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Biomedical subjects

A Andreev

Publications and source records attributed to A Andreev.

At least 19 recordsLinked to original sources
PubMed2006

Quasimonoenergetic deuteron bursts produced by ultraintense laser pulses.

We report on the generation and laser acceleration of bunches of energetic deuterons with a small energy spread at about 2 MeV. This quasimonoenergetic peak within the ion energy spectrum was observed when heavy-water microdroplets were irradiated with ultrashort laser pulses of about 40 fs duration and high (10(-8)) temporal contrast, at an intensity of 10(19) W/cm(2). The results can be explained by a simple physical model related to spatial separation of two ion species within a finite-volume target. The production of quasimonoenergetic ions is a long-standing goal in laser-particle acceleration; it could have diverse applications such as in medicine or in the development of future compact ion accelerators.

Journal Article↗
PubMed2006

Single crystalline nature of para-sexiphenyl crystallites grown on KCl(100).

This work focuses on studies of the single crystal nature of para-sexiphenyl structures grown on freshly cleaved KCl(100) surfaces. Two different kinds of morphologies, namely terrace like structures and needle like structures, are found by atomic force microscopy as well as by electron microscopy. Regardless of the morphology the individual crystallites show highly regular shapes. The crystalline alignment and the degree of order of the crystallites on the surface are determined by X-ray diffraction. Several epitaxial alignments of para-sexiphenyl on KCl(100) are observed and all of them are perfectly aligned on the surface. The rocking curve widths of the organic crystallites do not exceed 800" which is approximately only the four fold of the substrates' ones. The single crystalline nature of para-sexiphenyl crystallites is proven by transmission electron microscopy, diffraction patterns, dark field imaging and high resolution techniques. Single crystalline terraced mounds reach diameters of several microns and heights of 50 nm. Single crystal needles show heights and breadths of more than 100 nm and lengths of several microns.

Crystallization↗
PubMed2000

Counting statistics of an adiabatic pump

We use the Schwinger-Keldysh formalism to derive the charge counting statistics of an adiabatic pump based on an open quantum dot. The distribution function of the transmitted charge in terms of the time-dependent S matrix is obtained. It is applied to a few simple examples of the pumping cycles. By a chiral gauge transformation the problem is mapped onto a problem of pumping by voltage pulses. The role of the chiral anomaly arising in this mapping is emphasized. Conditions for the ideal noiseless quantized pump are discussed.

Journal Article↗
PubMed2000

Predictive inference, causal reasoning, and model assessment in nonparametric Bayesian analysis: a case study.

This paper continues our earlier analysis of a data set on acute ear infections in small children, presented in Andreev and Arjas (1998). The main goal here is to provide a method, based on the use of predictive distributions, for assessing the possible causal influence which the type of day care will have on the incidence of ear infections. A closely related technique is used for the assessment of the nonparametric Bayesian intensity model applied in the paper. Two graphical methods, supported by formal tests, are suggested for this purpose.

Algorithms↗
PubMed2000

[Antibiotic prophylaxis against serious wound infection in prosthetic arterial replacement].

Wound infection in arterial prosthetic replacement is the most hazardous complication in vascular surgery, associated with a high incidence rate of invalidity and lethality. The choice of antibiotic and administration scheme play a major role in its prevention. Clinical experience with implantation of synthetic vascular prostheses in a series of 103 patients where Cefuroxim prophylaxis according to a standard scheme is used (described in detail) is comprehensively analyzed. Wound infection grading is done in compliance with Salzman's classification. Against the background of antibiotic prophylaxis deep wound infection with vascular prosthesis involvement is registered in 1.94 per cent of operated patients only which is consistent with literature data on the issue. The obtained results are estimated as very good, and justify Cefuroxim prophylaxis recommendation to the wide practice for maximal reduction of deep wound infection in prosthetic replacement of arteries.

Adult↗
PubMed1998

Acute middle ear infection in small children: a Bayesian analysis using multiple time scales.

The study is based on a sample of 965 children living in Oulu region (Finland), who were monitored for acute middle ear infections from birth to the age of two years. We introduce a nonparametrically defined intensity model for ear infections, which involves both fixed and time dependent covariates, such as calendar time, current age, length of breast-feeding time until present, or current type of day care. Unmeasured heterogeneity, which manifests itself in frequent infections in some children and rare in others and which cannot be explained in terms of the known covariates, is modelled by using individual frailty parameters. A Bayesian approach is proposed to solve the inferential problem. The numerical work is carried out by Monte Carlo integration (Metropolis-Hastings algorithm).

Acute Disease↗
PubMed1998

Jugular venous aneurysms: when and how to operate.

BACKGROUND: Jugular venous aneurysms are rare, usually congenital, and present particular problems in management. Whether to perform surgery or not is controversial, cosmetic considerations being the primary factor in the decision. METHODS: Over the past nine years, 10 patients with unilateral jugular venous aneurysms have been closely followed up in our department. The most informative diagnostic procedure for the condition was considered to be ultrasonographic imaging after a positive Valsalva manoeuver, but in six cases phlebography was necessary. Various operative techniques were used--venous ligation, tangential venorrhaphy with or without aneurysm resection and autovenous banding, according to the pathological findings. RESULTS: No complications from the surgery were reported. Over a follow-up period ranging from six months to eight years both operated and non-operated patients were found to be doing equally well. CONCLUSIONS: Problems with the terminology of the disease, its diagnosis and the indications for surgery are discussed. Surgical methods are reviewed and a new operative technique is presented. We conclude that apart from cosmetic considerations, thrombosis and aneurysmal expansion are the principal indications for surgery.

Adolescent↗
PubMed1995

Severe acute hand ischemia following an accidental intraarterial drug injection, successfully treated with thrombolysis and intraarterial Iloprost infusion. Case report.

A young woman with acute upper extremity edema and ischemia after intraarterial drug injection is presented. Unsatisfactory results from standard treatment were the reason for changing the therapy to temporary thrombolysis, which led to significant improvement. Some days later severe impairment forced another attempt at applying standard therapy, again unsuccessful. Only after continuous intraarterial infusion of Iloprost, a new improvement occurred and saving of the hand was possible. It became obvious that more effective therapeutic measures ought to be applied when severe hand ischemia following intraarterial drug injection is present.

Acute Disease↗
PubMed1995

[A 10-year follow-up study of bypass operations with double-velour dacron in the aortoiliofemoral position].

The results of the follow-up study of 271 bypass operations in aortoiliofemoral position are analyzed. The interventions are done using monotype double-velour dacron prosthesis, standard operative technique and tactics. At 5.4 percent operative lethality, the postoperative complications include infection (2%) and rethrombosis (4%), necessitating reoperation which is successful in 64 per cent. Secondary cumulative patency of the prostheses implanted, amounting to 90 percent at three years, 80 percent at 5 years, and 66 percent at ten years postoperatively, is recorded, with aortobifemoral bypasses yielding superior results. Serious late complications are registered, such as prosthesis infection, abnormal dilatation of the implant, periprosthetic seromas and aneurysms by anastomosis. The underlying causes of complications and the indications for reoperation are discussed. The role played by late reoperations, leading to a successful outcome in 63 percent of cases is underscored. Attention is called to a number of characteristic features of the prosthesis employed, including the need of precise preclotting, restrained post-implantation increase in its diameter up to 20 percent necessitating implantation of prostheses isodiametric to the recipient artery, high incidence of postoperative complications making mandatory, periodic check-ups of operated patients and the like. In conclusion, it is estimated that over the 10-year observation period, the prosthesis suggested yields satisfactory results upon implantation in the aortoiliofemoral segment, and these results may be accepted as a basis for comparison with new vascular prosthesis designs.

Adult↗
PubMed1994

Blindness in different types of eye disease. A study based on the records of the Department of Eye Diseases in the Medical University, Plovdiv for the period 1982-1991.

Between 1982 and 1991, inclusive, a total of 13718 patients were treated in the Department of Eye Diseases in Plovdiv University of Medicine. Cataract patients formed the most numerous group (19.71%), followed by those with diseases of the retina (9.53%), glaucoma (7.95%), uveitis (4.9%), diseases of the cornea (3.86%), malignant tumors of the eyelids and the eyeball (2.29%) and diseases of the optic nerve (1.54%). Of these 13718 patients, 1727 (12.58%) had monocular and binocular vision below 0.08. The patients with visual acuity from 0 to 0.03 were 1330 (9.69%). Nosologically, they were distributed as follows: glacoma-422 (3.07%), eye traumas-281 (2.04%), diseases of the retina-270 (1.96%), diseases of the cornea-89 (0.64%), cataract-80 (0.58%), uveitis-77 (0.56%), malignant tumors of the eyelids and the eyeball-66 (0.48%), and diseases of the optic nerve-45 (0.32%). Glaucoma was found to be the most common cause of blindness among the patients treated in the Department of Eye Diseases, followed by eye traumas and disease of the retina. The importance of the vascular factor in inducing blindness is undeniably great. It is the underlying cause of the open-angle glaucoma, the diseases of the retina and the optic nerve.

Blindness↗
PubMed1994

[Combined heart injuries].

Cardiac injuries associated with a penetrating thoracic injury are not frequently encountered. The usual course is characterized by massive haemorrhage, cardiac tamponade and an entering wound in the cardiac area. Diagnostic problems arise if these clinical syndromes are absent. In the course of two years at the authors' department two cases of tangential cardiac lesions in the posterior left ventricular wall without penetration into the heart without massive haemorrhage and tamponade were absent as haemorrhage of the pericardial lesion into the pleural space occurred. It is not without interest that the entry wound was far away from the heart and the cardiac lesions were detected during surgical intervention made on account of other symptoms.

Adult↗
PubMed1993

[In situ femorodistal autovenous bypass].

Bypass in-situ surgical technique was applied in 49 cases of femorodistal arterial reconstructions. The operative technical details, as well as intra- and postoperative complications are discussed. A patency of the bypass in 87.5% after 18-month following are documented as well as limb salvation in 97.6%. The technical advantage of the bypass in-situ method are discussed and a recommendation for its appliance in suitable cases is given.

Aged↗
PubMed1992

Continuous positive airway pressure (CPAP) vs. intermittent mandatory pressure release ventilation (IMPRV) in patients with acute respiratory failure.

Intermittent Mandatory Pressure Release Ventilation (IMPRV) is a positive pressure spontaneous breathing ventilatory mode in which airway pressure is released intermittently and synchronously with patient's spontaneous expiration in order to provide ventilatory assistance. Eight critically ill patients free of any factor known to alter chest wall mechanics (group 1) and 8 critically ill patients whose spontaneous respiratory activity was markedly altered by a flail chest, or by a C5 quadraplegia and/or by the administration of opioids (group 2) were studied prospectively. CPAP and IMPRV were administered to each patient in a random order during a 1 h period using a CESAR ventilator. Gas flow, tidal volume, tracheal pressure, esophageal pressure, end-expiratory lung volume and hemodynamic parameters were measured. In group 1 patients, the ventilatory assistance provided by IMPRV was associated with a significant decrease in spontaneous tidal volume whereas all other respiratory parameters remained unchanged. In group 2 patients, IMPRV increased minute ventilation from 8.0 +/- 2.61/min to 12.2 +/- 1.81/min (p less than 0.05), decreased PaCO2 from 46 +/- 7.3 mmHg to 38 +/- 6.8 mmHg (p less than 0.05) and reduced respiratory frequency from 21 +/- 10 bpm to 14 +/- 5.7 bpm (p less than 0.07). These results show that IMPRV provides significant ventilatory assistance to patients with mild acute respiratory failure either by decreasing patient's contribution to minute ventilation or by increasing alveolar ventilation in presence of respiratory depression of central or peripheral origin.

Acute Disease↗
PubMed1992

Management of acute arterial trauma of the upper extremity.

During a 3.5 year period ending in September 1991, 50 patients with 51 arterial injuries of the upper extremity were operated on and followed up for more than 6 months. The majority of the cases suffered penetrating injuries, but in 18% blunt trauma led to thrombosis. The most frequently observed signs were haemorrhage, neurological disorders and a peripheral pulse deficit. The brachial artery was most frequently injured. Preoperative arteriography was performed in 20% and peroperative angiography in 16% of cases. Reconstructive surgery was performed in 88% and the brachial artery was ligated in a single patient who was in shock. An end to end anastomosis was possible in 55% and in 45% of cases an autogenous vein graft was used. A microsurgical technique was used in cases of forearm arterial injuries. In five patients with prolonged ischaemia, forearm fasciotomies were needed. Additional procedures such as venous, bone or nerve repair was also necessary. In four cases a temporary shunt was used. All patients were alive with late patency of 91% in the axillobrachial arterial segment. A single failure after repeated brachial artery reconstruction was observed following severe traumatic amputation with large tissue defects. Post-operative arteriography revealed a good anastomosis with patent grafts. Arterial reconstruction is clearly necessary in these injuries and we believe that an experienced vascular surgeon should be involved.

Adolescent↗
PubMed1991

Peripheral vascular effects of thiopental and propofol in humans with artificial hearts.

The peripheral vascular effects of thiopental 5 mg/kg and propofol 2.5 mg/kg were compared in five patients whose lungs were being ventilated and in whom a Jarvik-7 artificial heart had been implanted. The patients were monitored, using catheters that had been surgically inserted into the radial artery, the right and left atria, and the pulmonary artery. The Jarvik-7 settings were modified to render the artificial heart "preload independent" and to maintain cardiac output constant. Each patient received both drugs, with the interval between each drug ranging from 16 to 28 h. Hemodynamic parameters and catecholamine and atrial natriuretic peptide plasma concentrations were measured before drug administration and 5, 10, 15, 30, and 45 min later. Both drugs significantly decreased arterial pressure, systemic vascular resistance index, pulmonary arterial pressure (PAP), and right and left atrial pressures (RAP and LAP, respectively). However, propofol 2.5 mg/kg induced a significantly greater and more prolonged decrease in arterial pressure, systemic vascular resistance index, and RAP than that after administration of thiopental 5 mg/kg (P less than 0.05). Five minutes after drug injection, mean arterial pressure decreased by 21% after thiopental and by 39% after propofol (P less than 0.01); systemic vascular resistance index decreased by 21% after thiopental and by 44% after propofol (P less than 0.05); RAP decreased by 20% after thiopental and by 50% after propofol (P less than 0.05); mean PAP decreased by 18% after thiopental and by 32% after propofol (P less than 0.09); and LAP decreased by 40% after thiopental and by 46% after propofol (P less than 0.2). With both drugs, atrial natriuretic peptide, norepinephrine, and epinephrine plasma concentrations remained stable throughout the study period. Because cardiac output was maintained constant throughout the study, these results suggest that propofol 2.5 mg/kg is a more potent vasodilator of venous and arterial beds than is thiopental 5 mg/kg.

Adult↗
PubMed1990

Peripheral vascular effects of halothane and isoflurane in humans with an artificial heart.

The peripheral vascular effects of isoflurane and halothane were compared in five critically ill patients in whom a Jarvik-7 artificial heart had been implanted. The lungs of all patients were mechanically ventilated in the postoperative period and the patients were monitored with an arterial catheter and with catheters that had been surgically inserted into the right and left atria and into the pulmonary artery. Norepinephrine and epinephrine plasma concentrations were measured using a radioenzymatic assay. The Jarvik-7 settings were modified to render the artificial heart "preload independent" and to maintain cardiac output constant. Each patient was anesthetized twice using halothane and isoflurane at two different MAC levels, 1 and 1.5 (Datex vapour analyzer), with the interval between each anesthetic ranging from 12 to 26 h. Both anesthetics significantly decreased mean arterial pressure (from 100 +/- 11 mmHg to 66 +/- 13 mmHg for halothane and from 102 +/- 17 mmHg to 48 +/- 11 mmHg for isoflurane; mean +/- SD) and systemic vascular resistance index (from 27 +/- 11 Wood units/m2 to 18 +/- 6 Wood units/m2 for halothane and from 30 +/- 6 Wood units/m2 to 13 +/- 3 Wood units/m2 for isoflurane; mean +/- SD), but with isoflurane to a significantly greater extent than with halothane (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗