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Biomedical subjects

T Ivanova

Publications and source records attributed to T Ivanova.

At least 37 records · Page 2Linked to original sources
PubMed1997

Motor unit discharge rate is not associated with muscle relaxation time in sustained submaximal contractions in humans.

The muscle wisdom hypothesis suggests that motor unit discharge rates decrease in parallel with the slowing of muscle contractile properties during fatigue. In this study, the discharge rates of single motor units and the muscle contractile properties were measured during a sustained submaximal contraction. The majority of motor units that were active from the beginning of the task demonstrated a decline in discharge rate in the absence of any slowing of muscle relaxation time. These findings suggest that the muscle wisdom hypothesis may not apply to sustained submaximal contractions.

Adult↗
PubMed1997

Preventive role of lyophilic dairy products bulgaricum and biostim.

The purpose of the study was to examine the protective role of lyophilic dairy products bulgaricum and biostim with active bacteria lactic acid strain. Protective effect was determined as a phagocytosis activity and activity of major immunoglobulins. In total 120 men aged 30-35 years were included in three groups (30 controls with placebo). Daily doses (50 g) of these products were taken during a month. Positive responses from investigation links of immune system and paraspecific resistance were observed. Immunologic response was significantly higher after lyophilic dairy diet and this indicates that bulgaricum and biostim are products with protective role due to specific influence of bacteria lactic acid.

Adult↗
PubMed1997

Motor unit recruitment and discharge behavior in movements and isometric contractions.

The purpose of this study was to contrast the discharge patterns of the same motor units during movements and during isometric contractions that were produced with comparable torque-time characteristics. Subjects performed elbow flexion and extension movements with predetermined acceleration characteristics. The average acceleration and deceleration profiles for the movements were reproduced in the isometric setting by presenting the kinematic profiles as templates for torque production. Trained subjects were able to match the first agonist (AG1) and antagonist (ANT) electromyographic (EMG) bursts, but tended to produce a smaller second agonist burst (AG2) in the isometric contraction. Twenty-five motor units from triceps brachii were studied. The same motor units (with one exception) were recruited and subsequently discharged in a similar fashion in both the isometric and movement tasks in the AG1 and ANT EMG bursts, with fewer motor unit discharges in the AG2 burst in the isometric contraction. The central control mechanisms appear to be the same for the acceleration phase of movement and isometric contraction, but differ during the deceleration phase.

Adult↗
PubMed1997

Cystic fibrosis mutations and associated haplotypes in Bulgaria - a comparative population genetic study.

We present data on the population genetics of cystic fibrosis (CF) in Bulgaria, obtained by comprehensive mutation analysis and the construction of intragenic microsatellite haplotypes. The sample of 262 CF alleles analysed is representative of the patients diagnosed during the period of referral and of the three main ethnic groups in the country. deltaF508 accounted for 100% of Gypsy CF alleles, which thus differed significantly from both Bulgarians and ethnic Turks. In Bulgarian and Turkish CF patients, 92% of the mutant alleles were identified, yielding a total of 25 different mutations, of which only 7 occurred at frequencies higher than 1%. The findings were compared to other European populations and to the distribution of phenylketonuria mutations. Genetic distances and population trees demonstrated that in the south-eastern tip of Europe, the overall distribution of CF mutations and polymorphic haplotypes is very close to that of Mediterranean populations, with a high frequency of N1303K and G542X, a large number of rare mutations and a prevalence of the 23 31 13 haplotype in association with deltaF508. These findings are consistent with a main role for the Neolithic expansion in the shaping of the CF mutation spectrum in Bulgaria and southern Europe.

Bulgaria↗
PubMed1997

Postural responses to unilateral arm perturbation in young, elderly, and hemiplegic subjects.

OBJECTIVE: To compare postural responses during standing associated with self-paced unilateral arm flexion exhibited by young and elderly healthy subjects and subjects with hemiplegia from stroke. DESIGN AND SETTING: Descriptive cross-sectional study in a laboratory setting. PATIENTS: Ten young, 10 elderly healthy subjects, and 12 volunteers with longstanding hemiparesis following stroke were tested. The hemiplegic group had good functional balance scores on the Berg Balance Scale (BBS). MAIN OUTCOME MEASURES: The peak arm acceleration, center of pressure (CP) excursion speed, and the electromyographic activity in the posterior leg muscles (bilateral hamstrings and triceps surae) were monitored during self-initiated rapid unilateral arm flexion and during quiet stance. RESULTS: During unilateral arm flexion, the young group showed the highest arm accelerations and lowest CP excursion speeds. The variability of postural responses was largest in the elderly and hemiplegic groups with hemiplegic subjects showing the greatest CP excursion speeds for the lowest arm accelerations. The first burst of activity in ipsilateral hamstrings muscle was the same in all subjects. However, the hemiplegic group had less activation (latency and amplitude) of other posterior leg muscles. CONCLUSION: The elderly subjects had more variable responses to perturbation than the young subjects despite similar BBS scores. This may indicate that the BBS fails to detect differences in balance at the high end of the scale. Although the hemiplegic subjects demonstrated some anticipatory control of standing balance, they consistently performed poorer than elderly and young controls. The failure to coordinate postural leg muscle activity with focal movement may contribute to the instability of subjects with hemiplegia.

Adult↗
PubMed1996

The synthesis and localization of alternatively spliced fibronectin EIIIB in resting and thrombin-treated megakaryocytes.

There are several species of alternatively spliced fibronectin (FN). One of these, FN EIIIB, is primarily present in embryonic and in proliferating and migrating cells and is believed to be important for cell maturation. We have studied the synthesis, localization, and secretion of this FN isoform in isolated guinea pig megakaryocytes, nonmegakaryocytic bone marrow cells, and platelets. There was 7.5 times more general FN in megakaryocytes than in nonmegakaryocytic cells based on the analysis of equivalent amounts of protein. FN EIIIB was detected by Western blotting in megakaryocytes but not in nonmegakaryocytic cells present in bone marrow. Neither megakaryocytes nor platelets secreted FN EIIIB, while megakaryocytes secreted 25.3% +/- 4.6% general FN and platelets secreted about 61% general FN in response to thrombin. Analysis of immunostained cells by confocal microscopy revealed that FN EIIIB had been redistributed to the surface of megakaryocytes in response to thrombin. Synthesis was studied by metabolic labeling, and megakaryocytes were shown to synthesize FN and FN EIIIB. Thus, megakaryocytes and platelets are among a small number of adult cells and tissues that synthesize and contain FN EIIIB. The expression of FN EIIIB on the megakaryocyte surface may influence migration and maturation.

Animals↗
PubMed1996

Kinetics of liposome disintegration from foam film studies: effect of the lipid bilayer phase state.

The kinetics of interfacial liposome breakdown is investigated in the thin liquid film microinterferometric set up of Scheludko et al. Suspensions of small unilamellar vesicles of dimyristoylphosphatidylcholine are studied at temperatures above and below the temperature of the main gel-liquid crystal first order phase transition. The experimentally established time traces of the velocity of thinning of foam films are used to estimate the kinetic (rate) constants of interfacial liposome disintegration. New and previously established data for other lipids are summarized and compared with results from kinetic measurements of lipid monolayer formation. The thin film experiments confirm the existence of interfacial liposomal aggregates. A change in the kinetic behaviour is observed, due to the 'melting' of the hydrophobic tails in the lipid aggregates. This may have various consequences of biological and pharmacological importance.

Journal Article↗
PubMed1996

Motor-unit behavior in humans during fatiguing arm movements.

1. The activity of 40 triceps brachii motor units was recorded from the dominant arms of 9 healthy adult volunteers (age 27.8 +/- 4.4 yr, mean +/- SD) during a fatigue task that included both isometric and anisometric contractions. The fatigue task lasted 8.3 min and consisted of 50 extension and 50 flexion movements of the elbow. Each movement (40 degrees in 0.8s) was separated by an isometric contraction. A constant load resisting extension of 17.7 +/- 3.0% of maximal voluntary contractions (MVC) was applied throughout the task. This paradigm enabled the direct contrast of motor-unit discharge behavior during the different types of fatiguing contractions. 2. Motor-unit behavior was examined to determine the relative contribution of two mechanisms for optimizing force production under fatiguing conditions: recruitment of motor units and modulation of motor-unit discharge following recruitment. Threshold torques for motor-unit recruitment thresholds were determined by ramp-and-hold isometric contractions. Motor-unit discharge was evaluated during the fatigue task by contrasting the number of motor-unit potentials (spikes) per contraction for concentric eccentric, and isometric contractions. 3. The fatigue task resulted in a 30 +/- 12% decline in the mean MVC of elbow extension. Recruitment of nine new motor units (23%) was evident during the fatiguing extension movements, often within five to seven movements (i.e., within 25-35 s). Each newly recruited motor unit had the largest recruitment threshold torque in that experiment. 4. Analysis of the motor units that were active from the beginning of the fatigue task revealed that the mean number of motor-unit spikes per contraction increased, or remained constant as fatigue ensued, yet for the majority of motor units it increased or remained constant. None of the newly recruited motor units demonstrated decreased number of mean spikes per contraction after recruitment. Further, concurrently active motor units displayed different discharge behavior in two-thirds of the subjects. It is proposed that if the neural drive to the muscle is distributed uniformly upon the motoneuron pool, peripheral feedback from the exercising muscle may modulate specific motoneuron discharge levels during fatigue.

Adult↗
PubMed1996

Motor unit activity during human single joint movements.

1. To explore the neural control of single joint movements in humans, the activity of 47 motor units in triceps brachii muscle was recorded during elbow flexion and extension movements. Movements were performed with different but changing deceleration magnitudes, while the acceleration magnitude was kept constant, to determine the relationship between motor unit activity and the acceleration and deceleration characteristics of single joint movements. 2. The number of motor unit action potentials was found to vary with the magnitude of the movement deceleration. In addition the duration of the discharge of a motor unit was found to parallel the duration of the acceleration phase of the movement, when the acceleration duration was varied while acceleration magnitude was kept constant. 3. Approximately half of the recorded motor units in triceps brachii were active both in the initiation and in the termination of the extension movements. However, motor units were identified that participated in specific phases of the movement (i.e., either during the 1st agonist or 2nd agonist burst of muscle activity) depending on the magnitude of the acceleration or deceleration. 4. During flexion movements, when the triceps muscle served as an antagonist, approximately half of the motor units were recruited only when the magnitude of the flexion deceleration was large. Further, this deceleration magnitude was larger than that evident during the extension movements in which the motor unit discharged. 5. The findings of this study demonstrate that the nervous system activates the same motor units whether the muscle is functioning as an agonist or antagonist so as to control the characteristics of acceleration and deceleration of single joint movements.

Acceleration↗
PubMed1995

Child abuse prevalence in Russian urban population: a preliminary report.

Self-reported data from 375 early and mid-adolescent school children in a Siberian city estimated a prevalence of child abuse at 28.9%. Of these children, 3.8% suffered injuries that required medical attention. This prevalence of child abuse indicates the need for additional research and development of a system to identify and manage child abuse in Russia.

Adolescent↗
PubMed1995

Mapping of a distal form of spinal muscular atrophy with upper limb predominance to chromosome 7p.

An autosomal dominant distal form of spinal muscular atrophy mainly affecting the upper limbs with a mean age of onset of 17 years has been identified in a large Bulgarian family. Linkage of the above family to the spinal muscular atrophy type I, II and III locus on chromosome 5 has been excluded. In an attempt to map this disease gene we have analysed individuals of this family, with more than 140 microsatellite polymorphic markers of the human genome. A maximum lod score of 5.99 at theta = 0.007 has been obtained with locus D7S795. We have thus mapped the gene for this hereditary form of distal spinal muscular atrophy to chromosome 7p.

Adolescent↗
PubMed1994

'SVET' space greenhouse onboard experiment data received from 'MIR' station and future prospects.

The paper describes operation of 'SVET' space greenhouse onboard the 'MIR' orbital station since 15 June 1990 and the adopted biotechnological principles. The microprocessor and measuring systems for monitoring and control of the environmental parameters in the Plants growth chamber are presented. Information about the dynamic of these parameters in the course of the first space experiments with vegetables, obtained by means of telemetric data processing, is given. A draft program for the development of next generations of greenhouses of the same type as 'SVET', but with a larger area and capabilities, is worked out.

Air Conditioning↗
PubMed1994

Tissue distribution of polybutylcyanoacrylate nanoparticles loaded with spin-labelled nitrosourea in Lewis lung carcinoma-bearing mice.

The tissue distribution of polybutylcyanoacrylate nanoparticles (PBCN) with a diameter of 127 nm, loaded with 1-(2-chloroethyl)-3-(1-oxyl-2,2,6,6-tetramethylpiperidinyl)-1- nitrosourea (spin-labelled nitrosourea, SLCNU) is described. PBCN-suspensions were intraperitoneally (i.p.) injected into Lewis lung carcinoma bearing mice. The biodistribution of PBCN in the visceral organs, blood and tumor was studied by electron spin resonance (ESR) spectroscopy. A relatively low accumulation of nanoparticles in the liver and spleen was found. The accumulation was negligible in the i.m. implanted primary tumor. SLCNU-loaded nanoparticles were mainly found in the lungs, kidneys, and heart. The highest content of the particles studied was observed in the lungs of tumor bearing experimental animals damaged by metastases. These findings suggest that PBCN offer some opportunities in the targeting of SLCNU to lung metastases.

Animals↗
PubMed1991

Nanoparticles as drug carriers for vinblastine. Acute toxicity of vinblastine in a free form and associated to polybutylcyanoacrylate nanoparticles.

The possibility of reducing toxicity of Vinblastine by fixing it in polybutyl-2-cyanoacrylate nanoparticles was studied. A significant reduction of mortality of mice was recorded after a single intraperitoneal (i. p.) injection of nanoparticle-associated Vinblastine. A wide range of doses of Vinblastine (1.04-6.25 mg/kg) were used. There was a considerable decrease of leucopenia caused by Vinblastine-loaded polybutyl-2-cyanoacrylate nanoparticles as compared to that induced by free Vinblastine.

Animals↗
PubMed1986

[Motivation in the choice of profession by students of veterinary medicine].

Elucidated were the motives in choosing the profession with the student in veterinary medicine, stating the sociologic characteristic of the vet students in connection with the choice made. Stated was the effect of some factors that belonged to the social origin (so-called external factors) as well as the effect of the personal reasons for vocational orientation. The education at the Faculty of Veterinary Medicine was also found to be of importance in this respect. It was established that the most effective external factor was the influence of the family circle, although it was not as significant as in other similar studies in terms of value. In most of the students in veterinary medicine the choice of profession was determined mainly by personal motives: the interest the students took in biologic sciences, the affection for animals, etc.,--which spoke of a decision-making of their own. The effect of institutions of the social past, such as education, school, teachers. Studies of professional orientation on the choice of a profession was said to be negligible. Negative deviations as to the stability of decision-making, particularly in the fourth year of education, were also established, and this made it necessary to combine professional training with didactical means in order to make it optimal.

Bulgaria↗
PubMed1986

Motor unit activity during different functional states of the neuromuscular system.

The study showed that the mean interspike interval (ISI) and the variability of ISIs increased with fatigue for both low and high threshold motor units (MUs). The recruitment threshold tension decreased for both the low and high threshold MUs while the recruitment threshold in % of maximal voluntary contraction changed selectively because of decrease of muscle force. During ischaemia after an initial decrease of mean ISI and ISIs' variability there was an essential increase of variability of ISIs at almost the same mean ISI followed by a considerable final increase of both parameters. MUs' recruitment thresholds lowered with ischaemia more rapidly in the beginning and especially in the final stage of ischaemia.

Action Potentials↗