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Biomedical subjects

I Petrov

Publications and source records attributed to I Petrov.

At least 19 recordsLinked to original sources
PubMed2005

Directed self-assembly of Ge nanostructures on very high index, highly anisotropic Si(hkl) surfaces.

Families of very high-index planes, such as those which bifurcate spontaneously to form a hill-and-valley structure composed of opposing facets, provide natural templates for the directed growth of position-controlled self-organized nanostructures with shapes determined by the facet width ratio R. For example, deposition of a few ML of Ge on Si(173 100 373), corresponding to R(113/517) = 1.7, results in a field of 40-nm-wide Ge nanowires along [72 187] with a uniform period of 60 nm.

Anisotropy↗
PubMed2004

Dislocation-driven surface dynamics on solids.

Dislocations are line defects that bound plastically deformed regions in crystalline solids. Dislocations terminating on the surface of materials can strongly influence nanostructural and interfacial stability, mechanical properties, chemical reactions, transport phenomena, and other surface processes. While most theoretical and experimental studies have focused on dislocation motion in bulk solids under applied stress and step formation due to dislocations at surfaces during crystal growth, very little is known about the effects of dislocations on surface dynamics and morphological evolution. Here we investigate the near-equilibrium dynamics of surface-terminated dislocations using low-energy electron microscopy. We observe, in real time, the thermally driven nucleation and shape-preserving growth of spiral steps rotating at constant temperature-dependent angular velocities around cores of dislocations terminating on the (111) surface of TiN in the absence of applied external stress or net mass change. We attribute this phenomenon to point-defect migration from the bulk to the surface along dislocation lines. Our results demonstrate that dislocation-mediated surface roughening can occur even in the absence of deposition or evaporation, and provide fundamental insights into mechanisms controlling nanostructural stability.

Journal Article↗
PubMed2004

Coherent nano-area electron diffraction.

We describe the new coherent nano-area electron diffraction (NED) and its application for structure determination of individual nanostructures. The study is motivated by the challenge and the general lack of analytical techniques for characterizing nanometer-sized, heterogeneous phases. We show that by focusing electrons on the focal plane of the pre-objective lens using a 3rd condenser lens and a small condense aperture, it is possible to achieve a nanometer-sized highly parallel illumination or probe. The high angular resolution of diffraction pattern from the parallel illumination allows over-sampling and consequently the solution of phase problem based on the recently developed ab initio phase retrieval technique. From this, a high-contrast and high-resolution image can be reconstructed at resolution beyond the performance limit of the image-forming objective lens. The significance of NED for nanostructure characterization will be exemplified by single-wall carbon nanotubes and small metallic clusters. Imaging from diffraction patterns, or diffractive imaging, will be demonstrated using double-wall carbon nanotubes.

Computer Simulation↗
PubMed2003

[Angioplasty and stenting of extracranial cerebral vessels].

UNLABELLED: The stroke is one of the major causes for death and invalidization in the modern society. In about 30% of the cases the stroke is attributed to stenosis of a supraaortic vessel. In the last few years the percutaneous angioplasty and stenting is an alternative method of the classical surgical treatment--the carotid thrombendarterectomy. Crucial moment in the evolution of the method is the introduction in the practice of the systems for distal embolic protection of the brain and the routine implantation of stents with new design. One of the main conditions for successful and noncomplicated stenting is the respect of a strict procedural protocol. In the article we present the results of 17 cases with angioplasty and stenting of supraaortic vessels performed in our Clinic in the period 07.02.2001-01.07.2001. The immediate success rate is 100%. No major complications (stroke, myocardial infarction and death) were registered. In the midterm follow-up there were no thrombosis and restenosis of the implanted stents. We present four interesting case reports: 1. One stage stenting of right coronary artery and right internal carotid artery, 2. Stenting of a subocclusive right internal carotid stenosis with balloonexpandable stent and 3. Stenting of a vertebral artery as the unique brain supplying vessel and 4. Stenting of subocclusive aortoostial lesion of the brachiocephalic trunk in a patient with totally occluded contralateral internal carotid artery. CONCLUSIONS: Stenting of supraaortic vessels is a safe and reliable method when performed by experienced operator and when are applied the ultimate methods of cerebral protection and the new stent designs. The carotid stenting is a reliable alternative of the surgery and gains more and more popularity.

Adult↗
PubMed2003

[Endovascular therapy of acute traumatic vascular peripheral dissections using self-expandable stents].

Percutaneous peripheral and coronary interventions as well as surgical procedures can be complicated by dissections and traumatic lesions of peripheral arteries. Posttraumatic peripheral dissections can be threatening for the extremities and often their management might be a challenge. Open surgery requires wide exposure and dissection of posttraumatic tissues. Endovascular techniques using selfexpandable stents gains popularity because of high efficiency, safety and good results. This technique is associated with decreased trauma, no requirements for anesthesia, short hospital stay. We present two cases of posttraumatic iliac dissections treated with self expandable stents.

Aged↗
PubMed2003

[The first case of one stage endovascular treatment of the stenosis in the celiac trunk, bilateral renal arteries, and right common iliac arteries].

Although not very often diagnosed, the acute and chronic mesenterial ischemia is advancing and life threatening condition. When associated with multivascular pathology compromising the perfusion and causing multiple organ failure the choice of treatment is a challenge. In such cases the radical surgical treatment is associated with high morbidity and mortality. In recent years endovascular methods of treatment (angioplasty and stenting) are gaining popularity in the treatment of these patients. We report a case of chronic mesenteric ischemia that caused abdominal angina and weight loss in a 63-year-old man with renovasal hypertension, renal insufficiency and peripheral vascular disease. Angiographic study revealed multivascular pathology including total occlusion of the superior mesenteric artery, 90% stenosis of the celiac trunk, bilateral high grade renal stenoses and obstructive pathology of both iliac arteries. One stage successful endovascular treatment was performed in the three vascular territories. In the Celiac trunk, left renal artery and right common iliac artery were implanted stents. A double right renal artery was treated successfully with kissing balloon. A clinical follow-up demonstrated success with no recurrence of abdominal pain, body weight gain, better control of the hypertension and improvement of the renal function. This is the first reported case of one stage endovascular treatment of a visceral artery, bilateral renal arteries and iliac artery. This case report illustrates the value of endovascular treatment in a patient with atherosclerotic narrowing of multiple abdominal visceral arteries.

Angiography↗
PubMed2002

Size-dependent detachment-limited decay kinetics of two-dimensional TiN islands on TiN(111).

In situ high-temperature (T(a)=1050-1250 K) scanning tunneling microscopy was used to determine the coarsening and decay kinetics of two-dimensional TiN adatom and vacancy islands on atomically smooth TiN(111) terraces. We report the first observation of an abrupt decrease in decay rates, irrespective of T(a), of adatom islands with areas less than a critical value of 1600 A(2). However, no decay rate transition was observed for vacancy islands. We attribute the size-dependent island decay behavior, which is consistent with detachment-limited kinetics, to anisotropic attachment and detachment barriers.

Journal Article↗
PubMed2002

Absolute TiN(111) step energies from analysis of anisotropic island shape fluctuations.

In situ high-temperature (1165-1248 K) scanning tunneling microscopy was used to measure fluctuations around the equilibrium shape of two-dimensional vacancy islands on TiN(111) terraces. From the equilibrium shape, the ratio of the two <110> step energies was found to be 0.72 +/- 0.02. Combining this with the results of an exact approach for analysis of shape fluctuations, applicable to highly anisotropic islands, we obtain absolute values for step energies and step stiffnesses as a function of orientation.

Journal Article↗
PubMed2001

[Stenting of the right subclavian artery posttraumatic false aneurysm].

Posttraumatic false aneUrysms can be life threatening and often their management might be a challenge, because of poor general condition as well as because of specific technical difficulties. Open surgery requires wide exposure and dissection of posttraumatic tissues. Endovascular techniques using stent-grafts gains popularity because of high efficiency, safety and good results. We present a case of posttraumatic false aneurysm of right subclavian artery treated with a stent-graft.

Aneurysm, False↗
PubMed1999

Empirical versus mechanistic modelling: comparison of an artificial neural network to a mechanistically based model for quantitative structure pharmacokinetic relationships of a homologous series of barbiturates.

The aim of the current study was to compare the predictive performance of a mechanistically based model and an empirical artificial neural network (ANN) model to describe the relationship between the tissue-to-unbound plasma concentration ratios (Kpu's) of 14 rat tissues and the lipophilicity (LogP) of a series of nine 5-n-alkyl-5-ethyl barbituric acids. The mechanistic model comprised the water content, binding capacity, number of the binding sites, and binding association constant of each tissue. A backpropagation ANN with 2 hidden layers (33 neurons in the first layer, 9 neurons in the second) was used for the comparison. The network was trained by an algorithm with adaptive momentum and learning rate, programmed using the ANN Toolbox of MATLAB. The predictive performance of both models was evaluated using a leave-one-out procedure and computation of both the mean prediction error (ME, showing the prediction bias) and the mean squared prediction error (MSE, showing the prediction accuracy). The ME of the mechanistic model was 18% (range, 20 to 57%), indicating a tendency for overprediction; the MSE is 32% (range, 6 to 104%). The ANN had almost no bias: the ME was 2% (range, 36 to 64%) and had greater precision than the mechanistic model, MSE 18% (range, 4 to 70%). Generally, neither model appeared to be a significantly better predictor of the Kpu's in the rat.

Algorithms↗
PubMed1998

Differentiation-dependent expression of alpha-2,3-sialyltransferase in rabbit corneal epithelium.

PURPOSE: Lectin studies have shown that in the rabbit corneal epithelium, alpha-2,3 sialylation of O-linked glycans differentiates limbal and corneal epithelial cell phenotypes. Because sialic acid can be regulated at the level of the expression of sialyltransferases (STs), the purpose of the present study was to analyze the expression of alpha-2,3STs in this tissue. METHODS: Reverse transcription-polymerase chain reaction (RT-PCR) was used to generate ST cDNA from total rabbit corneal epithelium RNA using primers selected from the sequences of three previously cloned STs capable of catalyzing the transfer of sialic acid to O-linked oligosaccharides, human placental Galbeta-1,3GalNAc-Galbeta-1,4GluNAcalpha-2,3ST (STZ), and mouse brain Galbeta-1,3GalNAcalpha-2,3ST types I and II (ST3Gal I and ST3Gal II). Tissue distribution of mRNA was assayed by fluorescent in situ hybridization. A synthetic peptide whose sequence was deduced from a cloned cDNA fragment was synthesized and used to prepare an anti-ST goat antiserum. The molecular weights of immunodetectable polypeptides and their distribution in cryostat sections of the limbocorneal area were investigated by western blot analysis and indirect immunofluorescence, respectively. RESULTS: RT-PCR yielded cDNA of expected basepair length for STZ and ST3(Gal II. The rabbit STZ cDNA was 86% identical with its human equivalent. Its mRNA was confined to the cornea, mainly in basal epithelial cells, and was not expressed in the limbus. Western blot analysis identified a band at 37 kDa whose binding was abolished by preincubation of the antiserum with the immunization peptide. Immunohistologic analysis revealed the presence of immunoreactive epitopes in all basal cells of the cornea but not in the limbus. CONCLUSIONS: STZ mRNA and the enzyme itself are expressed in the basal layer of the corneal epithelium but are absent in the limbus. This enzyme's de novo expression seems thus responsible for the differential expression of alpha-2,3 sialylation along the limbocorneal differentiation axes. At least one more alpha-2,3ST is also present in the epithelium.

Animals↗
PubMed1995

[The summary results of percutaneous transluminal coronary angioplasty at the Sveta Ekaterina State University Hospital in 1991-1994].

OBJECTIVES: The article reviews the results of PTCA in 164 patients in Hospital "St Ekaterina" in the period January 1994-April 1994. METHODS: Patients were divided in four groups: I Stable angina II Unstable angina a) primary stabilized b) refractory to medical treatment III Acute myocardial infarction (AMI) IV Silent ischaemia Patients were followed for: 1.) Acute complications a) mortality b) myocardial infarction (MI) c) emergency CABG 2.) Late complications a) recurrent angina b) MI c) elective CABG d) re-PTCA e) late mortality Follow-up period was 6-12 months RESULTS: I group 1) acute complications--early mortality--0%; acute MI--0%; emergency CABG--5%; 2) Late complications--recurrent angina--8.4%; MI--1.5%; late mortality--0%; elective CABG--0%; re-PTCA--6.5%. I group 1) acute complications--early mortality--0%; acute MI--6%; emergency CABG--3%; 2) Late complications--late mortality--6%; recurrent angina--10%; MI--6%; elective CABG--1%; re-PTCA--14%. III group 1) acute complications-early mortality--0%; acute MI--17%; emergency CABG--17%; 2) Late complications--recurrent angina--17%; MI--17%; late mortality--17%; elective CABG--0%; re-PTCA--0%. IV group 1) acute complications--early mortality--0%; acute MI--0%; emergency CABG--0%; 2) recurrent angina--18%; late MI--0%; late mortality--0%; elective CABG--0%; re-PTCA--18%. CONCLUSIONS: PTCA is a safe and reliable method for revascularization not only in patients with stable angina, but also in patients with acute coronary syndromes.

Aged↗
PubMed1995

[The anatomical characteristics of the a. mammaria interna and their importance for the surgical results in aortocoronary bypass (a report on 2 clinical cases with large intercostal branches of the a. mammaria interna)].

OBJECTIVES: This study attempted to determine the possibility for steal phenomenon after coronary surgery using internal mammary artery (IMA) as graft with unligated big side branches. The internal mammary artery (IMA) is considered to be the conduct of choice in coronary artery bypass grafting (CABH). The more IMA grafts are used, the more increases the significance of IMA anomalies and notably the large side branches for the surgical results. The importance of coronary subclavian steal syndrome is well known. We represent two clinical cases with big intercostal branches visualised at the postoperative coronary angiography, performed to evaluate the coronary and graft status cause of recurrent postoperative anginal pain. After cardiac catheterization we performed ECG stress test as follows: 1. A conventional stress test on treadmill (for control) and 2. Modified stress test loading the chest wall muscles in spine position. We expected to provoke and to evaluate steal phenomenon by the main IMA graft to the big lateral branches. At both of the patients on the arteriographic study IMA graft was patent and both had unusual large (> 50% of the IMA lumen) side branches, reducing the blood flow in the IMA graft. The modified stress test loading the chest wall muscles didn't provoke anginal pain at both patients. At the first (50 years old white male, CABG x 3-July 1193) it was evident non significant ST depression (< 2 mm) in V4-V% (suspicion of silent ischemia). At the second (70 years old white male, anterior MI-1990, GABG x 4-1992) the stress test was interrupted because of fatigue at the arm. No evident significant ecg changes. Despite we couldn't prove steal phenomenon through the angiographic study and the modified ECG stress test we suggest several logic.

Aged↗
PubMed1995

[The assessment of arsenic exposure in copper smelting].

The arsenic exposure in the main departments and occupational groups of the copper smelter in Pirdop has been estimated in the present study. The contents of arsenic is measured in the air and in biological samples--urine and nails. At most of the workplaces the time-weighted average (TWA) concentrations do not exceed the threshold limit value (0.05 mg/m3). The maximum TWA level is about three times higher. The intake of arsenic is significantly increased in almost all observed occupational groups. However, the excretion of only 8% of the workers is higher than the maximum background level (100 micrograms/l). The estimated degree of exposure corresponds to a low health risk. Some of the most heavily exposed occupational groups may be expected to reach higher levels of intake and health risk.

Air Pollutants, Occupational↗
PubMed1994

Placental arsenic and cadmium in relation to lipid peroxides and glutathione levels in maternal-infant pairs from a copper smelter area.

Arsenic exposure may enhance oxidative damage causing adverse health effects in pregnant women. The purposes of this paper are: (i) to evaluate placental arsenic concentration as a biomarker of arsenic exposure for pregnant women; and (ii) to examine the relationship between metal exposure from a copper smelter area in Bulgaria and oxidative damage during pregnancy (as measured by glutathione and lipid peroxides) in 49 maternal-infant pairs. Placental levels of arsenic were highest in areas with the highest environmental contamination, and environmental variables (residency, smoking and occupational exposure) explained a large portion of the observed variability in placental arsenic levels (linear regression R2 = 0.71). The combined exposures of smoking and living in the smelter area were associated with lower glutathione antioxidant protection. The per cent maternal and cord blood glutathione in reduced form was significantly lower for smokers compared to non-smokers in the smelter area (47 versus 66 per cent in maternal blood, P < 0.01, and 60 versus 75 per cent in cord blood, P < 0.05). Higher concentrations of lipid peroxides in maternal blood, cord blood and placenta, though not statistically significant, suggested that pregnant women with both exposures may be at higher risk of oxidative damage.

Adult↗
PubMed1992

[Lipid and mineral metabolism and morbidity with temporary loss of work capacity in miners].

Examination is performed on 87 miners from mine for copper production subject to intensive local vibrations with average rate of increase (K) of the norms for the individual octave frequencies 2.4 times for 3 h exposure of the working shift, as well as to intensive noise--113-115 dB/A equivalent level, general dust--23 mg/m3, fine dust--3.5 mg/m3 and fine quartz--0.43 mg/m3. There are data for vibration effect--changes in the cold test, vibration sensoriness, ultra sound sonometry, in all miners. In a significant part of them are established dyslipoproteinemia--increase of triglycerides, total and LDL cholesterol, values beyond reference (mainly above the norm) of 10 electrolytes and microelements in blood serum (blood). An extremely high prevalence of the cases and the days of total morbidity with temporary disability (respectively 189.7 and 2935 per 100), with predominance in its structure of diseases of the central and peripheral nervous systems, hypertension disease, etc. The importance of vibrations for disorder in the metabolic processes in the organism and development of temporary diseases are underlined.

Absenteeism↗