decreased somewhat. The total RCA resistance decreased in RVH mainly because the total cross-sectional area (CSA) of every order was increased. Because the diameters of the resistance vessels decreased, this decrease in total RCA resistance was due to a numerical increase in resistance vessels. These findings indicate that new flow channels have been established. In contrast, the RCA was remodeled in that the lumen diameter increased. Pressure-flow curves showed a decrease of coronary resistance in RVH, in agreement with the morphometric findings. We conclude that there is significant remodeling of the coronary arterial vasculature in RVH, and any future analysis of coronary hemodynamics of the right ventricle in hypertrophy must take the morphometric remodeling into account.

Adaptation, Physiological↗
PubMed1993

[Unusual non-infective inflammatory responses around a collagen impregnated vascular prosthesis].

Causes of some complications such as pyrexia, fluid accumulation and unusual scar formation around the graft in "Hemashield" implantation were examined both in vivo and in vitro. In an animal study, the grafts were implanted in the thoracic descending aorta of 9 dogs, and were explanted at 2 weeks after implantation. Macroscopic evaluation of the explants revealed that the graft had no infection, but fluid accumulation and a thick scar layer formation were noticed in the pleural cavity and around the graft. Microscopical observations demonstrated that the impregnated collagen was almost absorbed and numerous plasma cells, lymphocytes and macrophages had infiltrated in the interstices of the Dacron fibers, but neither fibroblasts nor capillary blood vessels. Numerous erythrocyte were also noticed in the graft wall. In vivo experiment of the extract from Hemashield, endotoxin and/or (1-3) beta-D-glucan were detected by the special quantitative methods; Toxicolor and Endospecy. These results indicated that the graft had some contaminants which contained a certain amount of endotoxin, (1-3) beta-D-glucan, resulting in non-infective inflammatory responses around the graft.

Animals↗
PubMed1993

[External work of canine latissimus dorsi muscle after vascular delay].

The first purpose of this study was to estimate physiological performance of skeletal muscle for circulatory assist. External work in the form of linear dynamic contraction was studied in canine latissimus dorsi muscle (LDM). The second purpose was to relate the effect of vascular delay of the LDM to the physiological performance. The left LDM with vascular delay (VD) were compared to the right control LDM (CTR) without vascular delay. Simultaneous dynamic contraction of both VD and CTR LDM were studied under various settings of the preloads and the afterloads. Maximal external work per single contraction were 136 +/- 38 mJ in VD and 81 +/- 21 mJ in CTR. Maximal total work, which includes external work and preload work, were 578 +/- 195 mJ in VD and 407 +/- 146 mJ in CTR. Maximal fractional shortenings of the LDMs were 22.8 +/- 4.7% in VD and 17.5 +/- 2.6% in CTR. The maximal external work of VD was 81% of canine LV stroke work and 620% of canine RV stroke work. The maximal total work of VD was 340% of canine LV stroke work. The fractional shortenings, external work and total work of VD were higher than those of CTR under all loading conditions. The physiologic performance of canine LDM was improved after vascular delay.

Animals↗
PubMed1993

[A successful case of emergency coronary artery bypass grafting for a patient with cardiopulmonary arrest on arrival at our hospital due to acute myocardial infarction].

A successful case of emergency coronary artery bypass grafting for a 62-year-old man with cardiopulmonary arrest due to acute myocardial infarction was reported. He developed cardiopulmonary arrest 4 minutes before arrival at Critical care and Emergency Department of our hospital. The ECG of the patient showed ventricular fibrillation. He was resuscitated successfully 26 minutes after cardiopulmonary arrest. Emergency coronary angiography revealed that LAD just proximal was totally occluded and LCx just proximal was 90% stenosed. As he was still in the state of shock after resuscitation, emergency CABG was performed to LAD and LCx using saphenous vein grafts. The post operative course was uneventful. The patient has resumed a normal and active life-style as a deput principal of a high school one year after operation.

Cardiopulmonary Resuscitation↗
PubMed1993

[Disadvantages of "Gelseal graft" as a vascular prosthesis].

In clinical use, the Gelseal Triaxial graft have been shown to have several problems, such as pyrexia, pleural effusion and seroma formation around the graft. To investigate the cause of these complications, we examined mechanical and biological properties of the graft. The water permeability was found to be 0 ml at 120 mmHg in an in vitro study. Scanning electron microscopical observation revealed that gelatin in the graft wall was not uniform and easily detached from the luminal surface. The amount of impregnated gelatin in the graft was found to be 6.73 mg/cm2. In addition, this graft contained 297 and 73 pg endotoxin in extract/g of graft wt at 25 degrees C 72 hrs as assessed by Toxicolor and Endospecy pyrogen tests, respectively. The grafts were implanted in the descending aorta of 8 dogs for 2 weeks in an animal study. Three out of 8 animals died of graft occlusion. Both macroscopic and microscopic evaluations of the explants from 5 dogs showed that neither fibroblasts nor capillary blood vessels had infiltrated in some area of the graft wall. Serous fluid was found to be retained between the graft and the surrounding host tissue in three cases. These results indicated that the Gelseal graft was easy to implant due to zero porosity, but the coated gelatin was not clean and gelatin was easily detachable. Hence, the graft would be prone to some complications such as pyrexia, immune response, thromboembolism, seroma, and pleural effusion. One must be aware of the potential disadvantages of the Gelseal grafts before using it in patients.

Animals↗
PubMed1993

[Clinical assessment of cerebral infarction, complicated with aortic arch replacement under selective cerebral perfusion].

Since October 1984 to December 1992, 47 aortic arch replacements were performed under selective cerebral perfusion (SCP). Patient age ranged from 19 to 81 years, with an average of 60.2 years. Thirty one patients were male and 16 female. Twenty patients were diagnosed with dissecting aneurysms, 27 true aneurysms. The operative mortality was 14 out of 47 (29.8%) over all. The mortality of dissecting aneurysm related acuity that is 5 of 9 (55.6%) for patients in acute phase, against none in chronic. The operative mortality of true aneurysms was 6 out of 11 (54.5%) for patients who had emergency operation, against 3 out of 16 (18.8%) scheduled, extensive surgery. Cerebral disorders developed on 8 patients out of 44 (18.2%, except 3 operative deaths). The mortality rate of cerebral disorder was 6 out of 8 (75.0%). Six patients with true aneurysm had cerebral infarctions after the surgery. Two patients had already cerebral disorders in advance the surgery. The cause of cerebral infarction was resumed by atherosclerotic materials. Our operative results indicate that cerebral disorder subsequently affects the mortality of aortic arch replacement. For the prevention of cerebral infarction, we modified the method of SCP. We start the SCP at the initiation of total cardiopulmonary bypass, routinely associated to an aortic clamp and cardiac arrest under myocardial protective procedure that is the use of perfusion cooling (30 degrees C, monitored at the esophagus), topical cooling and cold Saint Thomas solution infused in the coronary arteries. When aortic arch replacement is done, we need to make sure a good restarting of the heart and a good recovery of the systemic circulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

[Long-term results of closed mitral commissurotomy--comparative study of closed mitral commissurotomy (CMC), open mitral commissurotomy (OMC) and mitral valve replacement (MVR)].

As the technique of open heart surgery has improved, CMC has been abandoned in favor of OMC and MVR. We evaluated and compared the results of CMC, OMC and MVR. METHOD. Between 1965 and 1978, 141 patients with mitral stenosis (MS) underwent CMC, and late follow-up obtained in 117 (83%) of them (CMC group). Between 1980 and 1989, 72 patients and 37 patients underwent OMC (OMC group) and MVR (MVR group), respectively. Cumulative follow-up periods were 1982, 632 and 200 patient-years in the CMC, OMC and MVR groups, respectively. RESULTS. (1) Survival rate; In the CMC group there were 2 operative deaths due to severe mitral regurgitation (MR). There were 17 late deaths, due to reoperations in 4 patients, cerebral infarction in 4 patients, congestive heart failure in 3 patients, myocardial infarction in 2 patients and unknown causes in 4 patients. The survival rate was 95%, 91% and 86% at 5, 10 and 15 years, respectively, in the CMC group. In the OMC and MVR groups there was no death. (2) The event free rate was 89%, 79% and 58% at 5, 10 and 15 years, respectively, in the CMC group, 97% and 97% at 5 and 10 years in the OMC group, and 95% and 90% at 4 and 5 years in the MVR group. (3) Reoperations; In the CMC group of 40 patients (34%) required reoperations in an average of 10.4 years after the initial operation, due to re-MS in 22 patients, MR in 10 patients and MRS in the 8 patients. Reoperative findings consisted of clefts in the mitral leaflets in 7 patients. There were pulmonary hypertension in 15 patients and tricuspid regurgitation in 22 patients. Fourteen patients underwent tricuspid anuloplasty and one patient underwent a tricuspid valve replacement. In the OMC group one patient required a reoperation due to MR; in the MVR group one patient required a reoperation due to a thrombosed valve. CONCLUSION. In the CMC group the survival rate and the event free rate were lower, and the rate of reoperation was higher than in the other two groups.

Adult↗
PubMed1993

[A case of mitral regurgitation caused by total rupture of the posterior papillary muscle after acute myocardial infarction].

We observed a case of severe mitral regurgitation caused by total rupture of the posterior papillary muscle 13 days after acute myocardial infarction. The patient was a 76-year-old man who suddenly felt anterior chest pain. He was admitted to another hospital with the diagnosis of acute myocardial infarction. Electrocardiogram suggested a posterior infarction. He did well during the first 12 days of hospitalization, but at noon on the 13th day he developed anterior chest pain and dyspnea. Echocardiography demonstrated rupture of the posterior papillary muscle. He was subsequently transferred to our hospital with acute heart failure. He was initially treated with an intra-aortic balloon pump. Cardiac catheterization demonstrated 99% stenosis of segment 2 of the right coronary artery and mitral regurgitation, Sellers' stage IV. Intraoperative findings included total rupture of the posterior papillary muscle. Mitral valve replacement was performed using a Carbomedics prosthetic valve. The patient was discharged 53 days after surgery without heart failure or angina pectoris. This case represents the 6th successful operation of total papillary muscle rupture in Japan.

Aged↗
PubMed1992

Primary structure and distribution of a novel ryanodine receptor/calcium release channel from rabbit brain.

The complete amino acid sequence of a novel ryanodine receptor/calcium release channel from rabbit brain has been deduced by cloning and sequence analysis of the cDNA. This protein is composed of 4872 amino acids and shares characteristic structural features with the skeletal muscle and cardiac ryanodine receptors. RNA blot hybridization analysis shows that the brain ryanodine receptor is abundantly expressed in corpus striatum, thalamus and hippocampus, whereas the cardiac ryanodine receptor is more uniformly expressed in the brain. The brain ryanodine receptor gene is transcribed also in smooth muscle.

Amino Acid Sequence↗
PubMed1992

Pore size and negative charge as structural determinants of permeability in the Torpedo nicotinic acetylcholine receptor channel.

To gain an insight into the molecular basis of ion permeation mechanism through the nicotinic acetylcholine receptor (AChR) channel, we have determined permeability ratios of organic cations relative to Na+ of specifically mutated Torpedo californica AChR channels expressed in Xenopus oocytes. The mutations involved mainly the side chains of the amino acid residues in the intermediate ring, where mutations have been found to exert strong effects on single-channel conductance and ion selectivity among alkali metal cations. The results obtained reveal that both the size and the net charge of the side chains of the intermediate ring are involved in determining the permeability, and provide experimental evidence that the pore size at the intermediate ring is a critical determinant of permeability. Our findings further suggest that changes in net charge exert effects on permeability by affecting the pore size of the channel.

Amino Acid Sequence↗
PubMed1992

Calcium channel characteristics conferred on the sodium channel by single mutations.

The sodium channel, one of the family of structurally homologous voltage-gated ion channels, differs from other members, such as the calcium and the potassium channels, in its high selectivity for Na+. This selectivity presumably reflects a distinct structure of its ion-conducting pore. We have recently identified two clusters of predominantly negatively charged amino-acid residues, located at equivalent positions in the four internal repeats of the sodium channel as the main determinants of sensitivity to the blockers tetrodotoxin and saxitoxin. All site-directed mutations reducing net negative charge at these positions also caused a marked decrease in single-channel conductance. Thus these two amino-acid clusters probably form part of the extracellular mouth and/or the pore wall of the sodium channel. We report here the effects on ion selectivity of replacing lysine at position 1,422 in repeat III and/or alanine at position 1,714 in repeat IV of rat sodium channel II (ref. 3), each located in one of the two clusters, by glutamic acid, which occurs at the equivalent positions in calcium channels. These amino-acid substitutions, unlike other substitutions in the adjacent regions, alter ion-selection properties of the sodium channel to resemble those of calcium channels. This result indicates that lysine 1,422 and alanine 1,714 are critical in determining the ion selectivity of the sodium channel, suggesting that these residues constitute part of the selectivity filter of the channel.

Amino Acid Sequence↗
PubMed1992

Molecular basis for pharmacological differences between brain and cardiac sodium channels.

Sodium channels from brain and heart, whose primary structures are known, differ in their sensitivity to block by the guadinium toxins tetrodotoxin and saxitoxin and to block by external Zn2+ and Cd2+. Studies using site-directed mutagenesis have identified the SS2 and adjacent regions of all four repeats as critical determinants for toxin sensitivity. Within and in the immediate vicinities of the SS2 segments, there are only two amino-acid differences between rat brain sodium channel II and rat heart I sodium channel, both located in repeat I. Here we show that replacement of phenylalanine 385 of brain sodium channel by cysteine that is present at the equivalent position in heart channel (F385C) not only reduces sensitivity to the guadinium toxins but also increases sensitivity to Zn2+ and Cd2+, thus conferring properties of heart sodium channel on brain sodium channel. Replacement of asparagine at the second non-conserved position by arginine (N388R) only marginally affects sensitivity to the toxins, Zn2+ or Cd2+, but this mutation markedly reduces sensitivity to block by Ca2+ and Co2+. The double mutant channel (F385C.N388R) shows combined properties of the two mutant channels. These results give a structural insight into the different properties of the two channel proteins.

Animals↗
PubMed1992

[Comparison of long-term outcome of closed mitral commissurotomy (CMC) versus open mitral commissurotomy (OMC) and mitral valve replacement (MVR)].

To predict the late result of percutaneous mitral balloon valvotomy (PMV), we studied long term outcome of CMC which is similar to PMV in terms of closed heart technic, comparing with those of OMC and MVR. 226 patients with mitral stenosis were studied. 117 patients had CMC, 72 had OMC and 37 had MVR. The cumulative follow up period in these groups were 1892 patient year, 632 patient year and 200 patient year respectively. Postoperative actual survival rate at 5, 10, 15 years in CMC patients were 95 +/- 2%, 91 +/- 3%, 86 +/- 3% respectively. No operative or late death was seen in OMC or MVR patients. Postoperative event free rate at 10 years in OMC or MVR patients (97 +/- 2%, 90 +/- 6%, respectively) were higher than that in CMC patients (79 +/- 4%). Thromboembolism developed in 7 (6%) CMC patients, and 4 of these patients died from cerebral embolism. No patient in OMC or MVR group had thromboembolism. Reoperation was done for mitral restenosis or regurgitation in 40 CMC patients. 15 (38%) of these patients were associated with pulmonary hypertension, and 22 (55%) patients had secondary tricuspid regurgitation. On the other hand, only 1 OMC patient and 1 MVR patient had reoperation due to restenosis or thrombosed artificial valve. These results suggest that PMV should be indicated for restricted cases of mitral stenosis.

Adult↗
PubMed1992

[Recurrent thromboses of the Björk-Shiley valve in a patient with gout].

A 56-year-old male, who had mitral stenosis and gout, underwent mitral valve replacement with the Björk-Shiley valve prosthesis. Four years after the surgery, the patient suddenly became dyspneic on exercise due to malfunctioning valve. Thrombosis was found on the prosthesis, which was replaced again by Björk-Shiley valve. Thrombotest value had been satisfactorily controlled at 12.8 +/- 4.2% with warfarin since the first surgery. Dilazep chlorate also had been prescribed. Hyperuricemia had been controlled with allopurinol. In spite of these combined medical therapy, thrombosed valve recurred. Clotted prosthesis was superseded by Carpentier-Edwards Bioprosthesis. Enhancement of platelet function of the patients with gout and hyperuricemia has been reported. Gout in this case might have influence on the recurrent episodes of thrombosis. Monitoring of platelet function would be necessary in follow-up of a patients with gout and valve replacement.

Equipment Failure↗
PubMed1991

Mapping the site of block by tetrodotoxin and saxitoxin of sodium channel II.

The SS2 and adjacent regions of the 4 internal repeats of sodium channel II were subjected to single mutations involving, mainly, charged amino acid residues. These sodium channel mutants, expressed in Xenopus oocytes by microinjection of cDNA-derived mRNAs, were tested for sensitivity to tetrodotoxin and saxitoxin and for single-channel conductance. The results obtained show that mutations involving 2 clusters of predominantly negatively charged residues, located at equivalent positions in the SS2 segment of the 4 repeats, strongly reduce toxin sensitivity, whereas mutations of adjacent residues exert much smaller or no effects. This suggests that the 2 clusters of residues, probably forming ring structures, take part in the extracellular mouth and/or the pore wall of the sodium channel. This view is further supported by our finding that all mutations reducing net negative charge in these amino acid clusters cause a marked decrease in single-channel conductance.

Action Potentials↗
PubMed1991

A ring of uncharged polar amino acids as a component of channel constriction in the nicotinic acetylcholine receptor.

The channel pore of the nicotinic acetylcholine receptor (AChR) has been investigated by analysing single-channel conductances of systematically mutated Torpedo receptors expressed in Xenopus oocytes. The mutations mainly alter the size and polarity of uncharged polar amino acid residues of the acetylcholine receptor subunits positioned between the cytoplasmic ring and the extracellular ring. From the results obtained, we conclude that a ring of uncharged polar residues comprising threonine 244 of the alpha-subunit (alpha T244), beta S250, gamma T253 and delta S258 (referred to as the central ring) and the anionic intermediate ring, which are adjacent to each other in the assumed alpha-helical configuration of the M2-containing transmembrane segment, together form a narrow channel constriction of short length, located close to the cytoplasmic side of the membrane. Our results also suggest that individual subunits, particularly the gamma-subunit, are asymmetrically positioned at the channel constriction.

Amino Acid Sequence↗
PubMed1991

Rings of anionic amino acids as structural determinants of ion selectivity in the acetylcholine receptor channel.

To gain an insight into the molecular basis of the weak but significant selectivity among alkali metal cations of the nicotinic acetylcholine receptor (AChR) channel, we have determined single-channel conductance and permeability ratios for alkali metal cations on specifically mutated Torpedo californica AChR channels expressed in Xenopus oocytes. The mutations involved charged and polar side chains in the three anionic rings (extracellular, intermediate and cytoplasmic ring) which have previously been found to determine the rate of K+ transport through the AChR channel. The results obtained reveal that mutations in the intermediate ring exert much stronger effects on ion selectivity than do mutations in the extracellular and the cytoplasmic ring. The experimental results, together with simulations of the channel's energy profile, suggest that the amino acid residues forming the intermediate ring come into close contact with permeating cations and possibly represent part of the physical correlate of the postulated selectivity filter in the AChR channel.

Amino Acid Sequence↗