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At least 199 records · Page 11Linked to original sources
PubMed1982

Stopped-flow studies on drug-protein binding. Analog-computer analysis of the pH-dependent binding kinetics of warfarin and human serum albumin.

Binding curves obtained by the stopped-flow method for the association of warfarin and human serum albumin (HSA) at pH 6.0 and 9.0 have been analysed with digital- and analog computers. The first association product (WHSA') at pH 6-9 does not contribute to the observed fluorescence enhancement during warfarin-HSA complex formation. A similar consecutive relaxation process leads to a more stable warfarin-HSA complex, with HSA in the neutral (N)-form (pH 6) and base (B)-form (pH 9). This rearrangement can be measured by stopped-flow (k 2 = 31 s-1 at pH 6; K'2 = 63 s-1 at pH 9). At pH 6 a further concentration dependent relaxation process has been observed indicating that the complex of warfarin with the N-form of HSA gets partially converted into its B-form with a half-time for this N leads to B transition in the range of 0.2-0.4 s. A drug such as warfarin can act as effector molecule for conformational changes of the HSA tertiary and quaternary structure during the formation of a high affinity complex.

Computers, Analog↗
PubMed1982

Analog computer simulation of maternal - fetal transfer of cefazolin.

Cefazolin concentration-time data after normal vaginal delivery were obtained for maternal serum, placenta, umbilical cord blood, and amniotic fluid. After normalizing of the data, concentration-time profiles were generated for each sampling compartment. A pharmacokinetic model for analog computer simulation was developed. Multiple dosing simulation suggests a higher accumulation of cefazolin in fetal than in maternal blood, and a slow accumulation in amniotic fluid, which acts as a depot or storage. The drug is transferred diaplacentally; paraplacental transfer seems to be absent for cefazolin.

Amniotic Fluid↗
PubMed1977

Agarose gel electrophoresis of cerebrospinal fluid proteins and analysis of the pherogram profiles by analog computer.

A micro-method of agarose gel electrophoresis requiring 1--3 ml of cerebrospinal fluid for quantitative analysis of cerebrospinal fluid proteins is described. After concentration of CSF to about 50 microliter by ultrafiltration and refractometric determination of protein, approximately 20--40 microgram of total protein are used for electrophoresis. Photometric scanning of the electrophoretic pattern at two different wavelengths permits quantitative evaluation. The pherograms are analysed by means of a modified DU-PONT analog computer. Factors which influence quantitative electrophoresis are examined. In cerebrospinal fluid of normal children 15 protein fractions are demonstrated: 2 prealbumins, albumin, 5 alpha-, 3 beta- and 4 gamma-globulins.

Adolescent↗
PubMed1983

Design and pharmacokinetic application of an analog computer program (MULS) for multiple dose simulation.

MULS is a simulation program developed on an analog computer equipped with logic elements. It is designed for multiple dose simulation of commonly encountered dosing schemes: equal or unequal dosing intervals, bolus and/or constant rate drug input, with or without loading dose. Appropriate pharmacokinetic models are defined independently of dosage regimen selection. The program can be used in routine operation for visualization of drug accumulation and optimum dosage regimen. Examples of the program outputs are presented.

Computers↗
PubMed1982

Lymph flow characteristics and microvascular exchange: an analog computer simulation.

Lymphatic flow characteristics, which include both progressive lymphatic blockage and plateau of lymph flow with increasing interstitial fluid volume, were incorporated into an analog computer simulation of microvascular exchange, and their effects on interstitial fluid volume and protein content were investigated. The steady state and transient response of the microcirculation to changes in the properties of the lymph flow system are reported. The interstitial fluid and protein content is investigated as a function of venous pressure and for changes associated with the lymph flow characteristics. The interstitial protein content is generally more sensitive to changes in the lymph flow properties than is interstitial fluid volume. Properties of lymphatic drainage of tissues as they effect microvascular exchange are discussed.

Computers↗
PubMed1981

Real time analog computation of left ventricular systolic pressure volume area as predictor of oxygen consumption.

An analog circuit was devised for real time determination of the left ventricular systolic pressure volume area (PVA), which we had recently identified as a reliable predictor of cardiac oxygen consumption rate per beat. PVA is the specific area in the pressure-volume diagram that is bounded by the end-systolic and end-diastolic pressure-volume relationship lines and the systolic segment of the pressure-volume loop trajectory of the left ventricle. The computed PVA was compared with PVA obtained as usual by planimetry. Correlation coefficient between the two PVA's was 0.997 (N=31, P less than 0.001) and the standard error of mean of the difference between th two PVA's was as small as practically negligible 8 mmHg ml in the PVA range from 0 to 2,000 mmHg ml. We concluded that this PVA analog computer can be used for real time determination of PVA, expediting the future studies of the relationship between PVA and cardiac oxygen consumption.

Animals↗
PubMedDate not supplied

[Sialography with direct multiple image enlargement and the processing of the sialograms on an analog computer].

To extend the potentialities of sialography, we used roentgenography with direct multiple amplification of the image by Reis microfocal portable x-ray diagnostic device and analyzed this image by analog UAR-1 computer operating in a high-frequency harmonization mode. The basic feature of such roentgenography is spatial stratification of the object shadow simultaneously forming its spatial image. High-frequency harmonization of an x-ray image essentially improved its contrast, this permitting detection of small formations poorly shown on sialogram, the contours of these formations and relationships between them. A total of 85 patients were examined using this method. Analysis of the resultant sialograms showed that using this method it is possible to assess the status of small structures of the gland, detect the changes in the pharyngeal process of the parotid gland. Sialogram direct projection is no longer needed.

Computers, Analog↗
PubMed1982

Assessment of severity of tricuspid regurgitation by analog computer analysis of dilution curves recorded by scintillation camera.

To estimate the severity of tricuspid regurgitation, we developed a new mathematical model of the circulatory system, in which the right atrium and the right ventricle were represented by a single mixing chamber and tricuspid regurgitation was expressed as a reverse flow from the right ventricle to the right atrium with a time delay equivalent to one cardiac cycle. The actual dilution curves obtained from the right atrium and the right ventricle following rapid intravenous injection of Technetium-99m-macroaggregated human albumin were fitted to the theoretical curves based on the above-described model. The use of macroaggregated albumin avoided the contamination of the dilution curves by radio-activity from the left heart or by the recirculation of the tracer due to left to right shunt. Mean transit times and percentage of regurgitation, as given by the ratio of regurgitant flow to total outflow from the right ventricle, were determined by an analog computer. The correlations of these results with the findings of other examinations, including contrast echocardiography, demonstrated that the present method may be useful in detecting tricuspid regurgitation and in grading its severity.

Cardiac Output↗
PubMed1975

The role of myocardial membrane leakage channels in the production of fibrillation: studies with an analog computer model.

The conditions under which automatic activity and fibrillation can occur were studied through the use of an analog model. Parameters (transmembrane active and passive properties) were established from biological data of mammalian myocardial fibers. The definition of instability of membrane potential can be given by the following functions of inward and outward steady state current (I) to voltage relationships of the membrane. 1) With decreasing angle between the tangent of the slope of the Iout and (-1) Iin, instability increases at constant potential. 2) Instability is also a function of the membrane potential as related to peak inward current (nonsteady state) at a given angle. 3) Maximum peak inward current and minimum angle produced such instability as to cause fibrillation. The most likely explanation is that automaticity and/or fibrillation is induced by leakage currents which change the normal current/voltage relatiosnhip in the described manner. The membrane leakage currents could be specific to sodium or unspecific.

Biological Transport, Active↗
PubMed1978

Computer analog simulation of a model for the regulation of ago-antagonistic couples.

A system of quadratic differential equations is proposed within the framework of 'non-linear mechanics', but also outside this framework in respect of certain features, and it is used with a view to formalising a feedback control system. The model helps to simulate states of balance or imbalance within an ago-antagonistic couple and to suggest methods for correcting the imbalances, which do not require modification of the parameter space. Its possibilities of synchronic or diachronic functioning are emphasised. The model may apparently be used for the construction of similar models which include several ago-antagonistic couples. Finally, the aims of such a model, which could be considered as an 'action' model, are defined; its place would be assigned midway between a black-box system and 'knowledge' models.

Computers↗
PubMed1980

Analog computer monitoring and evaluation of a dosing nomogram for gentamicin based on the C'min-method, part II.

Present methods for dosing gentamicin are based on usual doses or desired peak concentrations. The effective range is believed to be between 3 and 10 micrograms/ml. A method is proposed to maintain the minimum steady state concentration at a desired MIC with peak concentrations not exceeding 10 micrograms/ml. After determination of the log serum creatinine-log creatinine clearance relationship in a specific population group (Peruvian mestizos), a nomogram for dosing gentamicin was developed. The applicability of the nomogram or the corresponding equation upon which the nomogram was based was tested in patients for desired MIC of 0.5, 1.0, 1.5 and 2.0 micrograms/ml, and the actual c'min values obtained were compared with predicted levels. Using a correction factor, the nomogram is applicable for the United States and European population. The importance of drug level monitoring is emphasized.

Adolescent↗
PubMed1987

Analog and digital computer theory.

Analog signals abound in the natural world. With appropriate transducers these signals can be converted to continuous voltages and can be displayed, transmitted, stored, or copied. They can be processed by analog computers, the simplest of which is an audio amplifier. With analog signals, however, there can be errors because of signals loss, interference, and noise. Binary digital signals permit only two values, either 0 ('off' or 'low') or 1 ('on' or 'high'). These signals are much less susceptible to transmission problems. Binary signals are commonly organized into 8-bit groups which can represent 256 different numbers or meanings. These data can be transmitted in either serial or parallel fashion at high rates of speed. Analog-to-digital converters permit analog signals to be transformed to digital signals. A computer consists of the memory, the processor, and the input/output devices. Memory includes the fastest registers, the very fast core memory, the peripheral storage devices such as diskettes and disks, and the very slow peripheral devices such as magnetic tape. The processor can only load and store numbers in memory, add two numbers, test a number, and provide input and output. The program counter indicates the next computer instruction to be performed. Input/output devices allow communication with the outside world and may assume many forms. A computer by itself can do nothing. A program or series of instructions is required. The most simplistic program language is assembler or machine language. Most programming is done in more sophisticated languages, however.(ABSTRACT TRUNCATED AT 250 WORDS)

Analog-Digital Conversion↗