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At least 199 records · Page 11Linked to original sources
PubMed1987

Continuous, real-time, noninvasive monitor of blood pressure: Penaz methodology applied to the finger.

The finger blood pressure monitor measures blood pressure continuously and noninvasively by means of a technique described by J. Penaz. The size of the artery is measured when its internal pressure (arterial pressure) equals the external pressure. (At this point, transmural pressure equals zero and the arterial wall is said to be "unloaded.") This unloaded condition is maintained by continuous, automatic adjustments of external pressure on the artery, adjustments that are made simultaneously with and parallel to intraarterial pressure variations. The external pressure then constantly equals internal pressure (arterial blood pressure) and is reported by the monitor as values for systolic, mean, and diastolic pressure. A finger cuff with a built-in light source and detector is used to measure finger artery size, and an inflatable bladder is used to apply the external pressure to the artery. The monitor is microprocessor based; algorithms determine the unloaded artery size approximately every minute and automatically correct for changes possibly induced by smooth muscle contraction or relaxation, and a high-speed electropneumatic servo control system enables automatic calibration and adjustment.

Blood Pressure Determination↗
PubMed1992

[Neoplastic involvement of pulmonary fissures. Diagnostic possibility of high resolution x-ray computed tomography].

Acknowledging fissure invasion by pulmonary tumors located in contact with or in the vicinity of a fissure is an important piece of information for the therapeutic choice, especially in patients whose functional respiratory impairments are a contraindication of pneumonectomy. Fifteen patients with pulmonary neoplasms adjacent to a fissure were studied with standard computed tomography (10 mm sections), completed by high-resolution CT. The findings of the CT studies were compared with those operative reports. On surgery, the oblique fissure was infiltrated in 12 patients, unharmed in 2 others, while the horizontal fissure was infiltrated in 3 patients. Standard CT allowed diagnosing the involvement of the oblique fissure in 4 patients. Thin sections with high-resolution reconstruction algorithms allowed detecting the involvement of the oblique fissure in 13 cases, including one false-positive result. On thin sections, the fissures appear as well-delineated, dense lines. This allows an accurate study of the relationships between the tumor and the fissure, thus increasing the sensitivity of CT for the detection of tumoral extension across the fissures. The orientation of the horizontal fissure, which is almost parallel to the plane of section, makes the study of its relationships with an adjacent mass difficult, even in high-resolution CT.

Humans↗
PubMed1990

Influence of plasma glucose concentration on lumped constant of the deoxyglucose method: effects of hyperglycemia in the rat.

The lumped constant of the deoxyglucose method was determined by the steady-state, model-independent method in the brain of normal conscious rats with arterial plasma glucose concentrations varying from normoglycemia (i.e., 8 mM) to hyperglycemia (i.e., 31 mM). The lumped constant for brain was found to decrease very gradually with increasing arterial plasma glucose concentration from a value of approximately 0.45 in the midnormoglycemic range (i.e., 7-8 mM) to approximately 0.38 at 28-31 mM. 3-O-[14C]Methylglucose was used to assess the distribution of glucose within the brain structures in hyperglycemia; the results indicated that the glucose concentration, and therefore also the values for the lumped constant, remain relatively uniform in hyperglycemia with arterial plasma glucose concentrations as high as 34 mM. The values for the lumped constant for rat brain determined in the present studies were combined with those previously determined in this laboratory for hypoglycemia and normoglycemia by the same method to provide a single source for the values for the lumped constant to be used over the full range of arterial plasma glucose concentrations. In several rats the lumped constant for cephalic extracerebral tissues was also evaluated in parallel with those for the brain. The lumped constant for the cephalic extracerebral tissues was found to be about twice that for brain and to be unaffected by changes in arterial plasma glucose levels.

Algorithms↗
PubMed1989

The analysis of titration studies in phase III clinical trials.

Clinical trials commonly employ the titration design for certain drugs such as antihypertensives. In a Phase III trial the design has purposes distinct from those of a Phase I or II trial, as well as from those of a trial with a parallel design. In this paper we compare the titration design with the usual parallel design in their respective purposes for Phase III trials, explore the relevant questions addressed, and examine typical data from such trials. We also discuss work which focuses primarily on the Phase I or II titration trials. We formulate the problem in the framework of one-way contingency table augmented with incomplete data and obtain the maximum likelihood estimates of the parameters and their estimated variances/covariances via the EM algorithm. An example of a Phase III study of an antihypertensive agent illustrates the proposed procedure.

Analysis of Variance↗
PubMed1988

Three-dimensional structure of acyl carrier protein in solution determined by nuclear magnetic resonance and the combined use of dynamical simulated annealing and distance geometry.

The solution conformation of acyl carrier protein from Escherichia coli (77 residues) has been determined on the basis of 423 interproton-distance restraints and 32 hydrogen-bonding restraints derived from NMR measurements. A total of nine structures were computed using a hybrid approach combining metric matrix distance geometry and dynamic simulated annealing. The polypeptide fold is well defined with an average backbone atomic root-mean-square difference of 0.20 +/- 0.03 nm between the final nine converged structures and the mean structure obtained by averaging their coordinates. The principal structural motif is composed of three helices: 1 (residues 3-12), 2 (residues 37-47) and 4 (residues 65-75) which line a hydrophobic cavity. Helices 2 and 4 are approximately parallel to each other and anti-parallel at an angle of approximately equal to 150 degrees to helix 1. The smaller helix 3 (residues 56-63) is at an angle of approximately equal to 100 degrees to helix 4.

Acyl Carrier Protein↗
PubMed1978

A new method of multiplanar emission tomography using a seven pinhole collimator and an Anger scintillation camera.

A new method of multiplanar emission tomography is described; it uses a wide-field Anger scintillation camera (37.5 cm crystal diameter) and a seven-pinhole collimator. The pinholes (5.5 mm) acquire data simultaneously from the emissing source and project the data onto seven independent regions of the camera crystal. Multiple planes are reconstructed from the initial seven-view data acquisition through the use of a computerized addition-multiplication algorithm and variation of the superposition relationships among the projected views. These planes are then altered iteratively by a least-error criterion following ray-sum comparison with the original views. Planar resolution (full-width-half-maximum) is 1.0 cm and depth resolution is 1.5 cm. In 42 patients with angiographically demonstrated coronary-artery disease, studies of myocardial Tl-201 perfusion, under exercise, have shown improved detection sensitivity in comparison with scintigraphy using parallel-hole collimation.

Coronary Disease↗
PubMed1986

Apparent response incompatibility effects on P3 latency depend on the task.

Ten young women were tested with an ERP paradigm that used the words 'left,' 'right,' 'LEFT,' 'RIGHT' as stimuli. The stimulus sequence was presented as several separate runs with varying response instructions. Subjects were instructed to respond according to the meaning of the stimulus in the (WORD task), to the case in which the stimulus was written (CASE task), or to both the case and meaning of the stimulus (CASE/WORD) task. In each task, half the trials called for a response that was incompatible with the stimulus. For the WORD task, compatible and incompatible trials were presented as separate blocks of trials. For all 3 tasks an additional stimulus sequence was presented in which the words were degraded with superimposed visual random noise. Reaction time (RT) in the CASE/WORD task was more than 100 msec later than in the other tasks. In the WORD and CASE/WORD tasks, RT was delayed more than 100 msec when the response was incompatible with the stimulus. Degrading the stimulus additionally delayed RT by about 100 msec. In the WORD and CASE tasks, error RTs were earlier than correct RTs. P3 latency was measured with a single-trial latency adjustment algorithm. P3 latency was delayed in the CASE/WORD task compared to the other 2 tasks. P3 was delayed by degrading the stimuli. Contrary to some previous reports, P3 was delayed by about 70 msec when incompatible responses were required, but only in the WORD task. Taken together with error and RT data, these P3 latency data are consistent with the notion that the task causes subjects to adopt different strategies and hence different types of processing (i.e., serial vs. parallel). Depending on the type of processing, P3 may appear to be affected by response incompatibility.

Adult↗
PubMed1990

On the control of automatic processes: a parallel distributed processing account of the Stroop effect.

Traditional views of automaticity are in need of revision. For example, automaticity often has been treated as an all-or-none phenomenon, and traditional theories have held that automatic processes are independent of attention. Yet recent empirical data suggest that automatic processes are continuous, and furthermore are subject to attentional control. A model of attention is presented to address these issues. Within a parallel distributed processing framework, it is proposed that the attributes of automaticity depend on the strength of a processing pathway and that strength increases with training. With the Stroop effect as an example, automatic processes are shown to be continuous and to emerge gradually with practice. Specifically, a computational model of the Stroop task simulates the time course of processing as well as the effects of learning. This was accomplished by combining the cascade mechanism described by McClelland (1979) with the backpropagation learning algorithm (Rumelhart, Hinton, & Williams, 1986). The model can simulate performance in the standard Stroop task, as well as aspects of performance in variants of this task that manipulate stimulus-onset asynchrony, response set, and degree of practice. The model presented is contrasted against other models, and its relation to many of the central issues in the literature on attention, automaticity, and interference is discussed.

Attention↗
PubMed1987

Deformation analyses in cell and developmental biology. Part II--Mechanical experiments on cells.

This study employs the finite element approach developed in Part I to analyze mechanical experiments on cells. It views cells as axisymmetric membrane structures containing a body of incompressible material, and models the mechanical contact between a cell and the loading apparatus by a contact algorithm. Since the method is valid for analyzing axisymmetric shell-like bodies with arbitrary shapes, it treates various mechanical experiments on cells in a unified manner. For demonstration purposes, three commonly used mechanical experiments on cells are considered; the compression experiment; the suction (micropipette aspiration) experiment; and the magnetic particle experiment. Based on an estimate of the mechanical property data for unfertilized sea urchin eggs, this analysis method predicts the responses for all three experiments using the same assumptions and approximations. This parallel treatment gives a broad basis for data correlation with experiments. The method also provides insights into mechanical experiments not offered by other approximate methods. For example, it gives the distributions of tensions and stretches on the cell cortex, and suggests the role of friction in the suction experiment.

Animals↗
PubMed1989

Frequency domain analysis of contrast echocardiographic images.

Sequences of echocontrastographic images of the dog's myocardium are analysed in the frequency domain for the identification of underperfused areas. Owing to the fact that echo images are contaminated by noise and artifacts, we have applied filtering techniques based on Fourier's methods in sequences of raw frames recorded during perfusion with a contrast agent. Thus we have been able to assess correctly the spatial and temporal distribution of the contrast, i.e. the agent kinetics which parallel the distribution of coronary blood flow, in terms of the time necessary for the flow gradient to reach its maximum value, and to describe such a distribution by a functional image obtained by means of an original procedure.

Algorithms↗
PubMed1992

Bacterial monitoring in vials using a spectrophotometric assimilation method.

Aseptic-filling processes are often used with fragile parenteral products that might be destroyed by terminal autoclaving. However, aseptic filling is not as effective as autoclaving in reducing contamination. As a result, time-consuming microbiological methods and turbidimetry are employed currently as product inspection techniques, but these processes can destroy the product and might not detect low levels of contamination. Thus, near-infrared (IR) light scattering was evaluated in this study as a new method for determining low levels of contamination noninvasively and nondestructively. A new parallel mathematical technique was used in conjunction with near-IR spectrophotometry to detect successfully contamination by several species of bacteria through intact glass vials. Using the near-IR method, products can be evaluated without introducing contamination, preserving the sample vial for dispensing or evaluation by another method.

Algorithms↗
PubMed1992

Combining logistic regression and neural networks to create predictive models.

Neural networks are being used widely in medicine and other areas to create predictive models from data. The statistical method that most closely parallels neural networks is logistic regression. This paper outlines some ways in which neural networks and logistic regression are similar, shows how a small modification of logistic regression can be used in the training of neural network models, and illustrates the use of this modification for variable selection and predictive model building with neural networks.

Algorithms↗
PubMed1990

Intracellular signalling as a parallel distributed process.

Living cells respond to their environment by means of an interconnected network of receptors, second messengers, protein kinases and other signalling molecules. This article suggests that the performance of cell signalling pathways taken as a whole has similarities to that of the parallel distributed process networks (PDP networks) used in computer-based pattern recognition. Using the response of hepatocytes to glucagon as an example, a procedure is described by which a PDP network could simulate a cell signalling pathway. This procedure involves the following steps: (a) a bounded set of molecules is defined that carry the signals of interest; (b) each of these molecules is represented by a PDP-type of unit, with input and output functions and connection weights corresponding to specific biochemical parameters; (c) a "learning algorithm" is applied in which small random changes are made in the parameters of the cell signalling units and the new network is then tested by a selection procedure in favour of a specific input-output relationship. The analogy with PDP networks shows how living cells can recognize combinations of environmental influences, how cell responses can be stabilized and made resistant to damage, and how novel cell signalling pathways might appear during evolution.

Animals↗
PubMed1991

A simulation study comparing designs for dose ranging.

Only with knowledge of the (prior) distribution of dose-response parameters in a population, can one determine both the initial dose of a drug for chronic administration to an individual (such as the dose producing a fixed degree of response in a fixed proportion of the population) and an appropriate subsequent (adjusted) dose (such as the dose yielding a desirable response according to the posterior parameter distribution, given an observed response to an initial dose). The currently FDA-sanctioned design for a dose-ranging study, the parallel-dose design, assigns just one of several doses to each patient. It does not provide good information on the distribution of individual dose-response parameters. A cross-over design assigns several dose levels to each patient. It therefore can provide better information, but does not resemble clinical practice. Consequently, study participants must be restricted to patients who can tolerate such non-therapeutic drug exposure, posing problems in extrapolation of study results to other types of patients. A titration or dose-escalation design begins all patients on placebo and, except for those patients assigned to a placebo-only group, escalates the dose for a patient at preset intervals only when clinical response at lower doses is inadequate. It both exposes patients to several dose levels and resembles good clinical practice, allowing study of a representative patient sample. We report here the simulation results of parameter estimation for the three designs when the data arise from complex and realistic dose-response models and/or with certain complications in study execution. The dose-escalation design clearly performs better overall than the parallel-dose design for the models considered here, and generally, just a little worse than the cross-over design. These results support the conclusion that for dose ranging, depending on the demands of the clinical situation, one should use either the cross-over or the dose-escalation design.

Algorithms↗
PubMed1989

[Clinico-pathogenetic substantiation of medical tactics in combined benign hyperplastic processes in the uterus of patients of reproductive age].

The definition of concomitant benign hyperplastic diseases of the uterus relates to the abnormalities of the female reproductive system which are accompanied with a simultaneous development of uterine hyperplasias or endometrial polyps, myomas and/or endometriosis. The investigation of 290 patients of reproductive age revealed a multifactorial origin of the aforementioned diseases. Anamnestic, gynecological, dermatoglyphic, hormonal and receptor investigation techniques used in parallel with a routine general clinical examination evidenced systemic lesions and defined clinical and pathogenetic differences in the conditions associated with hyperplasia or endometrial polyps. The authors substantiated the use of various methods in the system of treatment: the use of nonsteroidal drugs with gestagen properties and cryogenic application to the walls of the uterus.

Adult↗
PubMed1992

Grand challenges in biomedical computing.

Advances in computing technology (both algorithms and hardware) over the next several years promise to make increasingly sophisticated computer modeling of biomedical phenomena a routine part of biomedical research. Improvements in both the absolute speed of processors and in their programming and graphics interfaces will allow nonexpert users to bring computing power equivalent to the supercomputers of a few years ago to bear on routine research problems and to display complex data in understandable ways (visualization). Although biomedical applications have traditionally not driven the leading edge of computing and supercomputing, such applications are increasingly being ported to advanced parallel and vector processors. This paper summarizes the current state of biomedical computing, citing examples of the best practice in research today. A number of projects enabled by advanced computing from various subdisciplines are described. Trends in technology for both inexpensive (workstation) and high-end computing (vector supercomputers and parallel processors) are cited; the implications of these for biomedical computing are discussed. "Grand challenges" in biomedical computing, i.e., computational problems of major scientific importance that are beyond our current capabilities but that might be achieved in a 5-year time frame, are outlined.

Attitude to Computers↗
PubMed1990

An optimal control model for maximum-height human jumping.

To understand how intermuscular control, inertial interactions among body segments, and musculotendon dynamics coordinate human movement, we have chosen to study maximum-height jumping. Because this activity presents a relatively unambiguous performance criterion, it fits well into the framework of optimal control theory. The human body is modeled as a four-segment, planar, articulated linkage, with adjacent links joined together by frictionless revolutes. Driving the skeletal system are eight musculotendon actuators, each muscle modeled as a three-element, lumped-parameter entity, in series with tendon. Tendon is assumed to be elastic, and its properties are defined by a stress-strain curve. The mechanical behavior of muscle is described by a Hill-type contractile element, including both series and parallel elasticity. Driving the musculotendon model is a first-order representation of excitation-contraction (activation) dynamics. The optimal control problem is to maximize the height reached by the center of mass of the body subject to body-segmental, musculotendon, and activation dynamics, a zero vertical ground reaction force at lift-off, and constraints which limit the magnitude of the incoming neural control signals to lie between zero (no excitation) and one (full excitation). A computational solution to this problem was found on the basis of a Mayne-Polak dynamic optimization algorithm. Qualitative comparisons between the predictions of the model and previously reported experimental findings indicate that the model reproduces the major features of a maximum-height squat jump (i.e. limb-segmental angular displacements, vertical and horizontal ground reaction forces, sequence of muscular activity, overall jump height, and final lift-off time).

Biomechanical Phenomena↗
PubMed1981

Analysis and predication of structural motifs in the glycolytic enzymes.

Protein crystallography has determined the three-dimensional structures of 10 of the 13 enzymes of the glycolytic pathway. Diagrams and details of these enzyme structures are given in the paper. Most of the enzyme domains are variations and extensions of a many (4--9)-stranded, predominantly or totally parallel, beta-sheet that is shielded from solvent by alpha-helices (i.e. alpha/beta structures). There are strong structural similarities between the domains of some, but not all, of the enzymes. In particular the dinucleotide binding fold of lactate dehydrogenase and the beta-barrel of triose phosphate isomerase are found in other domains. General rules governing the topology and packing of alpha-helices against a beta-sheet provide a basis for the combinatorial prediction of the tertiary fold of glycolytic domains from their amino acid sequence and observed secondary structure. The predication algorithm demonstrates that there are severe restrictions on the number of possible structures. However, these restrictions do not fully explain some of the remarkable structural similarities between different enzymes that probably result from evolution from a common ancestor.

Animals↗