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Biomedical subjects

P A Ribeiro

Publications and source records attributed to P A Ribeiro.

At least 19 recordsLinked to original sources
PubMed2006

VUV spectroscopy of water under cellular conditions.

The understanding of radiation damage within cells, and thence mutagenesis, depends upon a detailed knowledge of the spectroscopy and dissociation dynamics of water. Results of a new study of the electronic state spectroscopy of water, using synchrotron radiation are reported. In order to gain some insight into how the spectroscopy and dissociation dynamics of water is influenced by its environment we also report photo-absorption spectra of water within thin films of poly(o-methoxyaniline) which have been suggested as a good mimic for biological membranes in the cellular environment. Comparison of these spectra with those of gaseous water and condensed amorphous water ice suggest that water in such films is similar to gaseous water and does not show the blue shift suggested in some cellular models. The lowest energy of OH production from dissociation of water in the cellular environment may therefore be around 6.7 eV (185 nm).

Cell Membrane↗
PubMed2006

Novel vasopressin type 2 (AVPR2) gene mutations in Brazilian nephrogenic diabetes insipidus patients.

Nephrogenic diabetes insipidus (NDI) is an inherited disorder characterized by renal resistance to the antidiuretic effect of arginine vasopressin (AVP), resulting in polyuria, polydipsia, and hypoosmolar urine. In the vast majority of cases, NDI is associated with germ-line mutations in the vasopressin receptor type 2 gene (AVPR2) and in about 8% of the cases with the water channel aquaporin-2 gene (AQP-2) mutations. To date, approximately 277 families with 185 germ-line mutations in the AVPR2 gene have been described worldwide. In the present study, the AVPR2 gene was genotyped in eight unrelated Brazilian kindred with NDI. In five of these NDI families, novel mutations were noted (S54R, I130L, S187R, 219delT, and R230P), whereas three seemingly unrelated probands were found to harbor previously described AVPR2 gene mutations (R106C, R137H, R337X). Additionally a novel polymorphism (V281V) was detected. In conclusion, although NDI is a rare disease, the findings of mutations scattered over the entire coding region of the AVPR2 gene are a valuable model to determine structure function relationship in G-protein-coupled receptor related diseases. Furthermore, our data indicate that in Brazil the spectrum of AVPR2 gene mutations is "family specific".

Amino Acid Sequence↗
PubMed2000

Long-term clinical results after stent implantation in old obstructed saphenous vein grafts.

STUDY OBJECTIVE: To assess the long-term clinical outcome of treating patients with coronary artery disease and obstructed saphenous vein grafts (SVGs) with stents deployed by oversized balloon catheters. DESIGN: The study included 89 of 92 consecutive patients who had 121 SVG stent implants (average, 1.4 stents per patient). We aimed at achieving a negative stenosis using oversized balloons to achieve a catheter to artery ratio of 1.1:1, and a 100% follow-up at 24+/-14 months (range, 0 to 54 months) was achieved. PATIENTS: As 3 of 92 patients died during hospital admission, the study follow-up population consisted of 89 of 92 patients (mean age, 67+/-10 years). The age of the SVGs was 10+/-4 years. RESULTS: We implanted 118 Palmaz-Schatz and 3 Gianturco-Roubin stents. Procedural success was achieved in 87 of 92 patients (94.5%; < 50% stenosis, and no death, Q-wave acute myocardial infarction, or coronary artery bypass graft [CABG]). Mean SVG stenosis diameter was reduced from 80+/-13% to -11+/-12% (p<0.001) and mean luminal diameter increased from 0.6+/-0.5 mm to 3.3+/-0.8 mm (p<0.001). At follow-up, angina pectoris had developed in 42 of 89 patients (47%), acute myocardial infarction in 12 of 89 patients (14%), reperformed CABG in 12 of 89 patients (14%), cardiac death in 10 of 89 patients (11%), and unrelated death in 6 of 89 patients (7%). Coronary angiography was performed in 37 of 89 patients (42%), with restenosis in 16 of 37 patients (43%) and disease progression at other sites in 11 of 37 patients (30%). Only 25 of 89 patients (28%) experienced event-free survival at follow-up. CONCLUSIONS: Despite high procedural success and excellent angiographic results with oversized balloon catheters, the long-term clinical outcome of SVG stent implantation is suboptimal.

Aged↗
PubMed2000

Immediate and long-term results comparing coronary versus biliary tubular-slotted stents to treat old obstructed saphenous vein grafts.

Stenting of old obstructed saphenous vein grafts improves immediate angiographic results and long-term clinical outcome compared to standard balloon angioplasty. Comparison of results and long-term clinical outcome between different types of stents in the treatment of vein graft disease is scarce. The authors studied two matched groups of 33 patients each, receiving either coronary or biliary tubular-slotted stents in old vein graft lesions to compare immediate results and long-term clinical outcome. Patients in the two groups were matched for age and left ventricular function. Baseline angiographic characteristics, the minimal luminal diameter (MLD) (0.68 +/- 0.56 mm vs 0.61 +/- 0.51 mm, p = 0.9), and diameter stenosis (DS) (81 +/- 14% vs 82 +/- 15%) were similar between the groups. After stenting, the MLD (3.15 +/- 0.65 mm vs 3.37 +/- 0.63 mm, p = 0.9) and residual stenosis (-7 +/- 19% vs -11 +/- 21%) were also similar. The in-hospital major complications (myocardial infarction and death) (one vs eight, p = 0.01) and the combination of major and minor (bleeding and vascular) complications (eight vs 17, p = 0.02) were higher in the biliary stent group. At long-term follow-up, both groups of patients had high but comparable rates of major cardiovascular events (39% vs 45%, p = 0.62). Kaplan-Meier event-free survival analysis did not show any statistically significant difference in event-free survival (log-rank statistic 0.98). The authors conclude that patients receiving biliary stents had higher rates of immediate minor and major complications, but at long-term follow up, major cardiovascular event rates were comparable between the two groups of patients.

Aged↗
PubMed1999

Results of saphenous vein graft stent implantation: single center results from use of oversized balloon catheters.

The results and complications of a single-center experience of stent implantation in old saphenous vein grafts (SVGs) need to be defined. The authors studied their initial consecutive 92 patients (125 stents, 1.4 stents/per patient) with a mean age of 67+/-9 years. The patients' mean saphenous vein graft (SVG) age was 10+/-4 years, and the mean left ventricular ejection fraction was 46%+/-15. Patient population included unstable angina (65%), stable angina (10%), myocardial infarction (21%), and silent ischemia (4%). The authors implanted 122 Palmaz-Schatz/biliary and three Gianturco-Roubin stents. They aimed at a balloon-artery ratio of 1.1/1.0. Procedural success, defined as stent deployment with <50% stenosis without death/Q-wave myocardial infarction/coronary artery bypass grafting (MI/CABG) was 95%. The mean luminal diameter (MLD) increased from 0.6+/-0.5 to 3.3+/-0.8 mm (p<0.001) and mean SVG stenosis diameter was decreased from 80%+/-14 to -10%+/-11 (p<0.001). Angiographic SVG lesions exhibited thrombus (17%), ulceration (38%), and plaque rupture (28%). Sixty-two patients were treated with warfarin and aspirin and 30 with ticlid and aspirin. Complications included death in three patients (3.3%) who sustained subacute stent thrombosis, and two of three had Q-wave MI. Distal embolization occurred in seven patients (8%); six of seven sustained a non Q-wave acute myocardial infarction (AMI); and one of seven a Q-wave MI. Eight (9%) patients had major groin hematoma, two had pseudoaneurysm (2.2%), one had arteriovenous (A-V) fistula (1.1%), two had vascular surgery (2.2%), nine had blood transfusion (9.8%), and three had stent migration (3.3%). Single-center experience with stents in SVGs indicates a highly successful procedural and angiographic immediate result. However, it was complicated by significant risk of non Q-wave MI due to distal coronary embolization which may affect prognosis.

Aged↗
PubMed1998

Dobutamine stress echocardiography for assessing coronary artery disease after transplantation in children.

OBJECTIVES: The purpose of this study was to determine the feasibility, safety and diagnostic accuracy of dobutamine stress echocardiography (DSE) for evaluating posttransplant coronary artery disease (TxCAD) in children, and to determine the frequency of selected cardiac events after normal or abnormal DSE. BACKGROUND: Posttransplant coronary artery disease is the most common cause of graft loss (late death or retransplantation) after cardiac transplantation (CTx) in children. Coronary angiography, routinely performed to screen for TxCAD, is an invasive procedure with limited sensitivity. The efficacy of DSE for detecting atherosclerotic coronary artery disease is established, but is unknown in children after CTx. METHODS: Of the 78 children (median age 5.7 years, range 3 to 18) entered into the study, 72 (92%) underwent diagnostic DSE by means of a standard protocol, 4.6 +/- 1.9 years after CTx. The results of coronary angiography performed in 70 patients were compared with DSE findings. After DSE, subjects were monitored for TxCAD-related cardiac events, including death, retransplantation and new angiographic diagnosis of TxCAD. RESULTS: No major complications occurred. Minor complications, most often hypertension, occurred in 11% of the 72 subjects. The sensitivity and specificity of DSE were 72% and 80%, respectively, when compared with coronary angiography. At follow-up (21 +/- 8 months), TxCAD-related cardiac events occurred in 2 of 50 children (4%) with negative DSE, versus 6 of 22 children (27%) with positive DSE (p < 0.01). CONCLUSIONS: DSE is a feasible, safe and accurate screening method for TxCAD in children. Positive DSE identifies patients at increased risk of TxCAD-related cardiac events. Negative DSE predicts short-term freedom from such events.

Adolescent↗
PubMed1993

A new expandable intracoronary tantalum (Strecker) stent: early experimental results and follow-up to twelve months.

A new radiopaque balloon expandable tantalum stent was tested in the coronary arteries of sheep. A total of 28 stents with a diameter of 2.0 to 3.8 mm were successfully deployed. The stent to coronary artery diameter ratio was 1.1-1.2:1. The animals were heparinized with 100 U/kg of heparin but did not receive antiplatelet drugs. Coronary angiography that was performed 10 minutes after stent implantation showed 100% patency with no side-branch occlusion. Four sheep died within 2 hours of stent implantation, and pathologic studies showed thrombosis of the smaller sized stents: 2 mm (n = 2), 2.8 mm (n = 1), and 3.2 mm (n = 1); three fourths of the sheep had two stents implanted. An oversized stent caused coronary rupture and cardiac tamponade in one other sheep. Follow-up study protocol included coronary angiography before animal sacrifice and pathologic studies within 48 hours (n = 11), 2 weeks (n = 1), 3 months (n = 2), 5 months (n = 1), 10 months (n = 7), and 12 months (n = 1). At 3 to 12 months of follow-up the coronary stent was completely covered with a layer of neointima, and there was no angiographic evidence of coronary stenosis and patent side branches. According to histologic examination, the neointima had nonuniform thickness (20 to 330 microns) and consisted of smooth muscle cells and some collagen. At 7 months of follow-up one of seven stents had angiographic (20%) and pathologic evidence of stenosis, which was secondary to thrombus. The tantalum device is easily deployed technically and notable for its excellent fluoroscopic visibility and flexibility. Thrombosis with a tantalum stent remains a problem, and therefore the larger diameter stents > or = 3.2 mm, antiplatelet drugs, and anticoagulation therapy are indicated for human studies. Implantation of multiple coronary stents increases the risk of stent thrombosis. The long-term, mild neointimal thickness and the patency of the stent and side branches are encouraging.

Animals↗
PubMed1993

Pulmonary artery pressure and pulmonary vascular resistance before and after mitral balloon valvotomy in 100 patients with severe mitral valve stenosis.

We studied the pulmonary vascular hemodynamics before and after mitral balloon valvotomy in 100 patients with severe mitral valve stenosis. Before balloon valvotomy 23 patients had a pulmonary artery systolic pressure of < 31 mm Hg (group 1), 54 patients had a pulmonary artery systolic pressure between 31 and 50 mm Hg (group 2), and 23 patients had a pulmonary artery systolic pressure of > 50 mm Hg (group 3). After balloon valvotomy the mean systolic pulmonary artery pressure in group 1 decreased from 28 +/- 3 to 26 +/- 5 mm Hg (p = NS). In group 2 the systolic pulmonary artery pressure after balloon valvotomy decreased from 41 +/- 5 to 33 +/- 7 mm Hg (p < 0.0001) and normalized to < 31mm Hg in 27 patients (50%). The mean left atrial pressure was abnormal (> or = 13 mm Hg) in 6 of 27 patients (22%) who had a systolic pulmonary artery systolic pressure of < 31 mm Hg and in 6 of 27 patients (22%) with a pulmonary artery systolic pressure of > or = 31 mm Hg. The pulmonary vascular resistance was abnormal in 36 of 54 patients (67%) after mitral balloon valvotomy; only 5 of 36 patients (14%) had a raised left atrial pressure (> or = 13 mm Hg). In group 3 the pulmonary vascular resistance was abnormal (> 125 dynes/sec/cm-5) in all 23 patients before and in 19 of 31 patients (91%) after balloon valvotomy.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Mitral restenosis and mitral regurgitation 1 year after Inoue mitral balloon valvotomy in a population of patients with pliable mitral valve stenosis.

To determine the rate of mitral restenosis and mitral regurgitation increase 1 year after mitral valvotomy using the Inoue balloon catheter, 66 consecutive patients with severe, pliable mitral stenosis had their mitral valve area (MVA) calculated by two-dimensional echocardiography (2DE) and Doppler before, immediately after balloon valvotomy, and at 1-year follow-up. Color Doppler studies were also done to detect small atrial septal defects (ASDs) and mitral regurgitation. The mean age of the patients was 31 +/- 12 years. Three patients were in New York Heart Association (NYHA) class II and 63 patients were in NYHA class III to IV. Sixty-two of the 66 patients had an echo score (Boston) of < or = 8. After Inoue balloon valvotomy (IBV), the MVA (2DE) increased from 0.8 +/- 0.2 to 1.9 +/- 0.3 cm2 (p < 0.001), and the Doppler MVA increased from 0.8 +/- 0.2 to 1.8 +/- 0.3 cm2 (p < 0.001). We detected 4 of 66 cases (6%) with significant residual mitral stenosis (MVA < 1.5 cm2). Mitral regurgitation increased in 14 of 66 patients (21%), but no patient developed severe mitral regurgitation. Fourteen out of 66 patients (20%) had ASDs that were detected on color Doppler. At 1-year follow-up the mean Doppler MVA was maintained at 1.8 +/- 0.4 cm2, with 6 of 66 patients (9%) exhibiting significant mitral valve restenosis. Residual significant mitral stenosis must be differentiated from mitral restenosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

The role of coronary stents in interventional cardiology.

Coronary angioplasty is hampered with the problems of acute occlusions and coronary restenosis. Intravascular stents were used to prevent restenosis of arterial vessels after dilatation studies in animals have demonstrated the feasibility of stenting coronary arteries with several types of devices. However thrombosis is the major limitation for widespread use of coronary stents in animals and humans. New potent antithrombotic drugs need to be developed to prevent this complication. The emergence of biodegradable and temporary coronary stent may overcome some of current problems inherent to these irretrievable devices.

Animals↗
PubMed1992

Balloon valvotomy for pregnant patients with severe pliable mitral stenosis using the Inoue technique with total abdominal and pelvic shielding.

Balloon valvotomy by means of the Inoue technique was attempted in seven pregnant (5 to 9 months) patients with severe mitral stenosis; the mean age of the patients was 32 +/- 8 years, and all had a two-dimensional echocardiographic mitral valve score of < 8. Indications for Inoue balloon valvotomy included severe symptomatic mitral stenosis with a Doppler mitral valve area < or = 1 cm2 and heart failure refractory to medical therapy, or absolute contraindications for the use of beta-blockade; Inoue valvotomy was also indicated for patients who lived a long distance from the hospital. Inoue balloon valvotomy was performed with no angiography and total pelvic and abdominal shielding; the balloon catheter was introduced into the right atrium without the aid of fluoroscopy, which was used for the transseptal puncture. Stepwise two-dimensional echocardiographic Doppler mitral valve dilatation was done. After Inoue balloon valvotomy the mean Doppler mitral valve area increased from 0.8 +/- 0.1 to 2.0 +/- 0.3 cm2 (p < 0.01) and by two-dimensional echocardiography from 0.8 +/- 0.2 to 1.9 +/- 0.3 cm2 (p < 0.01), with no significant Doppler residual stenosis (defined as mitral valve area < or = 1.5 cm2). The mean total fluoroscopy time was 16 +/- 7 minutes. The degree of mitral regurgitation increased in two patients from grade 1+/4+ to grade 2+/4+ and from grade 0+/4+ to grade 2+/4+, respectively. There was no mortality or significant morbidity. Pregnancy was uneventful in all patients, and all were delivered of normal babies without complications.(ABSTRACT TRUNCATED AT 250 WORDS)

Abdomen↗
PubMed1992

Percutaneous mitral valvotomy with the Inoue balloon catheter in children and adults: immediate results and early follow-up.

Percutaneous mitral balloon valvotomy (PMV) using the Inoue balloon catheter was attempted in 60 consecutive patients with severe symptomatic mitral stenosis. There were 10 children (mean age 13 years) and 50 adults (mean age 31 years). Forty patients were females and 20 were males; 53 were in sinus rhythm. The procedure was technically successfully performed in 57 (95%) patients. There were no deaths or thromboembolic complications. Balloon valvotomy was done using a 22 to 30 mm diameter catheter with the echo/Doppler guided stepwise mitral dilatation technique. After PMV the mean left atrial pressure decreased from 23.0 +/- 5.0 to 14.0 +/- 4.0 mm Hg (p less than 0.001). The mean mitral valve gradient (MVG) decreased from 15.0 +/- 4.0 to 6.0 +/- 2.0 mm Hg (p less than 0.001). The mitral valve area (Gorlin formula) increased from 0.7 +/- 0.2 to 1.6 +/- 0.4 cm2 (p less than 0.001). The mitral valve area as determined by echocardiography increased from 0.8 +/- 0.1 to 1.9 +/- 0.3 cm2 (p less than 0.001). Mild mitral regurgitation (MR) developed in six patients (11%) and increased by one grade in another five patients (9%). No patient developed severe mitral regurgitation. Mitral valve area at mean follow-up of 4.8 months remained unchanged at 1.9 +/- 0.3 cm2. We conclude that PMV, using the Inoue balloon catheter, is safe and effective in the treatment of severe mitral stenosis in children and adults, without inducing significant mitral regurgitation.

Adolescent↗
PubMed1992

Right-sided endomyocardial fibrosis with recurrent pulmonary emboli leading to irreversible pulmonary hypertension.

A 26 year old Saudi man with features of both Loeffer's endocarditis and endomyocardial fibrosis presented with mild symptoms and pulmonary emboli. Echocardiographic examination showed obliteration of the right ventricular apex by an attached mass. The results of haemodynamic studies were somewhat abnormal and medical treatment was started. Despite anticoagulation with warfarin the patient's condition deteriorated rapidly over a four month period after a further episode of pulmonary embolism and the development of pulmonary hypertension. Two haemodynamic studies performed four months apart were typical of pulmonary hypertension and later right ventricular failure; they showed none of the characteristics of restriction. Pulmonary embolectomy was attempted but there was no cleavage plane between the organised thrombi and the endothelium of the pulmonary artery. The patient died of severe pulmonary hypertension and right ventricular failure several days after operation. Surgical intervention in the early stages of right-sided endomyocardial fibrosis might have prevented the development of pulmonary embolism and pulmonary hypertension.

Adult↗