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Biomedical subjects

I Christov

Publications and source records attributed to I Christov.

11 recordsLinked to original sources
PubMed2000

Modulation of steroidogenesis in human ovarian granulosa cells during aging.

OBJECTIVE: To investigate the in vitro effect of endothelin-1 (ET-1) on the steroid production (progesterone [P] and estradiol [E2]) by cultured human granulosa cells (GCs) during aging. MATERIAL AND METHODS: Human ovarian GCs and granulosa-luteal cells (GLCs) were isolated from ovaries of female patients (young and premenopausal) undergoing surgery for non-ovarian benign gynecological conditions. Cells were cultured with ET-1 in the presence or in the absence of FSH. The concentrations of P and E2 in conditioned media were determined by means of RIA. RESULTS: In human GCs and GLCs obtained from young and premenopausal women, ET-1 in vitro can significantly reduce the FSH stimulated biosynthesis of P, whereas the basal P biosynthesis is only insignificantly diminished. The in vitro application of ET-1 have only a sparse inhibitory effect on both the basal and FSH stimulated biosynthesis of E2 in GCs from the two patient groups. CONCLUSIONS: Our findings support the opinion that ET-1 is a local regulator of ovarian steroidogenesis which might modulate the steroid production and the stimulatory effect of FSH in cultured GCs and GLCs obtained from women at various ages.

Adult↗
PubMed1998

In-house development of test equipment for quality control and training. Case study: a prototype ECG simulator-tester.

The support services for biomedical technology address a variety of technical and administrative issues, concerning the safe and efficient operation of medical equipment over the period of its intended use and the training of hospital personnel in issues concerning safety and quality. Clinical Engineering Departments undertake the responsibility of developing and operating training programs in medical equipment utilisation apart from the traditional role of training and supervising technicians involved in testing, calibration and preventive/corrective maintenance of electromedical equipment. In view of the above, the Institute of Biomedical Technology and the Centre of Biomedical Engineering collaborated for the design and development of a prototype digital ECG and arrhythmia simulator. In the absence of internationally accepted inspection protocols for ECG simulators, the verification phase of the project involved mainly the inspection of the device's conformity to its initial technical specifications. The results demonstrated that this tester. due to simplicity in construction and easiness of use could be a practical, reliable and economical solution for electrocardiograph and ECG monitor testing and waveform recognition training.

Arrhythmias, Cardiac↗
PubMed1997

High-pass filtering of the electrogastrogram.

The recording and processing of an electrogastrogram require adequate band-pass filtering, to suppress unwanted artefacts but preserve the original signal waveform. High-pass filtering of various types, of different time constants tau, filter order, analogue and digital implementation, have been used to obtain higher baseline stability and faster signal recovery after strong artefacts. Special attention should be given to possible signal amplitude and phase distortions due to high-pass filtering, which can strongly influence accurate amplitude measurements or studies of signal propagation from multichannel recordings. Synthesised and original signals are used to demonstrate the effect of high-pass filtering. The use of a first-order filter with tau = 5 s is recommended for EGG studies if not especially directed to investigation of bradygastria. In the opposite case, tau = 15 s should be used, and with backward filtering a full restoration of the original signal can be obtained. The same is valid for recording the electrical activity of the colon. Lower time constants (tau = 5 s or less) can be applied to acquire signals from the small intestines. A radical solution is the use of a DC amplifier with controllable subtraction of the DC component.

Electromyography↗
PubMed1997

Improvement of resolution in measurement of electrocardiogram RR intervals by interpolation.

The measurement of successive RR intervals, obtained from the electrocardiogram (ECG), is the basis of any subsequent method for the assessment of variations in heart rate, for example using intervalograms, histograms, trend curves, spectral analysis, etc. The accuracy of measurement directly depends on the sampling rate used for the acquisition of the ECG signal. Depending on specific applications, rates down to 128 Hz are not uncommon. This considerably limits the resolution if RR interval data are to be derived. Interpolation is often employed for solving problems of this type. Linear, cubic and spline interpolations, obtained directly from the MATLAB software product, were applied and compared for the purpose of RR interval measurement. The cubic method was found to combine the improvement of resolution (+/-1 ms) at sampling rates successfully down to 100 Hz, with a rapid operating speed. Comparison examples are given with ECG signals acquired with 1000 Hz, 16-bit sampling.

Adult↗
PubMed1995

Non-invasive electrogastrography. Part 1: Correlation between the gastric electrical activity in dogs with implanted and cutaneous electrodes.

Experiments were made on dogs with bipolar silver ball-shaped electrodes chronically implanted on the muscle wall of the stomach. The electrical activity of the gastric muscle wall (electrogastromyogram-EGMG) was characterized by slow potential changes during the quiescent period of the migrating myoelectric complex (MMC) and bursts of spike potentials during the activity period of MMC. Cutaneous (surface) electrodes were placed on the abdominal wall. Waves with a rhythm of 4.5-5 cpm were led off by the cutaneous electrodes (electrogastrogram-EGG), simultaneously with the EGMg. The bursts of spike potentials with the slow gastric potentials in the EGMG corresponded to an increase of the amplitude of the waves in the EGG. Good correlation was found between the number and frequency of spike potentials in a group and the wave amplitude in the EGG. EGG recorded on an electrogastrograph designed by us was characterized by low-amplitude waves corresponding to the slow waves during the period of quiescence of MMC and high-amplitude waves corresponding to the bursts of spike potentials during the activity period of MMC. Therefore it is possible to determine the MMC of the stomach by the changes in the amplitude of the waves in the EGG.

Action Potentials↗
PubMed1995

Non-invasive electrogastrography. Part 2. Human electrogastrogram.

The electrical activity of human stomach muscle wall-electrogastrogram (EGG), was led off by surface (cutaneous) electrodes placed on the abdominal wall and recorded on an electrogastrograph. A method for complete elimination of the cardiac artefact was elaborated and successfully implemented. It consists of a preliminary elimination of the QRS complex, based on its higher amplitude and slope. The eliminated intervals were replaced by linear segments. A subsequent low-pass filtering allowed to obtain a high quality EGG signal. The electrical activity of the stomach of healthy volunteers was characterized by waves with a frequency of 3.35 +/- 0.09 cpm during the quiescent periods and 2.99 +/- 0.14 cpm during the activity periods of the migrating myoelectrical complex (MMC). Bearing in mind the correlation between the bursts of spike potentials with the slow waves in the dog EGMG and the high-amplitude waves, characterizing the periods of activity in the dog EGG, we can better differentiate the periods of quiescence and activity by the amplitude of the waves. The wave amplitude during periods of quiescence was 81.13 +/- 20.61 microV, significantly different from the wave amplitude during periods of activity being 164.74 +/- 43.34 microV (n = 7). Thus with this method in visual inspection it is possible to identify MMC of the human stomach by the changes in the amplitude of the waves in the EGG.

Action Potentials↗
PubMed1992

A stable line of turkey bone marrow cells transformed by the myelocytomatosis virus strain MC31. Ultrastructural characteristics and localization of the DNA replication sites.

Attempts were made to characterize cells of the LSTC-SF2 line by scanning electron microscopy and transmission electron microscopy on the ultrastructural level. The virus-transformed cells are of oval, slightly elongated shape with an undulating surface. The cell nucleus is well outlined, poor in heterochromatin but with a strongly developed nucleolus. The cytoplasm is not rich in organelles except for an abundance of mitochondria with dense granules that are often found in them. With high-resolution autoradiography the DNA synthesis sites were identified mainly in proximity to the nuclear membrane and in the perinuclear spaces. The cells under study can be regarded as immature forms of the blood series and most likely as precursors of cells of the granulocyte or monocyte series.

Animals↗
PubMed1978

Delayed hypersensitivity reactions in patients with breast cancer.

Fifty six patients with metastatic cancer of the breast (stage IV) were treated with Cyclophosphamide, 5-Fluorouracil and Cyclophosphamide + 5-Fluorouracil. Tests for delayed hypersensitivity to homologous tumor antigen before treatment were positive in 83.9% and negative in 16.1%. Response to DNCB was positive before treatment in 51.8% and negative in 48.2%. Following chemotherapy the skin reaction, to homologous tumor antigen remained positive, only in 12.6% and negative in 87.4%. The reaction of DNCB remained positive after treatment only in 17.8%. In the remaining 82.2% suppression of the reaction occurred. These data show that chemotherapy may suppress, to a certain excent, immune responses. It is established that among patients who have shown a positive reaction to homologous tumor antigen 55.3% of all cases have displayed objective response to the treatment, and among these with negative skin reactions objective responses were observed in 22.22% of all cases. In patients with positive DNCB reactions objective responses were observed in 79.3% and among the negative ones--in 37.4%.

Adult↗